1                          Kernel Parameters
   2                          ~~~~~~~~~~~~~~~~~
   4The following is a consolidated list of the kernel parameters as
   5implemented by the __setup(), core_param() and module_param() macros
   6and sorted into English Dictionary order (defined as ignoring all
   7punctuation and sorting digits before letters in a case insensitive
   8manner), and with descriptions where known.
  10The kernel parses parameters from the kernel command line up to "--";
  11if it doesn't recognize a parameter and it doesn't contain a '.', the
  12parameter gets passed to init: parameters with '=' go into init's
  13environment, others are passed as command line arguments to init.
  14Everything after "--" is passed as an argument to init.
  16Module parameters can be specified in two ways: via the kernel command
  17line with a module name prefix, or via modprobe, e.g.:
  19        (kernel command line) usbcore.blinkenlights=1
  20        (modprobe command line) modprobe usbcore blinkenlights=1
  22Parameters for modules which are built into the kernel need to be
  23specified on the kernel command line.  modprobe looks through the
  24kernel command line (/proc/cmdline) and collects module parameters
  25when it loads a module, so the kernel command line can be used for
  26loadable modules too.
  28Hyphens (dashes) and underscores are equivalent in parameter names, so
  29        log_buf_len=1M print-fatal-signals=1
  30can also be entered as
  31        log-buf-len=1M print_fatal_signals=1
  33Double-quotes can be used to protect spaces in values, e.g.:
  34        param="spaces in here"
  36cpu lists:
  39Some kernel parameters take a list of CPUs as a value, e.g.  isolcpus,
  40nohz_full, irqaffinity, rcu_nocbs.  The format of this list is:
  42        <cpu number>,...,<cpu number>
  46        <cpu number>-<cpu number>
  47        (must be a positive range in ascending order)
  49or a mixture
  51<cpu number>,...,<cpu number>-<cpu number>
  53Note that for the special case of a range one can split the range into equal
  54sized groups and for each group use some amount from the beginning of that
  57        <cpu number>-cpu number>:<used size>/<group size>
  59For example one can add to the command line following parameter:
  61        isolcpus=1,2,10-20,100-2000:2/25
  63where the final item represents CPUs 100,101,125,126,150,151,...
  67This document may not be entirely up to date and comprehensive. The command
  68"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
  69module. Loadable modules, after being loaded into the running kernel, also
  70reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
  71parameters may be changed at runtime by the command
  72"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
  74The parameters listed below are only valid if certain kernel build options were
  75enabled and if respective hardware is present. The text in square brackets at
  76the beginning of each description states the restrictions within which a
  77parameter is applicable:
  79        ACPI    ACPI support is enabled.
  80        AGP     AGP (Accelerated Graphics Port) is enabled.
  81        ALSA    ALSA sound support is enabled.
  82        APIC    APIC support is enabled.
  83        APM     Advanced Power Management support is enabled.
  84        ARM     ARM architecture is enabled.
  85        AVR32   AVR32 architecture is enabled.
  86        AX25    Appropriate AX.25 support is enabled.
  87        BLACKFIN Blackfin architecture is enabled.
  88        CLK     Common clock infrastructure is enabled.
  89        CMA     Contiguous Memory Area support is enabled.
  90        DRM     Direct Rendering Management support is enabled.
  91        DYNAMIC_DEBUG Build in debug messages and enable them at runtime
  92        EDD     BIOS Enhanced Disk Drive Services (EDD) is enabled
  93        EFI     EFI Partitioning (GPT) is enabled
  94        EIDE    EIDE/ATAPI support is enabled.
  95        EVM     Extended Verification Module
  96        FB      The frame buffer device is enabled.
  97        FTRACE  Function tracing enabled.
  98        GCOV    GCOV profiling is enabled.
  99        HW      Appropriate hardware is enabled.
 100        IA-64   IA-64 architecture is enabled.
 101        IMA     Integrity measurement architecture is enabled.
 102        IOSCHED More than one I/O scheduler is enabled.
 103        IP_PNP  IP DHCP, BOOTP, or RARP is enabled.
 104        IPV6    IPv6 support is enabled.
 105        ISAPNP  ISA PnP code is enabled.
 106        ISDN    Appropriate ISDN support is enabled.
 107        JOY     Appropriate joystick support is enabled.
 108        KGDB    Kernel debugger support is enabled.
 109        KVM     Kernel Virtual Machine support is enabled.
 110        LIBATA  Libata driver is enabled
 111        LP      Printer support is enabled.
 112        LOOP    Loopback device support is enabled.
 113        M68k    M68k architecture is enabled.
 114                        These options have more detailed description inside of
 115                        Documentation/m68k/kernel-options.txt.
 116        MDA     MDA console support is enabled.
 117        MIPS    MIPS architecture is enabled.
 118        MOUSE   Appropriate mouse support is enabled.
 119        MSI     Message Signaled Interrupts (PCI).
 120        MTD     MTD (Memory Technology Device) support is enabled.
 121        NET     Appropriate network support is enabled.
 122        NUMA    NUMA support is enabled.
 123        NFS     Appropriate NFS support is enabled.
 124        OSS     OSS sound support is enabled.
 125        PV_OPS  A paravirtualized kernel is enabled.
 126        PARIDE  The ParIDE (parallel port IDE) subsystem is enabled.
 127        PARISC  The PA-RISC architecture is enabled.
 128        PCI     PCI bus support is enabled.
 129        PCIE    PCI Express support is enabled.
 130        PCMCIA  The PCMCIA subsystem is enabled.
 131        PNP     Plug & Play support is enabled.
 132        PPC     PowerPC architecture is enabled.
 133        PPT     Parallel port support is enabled.
 134        PS2     Appropriate PS/2 support is enabled.
 135        RAM     RAM disk support is enabled.
 136        S390    S390 architecture is enabled.
 137        SCSI    Appropriate SCSI support is enabled.
 138                        A lot of drivers have their options described inside
 139                        the Documentation/scsi/ sub-directory.
 140        SECURITY Different security models are enabled.
 141        SELINUX SELinux support is enabled.
 142        APPARMOR AppArmor support is enabled.
 143        SERIAL  Serial support is enabled.
 144        SH      SuperH architecture is enabled.
 145        SMP     The kernel is an SMP kernel.
 146        SPARC   Sparc architecture is enabled.
 147        SWSUSP  Software suspend (hibernation) is enabled.
 148        SUSPEND System suspend states are enabled.
 149        TPM     TPM drivers are enabled.
 150        TS      Appropriate touchscreen support is enabled.
 151        UMS     USB Mass Storage support is enabled.
 152        USB     USB support is enabled.
 153        USBHID  USB Human Interface Device support is enabled.
 154        V4L     Video For Linux support is enabled.
 155        VMMIO   Driver for memory mapped virtio devices is enabled.
 156        VGA     The VGA console has been enabled.
 157        VT      Virtual terminal support is enabled.
 158        WDT     Watchdog support is enabled.
 159        XT      IBM PC/XT MFM hard disk support is enabled.
 160        X86-32  X86-32, aka i386 architecture is enabled.
 161        X86-64  X86-64 architecture is enabled.
 162                        More X86-64 boot options can be found in
 163                        Documentation/x86/x86_64/boot-options.txt .
 164        X86     Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
 165        X86_UV  SGI UV support is enabled.
 166        XEN     Xen support is enabled
 168In addition, the following text indicates that the option:
 170        BUGS=   Relates to possible processor bugs on the said processor.
 171        KNL     Is a kernel start-up parameter.
 172        BOOT    Is a boot loader parameter.
 174Parameters denoted with BOOT are actually interpreted by the boot
 175loader, and have no meaning to the kernel directly.
 176Do not modify the syntax of boot loader parameters without extreme
 177need or coordination with <Documentation/x86/boot.txt>.
 179There are also arch-specific kernel-parameters not documented here.
 180See for example <Documentation/x86/x86_64/boot-options.txt>.
 182Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
 183a trailing = on the name of any parameter states that that parameter will
 184be entered as an environment variable, whereas its absence indicates that
 185it will appear as a kernel argument readable via /proc/cmdline by programs
 186running once the system is up.
 188The number of kernel parameters is not limited, but the length of the
 189complete command line (parameters including spaces etc.) is limited to
 190a fixed number of characters. This limit depends on the architecture
 191and is between 256 and 4096 characters. It is defined in the file
 192./include/asm/setup.h as COMMAND_LINE_SIZE.
 194Finally, the [KMG] suffix is commonly described after a number of kernel
 195parameter values. These 'K', 'M', and 'G' letters represent the _binary_
 196multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
 197bytes respectively. Such letter suffixes can also be entirely omitted.
 200        acpi=           [HW,ACPI,X86,ARM64]
 201                        Advanced Configuration and Power Interface
 202                        Format: { force | on | off | strict | noirq | rsdt |
 203                                  copy_dsdt }
 204                        force -- enable ACPI if default was off
 205                        on -- enable ACPI but allow fallback to DT [arm64]
 206                        off -- disable ACPI if default was on
 207                        noirq -- do not use ACPI for IRQ routing
 208                        strict -- Be less tolerant of platforms that are not
 209                                strictly ACPI specification compliant.
 210                        rsdt -- prefer RSDT over (default) XSDT
 211                        copy_dsdt -- copy DSDT to memory
 212                        For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
 213                        are available
 215                        See also Documentation/power/runtime_pm.txt, pci=noacpi
 217        acpi_apic_instance=     [ACPI, IOAPIC]
 218                        Format: <int>
 219                        2: use 2nd APIC table, if available
 220                        1,0: use 1st APIC table
 221                        default: 0
 223        acpi_backlight= [HW,ACPI]
 224                        acpi_backlight=vendor
 225                        acpi_backlight=video
 226                        If set to vendor, prefer vendor specific driver
 227                        (e.g. thinkpad_acpi, sony_acpi, etc.) instead
 228                        of the ACPI video.ko driver.
 230        acpi_force_32bit_fadt_addr
 231                        force FADT to use 32 bit addresses rather than the
 232                        64 bit X_* addresses. Some firmware have broken 64
 233                        bit addresses for force ACPI ignore these and use
 234                        the older legacy 32 bit addresses.
 236        acpica_no_return_repair [HW, ACPI]
 237                        Disable AML predefined validation mechanism
 238                        This mechanism can repair the evaluation result to make
 239                        the return objects more ACPI specification compliant.
 240                        This option is useful for developers to identify the
 241                        root cause of an AML interpreter issue when the issue
 242                        has something to do with the repair mechanism.
 244        acpi.debug_layer=       [HW,ACPI,ACPI_DEBUG]
 245        acpi.debug_level=       [HW,ACPI,ACPI_DEBUG]
 246                        Format: <int>
 247                        CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
 248                        debug output.  Bits in debug_layer correspond to a
 249                        _COMPONENT in an ACPI source file, e.g.,
 250                            #define _COMPONENT ACPI_PCI_COMPONENT
 251                        Bits in debug_level correspond to a level in
 252                        ACPI_DEBUG_PRINT statements, e.g.,
 253                            ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
 254                        The debug_level mask defaults to "info".  See
 255                        Documentation/acpi/debug.txt for more information about
 256                        debug layers and levels.
 258                        Enable processor driver info messages:
 259                            acpi.debug_layer=0x20000000
 260                        Enable PCI/PCI interrupt routing info messages:
 261                            acpi.debug_layer=0x400000
 262                        Enable AML "Debug" output, i.e., stores to the Debug
 263                        object while interpreting AML:
 264                            acpi.debug_layer=0xffffffff acpi.debug_level=0x2
 265                        Enable all messages related to ACPI hardware:
 266                            acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
 268                        Some values produce so much output that the system is
 269                        unusable.  The "log_buf_len" parameter may be useful
 270                        if you need to capture more output.
 272        acpi_enforce_resources= [ACPI]
 273                        { strict | lax | no }
 274                        Check for resource conflicts between native drivers
 275                        and ACPI OperationRegions (SystemIO and SystemMemory
 276                        only). IO ports and memory declared in ACPI might be
 277                        used by the ACPI subsystem in arbitrary AML code and
 278                        can interfere with legacy drivers.
 279                        strict (default): access to resources claimed by ACPI
 280                        is denied; legacy drivers trying to access reserved
 281                        resources will fail to bind to device using them.
 282                        lax: access to resources claimed by ACPI is allowed;
 283                        legacy drivers trying to access reserved resources
 284                        will bind successfully but a warning message is logged.
 285                        no: ACPI OperationRegions are not marked as reserved,
 286                        no further checks are performed.
 288        acpi_force_table_verification   [HW,ACPI]
 289                        Enable table checksum verification during early stage.
 290                        By default, this is disabled due to x86 early mapping
 291                        size limitation.
 293        acpi_irq_balance [HW,ACPI]
 294                        ACPI will balance active IRQs
 295                        default in APIC mode
 297        acpi_irq_nobalance [HW,ACPI]
 298                        ACPI will not move active IRQs (default)
 299                        default in PIC mode
 301        acpi_irq_isa=   [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
 302                        Format: <irq>,<irq>...
 304        acpi_irq_pci=   [HW,ACPI] If irq_balance, clear listed IRQs for
 305                        use by PCI
 306                        Format: <irq>,<irq>...
 308        acpi_no_auto_serialize  [HW,ACPI]
 309                        Disable auto-serialization of AML methods
 310                        AML control methods that contain the opcodes to create
 311                        named objects will be marked as "Serialized" by the
 312                        auto-serialization feature.
 313                        This feature is enabled by default.
 314                        This option allows to turn off the feature.
 316        acpi_no_memhotplug [ACPI] Disable memory hotplug.  Useful for kdump
 317                           kernels.
 319        acpi_no_static_ssdt     [HW,ACPI]
 320                        Disable installation of static SSDTs at early boot time
 321                        By default, SSDTs contained in the RSDT/XSDT will be
 322                        installed automatically and they will appear under
 323                        /sys/firmware/acpi/tables.
 324                        This option turns off this feature.
 325                        Note that specifying this option does not affect
 326                        dynamic table installation which will install SSDT
 327                        tables to /sys/firmware/acpi/tables/dynamic.
 329        acpi_rsdp=      [ACPI,EFI,KEXEC]
 330                        Pass the RSDP address to the kernel, mostly used
 331                        on machines running EFI runtime service to boot the
 332                        second kernel for kdump.
 334        acpi_os_name=   [HW,ACPI] Tell ACPI BIOS the name of the OS
 335                        Format: To spoof as Windows 98: ="Microsoft Windows"
 337        acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
 338                        of 2 which is mandated by ACPI 6) as the supported ACPI
 339                        specification revision (when using this switch, it may
 340                        be necessary to carry out a cold reboot _twice_ in a
 341                        row to make it take effect on the platform firmware).
 343        acpi_osi=       [HW,ACPI] Modify list of supported OS interface strings
 344                        acpi_osi="string1"      # add string1
 345                        acpi_osi="!string2"     # remove string2
 346                        acpi_osi=!*             # remove all strings
 347                        acpi_osi=!              # disable all built-in OS vendor
 348                                                  strings
 349                        acpi_osi=!!             # enable all built-in OS vendor
 350                                                  strings
 351                        acpi_osi=               # disable all strings
 353                        'acpi_osi=!' can be used in combination with single or
 354                        multiple 'acpi_osi="string1"' to support specific OS
 355                        vendor string(s).  Note that such command can only
 356                        affect the default state of the OS vendor strings, thus
 357                        it cannot affect the default state of the feature group
 358                        strings and the current state of the OS vendor strings,
 359                        specifying it multiple times through kernel command line
 360                        is meaningless.  This command is useful when one do not
 361                        care about the state of the feature group strings which
 362                        should be controlled by the OSPM.
 363                        Examples:
 364                          1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
 365                             to 'acpi_osi="Windows 2000" acpi_osi=!', they all
 366                             can make '_OSI("Windows 2000")' TRUE.
 368                        'acpi_osi=' cannot be used in combination with other
 369                        'acpi_osi=' command lines, the _OSI method will not
 370                        exist in the ACPI namespace.  NOTE that such command can
 371                        only affect the _OSI support state, thus specifying it
 372                        multiple times through kernel command line is also
 373                        meaningless.
 374                        Examples:
 375                          1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
 376                             FALSE.
 378                        'acpi_osi=!*' can be used in combination with single or
 379                        multiple 'acpi_osi="string1"' to support specific
 380                        string(s).  Note that such command can affect the
 381                        current state of both the OS vendor strings and the
 382                        feature group strings, thus specifying it multiple times
 383                        through kernel command line is meaningful.  But it may
 384                        still not able to affect the final state of a string if
 385                        there are quirks related to this string.  This command
 386                        is useful when one want to control the state of the
 387                        feature group strings to debug BIOS issues related to
 388                        the OSPM features.
 389                        Examples:
 390                          1. 'acpi_osi="Module Device" acpi_osi=!*' can make
 391                             '_OSI("Module Device")' FALSE.
 392                          2. 'acpi_osi=!* acpi_osi="Module Device"' can make
 393                             '_OSI("Module Device")' TRUE.
 394                          3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
 395                             equivalent to
 396                             'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
 397                             and
 398                             'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
 399                             they all will make '_OSI("Windows 2000")' TRUE.
 401        acpi_pm_good    [X86]
 402                        Override the pmtimer bug detection: force the kernel
 403                        to assume that this machine's pmtimer latches its value
 404                        and always returns good values.
 406        acpi_sci=       [HW,ACPI] ACPI System Control Interrupt trigger mode
 407                        Format: { level | edge | high | low }
 409        acpi_skip_timer_override [HW,ACPI]
 410                        Recognize and ignore IRQ0/pin2 Interrupt Override.
 411                        For broken nForce2 BIOS resulting in XT-PIC timer.
 413        acpi_sleep=     [HW,ACPI] Sleep options
 414                        Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
 415                                  old_ordering, nonvs, sci_force_enable }
 416                        See Documentation/power/video.txt for information on
 417                        s3_bios and s3_mode.
 418                        s3_beep is for debugging; it makes the PC's speaker beep
 419                        as soon as the kernel's real-mode entry point is called.
 420                        s4_nohwsig prevents ACPI hardware signature from being
 421                        used during resume from hibernation.
 422                        old_ordering causes the ACPI 1.0 ordering of the _PTS
 423                        control method, with respect to putting devices into
 424                        low power states, to be enforced (the ACPI 2.0 ordering
 425                        of _PTS is used by default).
 426                        nonvs prevents the kernel from saving/restoring the
 427                        ACPI NVS memory during suspend/hibernation and resume.
 428                        sci_force_enable causes the kernel to set SCI_EN directly
 429                        on resume from S1/S3 (which is against the ACPI spec,
 430                        but some broken systems don't work without it).
 432        acpi_use_timer_override [HW,ACPI]
 433                        Use timer override. For some broken Nvidia NF5 boards
 434                        that require a timer override, but don't have HPET
 436        add_efi_memmap  [EFI; X86] Include EFI memory map in
 437                        kernel's map of available physical RAM.
 439        agp=            [AGP]
 440                        { off | try_unsupported }
 441                        off: disable AGP support
 442                        try_unsupported: try to drive unsupported chipsets
 443                                (may crash computer or cause data corruption)
 445        ALSA            [HW,ALSA]
 446                        See Documentation/sound/alsa/alsa-parameters.txt
 448        alignment=      [KNL,ARM]
 449                        Allow the default userspace alignment fault handler
 450                        behaviour to be specified.  Bit 0 enables warnings,
 451                        bit 1 enables fixups, and bit 2 sends a segfault.
 453        align_va_addr=  [X86-64]
 454                        Align virtual addresses by clearing slice [14:12] when
 455                        allocating a VMA at process creation time. This option
 456                        gives you up to 3% performance improvement on AMD F15h
 457                        machines (where it is enabled by default) for a
 458                        CPU-intensive style benchmark, and it can vary highly in
 459                        a microbenchmark depending on workload and compiler.
 461                        32: only for 32-bit processes
 462                        64: only for 64-bit processes
 463                        on: enable for both 32- and 64-bit processes
 464                        off: disable for both 32- and 64-bit processes
 466        alloc_snapshot  [FTRACE]
 467                        Allocate the ftrace snapshot buffer on boot up when the
 468                        main buffer is allocated. This is handy if debugging
 469                        and you need to use tracing_snapshot() on boot up, and
 470                        do not want to use tracing_snapshot_alloc() as it needs
 471                        to be done where GFP_KERNEL allocations are allowed.
 473        amd_iommu=      [HW,X86-64]
 474                        Pass parameters to the AMD IOMMU driver in the system.
 475                        Possible values are:
 476                        fullflush - enable flushing of IO/TLB entries when
 477                                    they are unmapped. Otherwise they are
 478                                    flushed before they will be reused, which
 479                                    is a lot of faster
 480                        off       - do not initialize any AMD IOMMU found in
 481                                    the system
 482                        force_isolation - Force device isolation for all
 483                                          devices. The IOMMU driver is not
 484                                          allowed anymore to lift isolation
 485                                          requirements as needed. This option
 486                                          does not override iommu=pt
 488        amd_iommu_dump= [HW,X86-64]
 489                        Enable AMD IOMMU driver option to dump the ACPI table
 490                        for AMD IOMMU. With this option enabled, AMD IOMMU
 491                        driver will print ACPI tables for AMD IOMMU during
 492                        IOMMU initialization.
 494        amd_iommu_intr= [HW,X86-64]
 495                        Specifies one of the following AMD IOMMU interrupt
 496                        remapping modes:
 497                        legacy     - Use legacy interrupt remapping mode.
 498                        vapic      - Use virtual APIC mode, which allows IOMMU
 499                                     to inject interrupts directly into guest.
 500                                     This mode requires kvm-amd.avic=1.
 501                                     (Default when IOMMU HW support is present.)
 503     [HW,JOY] Amiga joystick support
 504                        Map of devices attached to JOY0DAT and JOY1DAT
 505                        Format: <a>,<b>
 506                        See also Documentation/input/joystick.txt
 508     [HW,JOY] Analog joystick and gamepad support
 509                        Specifies type or capabilities of an analog joystick
 510                        connected to one of 16 gameports
 511                        Format: <type1>,<type2>,..<type16>
 513        apc=            [HW,SPARC]
 514                        Power management functions (SPARCstation-4/5 + deriv.)
 515                        Format: noidle
 516                        Disable APC CPU standby support. SPARCstation-Fox does
 517                        not play well with APC CPU idle - disable it if you have
 518                        APC and your system crashes randomly.
 520        apic=           [APIC,X86-32] Advanced Programmable Interrupt Controller
 521                        Change the output verbosity whilst booting
 522                        Format: { quiet (default) | verbose | debug }
 523                        Change the amount of debugging information output
 524                        when initialising the APIC and IO-APIC components.
 526        apic_extnmi=    [APIC,X86] External NMI delivery setting
 527                        Format: { bsp (default) | all | none }
 528                        bsp:  External NMI is delivered only to CPU 0
 529                        all:  External NMIs are broadcast to all CPUs as a
 530                              backup of CPU 0
 531                        none: External NMI is masked for all CPUs. This is
 532                              useful so that a dump capture kernel won't be
 533                              shot down by NMI
 535        autoconf=       [IPV6]
 536                        See Documentation/networking/ipv6.txt.
 538        show_lapic=     [APIC,X86] Advanced Programmable Interrupt Controller
 539                        Limit apic dumping. The parameter defines the maximal
 540                        number of local apics being dumped. Also it is possible
 541                        to set it to "all" by meaning -- no limit here.
 542                        Format: { 1 (default) | 2 | ... | all }.
 543                        The parameter valid if only apic=debug or
 544                        apic=verbose is specified.
 545                        Example: apic=debug show_lapic=all
 547        apm=            [APM] Advanced Power Management
 548                        See header of arch/x86/kernel/apm_32.c.
 550        arcrimi=        [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
 551                        Format: <io>,<irq>,<nodeID>
 553        ataflop=        [HW,M68k]
 555        atarimouse=     [HW,MOUSE] Atari Mouse
 557        atkbd.extra=    [HW] Enable extra LEDs and keys on IBM RapidAccess,
 558                        EzKey and similar keyboards
 560        atkbd.reset=    [HW] Reset keyboard during initialization
 562        atkbd.set=      [HW] Select keyboard code set
 563                        Format: <int> (2 = AT (default), 3 = PS/2)
 565        atkbd.scroll=   [HW] Enable scroll wheel on MS Office and similar
 566                        keyboards
 568        atkbd.softraw=  [HW] Choose between synthetic and real raw mode
 569                        Format: <bool> (0 = real, 1 = synthetic (default))
 571        atkbd.softrepeat= [HW]
 572                        Use software keyboard repeat
 574        audit=          [KNL] Enable the audit sub-system
 575                        Format: { "0" | "1" } (0 = disabled, 1 = enabled)
 576                        0 - kernel audit is disabled and can not be enabled
 577                            until the next reboot
 578                        unset - kernel audit is initialized but disabled and
 579                            will be fully enabled by the userspace auditd.
 580                        1 - kernel audit is initialized and partially enabled,
 581                            storing at most audit_backlog_limit messages in
 582                            RAM until it is fully enabled by the userspace
 583                            auditd.
 584                        Default: unset
 586        audit_backlog_limit= [KNL] Set the audit queue size limit.
 587                        Format: <int> (must be >=0)
 588                        Default: 64
 590        bau=            [X86_UV] Enable the BAU on SGI UV.  The default
 591                        behavior is to disable the BAU (i.e. bau=0).
 592                        Format: { "0" | "1" }
 593                        0 - Disable the BAU.
 594                        1 - Enable the BAU.
 595                        unset - Disable the BAU.
 597        baycom_epp=     [HW,AX25]
 598                        Format: <io>,<mode>
 600        baycom_par=     [HW,AX25] BayCom Parallel Port AX.25 Modem
 601                        Format: <io>,<mode>
 602                        See header of drivers/net/hamradio/baycom_par.c.
 604        baycom_ser_fdx= [HW,AX25]
 605                        BayCom Serial Port AX.25 Modem (Full Duplex Mode)
 606                        Format: <io>,<irq>,<mode>[,<baud>]
 607                        See header of drivers/net/hamradio/baycom_ser_fdx.c.
 609        baycom_ser_hdx= [HW,AX25]
 610                        BayCom Serial Port AX.25 Modem (Half Duplex Mode)
 611                        Format: <io>,<irq>,<mode>
 612                        See header of drivers/net/hamradio/baycom_ser_hdx.c.
 614        blkdevparts=    Manual partition parsing of block device(s) for
 615                        embedded devices based on command line input.
 616                        See Documentation/block/cmdline-partition.txt
 618        boot_delay=     Milliseconds to delay each printk during boot.
 619                        Values larger than 10 seconds (10000) are changed to
 620                        no delay (0).
 621                        Format: integer
 623        bootmem_debug   [KNL] Enable bootmem allocator debug messages.
 625        bert_disable    [ACPI]
 626                        Disable BERT OS support on buggy BIOSes.
 628        bttv.card=      [HW,V4L] bttv (bt848 + bt878 based grabber cards)
 629     Most important insmod options are available as
 630                        kernel args too.
 631        bttv.pll=       See Documentation/video4linux/bttv/Insmod-options
 632        bttv.tuner=
 634        bulk_remove=off [PPC]  This parameter disables the use of the pSeries
 635                        firmware feature for flushing multiple hpte entries
 636                        at a time.
 638        c101=           [NET] Moxa C101 synchronous serial card
 640        cachesize=      [BUGS=X86-32] Override level 2 CPU cache size detection.
 641                        Sometimes CPU hardware bugs make them report the cache
 642                        size incorrectly. The kernel will attempt work arounds
 643                        to fix known problems, but for some CPUs it is not
 644                        possible to determine what the correct size should be.
 645                        This option provides an override for these situations.
 647        ca_keys=        [KEYS] This parameter identifies a specific key(s) on
 648                        the system trusted keyring to be used for certificate
 649                        trust validation.
 650                        format: { id:<keyid> | builtin }
 652        cca=            [MIPS] Override the kernel pages' cache coherency
 653                        algorithm.  Accepted values range from 0 to 7
 654                        inclusive. See arch/mips/include/asm/pgtable-bits.h
 655                        for platform specific values (SB1, Loongson3 and
 656                        others).
 658        ccw_timeout_log [S390]
 659                        See Documentation/s390/CommonIO for details.
 661        cgroup_disable= [KNL] Disable a particular controller
 662                        Format: {name of the controller(s) to disable}
 663                        The effects of cgroup_disable=foo are:
 664                        - foo isn't auto-mounted if you mount all cgroups in
 665                          a single hierarchy
 666                        - foo isn't visible as an individually mountable
 667                          subsystem
 668                        {Currently only "memory" controller deal with this and
 669                        cut the overhead, others just disable the usage. So
 670                        only cgroup_disable=memory is actually worthy}
 672        cgroup_no_v1=   [KNL] Disable one, multiple, all cgroup controllers in v1
 673                        Format: { controller[,controller...] | "all" }
 674                        Like cgroup_disable, but only applies to cgroup v1;
 675                        the blacklisted controllers remain available in cgroup2.
 677        cgroup.memory=  [KNL] Pass options to the cgroup memory controller.
 678                        Format: <string>
 679                        nosocket -- Disable socket memory accounting.
 680                        nokmem -- Disable kernel memory accounting.
 682        checkreqprot    [SELINUX] Set initial checkreqprot flag value.
 683                        Format: { "0" | "1" }
 684                        See security/selinux/Kconfig help text.
 685                        0 -- check protection applied by kernel (includes
 686                                any implied execute protection).
 687                        1 -- check protection requested by application.
 688                        Default value is set via a kernel config option.
 689                        Value can be changed at runtime via
 690                                /selinux/checkreqprot.
 692        cio_ignore=     [S390]
 693                        See Documentation/s390/CommonIO for details.
 694        clk_ignore_unused
 695                        [CLK]
 696                        Prevents the clock framework from automatically gating
 697                        clocks that have not been explicitly enabled by a Linux
 698                        device driver but are enabled in hardware at reset or
 699                        by the bootloader/firmware. Note that this does not
 700                        force such clocks to be always-on nor does it reserve
 701                        those clocks in any way. This parameter is useful for
 702                        debug and development, but should not be needed on a
 703                        platform with proper driver support.  For more
 704                        information, see Documentation/clk.txt.
 706        clock=          [BUGS=X86-32, HW] gettimeofday clocksource override.
 707                        [Deprecated]
 708                        Forces specified clocksource (if available) to be used
 709                        when calculating gettimeofday(). If specified
 710                        clocksource is not available, it defaults to PIT.
 711                        Format: { pit | tsc | cyclone | pmtmr }
 713        clocksource=    Override the default clocksource
 714                        Format: <string>
 715                        Override the default clocksource and use the clocksource
 716                        with the name specified.
 717                        Some clocksource names to choose from, depending on
 718                        the platform:
 719                        [all] jiffies (this is the base, fallback clocksource)
 720                        [ACPI] acpi_pm
 721                        [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
 722                                pxa_timer,timer3,32k_counter,timer0_1
 723                        [AVR32] avr32
 724                        [X86-32] pit,hpet,tsc;
 725                                scx200_hrt on Geode; cyclone on IBM x440
 726                        [MIPS] MIPS
 727                        [PARISC] cr16
 728                        [S390] tod
 729                        [SH] SuperH
 730                        [SPARC64] tick
 731                        [X86-64] hpet,tsc
 733        clocksource.arm_arch_timer.evtstrm=
 734                        [ARM,ARM64]
 735                        Format: <bool>
 736                        Enable/disable the eventstream feature of the ARM
 737                        architected timer so that code using WFE-based polling
 738                        loops can be debugged more effectively on production
 739                        systems.
 741        clocksource.arm_arch_timer.fsl-a008585=
 742                        [ARM64]
 743                        Format: <bool>
 744                        Enable/disable the workaround of Freescale/NXP
 745                        erratum A-008585.  This can be useful for KVM
 746                        guests, if the guest device tree doesn't show the
 747                        erratum.  If unspecified, the workaround is
 748                        enabled based on the device tree.
 750        clearcpuid=BITNUM [X86]
 751                        Disable CPUID feature X for the kernel. See
 752                        arch/x86/include/asm/cpufeatures.h for the valid bit
 753                        numbers. Note the Linux specific bits are not necessarily
 754                        stable over kernel options, but the vendor specific
 755                        ones should be.
 756                        Also note that user programs calling CPUID directly
 757                        or using the feature without checking anything
 758                        will still see it. This just prevents it from
 759                        being used by the kernel or shown in /proc/cpuinfo.
 760                        Also note the kernel might malfunction if you disable
 761                        some critical bits.
 763        cma=nn[MG]@[start[MG][-end[MG]]]
 764                        [ARM,X86,KNL]
 765                        Sets the size of kernel global memory area for
 766                        contiguous memory allocations and optionally the
 767                        placement constraint by the physical address range of
 768                        memory allocations. A value of 0 disables CMA
 769                        altogether. For more information, see
 770                        include/linux/dma-contiguous.h
 772        cmo_free_hint=  [PPC] Format: { yes | no }
 773                        Specify whether pages are marked as being inactive
 774                        when they are freed.  This is used in CMO environments
 775                        to determine OS memory pressure for page stealing by
 776                        a hypervisor.
 777                        Default: yes
 779        coherent_pool=nn[KMG]   [ARM,KNL]
 780                        Sets the size of memory pool for coherent, atomic dma
 781                        allocations, by default set to 256K.
 783        code_bytes      [X86] How many bytes of object code to print
 784                        in an oops report.
 785                        Range: 0 - 8192
 786                        Default: 64
 788        com20020=       [HW,NET] ARCnet - COM20020 chipset
 789                        Format:
 790                        <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
 792        com90io=        [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
 793                        Format: <io>[,<irq>]
 795        com90xx=        [HW,NET]
 796                        ARCnet - COM90xx chipset (memory-mapped buffers)
 797                        Format: <io>[,<irq>[,<memstart>]]
 799        condev=         [HW,S390] console device
 800        conmode=
 802        console=        [KNL] Output console device and options.
 804                tty<n>  Use the virtual console device <n>.
 806                ttyS<n>[,options]
 807                ttyUSB0[,options]
 808                        Use the specified serial port.  The options are of
 809                        the form "bbbbpnf", where "bbbb" is the baud rate,
 810                        "p" is parity ("n", "o", or "e"), "n" is number of
 811                        bits, and "f" is flow control ("r" for RTS or
 812                        omit it).  Default is "9600n8".
 814                        See Documentation/serial-console.txt for more
 815                        information.  See
 816                        Documentation/networking/netconsole.txt for an
 817                        alternative.
 819                uart[8250],io,<addr>[,options]
 820                uart[8250],mmio,<addr>[,options]
 821                uart[8250],mmio16,<addr>[,options]
 822                uart[8250],mmio32,<addr>[,options]
 823                uart[8250],0x<addr>[,options]
 824                        Start an early, polled-mode console on the 8250/16550
 825                        UART at the specified I/O port or MMIO address,
 826                        switching to the matching ttyS device later.
 827                        MMIO inter-register address stride is either 8-bit
 828                        (mmio), 16-bit (mmio16), or 32-bit (mmio32).
 829                        If none of [io|mmio|mmio16|mmio32], <addr> is assumed
 830                        to be equivalent to 'mmio'. 'options' are specified in
 831                        the same format described for ttyS above; if unspecified,
 832                        the h/w is not re-initialized.
 834                hvc<n>  Use the hypervisor console device <n>. This is for
 835                        both Xen and PowerPC hypervisors.
 837                If the device connected to the port is not a TTY but a braille
 838                device, prepend "brl," before the device type, for instance
 839                        console=brl,ttyS0
 840                For now, only VisioBraille is supported.
 842        consoleblank=   [KNL] The console blank (screen saver) timeout in
 843                        seconds. Defaults to 10*60 = 10mins. A value of 0
 844                        disables the blank timer.
 846        coredump_filter=
 847                        [KNL] Change the default value for
 848                        /proc/<pid>/coredump_filter.
 849                        See also Documentation/filesystems/proc.txt.
 851   [CPU_IDLE]
 852                        disable the cpuidle sub-system
 854        cpu_init_udelay=N
 855                        [X86] Delay for N microsec between assert and de-assert
 856                        of APIC INIT to start processors.  This delay occurs
 857                        on every CPU online, such as boot, and resume from suspend.
 858                        Default: 10000
 860        cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
 861                        Format:
 862                        <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
 864        crashkernel=size[KMG][@offset[KMG]]
 865                        [KNL] Using kexec, Linux can switch to a 'crash kernel'
 866                        upon panic. This parameter reserves the physical
 867                        memory region [offset, offset + size] for that kernel
 868                        image. If '@offset' is omitted, then a suitable offset
 869                        is selected automatically. Check
 870                        Documentation/kdump/kdump.txt for further details.
 872        crashkernel=range1:size1[,range2:size2,...][@offset]
 873                        [KNL] Same as above, but depends on the memory
 874                        in the running system. The syntax of range is
 875                        start-[end] where start and end are both
 876                        a memory unit (amount[KMG]). See also
 877                        Documentation/kdump/kdump.txt for an example.
 879        crashkernel=size[KMG],high
 880                        [KNL, x86_64] range could be above 4G. Allow kernel
 881                        to allocate physical memory region from top, so could
 882                        be above 4G if system have more than 4G ram installed.
 883                        Otherwise memory region will be allocated below 4G, if
 884                        available.
 885                        It will be ignored if crashkernel=X is specified.
 886        crashkernel=size[KMG],low
 887                        [KNL, x86_64] range under 4G. When crashkernel=X,high
 888                        is passed, kernel could allocate physical memory region
 889                        above 4G, that cause second kernel crash on system
 890                        that require some amount of low memory, e.g. swiotlb
 891                        requires at least 64M+32K low memory, also enough extra
 892                        low memory is needed to make sure DMA buffers for 32-bit
 893                        devices won't run out. Kernel would try to allocate at
 894                        at least 256M below 4G automatically.
 895                        This one let user to specify own low range under 4G
 896                        for second kernel instead.
 897                        0: to disable low allocation.
 898                        It will be ignored when crashkernel=X,high is not used
 899                        or memory reserved is below 4G.
 901        cryptomgr.notests
 902                        [KNL] Disable crypto self-tests
 904        cs89x0_dma=     [HW,NET]
 905                        Format: <dma>
 907        cs89x0_media=   [HW,NET]
 908                        Format: { rj45 | aui | bnc }
 910        dasd=           [HW,NET]
 911                        See header of drivers/s390/block/dasd_devmap.c.
 913[2|3]=   [HW,JOY] Multisystem joystick support via parallel port
 914                        (one device per port)
 915                        Format: <port#>,<type>
 916                        See also Documentation/input/joystick-parport.txt
 918        ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
 919                        time. See Documentation/dynamic-debug-howto.txt for
 920                        details.  Deprecated, see dyndbg.
 922        debug           [KNL] Enable kernel debugging (events log level).
 924        debug_locks_verbose=
 925                        [KNL] verbose self-tests
 926                        Format=<0|1>
 927                        Print debugging info while doing the locking API
 928                        self-tests.
 929                        We default to 0 (no extra messages), setting it to
 930                        1 will print _a lot_ more information - normally
 931                        only useful to kernel developers.
 933        debug_objects   [KNL] Enable object debugging
 935        no_debug_objects
 936                        [KNL] Disable object debugging
 938        debug_guardpage_minorder=
 939                        [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
 940                        parameter allows control of the order of pages that will
 941                        be intentionally kept free (and hence protected) by the
 942                        buddy allocator. Bigger value increase the probability
 943                        of catching random memory corruption, but reduce the
 944                        amount of memory for normal system use. The maximum
 945                        possible value is MAX_ORDER/2.  Setting this parameter
 946                        to 1 or 2 should be enough to identify most random
 947                        memory corruption problems caused by bugs in kernel or
 948                        driver code when a CPU writes to (or reads from) a
 949                        random memory location. Note that there exists a class
 950                        of memory corruptions problems caused by buggy H/W or
 951                        F/W or by drivers badly programing DMA (basically when
 952                        memory is written at bus level and the CPU MMU is
 953                        bypassed) which are not detectable by
 954                        CONFIG_DEBUG_PAGEALLOC, hence this option will not help
 955                        tracking down these problems.
 957        debug_pagealloc=
 958                        [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
 959                        parameter enables the feature at boot time. In
 960                        default, it is disabled. We can avoid allocating huge
 961                        chunk of memory for debug pagealloc if we don't enable
 962                        it at boot time and the system will work mostly same
 963                        with the kernel built without CONFIG_DEBUG_PAGEALLOC.
 964                        on: enable the feature
 966        debugpat        [X86] Enable PAT debugging
 968        decnet.addr=    [HW,NET]
 969                        Format: <area>[,<node>]
 970                        See also Documentation/networking/decnet.txt.
 972        default_hugepagesz=
 973                        [same as hugepagesz=] The size of the default
 974                        HugeTLB page size. This is the size represented by
 975                        the legacy /proc/ hugepages APIs, used for SHM, and
 976                        default size when mounting hugetlbfs filesystems.
 977                        Defaults to the default architecture's huge page size
 978                        if not specified.
 980        dhash_entries=  [KNL]
 981                        Set number of hash buckets for dentry cache.
 983        disable_1tb_segments [PPC]
 984                        Disables the use of 1TB hash page table segments. This
 985                        causes the kernel to fall back to 256MB segments which
 986                        can be useful when debugging issues that require an SLB
 987                        miss to occur.
 989        disable=        [IPV6]
 990                        See Documentation/networking/ipv6.txt.
 992        disable_radix   [PPC]
 993                        Disable RADIX MMU mode on POWER9
 995        disable_cpu_apicid= [X86,APIC,SMP]
 996                        Format: <int>
 997                        The number of initial APIC ID for the
 998                        corresponding CPU to be disabled at boot,
 999                        mostly used for the kdump 2nd kernel to
1000                        disable BSP to wake up multiple CPUs without
1001                        causing system reset or hang due to sending
1002                        INIT from AP to BSP.
1004        disable_ddw     [PPC/PSERIES]
1005                        Disable Dynamic DMA Window support. Use this if
1006                        to workaround buggy firmware.
1008        disable_ipv6=   [IPV6]
1009                        See Documentation/networking/ipv6.txt.
1011        disable_mtrr_cleanup [X86]
1012                        The kernel tries to adjust MTRR layout from continuous
1013                        to discrete, to make X server driver able to add WB
1014                        entry later. This parameter disables that.
1016        disable_mtrr_trim [X86, Intel and AMD only]
1017                        By default the kernel will trim any uncacheable
1018                        memory out of your available memory pool based on
1019                        MTRR settings.  This parameter disables that behavior,
1020                        possibly causing your machine to run very slowly.
1022        disable_timer_pin_1 [X86]
1023                        Disable PIN 1 of APIC timer
1024                        Can be useful to work around chipset bugs.
1026        dis_ucode_ldr   [X86] Disable the microcode loader.
1028        dma_debug=off   If the kernel is compiled with DMA_API_DEBUG support,
1029                        this option disables the debugging code at boot.
1031        dma_debug_entries=<number>
1032                        This option allows to tune the number of preallocated
1033                        entries for DMA-API debugging code. One entry is
1034                        required per DMA-API allocation. Use this if the
1035                        DMA-API debugging code disables itself because the
1036                        architectural default is too low.
1038        dma_debug_driver=<driver_name>
1039                        With this option the DMA-API debugging driver
1040                        filter feature can be enabled at boot time. Just
1041                        pass the driver to filter for as the parameter.
1042                        The filter can be disabled or changed to another
1043                        driver later using sysfs.
1045        drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
1046                        Broken monitors, graphic adapters, KVMs and EDIDless
1047                        panels may send no or incorrect EDID data sets.
1048                        This parameter allows to specify an EDID data sets
1049                        in the /lib/firmware directory that are used instead.
1050                        Generic built-in EDID data sets are used, if one of
1051                        edid/1024x768.bin, edid/1280x1024.bin,
1052                        edid/1680x1050.bin, or edid/1920x1080.bin is given
1053                        and no file with the same name exists. Details and
1054                        instructions how to build your own EDID data are
1055                        available in Documentation/EDID/HOWTO.txt. An EDID
1056                        data set will only be used for a particular connector,
1057                        if its name and a colon are prepended to the EDID
1058                        name. Each connector may use a unique EDID data
1059                        set by separating the files with a comma.  An EDID
1060                        data set with no connector name will be used for
1061                        any connectors not explicitly specified.
1063        dscc4.setup=    [NET]
1065        dyndbg[="val"]          [KNL,DYNAMIC_DEBUG]
1066        module.dyndbg[="val"]
1067                        Enable debug messages at boot time.  See
1068                        Documentation/dynamic-debug-howto.txt for details.
1070        nompx           [X86] Disables Intel Memory Protection Extensions.
1071                        See Documentation/x86/intel_mpx.txt for more
1072                        information about the feature.
1074        nopku           [X86] Disable Memory Protection Keys CPU feature found
1075                        in some Intel CPUs.
1077        eagerfpu=       [X86]
1078                        on      enable eager fpu restore
1079                        off     disable eager fpu restore
1080                        auto    selects the default scheme, which automatically
1081                                enables eagerfpu restore for xsaveopt.
1083        module.async_probe [KNL]
1084                        Enable asynchronous probe on this module.
1086        early_ioremap_debug [KNL]
1087                        Enable debug messages in early_ioremap support. This
1088                        is useful for tracking down temporary early mappings
1089                        which are not unmapped.
1091        earlycon=       [KNL] Output early console device and options.
1093                        When used with no options, the early console is
1094                        determined by the stdout-path property in device
1095                        tree's chosen node.
1097                cdns,<addr>[,options]
1098                        Start an early, polled-mode console on a Cadence
1099                        (xuartps) serial port at the specified address. Only
1100                        supported option is baud rate. If baud rate is not
1101                        specified, the serial port must already be setup and
1102                        configured.
1104                uart[8250],io,<addr>[,options]
1105                uart[8250],mmio,<addr>[,options]
1106                uart[8250],mmio32,<addr>[,options]
1107                uart[8250],mmio32be,<addr>[,options]
1108                uart[8250],0x<addr>[,options]
1109                        Start an early, polled-mode console on the 8250/16550
1110                        UART at the specified I/O port or MMIO address.
1111                        MMIO inter-register address stride is either 8-bit
1112                        (mmio) or 32-bit (mmio32 or mmio32be).
1113                        If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
1114                        to be equivalent to 'mmio'. 'options' are specified
1115                        in the same format described for "console=ttyS<n>"; if
1116                        unspecified, the h/w is not initialized.
1118                pl011,<addr>
1119                pl011,mmio32,<addr>
1120                        Start an early, polled-mode console on a pl011 serial
1121                        port at the specified address. The pl011 serial port
1122                        must already be setup and configured. Options are not
1123                        yet supported.  If 'mmio32' is specified, then only
1124                        the driver will use only 32-bit accessors to read/write
1125                        the device registers.
1127                meson,<addr>
1128                        Start an early, polled-mode console on a meson serial
1129                        port at the specified address. The serial port must
1130                        already be setup and configured. Options are not yet
1131                        supported.
1133                msm_serial,<addr>
1134                        Start an early, polled-mode console on an msm serial
1135                        port at the specified address. The serial port
1136                        must already be setup and configured. Options are not
1137                        yet supported.
1139                msm_serial_dm,<addr>
1140                        Start an early, polled-mode console on an msm serial
1141                        dm port at the specified address. The serial port
1142                        must already be setup and configured. Options are not
1143                        yet supported.
1145                smh     Use ARM semihosting calls for early console.
1147                s3c2410,<addr>
1148                s3c2412,<addr>
1149                s3c2440,<addr>
1150                s3c6400,<addr>
1151                s5pv210,<addr>
1152                exynos4210,<addr>
1153                        Use early console provided by serial driver available
1154                        on Samsung SoCs, requires selecting proper type and
1155                        a correct base address of the selected UART port. The
1156                        serial port must already be setup and configured.
1157                        Options are not yet supported.
1159                lpuart,<addr>
1160                lpuart32,<addr>
1161                        Use early console provided by Freescale LP UART driver
1162                        found on Freescale Vybrid and QorIQ LS1021A processors.
1163                        A valid base address must be provided, and the serial
1164                        port must already be setup and configured.
1166                armada3700_uart,<addr>
1167                        Start an early, polled-mode console on the
1168                        Armada 3700 serial port at the specified
1169                        address. The serial port must already be setup
1170                        and configured. Options are not yet supported.
1172        earlyprintk=    [X86,SH,BLACKFIN,ARM,M68k]
1173                        earlyprintk=vga
1174                        earlyprintk=efi
1175                        earlyprintk=xen
1176                        earlyprintk=serial[,ttySn[,baudrate]]
1177                        earlyprintk=serial[,0x...[,baudrate]]
1178                        earlyprintk=ttySn[,baudrate]
1179                        earlyprintk=dbgp[debugController#]
1180                        earlyprintk=pciserial,bus:device.function[,baudrate]
1182                        earlyprintk is useful when the kernel crashes before
1183                        the normal console is initialized. It is not enabled by
1184                        default because it has some cosmetic problems.
1186                        Append ",keep" to not disable it when the real console
1187                        takes over.
1189                        Only one of vga, efi, serial, or usb debug port can
1190                        be used at a time.
1192                        Currently only ttyS0 and ttyS1 may be specified by
1193                        name.  Other I/O ports may be explicitly specified
1194                        on some architectures (x86 and arm at least) by
1195                        replacing ttySn with an I/O port address, like this:
1196                                earlyprintk=serial,0x1008,115200
1197                        You can find the port for a given device in
1198                        /proc/tty/driver/serial:
1199                                2: uart:ST16650V2 port:00001008 irq:18 ...
1201                        Interaction with the standard serial driver is not
1202                        very good.
1204                        The VGA and EFI output is eventually overwritten by
1205                        the real console.
1207                        The xen output can only be used by Xen PV guests.
1209        edac_report=    [HW,EDAC] Control how to report EDAC event
1210                        Format: {"on" | "off" | "force"}
1211                        on: enable EDAC to report H/W event. May be overridden
1212                        by other higher priority error reporting module.
1213                        off: disable H/W event reporting through EDAC.
1214                        force: enforce the use of EDAC to report H/W event.
1215                        default: on.
1217        ekgdboc=        [X86,KGDB] Allow early kernel console debugging
1218                        ekgdboc=kbd
1220                        This is designed to be used in conjunction with
1221                        the boot argument: earlyprintk=vga
1223        edd=            [EDD]
1224                        Format: {"off" | "on" | "skip[mbr]"}
1226        efi=            [EFI]
1227                        Format: { "old_map", "nochunk", "noruntime", "debug" }
1228                        old_map [X86-64]: switch to the old ioremap-based EFI
1229                        runtime services mapping. 32-bit still uses this one by
1230                        default.
1231                        nochunk: disable reading files in "chunks" in the EFI
1232                        boot stub, as chunking can cause problems with some
1233                        firmware implementations.
1234                        noruntime : disable EFI runtime services support
1235                        debug: enable misc debug output
1237        efi_no_storage_paranoia [EFI; X86]
1238                        Using this parameter you can use more than 50% of
1239                        your efi variable storage. Use this parameter only if
1240                        you are really sure that your UEFI does sane gc and
1241                        fulfills the spec otherwise your board may brick.
1243        efi_fake_mem=   nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1244                        Add arbitrary attribute to specific memory range by
1245                        updating original EFI memory map.
1246                        Region of memory which aa attribute is added to is
1247                        from ss to ss+nn.
1248                        If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1249                        is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1250                        attribute is added to range 0x100000000-0x180000000 and
1251                        0x10a0000000-0x1120000000.
1253                        Using this parameter you can do debugging of EFI memmap
1254                        related feature. For example, you can do debugging of
1255                        Address Range Mirroring feature even if your box
1256                        doesn't support it.
1258        efivar_ssdt=    [EFI; X86] Name of an EFI variable that contains an SSDT
1259                        that is to be dynamically loaded by Linux. If there are
1260                        multiple variables with the same name but with different
1261                        vendor GUIDs, all of them will be loaded. See
1262                        Documentation/acpi/ssdt-overlays.txt for details.
1265        eisa_irq_edge=  [PARISC,HW]
1266                        See header of drivers/parisc/eisa.c.
1268        elanfreq=       [X86-32]
1269                        See comment before function elanfreq_setup() in
1270                        arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1272        elevator=       [IOSCHED]
1273                        Format: {"cfq" | "deadline" | "noop"}
1274                        See Documentation/block/cfq-iosched.txt and
1275                        Documentation/block/deadline-iosched.txt for details.
1277        elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1278                        Specifies physical address of start of kernel core
1279                        image elf header and optionally the size. Generally
1280                        kexec loader will pass this option to capture kernel.
1281                        See Documentation/kdump/kdump.txt for details.
1283        enable_mtrr_cleanup [X86]
1284                        The kernel tries to adjust MTRR layout from continuous
1285                        to discrete, to make X server driver able to add WB
1286                        entry later. This parameter enables that.
1288        enable_timer_pin_1 [X86]
1289                        Enable PIN 1 of APIC timer
1290                        Can be useful to work around chipset bugs
1291                        (in particular on some ATI chipsets).
1292                        The kernel tries to set a reasonable default.
1294        enforcing       [SELINUX] Set initial enforcing status.
1295                        Format: {"0" | "1"}
1296                        See security/selinux/Kconfig help text.
1297                        0 -- permissive (log only, no denials).
1298                        1 -- enforcing (deny and log).
1299                        Default value is 0.
1300                        Value can be changed at runtime via /selinux/enforce.
1302        erst_disable    [ACPI]
1303                        Disable Error Record Serialization Table (ERST)
1304                        support.
1306        ether=          [HW,NET] Ethernet cards parameters
1307                        This option is obsoleted by the "netdev=" option, which
1308                        has equivalent usage. See its documentation for details.
1310        evm=            [EVM]
1311                        Format: { "fix" }
1312                        Permit 'security.evm' to be updated regardless of
1313                        current integrity status.
1315        failslab=
1316        fail_page_alloc=
1317        fail_make_request=[KNL]
1318                        General fault injection mechanism.
1319                        Format: <interval>,<probability>,<space>,<times>
1320                        See also Documentation/fault-injection/.
1322        floppy=         [HW]
1323                        See Documentation/blockdev/floppy.txt.
1325        force_pal_cache_flush
1326                        [IA-64] Avoid check_sal_cache_flush which may hang on
1327                        buggy SAL_CACHE_FLUSH implementations. Using this
1328                        parameter will force ia64_sal_cache_flush to call
1329                        ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1331        forcepae [X86-32]
1332                        Forcefully enable Physical Address Extension (PAE).
1333                        Many Pentium M systems disable PAE but may have a
1334                        functionally usable PAE implementation.
1335                        Warning: use of this parameter will taint the kernel
1336                        and may cause unknown problems.
1338        ftrace=[tracer]
1339                        [FTRACE] will set and start the specified tracer
1340                        as early as possible in order to facilitate early
1341                        boot debugging.
1343        ftrace_dump_on_oops[=orig_cpu]
1344                        [FTRACE] will dump the trace buffers on oops.
1345                        If no parameter is passed, ftrace will dump
1346                        buffers of all CPUs, but if you pass orig_cpu, it will
1347                        dump only the buffer of the CPU that triggered the
1348                        oops.
1350        ftrace_filter=[function-list]
1351                        [FTRACE] Limit the functions traced by the function
1352                        tracer at boot up. function-list is a comma separated
1353                        list of functions. This list can be changed at run
1354                        time by the set_ftrace_filter file in the debugfs
1355                        tracing directory.
1357        ftrace_notrace=[function-list]
1358                        [FTRACE] Do not trace the functions specified in
1359                        function-list. This list can be changed at run time
1360                        by the set_ftrace_notrace file in the debugfs
1361                        tracing directory.
1363        ftrace_graph_filter=[function-list]
1364                        [FTRACE] Limit the top level callers functions traced
1365                        by the function graph tracer at boot up.
1366                        function-list is a comma separated list of functions
1367                        that can be changed at run time by the
1368                        set_graph_function file in the debugfs tracing directory.
1370        ftrace_graph_notrace=[function-list]
1371                        [FTRACE] Do not trace from the functions specified in
1372                        function-list.  This list is a comma separated list of
1373                        functions that can be changed at run time by the
1374                        set_graph_notrace file in the debugfs tracing directory.
1377                        [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1378                        support via parallel port (up to 5 devices per port)
1379                        Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1380                        See also Documentation/input/joystick-parport.txt
1382        gamma=          [HW,DRM]
1384        gart_fix_e820=  [X86_64] disable the fix e820 for K8 GART
1385                        Format: off | on
1386                        default: on
1388        gcov_persist=   [GCOV] When non-zero (default), profiling data for
1389                        kernel modules is saved and remains accessible via
1390                        debugfs, even when the module is unloaded/reloaded.
1391                        When zero, profiling data is discarded and associated
1392                        debugfs files are removed at module unload time.
1394        gpt             [EFI] Forces disk with valid GPT signature but
1395                        invalid Protective MBR to be treated as GPT. If the
1396                        primary GPT is corrupted, it enables the backup/alternate
1397                        GPT to be used instead.
1399        grcan.enable0=  [HW] Configuration of physical interface 0. Determines
1400                        the "Enable 0" bit of the configuration register.
1401                        Format: 0 | 1
1402                        Default: 0
1403        grcan.enable1=  [HW] Configuration of physical interface 1. Determines
1404                        the "Enable 0" bit of the configuration register.
1405                        Format: 0 | 1
1406                        Default: 0
1407   [HW] Select which physical interface to use.
1408                        Format: 0 | 1
1409                        Default: 0
1410        grcan.txsize=   [HW] Sets the size of the tx buffer.
1411                        Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1412                        Default: 1024
1413        grcan.rxsize=   [HW] Sets the size of the rx buffer.
1414                        Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1415                        Default: 1024
1417        gpio-mockup.gpio_mockup_ranges
1418                        [HW] Sets the ranges of gpiochip of for this device.
1419                        Format: <start1>,<end1>,<start2>,<end2>...
1421        hardlockup_all_cpu_backtrace=
1422                        [KNL] Should the hard-lockup detector generate
1423                        backtraces on all cpus.
1424                        Format: <integer>
1426        hashdist=       [KNL,NUMA] Large hashes allocated during boot
1427                        are distributed across NUMA nodes.  Defaults on
1428                        for 64-bit NUMA, off otherwise.
1429                        Format: 0 | 1 (for off | on)
1431        hcl=            [IA-64] SGI's Hardware Graph compatibility layer
1433        hd=             [EIDE] (E)IDE hard drive subsystem geometry
1434                        Format: <cyl>,<head>,<sect>
1436        hest_disable    [ACPI]
1437                        Disable Hardware Error Source Table (HEST) support;
1438                        corresponding firmware-first mode error processing
1439                        logic will be disabled.
1441        highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1442                        size of <nn>. This works even on boxes that have no
1443                        highmem otherwise. This also works to reduce highmem
1444                        size on bigger boxes.
1446        highres=        [KNL] Enable/disable high resolution timer mode.
1447                        Valid parameters: "on", "off"
1448                        Default: "on"
1450        hisax=          [HW,ISDN]
1451                        See Documentation/isdn/README.HiSax.
1453        hlt             [BUGS=ARM,SH]
1455        hpet=           [X86-32,HPET] option to control HPET usage
1456                        Format: { enable (default) | disable | force |
1457                                verbose }
1458                        disable: disable HPET and use PIT instead
1459                        force: allow force enabled of undocumented chips (ICH4,
1460                                VIA, nVidia)
1461                        verbose: show contents of HPET registers during setup
1463        hpet_mmap=      [X86, HPET_MMAP] Allow userspace to mmap HPET
1464                        registers.  Default set by CONFIG_HPET_MMAP_DEFAULT.
1466        hugepages=      [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1467        hugepagesz=     [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1468                        On x86-64 and powerpc, this option can be specified
1469                        multiple times interleaved with hugepages= to reserve
1470                        huge pages of different sizes. Valid pages sizes on
1471                        x86-64 are 2M (when the CPU supports "pse") and 1G
1472                        (when the CPU supports the "pdpe1gb" cpuinfo flag).
1474        hvc_iucv=       [S390] Number of z/VM IUCV hypervisor console (HVC)
1475                               terminal devices. Valid values: 0..8
1476        hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1477                               If specified, z/VM IUCV HVC accepts connections
1478                               from listed z/VM user IDs only.
1480        hwthread_map=   [METAG] Comma-separated list of Linux cpu id to
1481                                hardware thread id mappings.
1482                                Format: <cpu>:<hwthread>
1484        keep_bootcon    [KNL]
1485                        Do not unregister boot console at start. This is only
1486                        useful for debugging when something happens in the window
1487                        between unregistering the boot console and initializing
1488                        the real console.
1490        i2c_bus=        [HW] Override the default board specific I2C bus speed
1491                             or register an additional I2C bus that is not
1492                             registered from board initialization code.
1493                             Format:
1494                             <bus_id>,<clkrate>
1496        i8042.debug     [HW] Toggle i8042 debug mode
1497        i8042.unmask_kbd_data
1498                        [HW] Enable printing of interrupt data from the KBD port
1499                             (disabled by default, and as a pre-condition
1500                             requires that i8042.debug=1 be enabled)
1501    [HW] Put keyboard port into non-translated mode
1502        i8042.dumbkbd   [HW] Pretend that controller can only read data from
1503                             keyboard and cannot control its state
1504                             (Don't attempt to blink the leds)
1505        i8042.noaux     [HW] Don't check for auxiliary (== mouse) port
1506        i8042.nokbd     [HW] Don't check/create keyboard port
1507        i8042.noloop    [HW] Disable the AUX Loopback command while probing
1508                             for the AUX port
1509        i8042.nomux     [HW] Don't check presence of an active multiplexing
1510                             controller
1511        i8042.nopnp     [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1512                             controllers
1513        i8042.notimeout [HW] Ignore timeout condition signalled by controller
1514        i8042.reset     [HW] Reset the controller during init, cleanup and
1515                             suspend-to-ram transitions, only during s2r
1516                             transitions, or never reset
1517                        Format: { 1 | Y | y | 0 | N | n }
1518                        1, Y, y: always reset controller
1519                        0, N, n: don't ever reset controller
1520                        Default: only on s2r transitions on x86; most other
1521                        architectures force reset to be always executed
1522        i8042.unlock    [HW] Unlock (ignore) the keylock
1523        i8042.kbdreset  [HW] Reset device connected to KBD port
1525        i810=           [HW,DRM]
1527        i8k.ignore_dmi  [HW] Continue probing hardware even if DMI data
1528                        indicates that the driver is running on unsupported
1529                        hardware.
1530        i8k.force       [HW] Activate i8k driver even if SMM BIOS signature
1531                        does not match list of supported models.
1532        i8k.power_status
1533                        [HW] Report power status in /proc/i8k
1534                        (disabled by default)
1535        i8k.restricted  [HW] Allow controlling fans only if SYS_ADMIN
1536                        capability is set.
1538        i915.invert_brightness=
1539                        [DRM] Invert the sense of the variable that is used to
1540                        set the brightness of the panel backlight. Normally a
1541                        brightness value of 0 indicates backlight switched off,
1542                        and the maximum of the brightness value sets the backlight
1543                        to maximum brightness. If this parameter is set to 0
1544                        (default) and the machine requires it, or this parameter
1545                        is set to 1, a brightness value of 0 sets the backlight
1546                        to maximum brightness, and the maximum of the brightness
1547                        value switches the backlight off.
1548                        -1 -- never invert brightness
1549                         0 -- machine default
1550                         1 -- force brightness inversion
1552        icn=            [HW,ISDN]
1553                        Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1555        ide-core.nodma= [HW] (E)IDE subsystem
1556                        Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1557                        .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1558                        .cdrom .chs .ignore_cable are additional options
1559                        See Documentation/ide/ide.txt.
1561        ide-generic.probe-mask= [HW] (E)IDE subsystem
1562                        Format: <int>
1563                        Probe mask for legacy ISA IDE ports.  Depending on
1564                        platform up to 6 ports are supported, enabled by
1565                        setting corresponding bits in the mask to 1.  The
1566                        default value is 0x0, which has a special meaning.
1567                        On systems that have PCI, it triggers scanning the
1568                        PCI bus for the first and the second port, which
1569                        are then probed.  On systems without PCI the value
1570                        of 0x0 enables probing the two first ports as if it
1571                        was 0x3.
1573        ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1574                        Claim all unknown PCI IDE storage controllers.
1576        idle=           [X86]
1577                        Format: idle=poll, idle=halt, idle=nomwait
1578                        Poll forces a polling idle loop that can slightly
1579                        improve the performance of waking up a idle CPU, but
1580                        will use a lot of power and make the system run hot.
1581                        Not recommended.
1582                        idle=halt: Halt is forced to be used for CPU idle.
1583                        In such case C2/C3 won't be used again.
1584                        idle=nomwait: Disable mwait for CPU C-states
1586        ieee754=        [MIPS] Select IEEE Std 754 conformance mode
1587                        Format: { strict | legacy | 2008 | relaxed }
1588                        Default: strict
1590                        Choose which programs will be accepted for execution
1591                        based on the IEEE 754 NaN encoding(s) supported by
1592                        the FPU and the NaN encoding requested with the value
1593                        of an ELF file header flag individually set by each
1594                        binary.  Hardware implementations are permitted to
1595                        support either or both of the legacy and the 2008 NaN
1596                        encoding mode.
1598                        Available settings are as follows:
1599                        strict  accept binaries that request a NaN encoding
1600                                supported by the FPU
1601                        legacy  only accept legacy-NaN binaries, if supported
1602                                by the FPU
1603                        2008    only accept 2008-NaN binaries, if supported
1604                                by the FPU
1605                        relaxed accept any binaries regardless of whether
1606                                supported by the FPU
1608                        The FPU emulator is always able to support both NaN
1609                        encodings, so if no FPU hardware is present or it has
1610                        been disabled with 'nofpu', then the settings of
1611                        'legacy' and '2008' strap the emulator accordingly,
1612                        'relaxed' straps the emulator for both legacy-NaN and
1613                        2008-NaN, whereas 'strict' enables legacy-NaN only on
1614                        legacy processors and both NaN encodings on MIPS32 or
1615                        MIPS64 CPUs.
1617                        The setting for ABS.fmt/NEG.fmt instruction execution
1618                        mode generally follows that for the NaN encoding,
1619                        except where unsupported by hardware.
1621        ignore_loglevel [KNL]
1622                        Ignore loglevel setting - this will print /all/
1623                        kernel messages to the console. Useful for debugging.
1624                        We also add it as printk module parameter, so users
1625                        could change it dynamically, usually by
1626                        /sys/module/printk/parameters/ignore_loglevel.
1628        ignore_rlimit_data
1629                        Ignore RLIMIT_DATA setting for data mappings,
1630                        print warning at first misuse.  Can be changed via
1631                        /sys/module/kernel/parameters/ignore_rlimit_data.
1633        ihash_entries=  [KNL]
1634                        Set number of hash buckets for inode cache.
1636        ima_appraise=   [IMA] appraise integrity measurements
1637                        Format: { "off" | "enforce" | "fix" | "log" }
1638                        default: "enforce"
1640        ima_appraise_tcb [IMA]
1641                        The builtin appraise policy appraises all files
1642                        owned by uid=0.
1644        ima_hash=       [IMA]
1645                        Format: { md5 | sha1 | rmd160 | sha256 | sha384
1646                                   | sha512 | ... }
1647                        default: "sha1"
1649                        The list of supported hash algorithms is defined
1650                        in crypto/hash_info.h.
1652        ima_policy=     [IMA]
1653                        The builtin measurement policy to load during IMA
1654                        setup.  Specyfing "tcb" as the value, measures all
1655                        programs exec'd, files mmap'd for exec, and all files
1656                        opened with the read mode bit set by either the
1657                        effective uid (euid=0) or uid=0.
1658                        Format: "tcb"
1660        ima_tcb         [IMA] Deprecated.  Use ima_policy= instead.
1661                        Load a policy which meets the needs of the Trusted
1662                        Computing Base.  This means IMA will measure all
1663                        programs exec'd, files mmap'd for exec, and all files
1664                        opened for read by uid=0.
1666        ima_template=   [IMA]
1667                        Select one of defined IMA measurements template formats.
1668                        Formats: { "ima" | "ima-ng" | "ima-sig" }
1669                        Default: "ima-ng"
1671        ima_template_fmt=
1672                        [IMA] Define a custom template format.
1673                        Format: { "field1|...|fieldN" }
1675        ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1676                        Format: <min_file_size>
1677                        Set the minimal file size for using asynchronous hash.
1678                        If left unspecified, ahash usage is disabled.
1680                        ahash performance varies for different data sizes on
1681                        different crypto accelerators. This option can be used
1682                        to achieve the best performance for a particular HW.
1684        ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1685                        Format: <bufsize>
1686                        Set hashing buffer size. Default: 4k.
1688                        ahash performance varies for different chunk sizes on
1689                        different crypto accelerators. This option can be used
1690                        to achieve best performance for particular HW.
1692        init=           [KNL]
1693                        Format: <full_path>
1694                        Run specified binary instead of /sbin/init as init
1695                        process.
1697        initcall_debug  [KNL] Trace initcalls as they are executed.  Useful
1698                        for working out where the kernel is dying during
1699                        startup.
1701        initcall_blacklist=  [KNL] Do not execute a comma-separated list of
1702                        initcall functions.  Useful for debugging built-in
1703                        modules and initcalls.
1705        initrd=         [BOOT] Specify the location of the initial ramdisk
1707        init_pkru=      [x86] Specify the default memory protection keys rights
1708                        register contents for all processes.  0x55555554 by
1709                        default (disallow access to all but pkey 0).  Can
1710                        override in debugfs after boot.
1712        inport.irq=     [HW] Inport (ATI XL and Microsoft) busmouse driver
1713                        Format: <irq>
1715        int_pln_enable  [x86] Enable power limit notification interrupt
1717        integrity_audit=[IMA]
1718                        Format: { "0" | "1" }
1719                        0 -- basic integrity auditing messages. (Default)
1720                        1 -- additional integrity auditing messages.
1722        intel_iommu=    [DMAR] Intel IOMMU driver (DMAR) option
1723                on
1724                        Enable intel iommu driver.
1725                off
1726                        Disable intel iommu driver.
1727                igfx_off [Default Off]
1728                        By default, gfx is mapped as normal device. If a gfx
1729                        device has a dedicated DMAR unit, the DMAR unit is
1730                        bypassed by not enabling DMAR with this option. In
1731                        this case, gfx device will use physical address for
1732                        DMA.
1733                forcedac [x86_64]
1734                        With this option iommu will not optimize to look
1735                        for io virtual address below 32-bit forcing dual
1736                        address cycle on pci bus for cards supporting greater
1737                        than 32-bit addressing. The default is to look
1738                        for translation below 32-bit and if not available
1739                        then look in the higher range.
1740                strict [Default Off]
1741                        With this option on every unmap_single operation will
1742                        result in a hardware IOTLB flush operation as opposed
1743                        to batching them for performance.
1744                sp_off [Default Off]
1745                        By default, super page will be supported if Intel IOMMU
1746                        has the capability. With this option, super page will
1747                        not be supported.
1748                ecs_off [Default Off]
1749                        By default, extended context tables will be supported if
1750                        the hardware advertises that it has support both for the
1751                        extended tables themselves, and also PASID support. With
1752                        this option set, extended tables will not be used even
1753                        on hardware which claims to support them.
1755        intel_idle.max_cstate=  [KNL,HW,ACPI,X86]
1756                        0       disables intel_idle and fall back on acpi_idle.
1757                        1 to 9  specify maximum depth of C-state.
1759        intel_pstate=  [X86]
1760                       disable
1761                         Do not enable intel_pstate as the default
1762                         scaling driver for the supported processors
1763                       force
1764                         Enable intel_pstate on systems that prohibit it by default
1765                         in favor of acpi-cpufreq. Forcing the intel_pstate driver
1766                         instead of acpi-cpufreq may disable platform features, such
1767                         as thermal controls and power capping, that rely on ACPI
1768                         P-States information being indicated to OSPM and therefore
1769                         should be used with caution. This option does not work with
1770                         processors that aren't supported by the intel_pstate driver
1771                         or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1772                       no_hwp
1773                         Do not enable hardware P state control (HWP)
1774                         if available.
1775                hwp_only
1776                        Only load intel_pstate on systems which support
1777                        hardware P state control (HWP) if available.
1778                support_acpi_ppc
1779                        Enforce ACPI _PPC performance limits. If the Fixed ACPI
1780                        Description Table, specifies preferred power management
1781                        profile as "Enterprise Server" or "Performance Server",
1782                        then this feature is turned on by default.
1784        intremap=       [X86-64, Intel-IOMMU]
1785                        on      enable Interrupt Remapping (default)
1786                        off     disable Interrupt Remapping
1787                        nosid   disable Source ID checking
1788                        no_x2apic_optout
1789                                BIOS x2APIC opt-out request will be ignored
1790                        nopost  disable Interrupt Posting
1792        iomem=          Disable strict checking of access to MMIO memory
1793                strict  regions from userspace.
1794                relaxed
1796        iommu=          [x86]
1797                off
1798                force
1799                noforce
1800                biomerge
1801                panic
1802                nopanic
1803                merge
1804                nomerge
1805                forcesac
1806                soft
1807                pt              [x86, IA-64]
1808                nobypass        [PPC/POWERNV]
1809                        Disable IOMMU bypass, using IOMMU for PCI devices.
1812        io7=            [HW] IO7 for Marvel based alpha systems
1813                        See comment before marvel_specify_io7 in
1814                        arch/alpha/kernel/core_marvel.c.
1816        io_delay=       [X86] I/O delay method
1817                0x80
1818                        Standard port 0x80 based delay
1819                0xed
1820                        Alternate port 0xed based delay (needed on some systems)
1821                udelay
1822                        Simple two microseconds delay
1823                none
1824                        No delay
1826        ip=             [IP_PNP]
1827                        See Documentation/filesystems/nfs/nfsroot.txt.
1829        irqaffinity=    [SMP] Set the default irq affinity mask
1830                        The argument is a cpu list, as described above.
1832        irqfixup        [HW]
1833                        When an interrupt is not handled search all handlers
1834                        for it. Intended to get systems with badly broken
1835                        firmware running.
1837        irqpoll         [HW]
1838                        When an interrupt is not handled search all handlers
1839                        for it. Also check all handlers each timer
1840                        interrupt. Intended to get systems with badly broken
1841                        firmware running.
1843        isapnp=         [ISAPNP]
1844                        Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1846        isolcpus=       [KNL,SMP] Isolate CPUs from the general scheduler.
1847                        The argument is a cpu list, as described above.
1849                        This option can be used to specify one or more CPUs
1850                        to isolate from the general SMP balancing and scheduling
1851                        algorithms. You can move a process onto or off an
1852                        "isolated" CPU via the CPU affinity syscalls or cpuset.
1853                        <cpu number> begins at 0 and the maximum value is
1854                        "number of CPUs in system - 1".
1856                        This option is the preferred way to isolate CPUs. The
1857                        alternative -- manually setting the CPU mask of all
1858                        tasks in the system -- can cause problems and
1859                        suboptimal load balancer performance.
1861        iucv=           [HW,NET]
1863        ivrs_ioapic     [HW,X86_64]
1864                        Provide an override to the IOAPIC-ID<->DEVICE-ID
1865                        mapping provided in the IVRS ACPI table. For
1866                        example, to map IOAPIC-ID decimal 10 to
1867                        PCI device 00:14.0 write the parameter as:
1868                                ivrs_ioapic[10]=00:14.0
1870        ivrs_hpet       [HW,X86_64]
1871                        Provide an override to the HPET-ID<->DEVICE-ID
1872                        mapping provided in the IVRS ACPI table. For
1873                        example, to map HPET-ID decimal 0 to
1874                        PCI device 00:14.0 write the parameter as:
1875                                ivrs_hpet[0]=00:14.0
1877        ivrs_acpihid    [HW,X86_64]
1878                        Provide an override to the ACPI-HID:UID<->DEVICE-ID
1879                        mapping provided in the IVRS ACPI table. For
1880                        example, to map UART-HID:UID AMD0020:0 to
1881                        PCI device 00:14.5 write the parameter as:
1882                                ivrs_acpihid[00:14.5]=AMD0020:0
1884        js=             [HW,JOY] Analog joystick
1885                        See Documentation/input/joystick.txt.
1887        nokaslr         [KNL]
1888                        When CONFIG_RANDOMIZE_BASE is set, this disables
1889                        kernel and module base offset ASLR (Address Space
1890                        Layout Randomization).
1892        keepinitrd      [HW,ARM]
1894        kernelcore=     [KNL,X86,IA-64,PPC]
1895                        Format: nn[KMGTPE] | "mirror"
1896                        This parameter
1897                        specifies the amount of memory usable by the kernel
1898                        for non-movable allocations.  The requested amount is
1899                        spread evenly throughout all nodes in the system. The
1900                        remaining memory in each node is used for Movable
1901                        pages. In the event, a node is too small to have both
1902                        kernelcore and Movable pages, kernelcore pages will
1903                        take priority and other nodes will have a larger number
1904                        of Movable pages.  The Movable zone is used for the
1905                        allocation of pages that may be reclaimed or moved
1906                        by the page migration subsystem.  This means that
1907                        HugeTLB pages may not be allocated from this zone.
1908                        Note that allocations like PTEs-from-HighMem still
1909                        use the HighMem zone if it exists, and the Normal
1910                        zone if it does not.
1912                        Instead of specifying the amount of memory (nn[KMGTPE]),
1913                        you can specify "mirror" option. In case "mirror"
1914                        option is specified, mirrored (reliable) memory is used
1915                        for non-movable allocations and remaining memory is used
1916                        for Movable pages. nn[KMGTPE] and "mirror" are exclusive,
1917                        so you can NOT specify nn[KMGTPE] and "mirror" at the same
1918                        time.
1920        kgdbdbgp=       [KGDB,HW] kgdb over EHCI usb debug port.
1921                        Format: <Controller#>[,poll interval]
1922                        The controller # is the number of the ehci usb debug
1923                        port as it is probed via PCI.  The poll interval is
1924                        optional and is the number seconds in between
1925                        each poll cycle to the debug port in case you need
1926                        the functionality for interrupting the kernel with
1927                        gdb or control-c on the dbgp connection.  When
1928                        not using this parameter you use sysrq-g to break into
1929                        the kernel debugger.
1931        kgdboc=         [KGDB,HW] kgdb over consoles.
1932                        Requires a tty driver that supports console polling,
1933                        or a supported polling keyboard driver (non-usb).
1934                         Serial only format: <serial_device>[,baud]
1935                         keyboard only format: kbd
1936                         keyboard and serial format: kbd,<serial_device>[,baud]
1937                        Optional Kernel mode setting:
1938                         kms, kbd format: kms,kbd
1939                         kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1941        kgdbwait        [KGDB] Stop kernel execution and enter the
1942                        kernel debugger at the earliest opportunity.
1944        kmac=           [MIPS] korina ethernet MAC address.
1945                        Configure the RouterBoard 532 series on-chip
1946                        Ethernet adapter MAC address.
1948        kmemleak=       [KNL] Boot-time kmemleak enable/disable
1949                        Valid arguments: on, off
1950                        Default: on
1951                        Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1952                        the default is off.
1954        kmemcheck=      [X86] Boot-time kmemcheck enable/disable/one-shot mode
1955                        Valid arguments: 0, 1, 2
1956                        kmemcheck=0 (disabled)
1957                        kmemcheck=1 (enabled)
1958                        kmemcheck=2 (one-shot mode)
1959                        Default: 2 (one-shot mode)
1961        kstack=N        [X86] Print N words from the kernel stack
1962                        in oops dumps.
1964        kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1965                        Default is 0 (don't ignore, but inject #GP)
1967        kvm.mmu_audit=  [KVM] This is a R/W parameter which allows audit
1968                        KVM MMU at runtime.
1969                        Default is 0 (off)
1971        kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1972                        Default is 1 (enabled)
1974        kvm-amd.npt=    [KVM,AMD] Disable nested paging (virtualized MMU)
1975                        for all guests.
1976                        Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1978        kvm-intel.ept=  [KVM,Intel] Disable extended page tables
1979                        (virtualized MMU) support on capable Intel chips.
1980                        Default is 1 (enabled)
1982        kvm-intel.emulate_invalid_guest_state=
1983                        [KVM,Intel] Enable emulation of invalid guest states
1984                        Default is 0 (disabled)
1986        kvm-intel.flexpriority=
1987                        [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1988                        Default is 1 (enabled)
1990        kvm-intel.nested=
1991                        [KVM,Intel] Enable VMX nesting (nVMX).
1992                        Default is 0 (disabled)
1994        kvm-intel.unrestricted_guest=
1995                        [KVM,Intel] Disable unrestricted guest feature
1996                        (virtualized real and unpaged mode) on capable
1997                        Intel chips. Default is 1 (enabled)
1999        kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2000                        feature (tagged TLBs) on capable Intel chips.
2001                        Default is 1 (enabled)
2003        l2cr=           [PPC]
2005        l3cr=           [PPC]
2007        lapic           [X86-32,APIC] Enable the local APIC even if BIOS
2008                        disabled it.
2010        lapic=          [x86,APIC] "notscdeadline" Do not use TSC deadline
2011                        value for LAPIC timer one-shot implementation. Default
2012                        back to the programmable timer unit in the LAPIC.
2014        lapic_timer_c2_ok       [X86,APIC] trust the local apic timer
2015                        in C2 power state.
2017        libata.dma=     [LIBATA] DMA control
2018                        libata.dma=0      Disable all PATA and SATA DMA
2019                        libata.dma=1      PATA and SATA Disk DMA only
2020                        libata.dma=2      ATAPI (CDROM) DMA only
2021                        libata.dma=4      Compact Flash DMA only
2022                        Combinations also work, so libata.dma=3 enables DMA
2023                        for disks and CDROMs, but not CFs.
2025        libata.ignore_hpa=      [LIBATA] Ignore HPA limit
2026                        libata.ignore_hpa=0       keep BIOS limits (default)
2027                        libata.ignore_hpa=1       ignore limits, using full disk
2029        libata.noacpi   [LIBATA] Disables use of ACPI in libata suspend/resume
2030                        when set.
2031                        Format: <int>
2033        libata.force=   [LIBATA] Force configurations.  The format is comma
2034                        separated list of "[ID:]VAL" where ID is
2035                        PORT[.DEVICE].  PORT and DEVICE are decimal numbers
2036                        matching port, link or device.  Basically, it matches
2037                        the ATA ID string printed on console by libata.  If
2038                        the whole ID part is omitted, the last PORT and DEVICE
2039                        values are used.  If ID hasn't been specified yet, the
2040                        configuration applies to all ports, links and devices.
2042                        If only DEVICE is omitted, the parameter applies to
2043                        the port and all links and devices behind it.  DEVICE
2044                        number of 0 either selects the first device or the
2045                        first fan-out link behind PMP device.  It does not
2046                        select the host link.  DEVICE number of 15 selects the
2047                        host link and device attached to it.
2049                        The VAL specifies the configuration to force.  As long
2050                        as there's no ambiguity shortcut notation is allowed.
2051                        For example, both 1.5 and 1.5G would work for 1.5Gbps.
2052                        The following configurations can be forced.
2054                        * Cable type: 40c, 80c, short40c, unk, ign or sata.
2055                          Any ID with matching PORT is used.
2057                        * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2059                        * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2060                          udma[/][16,25,33,44,66,100,133] notation is also
2061                          allowed.
2063                        * [no]ncq: Turn on or off NCQ.
2065                        * [no]ncqtrim: Turn off queued DSM TRIM.
2067                        * nohrst, nosrst, norst: suppress hard, soft
2068                          and both resets.
2070                        * rstonce: only attempt one reset during
2071                          hot-unplug link recovery
2073                        * dump_id: dump IDENTIFY data.
2075                        * atapi_dmadir: Enable ATAPI DMADIR bridge support
2077                        * disable: Disable this device.
2079                        If there are multiple matching configurations changing
2080                        the same attribute, the last one is used.
2082        memblock=debug  [KNL] Enable memblock debug messages.
2084        load_ramdisk=   [RAM] List of ramdisks to load from floppy
2085                        See Documentation/blockdev/ramdisk.txt.
2087        lockd.nlm_grace_period=P  [NFS] Assign grace period.
2088                        Format: <integer>
2090        lockd.nlm_tcpport=N     [NFS] Assign TCP port.
2091                        Format: <integer>
2093        lockd.nlm_timeout=T     [NFS] Assign timeout value.
2094                        Format: <integer>
2096        lockd.nlm_udpport=M     [NFS] Assign UDP port.
2097                        Format: <integer>
2099        locktorture.nreaders_stress= [KNL]
2100                        Set the number of locking read-acquisition kthreads.
2101                        Defaults to being automatically set based on the
2102                        number of online CPUs.
2104        locktorture.nwriters_stress= [KNL]
2105                        Set the number of locking write-acquisition kthreads.
2107        locktorture.onoff_holdoff= [KNL]
2108                        Set time (s) after boot for CPU-hotplug testing.
2110        locktorture.onoff_interval= [KNL]
2111                        Set time (s) between CPU-hotplug operations, or
2112                        zero to disable CPU-hotplug testing.
2114        locktorture.shuffle_interval= [KNL]
2115                        Set task-shuffle interval (jiffies).  Shuffling
2116                        tasks allows some CPUs to go into dyntick-idle
2117                        mode during the locktorture test.
2119        locktorture.shutdown_secs= [KNL]
2120                        Set time (s) after boot system shutdown.  This
2121                        is useful for hands-off automated testing.
2123        locktorture.stat_interval= [KNL]
2124                        Time (s) between statistics printk()s.
2126        locktorture.stutter= [KNL]
2127                        Time (s) to stutter testing, for example,
2128                        specifying five seconds causes the test to run for
2129                        five seconds, wait for five seconds, and so on.
2130                        This tests the locking primitive's ability to
2131                        transition abruptly to and from idle.
2133        locktorture.torture_runnable= [BOOT]
2134                        Start locktorture running at boot time.
2136        locktorture.torture_type= [KNL]
2137                        Specify the locking implementation to test.
2139        locktorture.verbose= [KNL]
2140                        Enable additional printk() statements.
2142        logibm.irq=     [HW,MOUSE] Logitech Bus Mouse Driver
2143                        Format: <irq>
2145        loglevel=       All Kernel Messages with a loglevel smaller than the
2146                        console loglevel will be printed to the console. It can
2147                        also be changed with klogd or other programs. The
2148                        loglevels are defined as follows:
2150                        0 (KERN_EMERG)          system is unusable
2151                        1 (KERN_ALERT)          action must be taken immediately
2152                        2 (KERN_CRIT)           critical conditions
2153                        3 (KERN_ERR)            error conditions
2154                        4 (KERN_WARNING)        warning conditions
2155                        5 (KERN_NOTICE)         normal but significant condition
2156                        6 (KERN_INFO)           informational
2157                        7 (KERN_DEBUG)          debug-level messages
2159        log_buf_len=n[KMG]      Sets the size of the printk ring buffer,
2160                        in bytes.  n must be a power of two and greater
2161                        than the minimal size. The minimal size is defined
2162                        by LOG_BUF_SHIFT kernel config parameter. There is
2163                        also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2164                        that allows to increase the default size depending on
2165                        the number of CPUs. See init/Kconfig for more details.
2167        logo.nologo     [FB] Disables display of the built-in Linux logo.
2168                        This may be used to provide more screen space for
2169                        kernel log messages and is useful when debugging
2170                        kernel boot problems.
2172        lp=0            [LP]    Specify parallel ports to use, e.g,
2173        lp=port[,port...]       lp=none,parport0 (lp0 not configured, lp1 uses
2174        lp=reset                first parallel port). 'lp=0' disables the
2175        lp=auto                 printer driver. 'lp=reset' (which can be
2176                                specified in addition to the ports) causes
2177                                attached printers to be reset. Using
2178                                lp=port1,port2,... specifies the parallel ports
2179                                to associate lp devices with, starting with
2180                                lp0. A port specification may be 'none' to skip
2181                                that lp device, or a parport name such as
2182                                'parport0'. Specifying 'lp=auto' instead of a
2183                                port specification list means that device IDs
2184                                from each port should be examined, to see if
2185                                an IEEE 1284-compliant printer is attached; if
2186                                so, the driver will manage that printer.
2187                                See also header of drivers/char/lp.c.
2189        lpj=n           [KNL]
2190                        Sets loops_per_jiffy to given constant, thus avoiding
2191                        time-consuming boot-time autodetection (up to 250 ms per
2192                        CPU). 0 enables autodetection (default). To determine
2193                        the correct value for your kernel, boot with normal
2194                        autodetection and see what value is printed. Note that
2195                        on SMP systems the preset will be applied to all CPUs,
2196                        which is likely to cause problems if your CPUs need
2197                        significantly divergent settings. An incorrect value
2198                        will cause delays in the kernel to be wrong, leading to
2199                        unpredictable I/O errors and other breakage. Although
2200                        unlikely, in the extreme case this might damage your
2201                        hardware.
2203        ltpc=           [NET]
2204                        Format: <io>,<irq>,<dma>
2206        machvec=        [IA-64] Force the use of a particular machine-vector
2207                        (machvec) in a generic kernel.
2208                        Example: machvec=hpzx1_swiotlb
2210        machtype=       [Loongson] Share the same kernel image file between different
2211                         yeeloong laptop.
2212                        Example: machtype=lemote-yeeloong-2f-7inch
2214        max_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory greater
2215                        than or equal to this physical address is ignored.
2217        maxcpus=        [SMP] Maximum number of processors that an SMP kernel
2218                        will bring up during bootup.  maxcpus=n : n >= 0 limits
2219                        the kernel to bring up 'n' processors. Surely after
2220                        bootup you can bring up the other plugged cpu by executing
2221                        "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2222                        only takes effect during system bootup.
2223                        While n=0 is a special case, it is equivalent to "nosmp",
2224                        which also disables the IO APIC.
2226        max_loop=       [LOOP] The number of loop block devices that get
2227        (loop.max_loop) unconditionally pre-created at init time. The default
2228                        number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2229                        of statically allocating a predefined number, loop
2230                        devices can be requested on-demand with the
2231                        /dev/loop-control interface.
2233        mce             [X86-32] Machine Check Exception
2235        mce=option      [X86-64] See Documentation/x86/x86_64/boot-options.txt
2237        md=             [HW] RAID subsystems devices and level
2238                        See Documentation/md.txt.
2240        mdacon=         [MDA]
2241                        Format: <first>,<last>
2242                        Specifies range of consoles to be captured by the MDA.
2244        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
2245                        Amount of memory to be used when the kernel is not able
2246                        to see the whole system memory or for test.
2247                        [X86] Work as limiting max address. Use together
2248                        with memmap= to avoid physical address space collisions.
2249                        Without memmap= PCI devices could be placed at addresses
2250                        belonging to unused RAM.
2252        mem=nopentium   [BUGS=X86-32] Disable usage of 4MB pages for kernel
2253                        memory.
2255        memchunk=nn[KMG]
2256                        [KNL,SH] Allow user to override the default size for
2257                        per-device physically contiguous DMA buffers.
2259        memhp_default_state=online/offline
2260                        [KNL] Set the initial state for the memory hotplug
2261                        onlining policy. If not specified, the default value is
2262                        set according to the
2263                        CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2264                        option.
2265                        See Documentation/memory-hotplug.txt.
2267        memmap=exactmap [KNL,X86] Enable setting of an exact
2268                        E820 memory map, as specified by the user.
2269                        Such memmap=exactmap lines can be constructed based on
2270                        BIOS output or other requirements. See the memmap=nn@ss
2271                        option description.
2273        memmap=nn[KMG]@ss[KMG]
2274                        [KNL] Force usage of a specific region of memory.
2275                        Region of memory to be used is from ss to ss+nn.
2277        memmap=nn[KMG]#ss[KMG]
2278                        [KNL,ACPI] Mark specific memory as ACPI data.
2279                        Region of memory to be marked is from ss to ss+nn.
2281        memmap=nn[KMG]$ss[KMG]
2282                        [KNL,ACPI] Mark specific memory as reserved.
2283                        Region of memory to be reserved is from ss to ss+nn.
2284                        Example: Exclude memory from 0x18690000-0x1869ffff
2285                                 memmap=64K$0x18690000
2286                                 or
2287                                 memmap=0x10000$0x18690000
2289        memmap=nn[KMG]!ss[KMG]
2290                        [KNL,X86] Mark specific memory as protected.
2291                        Region of memory to be used, from ss to ss+nn.
2292                        The memory region may be marked as e820 type 12 (0xc)
2293                        and is NVDIMM or ADR memory.
2295        memory_corruption_check=0/1 [X86]
2296                        Some BIOSes seem to corrupt the first 64k of
2297                        memory when doing things like suspend/resume.
2298                        Setting this option will scan the memory
2299                        looking for corruption.  Enabling this will
2300                        both detect corruption and prevent the kernel
2301                        from using the memory being corrupted.
2302                        However, its intended as a diagnostic tool; if
2303                        repeatable BIOS-originated corruption always
2304                        affects the same memory, you can use memmap=
2305                        to prevent the kernel from using that memory.
2307        memory_corruption_check_size=size [X86]
2308                        By default it checks for corruption in the low
2309                        64k, making this memory unavailable for normal
2310                        use.  Use this parameter to scan for
2311                        corruption in more or less memory.
2313        memory_corruption_check_period=seconds [X86]
2314                        By default it checks for corruption every 60
2315                        seconds.  Use this parameter to check at some
2316                        other rate.  0 disables periodic checking.
2318        memtest=        [KNL,X86,ARM] Enable memtest
2319                        Format: <integer>
2320                        default : 0 <disable>
2321                        Specifies the number of memtest passes to be
2322                        performed. Each pass selects another test
2323                        pattern from a given set of patterns. Memtest
2324                        fills the memory with this pattern, validates
2325                        memory contents and reserves bad memory
2326                        regions that are detected.
2328        meye.*=         [HW] Set MotionEye Camera parameters
2329                        See Documentation/video4linux/meye.txt.
2331        mfgpt_irq=      [IA-32] Specify the IRQ to use for the
2332                        Multi-Function General Purpose Timers on AMD Geode
2333                        platforms.
2335        mfgptfix        [X86-32] Fix MFGPT timers on AMD Geode platforms when
2336                        the BIOS has incorrectly applied a workaround. TinyBIOS
2337                        version 0.98 is known to be affected, 0.99 fixes the
2338                        problem by letting the user disable the workaround.
2340        mga=            [HW,DRM]
2342        min_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory below this
2343                        physical address is ignored.
2345        mini2440=       [ARM,HW,KNL]
2346                        Format:[0..2][b][c][t]
2347                        Default: "0tb"
2348                        MINI2440 configuration specification:
2349                        0 - The attached screen is the 3.5" TFT
2350                        1 - The attached screen is the 7" TFT
2351                        2 - The VGA Shield is attached (1024x768)
2352                        Leaving out the screen size parameter will not load
2353                        the TFT driver, and the framebuffer will be left
2354                        unconfigured.
2355                        b - Enable backlight. The TFT backlight pin will be
2356                        linked to the kernel VESA blanking code and a GPIO
2357                        LED. This parameter is not necessary when using the
2358                        VGA shield.
2359                        c - Enable the s3c camera interface.
2360                        t - Reserved for enabling touchscreen support. The
2361                        touchscreen support is not enabled in the mainstream
2362                        kernel as of 2.6.30, a preliminary port can be found
2363                        in the "bleeding edge" mini2440 support kernel at
2366        mminit_loglevel=
2367                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2368                        parameter allows control of the logging verbosity for
2369                        the additional memory initialisation checks. A value
2370                        of 0 disables mminit logging and a level of 4 will
2371                        log everything. Information is printed at KERN_DEBUG
2372                        so loglevel=8 may also need to be specified.
2374        module.sig_enforce
2375                        [KNL] When CONFIG_MODULE_SIG is set, this means that
2376                        modules without (valid) signatures will fail to load.
2377                        Note that if CONFIG_MODULE_SIG_FORCE is set, that
2378                        is always true, so this option does nothing.
2380        module_blacklist=  [KNL] Do not load a comma-separated list of
2381                        modules.  Useful for debugging problem modules.
2383        mousedev.tap_time=
2384                        [MOUSE] Maximum time between finger touching and
2385                        leaving touchpad surface for touch to be considered
2386                        a tap and be reported as a left button click (for
2387                        touchpads working in absolute mode only).
2388                        Format: <msecs>
2389        mousedev.xres=  [MOUSE] Horizontal screen resolution, used for devices
2390                        reporting absolute coordinates, such as tablets
2391        mousedev.yres=  [MOUSE] Vertical screen resolution, used for devices
2392                        reporting absolute coordinates, such as tablets
2394        movablecore=nn[KMG]     [KNL,X86,IA-64,PPC] This parameter
2395                        is similar to kernelcore except it specifies the
2396                        amount of memory used for migratable allocations.
2397                        If both kernelcore and movablecore is specified,
2398                        then kernelcore will be at *least* the specified
2399                        value but may be more. If movablecore on its own
2400                        is specified, the administrator must be careful
2401                        that the amount of memory usable for all allocations
2402                        is not too small.
2404        movable_node    [KNL,X86] Boot-time switch to enable the effects
2405                        of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2407        MTD_Partition=  [MTD]
2408                        Format: <name>,<region-number>,<size>,<offset>
2410        MTD_Region=     [MTD] Format:
2411                        <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2413        mtdparts=       [MTD]
2414                        See drivers/mtd/cmdlinepart.c.
2416        multitce=off    [PPC]  This parameter disables the use of the pSeries
2417                        firmware feature for updating multiple TCE entries
2418                        at a time.
2420        onenand.bdry=   [HW,MTD] Flex-OneNAND Boundary Configuration
2422                        Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2424                        boundary - index of last SLC block on Flex-OneNAND.
2425                                   The remaining blocks are configured as MLC blocks.
2426                        lock     - Configure if Flex-OneNAND boundary should be locked.
2427                                   Once locked, the boundary cannot be changed.
2428                                   1 indicates lock status, 0 indicates unlock status.
2430        mtdset=         [ARM]
2431                        ARM/S3C2412 JIVE boot control
2433                        See arch/arm/mach-s3c2412/mach-jive.c
2435        mtouchusb.raw_coordinates=
2436                        [HW] Make the MicroTouch USB driver use raw coordinates
2437                        ('y', default) or cooked coordinates ('n')
2439        mtrr_chunk_size=nn[KMG] [X86]
2440                        used for mtrr cleanup. It is largest continuous chunk
2441                        that could hold holes aka. UC entries.
2443        mtrr_gran_size=nn[KMG] [X86]
2444                        Used for mtrr cleanup. It is granularity of mtrr block.
2445                        Default is 1.
2446                        Large value could prevent small alignment from
2447                        using up MTRRs.
2449        mtrr_spare_reg_nr=n [X86]
2450                        Format: <integer>
2451                        Range: 0,7 : spare reg number
2452                        Default : 1
2453                        Used for mtrr cleanup. It is spare mtrr entries number.
2454                        Set to 2 or more if your graphical card needs more.
2456        n2=             [NET] SDL Inc. RISCom/N2 synchronous serial card
2458        netdev=         [NET] Network devices parameters
2459                        Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2460                        Note that mem_start is often overloaded to mean
2461                        something different and driver-specific.
2462                        This usage is only documented in each driver source
2463                        file if at all.
2465        nf_conntrack.acct=
2466                        [NETFILTER] Enable connection tracking flow accounting
2467                        0 to disable accounting
2468                        1 to enable accounting
2469                        Default value is 0.
2471        nfsaddrs=       [NFS] Deprecated.  Use ip= instead.
2472                        See Documentation/filesystems/nfs/nfsroot.txt.
2474        nfsroot=        [NFS] nfs root filesystem for disk-less boxes.
2475                        See Documentation/filesystems/nfs/nfsroot.txt.
2477        nfsrootdebug    [NFS] enable nfsroot debugging messages.
2478                        See Documentation/filesystems/nfs/nfsroot.txt.
2480        nfs.callback_nr_threads=
2481                        [NFSv4] set the total number of threads that the
2482                        NFS client will assign to service NFSv4 callback
2483                        requests.
2485        nfs.callback_tcpport=
2486                        [NFS] set the TCP port on which the NFSv4 callback
2487                        channel should listen.
2489        nfs.cache_getent=
2490                        [NFS] sets the pathname to the program which is used
2491                        to update the NFS client cache entries.
2493        nfs.cache_getent_timeout=
2494                        [NFS] sets the timeout after which an attempt to
2495                        update a cache entry is deemed to have failed.
2497        nfs.idmap_cache_timeout=
2498                        [NFS] set the maximum lifetime for idmapper cache
2499                        entries.
2501        nfs.enable_ino64=
2502                        [NFS] enable 64-bit inode numbers.
2503                        If zero, the NFS client will fake up a 32-bit inode
2504                        number for the readdir() and stat() syscalls instead
2505                        of returning the full 64-bit number.
2506                        The default is to return 64-bit inode numbers.
2508        nfs.max_session_cb_slots=
2509                        [NFSv4.1] Sets the maximum number of session
2510                        slots the client will assign to the callback
2511                        channel. This determines the maximum number of
2512                        callbacks the client will process in parallel for
2513                        a particular server.
2515        nfs.max_session_slots=
2516                        [NFSv4.1] Sets the maximum number of session slots
2517                        the client will attempt to negotiate with the server.
2518                        This limits the number of simultaneous RPC requests
2519                        that the client can send to the NFSv4.1 server.
2520                        Note that there is little point in setting this
2521                        value higher than the max_tcp_slot_table_limit.
2523        nfs.nfs4_disable_idmapping=
2524                        [NFSv4] When set to the default of '1', this option
2525                        ensures that both the RPC level authentication
2526                        scheme and the NFS level operations agree to use
2527                        numeric uids/gids if the mount is using the
2528                        'sec=sys' security flavour. In effect it is
2529                        disabling idmapping, which can make migration from
2530                        legacy NFSv2/v3 systems to NFSv4 easier.
2531                        Servers that do not support this mode of operation
2532                        will be autodetected by the client, and it will fall
2533                        back to using the idmapper.
2534                        To turn off this behaviour, set the value to '0'.
2535        nfs.nfs4_unique_id=
2536                        [NFS4] Specify an additional fixed unique ident-
2537                        ification string that NFSv4 clients can insert into
2538                        their nfs_client_id4 string.  This is typically a
2539                        UUID that is generated at system install time.
2541        nfs.send_implementation_id =
2542                        [NFSv4.1] Send client implementation identification
2543                        information in exchange_id requests.
2544                        If zero, no implementation identification information
2545                        will be sent.
2546                        The default is to send the implementation identification
2547                        information.
2549        nfs.recover_lost_locks =
2550                        [NFSv4] Attempt to recover locks that were lost due
2551                        to a lease timeout on the server. Please note that
2552                        doing this risks data corruption, since there are
2553                        no guarantees that the file will remain unchanged
2554                        after the locks are lost.
2555                        If you want to enable the kernel legacy behaviour of
2556                        attempting to recover these locks, then set this
2557                        parameter to '1'.
2558                        The default parameter value of '0' causes the kernel
2559                        not to attempt recovery of lost locks.
2561        nfs4.layoutstats_timer =
2562                        [NFSv4.2] Change the rate at which the kernel sends
2563                        layoutstats to the pNFS metadata server.
2565                        Setting this to value to 0 causes the kernel to use
2566                        whatever value is the default set by the layout
2567                        driver. A non-zero value sets the minimum interval
2568                        in seconds between layoutstats transmissions.
2570        nfsd.nfs4_disable_idmapping=
2571                        [NFSv4] When set to the default of '1', the NFSv4
2572                        server will return only numeric uids and gids to
2573                        clients using auth_sys, and will accept numeric uids
2574                        and gids from such clients.  This is intended to ease
2575                        migration from NFSv2/v3.
2577        objlayoutdriver.osd_login_prog=
2578                        [NFS] [OBJLAYOUT] sets the pathname to the program which
2579                        is used to automatically discover and login into new
2580                        osd-targets. Please see:
2581                        Documentation/filesystems/pnfs.txt for more explanations
2583        nmi_debug=      [KNL,AVR32,SH] Specify one or more actions to take
2584                        when a NMI is triggered.
2585                        Format: [state][,regs][,debounce][,die]
2587        nmi_watchdog=   [KNL,BUGS=X86] Debugging features for SMP kernels
2588                        Format: [panic,][nopanic,][num]
2589                        Valid num: 0 or 1
2590                        0 - turn hardlockup detector in nmi_watchdog off
2591                        1 - turn hardlockup detector in nmi_watchdog on
2592                        When panic is specified, panic when an NMI watchdog
2593                        timeout occurs (or 'nopanic' to override the opposite
2594                        default). To disable both hard and soft lockup detectors,
2595                        please see 'nowatchdog'.
2596                        This is useful when you use a panic=... timeout and
2597                        need the box quickly up again.
2599        netpoll.carrier_timeout=
2600                        [NET] Specifies amount of time (in seconds) that
2601                        netpoll should wait for a carrier. By default netpoll
2602                        waits 4 seconds.
2604        no387           [BUGS=X86-32] Tells the kernel to use the 387 maths
2605                        emulation library even if a 387 maths coprocessor
2606                        is present.
2608        no_console_suspend
2609                        [HW] Never suspend the console
2610                        Disable suspending of consoles during suspend and
2611                        hibernate operations.  Once disabled, debugging
2612                        messages can reach various consoles while the rest
2613                        of the system is being put to sleep (ie, while
2614                        debugging driver suspend/resume hooks).  This may
2615                        not work reliably with all consoles, but is known
2616                        to work with serial and VGA consoles.
2617                        To facilitate more flexible debugging, we also add
2618                        console_suspend, a printk module parameter to control
2619                        it. Users could use console_suspend (usually
2620                        /sys/module/printk/parameters/console_suspend) to
2621                        turn on/off it dynamically.
2623        noaliencache    [MM, NUMA, SLAB] Disables the allocation of alien
2624                        caches in the slab allocator.  Saves per-node memory,
2625                        but will impact performance.
2627        noalign         [KNL,ARM]
2629        noapic          [SMP,APIC] Tells the kernel to not make use of any
2630                        IOAPICs that may be present in the system.
2632        noautogroup     Disable scheduler automatic task group creation.
2634        nobats          [PPC] Do not use BATs for mapping kernel lowmem
2635                        on "Classic" PPC cores.
2637        nocache         [ARM]
2639        noclflush       [BUGS=X86] Don't use the CLFLUSH instruction
2641        nodelayacct     [KNL] Disable per-task delay accounting
2643        nodsp           [SH] Disable hardware DSP at boot time.
2645        noefi           Disable EFI runtime services support.
2647        noexec          [IA-64]
2649        noexec          [X86]
2650                        On X86-32 available only on PAE configured kernels.
2651                        noexec=on: enable non-executable mappings (default)
2652                        noexec=off: disable non-executable mappings
2654        nosmap          [X86]
2655                        Disable SMAP (Supervisor Mode Access Prevention)
2656                        even if it is supported by processor.
2658        nosmep          [X86]
2659                        Disable SMEP (Supervisor Mode Execution Prevention)
2660                        even if it is supported by processor.
2662        noexec32        [X86-64]
2663                        This affects only 32-bit executables.
2664                        noexec32=on: enable non-executable mappings (default)
2665                                read doesn't imply executable mappings
2666                        noexec32=off: disable non-executable mappings
2667                                read implies executable mappings
2669        nofpu           [MIPS,SH] Disable hardware FPU at boot time.
2671        nofxsr          [BUGS=X86-32] Disables x86 floating point extended
2672                        register save and restore. The kernel will only save
2673                        legacy floating-point registers on task switch.
2675        nohugeiomap     [KNL,x86] Disable kernel huge I/O mappings.
2677        nosmt           [KNL,S390] Disable symmetric multithreading (SMT).
2678                        Equivalent to smt=1.
2680        noxsave         [BUGS=X86] Disables x86 extended register state save
2681                        and restore using xsave. The kernel will fallback to
2682                        enabling legacy floating-point and sse state.
2684        noxsaveopt      [X86] Disables xsaveopt used in saving x86 extended
2685                        register states. The kernel will fall back to use
2686                        xsave to save the states. By using this parameter,
2687                        performance of saving the states is degraded because
2688                        xsave doesn't support modified optimization while
2689                        xsaveopt supports it on xsaveopt enabled systems.
2691        noxsaves        [X86] Disables xsaves and xrstors used in saving and
2692                        restoring x86 extended register state in compacted
2693                        form of xsave area. The kernel will fall back to use
2694                        xsaveopt and xrstor to save and restore the states
2695                        in standard form of xsave area. By using this
2696                        parameter, xsave area per process might occupy more
2697                        memory on xsaves enabled systems.
2699        nohlt           [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2700                        wfi(ARM) instruction doesn't work correctly and not to
2701                        use it. This is also useful when using JTAG debugger.
2703        no_file_caps    Tells the kernel not to honor file capabilities.  The
2704                        only way then for a file to be executed with privilege
2705                        is to be setuid root or executed by root.
2707        nohalt          [IA-64] Tells the kernel not to use the power saving
2708                        function PAL_HALT_LIGHT when idle. This increases
2709                        power-consumption. On the positive side, it reduces
2710                        interrupt wake-up latency, which may improve performance
2711                        in certain environments such as networked servers or
2712                        real-time systems.
2714        nohibernate     [HIBERNATION] Disable hibernation and resume.
2716        nohz=           [KNL] Boottime enable/disable dynamic ticks
2717                        Valid arguments: on, off
2718                        Default: on
2720        nohz_full=      [KNL,BOOT]
2721                        The argument is a cpu list, as described above.
2722                        In kernels built with CONFIG_NO_HZ_FULL=y, set
2723                        the specified list of CPUs whose tick will be stopped
2724                        whenever possible. The boot CPU will be forced outside
2725                        the range to maintain the timekeeping.
2726                        The CPUs in this range must also be included in the
2727                        rcu_nocbs= set.
2729        noiotrap        [SH] Disables trapped I/O port accesses.
2731        noirqdebug      [X86-32] Disables the code which attempts to detect and
2732                        disable unhandled interrupt sources.
2734        no_timer_check  [X86,APIC] Disables the code which tests for
2735                        broken timer IRQ sources.
2737        noisapnp        [ISAPNP] Disables ISA PnP code.
2739        noinitrd        [RAM] Tells the kernel not to load any configured
2740                        initial RAM disk.
2742        nointremap      [X86-64, Intel-IOMMU] Do not enable interrupt
2743                        remapping.
2744                        [Deprecated - use intremap=off]
2746        nointroute      [IA-64]
2748        noinvpcid       [X86] Disable the INVPCID cpu feature.
2750        nojitter        [IA-64] Disables jitter checking for ITC timers.
2752        no-kvmclock     [X86,KVM] Disable paravirtualized KVM clock driver
2754        no-kvmapf       [X86,KVM] Disable paravirtualized asynchronous page
2755                        fault handling.
2757        no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
2758                        steal time is computed, but won't influence scheduler
2759                        behaviour
2761        nolapic         [X86-32,APIC] Do not enable or use the local APIC.
2763        nolapic_timer   [X86-32,APIC] Do not use the local APIC timer.
2765        noltlbs         [PPC] Do not use large page/tlb entries for kernel
2766                        lowmem mapping on PPC40x and PPC8xx
2768        nomca           [IA-64] Disable machine check abort handling
2770        nomce           [X86-32] Disable Machine Check Exception
2772        nomfgpt         [X86-32] Disable Multi-Function General Purpose
2773                        Timer usage (for AMD Geode machines).
2775        nonmi_ipi       [X86] Disable using NMI IPIs during panic/reboot to
2776                        shutdown the other cpus.  Instead use the REBOOT_VECTOR
2777                        irq.
2779        nomodule        Disable module load
2781        nopat           [X86] Disable PAT (page attribute table extension of
2782                        pagetables) support.
2784        norandmaps      Don't use address space randomization.  Equivalent to
2785                        echo 0 > /proc/sys/kernel/randomize_va_space
2787        noreplace-paravirt      [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2789        noreplace-smp   [X86-32,SMP] Don't replace SMP instructions
2790                        with UP alternatives
2792        nordrand        [X86] Disable kernel use of the RDRAND and
2793                        RDSEED instructions even if they are supported
2794                        by the processor.  RDRAND and RDSEED are still
2795                        available to user space applications.
2797        noresume        [SWSUSP] Disables resume and restores original swap
2798                        space.
2800        no-scroll       [VGA] Disables scrollback.
2801                        This is required for the Braillex ib80-piezo Braille
2802                        reader made by F.H. Papenmeier (Germany).
2804        nosbagart       [IA-64]
2806        nosep           [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2808        nosmp           [SMP] Tells an SMP kernel to act as a UP kernel,
2809                        and disable the IO APIC.  legacy for "maxcpus=0".
2811        nosoftlockup    [KNL] Disable the soft-lockup detector.
2813        nosync          [HW,M68K] Disables sync negotiation for all devices.
2815        notsc           [BUGS=X86-32] Disable Time Stamp Counter
2817        nowatchdog      [KNL] Disable both lockup detectors, i.e.
2818                        soft-lockup and NMI watchdog (hard-lockup).
2820        nowb            [ARM]
2822        nox2apic        [X86-64,APIC] Do not enable x2APIC mode.
2824        cpu0_hotplug    [X86] Turn on CPU0 hotplug feature when
2825                        CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2826                        Some features depend on CPU0. Known dependencies are:
2827                        1. Resume from suspend/hibernate depends on CPU0.
2828                        Suspend/hibernate will fail if CPU0 is offline and you
2829                        need to online CPU0 before suspend/hibernate.
2830                        2. PIC interrupts also depend on CPU0. CPU0 can't be
2831                        removed if a PIC interrupt is detected.
2832                        It's said poweroff/reboot may depend on CPU0 on some
2833                        machines although I haven't seen such issues so far
2834                        after CPU0 is offline on a few tested machines.
2835                        If the dependencies are under your control, you can
2836                        turn on cpu0_hotplug.
2838        nptcg=          [IA-64] Override max number of concurrent global TLB
2839                        purges which is reported from either PAL_VM_SUMMARY or
2840                        SAL PALO.
2842        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
2843                        could support.  nr_cpus=n : n >= 1 limits the kernel to
2844                        support 'n' processors. It could be larger than the
2845                        number of already plugged CPU during bootup, later in
2846                        runtime you can physically add extra cpu until it reaches
2847                        n. So during boot up some boot time memory for per-cpu
2848                        variables need be pre-allocated for later physical cpu
2849                        hot plugging.
2851        nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
2853        numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2854                        Allowed values are enable and disable
2856        numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2857                        one of ['zone', 'node', 'default'] can be specified
2858                        This can be set from sysctl after boot.
2859                        See Documentation/sysctl/vm.txt for details.
2861        ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
2862                        See Documentation/debugging-via-ohci1394.txt for more
2863                        info.
2865        olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2866                        Rather than timing out after 20 ms if an EC
2867                        command is not properly ACKed, override the length
2868                        of the timeout.  We have interrupts disabled while
2869                        waiting for the ACK, so if this is set too high
2870                        interrupts *may* be lost!
2872        omap_mux=       [OMAP] Override bootloader pin multiplexing.
2873                        Format: <mux_mode0.mode_name=value>...
2874                        For example, to override I2C bus2:
2875                        omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2877        oprofile.timer= [HW]
2878                        Use timer interrupt instead of performance counters
2880        oprofile.cpu_type=      Force an oprofile cpu type
2881                        This might be useful if you have an older oprofile
2882                        userland or if you want common events.
2883                        Format: { arch_perfmon }
2884                        arch_perfmon: [X86] Force use of architectural
2885                                perfmon on Intel CPUs instead of the
2886                                CPU specific event set.
2887                        timer: [X86] Force use of architectural NMI
2888                                timer mode (see also oprofile.timer
2889                                for generic hr timer mode)
2891        oops=panic      Always panic on oopses. Default is to just kill the
2892                        process, but there is a small probability of
2893                        deadlocking the machine.
2894                        This will also cause panics on machine check exceptions.
2895                        Useful together with panic=30 to trigger a reboot.
2897        OSS             [HW,OSS]
2898                        See Documentation/sound/oss/oss-parameters.txt
2900        page_owner=     [KNL] Boot-time page_owner enabling option.
2901                        Storage of the information about who allocated
2902                        each page is disabled in default. With this switch,
2903                        we can turn it on.
2904                        on: enable the feature
2906        page_poison=    [KNL] Boot-time parameter changing the state of
2907                        poisoning on the buddy allocator.
2908                        off: turn off poisoning
2909                        on: turn on poisoning
2911        panic=          [KNL] Kernel behaviour on panic: delay <timeout>
2912                        timeout > 0: seconds before rebooting
2913                        timeout = 0: wait forever
2914                        timeout < 0: reboot immediately
2915                        Format: <timeout>
2917        panic_on_warn   panic() instead of WARN().  Useful to cause kdump
2918                        on a WARN().
2920        crash_kexec_post_notifiers
2921                        Run kdump after running panic-notifiers and dumping
2922                        kmsg. This only for the users who doubt kdump always
2923                        succeeds in any situation.
2924                        Note that this also increases risks of kdump failure,
2925                        because some panic notifiers can make the crashed
2926                        kernel more unstable.
2928        parkbd.port=    [HW] Parallel port number the keyboard adapter is
2929                        connected to, default is 0.
2930                        Format: <parport#>
2931        parkbd.mode=    [HW] Parallel port keyboard adapter mode of operation,
2932                        0 for XT, 1 for AT (default is AT).
2933                        Format: <mode>
2935        parport=        [HW,PPT] Specify parallel ports. 0 disables.
2936                        Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2937                        Use 'auto' to force the driver to use any
2938                        IRQ/DMA settings detected (the default is to
2939                        ignore detected IRQ/DMA settings because of
2940                        possible conflicts). You can specify the base
2941                        address, IRQ, and DMA settings; IRQ and DMA
2942                        should be numbers, or 'auto' (for using detected
2943                        settings on that particular port), or 'nofifo'
2944                        (to avoid using a FIFO even if it is detected).
2945                        Parallel ports are assigned in the order they
2946                        are specified on the command line, starting
2947                        with parport0.
2949        parport_init_mode=      [HW,PPT]
2950                        Configure VIA parallel port to operate in
2951                        a specific mode. This is necessary on Pegasos
2952                        computer where firmware has no options for setting
2953                        up parallel port mode and sets it to spp.
2954                        Currently this function knows 686a and 8231 chips.
2955                        Format: [spp|ps2|epp|ecp|ecpepp]
2957        pause_on_oops=
2958                        Halt all CPUs after the first oops has been printed for
2959                        the specified number of seconds.  This is to be used if
2960                        your oopses keep scrolling off the screen.
2962        pcbit=          [HW,ISDN]
2964        pcd.            [PARIDE]
2965                        See header of drivers/block/paride/pcd.c.
2966                        See also Documentation/blockdev/paride.txt.
2968        pci=option[,option...]  [PCI] various PCI subsystem options:
2969                earlydump       [X86] dump PCI config space before the kernel
2970                                changes anything
2971                off             [X86] don't probe for the PCI bus
2972                bios            [X86-32] force use of PCI BIOS, don't access
2973                                the hardware directly. Use this if your machine
2974                                has a non-standard PCI host bridge.
2975                nobios          [X86-32] disallow use of PCI BIOS, only direct
2976                                hardware access methods are allowed. Use this
2977                                if you experience crashes upon bootup and you
2978                                suspect they are caused by the BIOS.
2979                conf1           [X86] Force use of PCI Configuration Access
2980                                Mechanism 1 (config address in IO port 0xCF8,
2981                                data in IO port 0xCFC, both 32-bit).
2982                conf2           [X86] Force use of PCI Configuration Access
2983                                Mechanism 2 (IO port 0xCF8 is an 8-bit port for
2984                                the function, IO port 0xCFA, also 8-bit, sets
2985                                bus number. The config space is then accessed
2986                                through ports 0xC000-0xCFFF).
2987                                See for more info
2988                                on the configuration access mechanisms.
2989                noaer           [PCIE] If the PCIEAER kernel config parameter is
2990                                enabled, this kernel boot option can be used to
2991                                disable the use of PCIE advanced error reporting.
2992                nodomains       [PCI] Disable support for multiple PCI
2993                                root domains (aka PCI segments, in ACPI-speak).
2994                nommconf        [X86] Disable use of MMCONFIG for PCI
2995                                Configuration
2996                check_enable_amd_mmconf [X86] check for and enable
2997                                properly configured MMIO access to PCI
2998                                config space on AMD family 10h CPU
2999                nomsi           [MSI] If the PCI_MSI kernel config parameter is
3000                                enabled, this kernel boot option can be used to
3001                                disable the use of MSI interrupts system-wide.
3002                noioapicquirk   [APIC] Disable all boot interrupt quirks.
3003                                Safety option to keep boot IRQs enabled. This
3004                                should never be necessary.
3005                ioapicreroute   [APIC] Enable rerouting of boot IRQs to the
3006                                primary IO-APIC for bridges that cannot disable
3007                                boot IRQs. This fixes a source of spurious IRQs
3008                                when the system masks IRQs.
3009                noioapicreroute [APIC] Disable workaround that uses the
3010                                boot IRQ equivalent of an IRQ that connects to
3011                                a chipset where boot IRQs cannot be disabled.
3012                                The opposite of ioapicreroute.
3013                biosirq         [X86-32] Use PCI BIOS calls to get the interrupt
3014                                routing table. These calls are known to be buggy
3015                                on several machines and they hang the machine
3016                                when used, but on other computers it's the only
3017                                way to get the interrupt routing table. Try
3018                                this option if the kernel is unable to allocate
3019                                IRQs or discover secondary PCI buses on your
3020                                motherboard.
3021                rom             [X86] Assign address space to expansion ROMs.
3022                                Use with caution as certain devices share
3023                                address decoders between ROMs and other
3024                                resources.
3025                norom           [X86] Do not assign address space to
3026                                expansion ROMs that do not already have
3027                                BIOS assigned address ranges.
3028                nobar           [X86] Do not assign address space to the
3029                                BARs that weren't assigned by the BIOS.
3030                irqmask=0xMMMM  [X86] Set a bit mask of IRQs allowed to be
3031                                assigned automatically to PCI devices. You can
3032                                make the kernel exclude IRQs of your ISA cards
3033                                this way.
3034                pirqaddr=0xAAAAA        [X86] Specify the physical address
3035                                of the PIRQ table (normally generated
3036                                by the BIOS) if it is outside the
3037                                F0000h-100000h range.
3038                lastbus=N       [X86] Scan all buses thru bus #N. Can be
3039                                useful if the kernel is unable to find your
3040                                secondary buses and you want to tell it
3041                                explicitly which ones they are.
3042                assign-busses   [X86] Always assign all PCI bus
3043                                numbers ourselves, overriding
3044                                whatever the firmware may have done.
3045                usepirqmask     [X86] Honor the possible IRQ mask stored
3046                                in the BIOS $PIR table. This is needed on
3047                                some systems with broken BIOSes, notably
3048                                some HP Pavilion N5400 and Omnibook XE3
3049                                notebooks. This will have no effect if ACPI
3050                                IRQ routing is enabled.
3051                noacpi          [X86] Do not use ACPI for IRQ routing
3052                                or for PCI scanning.
3053                use_crs         [X86] Use PCI host bridge window information
3054                                from ACPI.  On BIOSes from 2008 or later, this
3055                                is enabled by default.  If you need to use this,
3056                                please report a bug.
3057                nocrs           [X86] Ignore PCI host bridge windows from ACPI.
3058                                If you need to use this, please report a bug.
3059                routeirq        Do IRQ routing for all PCI devices.
3060                                This is normally done in pci_enable_device(),
3061                                so this option is a temporary workaround
3062                                for broken drivers that don't call it.
3063                skip_isa_align  [X86] do not align io start addr, so can
3064                                handle more pci cards
3065                noearly         [X86] Don't do any early type 1 scanning.
3066                                This might help on some broken boards which
3067                                machine check when some devices' config space
3068                                is read. But various workarounds are disabled
3069                                and some IOMMU drivers will not work.
3070                bfsort          Sort PCI devices into breadth-first order.
3071                                This sorting is done to get a device
3072                                order compatible with older (<= 2.4) kernels.
3073                nobfsort        Don't sort PCI devices into breadth-first order.
3074                pcie_bus_tune_off       Disable PCIe MPS (Max Payload Size)
3075                                tuning and use the BIOS-configured MPS defaults.
3076                pcie_bus_safe   Set every device's MPS to the largest value
3077                                supported by all devices below the root complex.
3078                pcie_bus_perf   Set device MPS to the largest allowable MPS
3079                                based on its parent bus. Also set MRRS (Max
3080                                Read Request Size) to the largest supported
3081                                value (no larger than the MPS that the device
3082                                or bus can support) for best performance.
3083                pcie_bus_peer2peer      Set every device's MPS to 128B, which
3084                                every device is guaranteed to support. This
3085                                configuration allows peer-to-peer DMA between
3086                                any pair of devices, possibly at the cost of
3087                                reduced performance.  This also guarantees
3088                                that hot-added devices will work.
3089                cbiosize=nn[KMG]        The fixed amount of bus space which is
3090                                reserved for the CardBus bridge's IO window.
3091                                The default value is 256 bytes.
3092                cbmemsize=nn[KMG]       The fixed amount of bus space which is
3093                                reserved for the CardBus bridge's memory
3094                                window. The default value is 64 megabytes.
3095                resource_alignment=
3096                                Format:
3097                                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3098                                [<order of align>@]pci:<vendor>:<device>\
3099                                                [:<subvendor>:<subdevice>][; ...]
3100                                Specifies alignment and device to reassign
3101                                aligned memory resources.
3102                                If <order of align> is not specified,
3103                                PAGE_SIZE is used as alignment.
3104                                PCI-PCI bridge can be specified, if resource
3105                                windows need to be expanded.
3106                                To specify the alignment for several
3107                                instances of a device, the PCI vendor,
3108                                device, subvendor, and subdevice may be
3109                                specified, e.g., 4096@pci:8086:9c22:103c:198f
3110                ecrc=           Enable/disable PCIe ECRC (transaction layer
3111                                end-to-end CRC checking).
3112                                bios: Use BIOS/firmware settings. This is the
3113                                the default.
3114                                off: Turn ECRC off
3115                                on: Turn ECRC on.
3116                hpiosize=nn[KMG]        The fixed amount of bus space which is
3117                                reserved for hotplug bridge's IO window.
3118                                Default size is 256 bytes.
3119                hpmemsize=nn[KMG]       The fixed amount of bus space which is
3120                                reserved for hotplug bridge's memory window.
3121                                Default size is 2 megabytes.
3122                hpbussize=nn    The minimum amount of additional bus numbers
3123                                reserved for buses below a hotplug bridge.
3124                                Default is 1.
3125                realloc=        Enable/disable reallocating PCI bridge resources
3126                                if allocations done by BIOS are too small to
3127                                accommodate resources required by all child
3128                                devices.
3129                                off: Turn realloc off
3130                                on: Turn realloc on
3131                realloc         same as realloc=on
3132                noari           do not use PCIe ARI.
3133                pcie_scan_all   Scan all possible PCIe devices.  Otherwise we
3134                                only look for one device below a PCIe downstream
3135                                port.
3137        pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
3138                        Management.
3139                off     Disable ASPM.
3140                force   Enable ASPM even on devices that claim not to support it.
3141                        WARNING: Forcing ASPM on may cause system lockups.
3143        pcie_hp=        [PCIE] PCI Express Hotplug driver options:
3144                nomsi   Do not use MSI for PCI Express Native Hotplug (this
3145                        makes all PCIe ports use INTx for hotplug services).
3147        pcie_ports=     [PCIE] PCIe ports handling:
3148                auto    Ask the BIOS whether or not to use native PCIe services
3149                        associated with PCIe ports (PME, hot-plug, AER).  Use
3150                        them only if that is allowed by the BIOS.
3151                native  Use native PCIe services associated with PCIe ports
3152                        unconditionally.
3153                compat  Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
3154                        ports driver.
3156        pcie_port_pm=   [PCIE] PCIe port power management handling:
3157                off     Disable power management of all PCIe ports
3158                force   Forcibly enable power management of all PCIe ports
3160        pcie_pme=       [PCIE,PM] Native PCIe PME signaling options:
3161                nomsi   Do not use MSI for native PCIe PME signaling (this makes
3162                        all PCIe root ports use INTx for all services).
3164        pcmv=           [HW,PCMCIA] BadgePAD 4
3166        pd_ignore_unused
3167                        [PM]
3168                        Keep all power-domains already enabled by bootloader on,
3169                        even if no driver has claimed them. This is useful
3170                        for debug and development, but should not be
3171                        needed on a platform with proper driver support.
3173        pd.             [PARIDE]
3174                        See Documentation/blockdev/paride.txt.
3176        pdcchassis=     [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3177                        boot time.
3178                        Format: { 0 | 1 }
3179                        See arch/parisc/kernel/pdc_chassis.c
3181        percpu_alloc=   Select which percpu first chunk allocator to use.
3182                        Currently supported values are "embed" and "page".
3183                        Archs may support subset or none of the selections.
3184                        See comments in mm/percpu.c for details on each
3185                        allocator.  This parameter is primarily for debugging
3186                        and performance comparison.
3188        pf.             [PARIDE]
3189                        See Documentation/blockdev/paride.txt.
3191        pg.             [PARIDE]
3192                        See Documentation/blockdev/paride.txt.
3194        pirq=           [SMP,APIC] Manual mp-table setup
3195                        See Documentation/x86/i386/IO-APIC.txt.
3197        plip=           [PPT,NET] Parallel port network link
3198                        Format: { parport<nr> | timid | 0 }
3199                        See also Documentation/parport.txt.
3201        pmtmr=          [X86] Manual setup of pmtmr I/O Port.
3202                        Override pmtimer IOPort with a hex value.
3203                        e.g. pmtmr=0x508
3205        pnp.debug=1     [PNP]
3206                        Enable PNP debug messages (depends on the
3207                        CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
3208                        via /sys/module/pnp/parameters/debug.  We always show
3209                        current resource usage; turning this on also shows
3210                        possible settings and some assignment information.
3212        pnpacpi=        [ACPI]
3213                        { off }
3215        pnpbios=        [ISAPNP]
3216                        { on | off | curr | res | no-curr | no-res }
3218        pnp_reserve_irq=
3219                        [ISAPNP] Exclude IRQs for the autoconfiguration
3221        pnp_reserve_dma=
3222                        [ISAPNP] Exclude DMAs for the autoconfiguration
3224        pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3225                        Ranges are in pairs (I/O port base and size).
3227        pnp_reserve_mem=
3228                        [ISAPNP] Exclude memory regions for the
3229                        autoconfiguration.
3230                        Ranges are in pairs (memory base and size).
3232        ports=          [IP_VS_FTP] IPVS ftp helper module
3233                        Default is 21.
3234                        Up to 8 (IP_VS_APP_MAX_PORTS) ports
3235                        may be specified.
3236                        Format: <port>,<port>....
3238        ppc_strict_facility_enable
3239                        [PPC] This option catches any kernel floating point,
3240                        Altivec, VSX and SPE outside of regions specifically
3241                        allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3242                        There is some performance impact when enabling this.
3244        print-fatal-signals=
3245                        [KNL] debug: print fatal signals
3247                        If enabled, warn about various signal handling
3248                        related application anomalies: too many signals,
3249                        too many POSIX.1 timers, fatal signals causing a
3250                        coredump - etc.
3252                        If you hit the warning due to signal overflow,
3253                        you might want to try "ulimit -i unlimited".
3255                        default: off.
3257        printk.always_kmsg_dump=
3258                        Trigger kmsg_dump for cases other than kernel oops or
3259                        panics
3260                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
3261                        default: disabled
3263        printk.devkmsg={on,off,ratelimit}
3264                        Control writing to /dev/kmsg.
3265                        on - unlimited logging to /dev/kmsg from userspace
3266                        off - logging to /dev/kmsg disabled
3267                        ratelimit - ratelimit the logging
3268                        Default: ratelimit
3270        printk.time=    Show timing data prefixed to each printk message line
3271                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
3273        processor.max_cstate=   [HW,ACPI]
3274                        Limit processor to maximum C-state
3275                        max_cstate=9 overrides any DMI blacklist limit.
3277        processor.nocst [HW,ACPI]
3278                        Ignore the _CST method to determine C-states,
3279                        instead using the legacy FADT method
3281        profile=        [KNL] Enable kernel profiling via /proc/profile
3282                        Format: [schedule,]<number>
3283                        Param: "schedule" - profile schedule points.
3284                        Param: <number> - step/bucket size as a power of 2 for
3285                                statistical time based profiling.
3286                        Param: "sleep" - profile D-state sleeping (millisecs).
3287                                Requires CONFIG_SCHEDSTATS
3288                        Param: "kvm" - profile VM exits.
3290        prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3291                        before loading.
3292                        See Documentation/blockdev/ramdisk.txt.
3294        psmouse.proto=  [HW,MOUSE] Highest PS2 mouse protocol extension to
3295                        probe for; one of (bare|imps|exps|lifebook|any).
3296        psmouse.rate=   [HW,MOUSE] Set desired mouse report rate, in reports
3297                        per second.
3298        psmouse.resetafter=     [HW,MOUSE]
3299                        Try to reset the device after so many bad packets
3300                        (0 = never).
3301        psmouse.resolution=
3302                        [HW,MOUSE] Set desired mouse resolution, in dpi.
3303        psmouse.smartscroll=
3304                        [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3305                        0 = disabled, 1 = enabled (default).
3307        pstore.backend= Specify the name of the pstore backend to use
3309        pt.             [PARIDE]
3310                        See Documentation/blockdev/paride.txt.
3312        pty.legacy_count=
3313                        [KNL] Number of legacy pty's. Overwrites compiled-in
3314                        default number.
3316        quiet           [KNL] Disable most log messages
3318        r128=           [HW,DRM]
3320        raid=           [HW,RAID]
3321                        See Documentation/md.txt.
3323        ramdisk_size=   [RAM] Sizes of RAM disks in kilobytes
3324                        See Documentation/blockdev/ramdisk.txt.
3326        rcu_nocbs=      [KNL]
3327                        The argument is a cpu list, as described above.
3329                        In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3330                        the specified list of CPUs to be no-callback CPUs.
3331                        Invocation of these CPUs' RCU callbacks will
3332                        be offloaded to "rcuox/N" kthreads created for
3333                        that purpose, where "x" is "b" for RCU-bh, "p"
3334                        for RCU-preempt, and "s" for RCU-sched, and "N"
3335                        is the CPU number.  This reduces OS jitter on the
3336                        offloaded CPUs, which can be useful for HPC and
3337                        real-time workloads.  It can also improve energy
3338                        efficiency for asymmetric multiprocessors.
3340        rcu_nocb_poll   [KNL]
3341                        Rather than requiring that offloaded CPUs
3342                        (specified by rcu_nocbs= above) explicitly
3343                        awaken the corresponding "rcuoN" kthreads,
3344                        make these kthreads poll for callbacks.
3345                        This improves the real-time response for the
3346                        offloaded CPUs by relieving them of the need to
3347                        wake up the corresponding kthread, but degrades
3348                        energy efficiency by requiring that the kthreads
3349                        periodically wake up to do the polling.
3351        rcutree.blimit= [KNL]
3352                        Set maximum number of finished RCU callbacks to
3353                        process in one batch.
3355        rcutree.dump_tree=      [KNL]
3356                        Dump the structure of the rcu_node combining tree
3357                        out at early boot.  This is used for diagnostic
3358                        purposes, to verify correct tree setup.
3360        rcutree.gp_cleanup_delay=       [KNL]
3361                        Set the number of jiffies to delay each step of
3362                        RCU grace-period cleanup.  This only has effect
3363                        when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3365        rcutree.gp_init_delay=  [KNL]
3366                        Set the number of jiffies to delay each step of
3367                        RCU grace-period initialization.  This only has
3368                        effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3369                        is set.
3371        rcutree.gp_preinit_delay=       [KNL]
3372                        Set the number of jiffies to delay each step of
3373                        RCU grace-period pre-initialization, that is,
3374                        the propagation of recent CPU-hotplug changes up
3375                        the rcu_node combining tree.  This only has effect
3376                        when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
3378        rcutree.rcu_fanout_exact= [KNL]
3379                        Disable autobalancing of the rcu_node combining
3380                        tree.  This is used by rcutorture, and might
3381                        possibly be useful for architectures having high
3382                        cache-to-cache transfer latencies.
3384        rcutree.rcu_fanout_leaf= [KNL]
3385                        Change the number of CPUs assigned to each
3386                        leaf rcu_node structure.  Useful for very
3387                        large systems, which will choose the value 64,
3388                        and for NUMA systems with large remote-access
3389                        latencies, which will choose a value aligned
3390                        with the appropriate hardware boundaries.
3392        rcutree.jiffies_till_sched_qs= [KNL]
3393                        Set required age in jiffies for a
3394                        given grace period before RCU starts
3395                        soliciting quiescent-state help from
3396                        rcu_note_context_switch().
3398        rcutree.jiffies_till_first_fqs= [KNL]
3399                        Set delay from grace-period initialization to
3400                        first attempt to force quiescent states.
3401                        Units are jiffies, minimum value is zero,
3402                        and maximum value is HZ.
3404        rcutree.jiffies_till_next_fqs= [KNL]
3405                        Set delay between subsequent attempts to force
3406                        quiescent states.  Units are jiffies, minimum
3407                        value is one, and maximum value is HZ.
3409        rcutree.kthread_prio=    [KNL,BOOT]
3410                        Set the SCHED_FIFO priority of the RCU per-CPU
3411                        kthreads (rcuc/N). This value is also used for
3412                        the priority of the RCU boost threads (rcub/N)
3413                        and for the RCU grace-period kthreads (rcu_bh,
3414                        rcu_preempt, and rcu_sched). If RCU_BOOST is
3415                        set, valid values are 1-99 and the default is 1
3416                        (the least-favored priority).  Otherwise, when
3417                        RCU_BOOST is not set, valid values are 0-99 and
3418                        the default is zero (non-realtime operation).
3420        rcutree.rcu_nocb_leader_stride= [KNL]
3421                        Set the number of NOCB kthread groups, which
3422                        defaults to the square root of the number of
3423                        CPUs.  Larger numbers reduces the wakeup overhead
3424                        on the per-CPU grace-period kthreads, but increases
3425                        that same overhead on each group's leader.
3427        rcutree.qhimark= [KNL]
3428                        Set threshold of queued RCU callbacks beyond which
3429                        batch limiting is disabled.
3431        rcutree.qlowmark= [KNL]
3432                        Set threshold of queued RCU callbacks below which
3433                        batch limiting is re-enabled.
3435        rcutree.rcu_idle_gp_delay= [KNL]
3436                        Set wakeup interval for idle CPUs that have
3437                        RCU callbacks (RCU_FAST_NO_HZ=y).
3439        rcutree.rcu_idle_lazy_gp_delay= [KNL]
3440                        Set wakeup interval for idle CPUs that have
3441                        only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3442                        Lazy RCU callbacks are those which RCU can
3443                        prove do nothing more than free memory.
3445        rcuperf.gp_exp= [KNL]
3446                        Measure performance of expedited synchronous
3447                        grace-period primitives.
3449        rcuperf.holdoff= [KNL]
3450                        Set test-start holdoff period.  The purpose of
3451                        this parameter is to delay the start of the
3452                        test until boot completes in order to avoid
3453                        interference.
3455        rcuperf.nreaders= [KNL]
3456                        Set number of RCU readers.  The value -1 selects
3457                        N, where N is the number of CPUs.  A value
3458                        "n" less than -1 selects N-n+1, where N is again
3459                        the number of CPUs.  For example, -2 selects N
3460                        (the number of CPUs), -3 selects N+1, and so on.
3461                        A value of "n" less than or equal to -N selects
3462                        a single reader.
3464        rcuperf.nwriters= [KNL]
3465                        Set number of RCU writers.  The values operate
3466                        the same as for rcuperf.nreaders.
3467                        N, where N is the number of CPUs
3469        rcuperf.perf_runnable= [BOOT]
3470                        Start rcuperf running at boot time.
3472        rcuperf.shutdown= [KNL]
3473                        Shut the system down after performance tests
3474                        complete.  This is useful for hands-off automated
3475                        testing.
3477        rcuperf.perf_type= [KNL]
3478                        Specify the RCU implementation to test.
3480        rcuperf.verbose= [KNL]
3481                        Enable additional printk() statements.
3483        rcutorture.cbflood_inter_holdoff= [KNL]
3484                        Set holdoff time (jiffies) between successive
3485                        callback-flood tests.
3487        rcutorture.cbflood_intra_holdoff= [KNL]
3488                        Set holdoff time (jiffies) between successive
3489                        bursts of callbacks within a given callback-flood
3490                        test.
3492        rcutorture.cbflood_n_burst= [KNL]
3493                        Set the number of bursts making up a given
3494                        callback-flood test.  Set this to zero to
3495                        disable callback-flood testing.
3497        rcutorture.cbflood_n_per_burst= [KNL]
3498                        Set the number of callbacks to be registered
3499                        in a given burst of a callback-flood test.
3501        rcutorture.fqs_duration= [KNL]
3502                        Set duration of force_quiescent_state bursts
3503                        in microseconds.
3505        rcutorture.fqs_holdoff= [KNL]
3506                        Set holdoff time within force_quiescent_state bursts
3507                        in microseconds.
3509        rcutorture.fqs_stutter= [KNL]
3510                        Set wait time between force_quiescent_state bursts
3511                        in seconds.
3513        rcutorture.gp_cond= [KNL]
3514                        Use conditional/asynchronous update-side
3515                        primitives, if available.
3517        rcutorture.gp_exp= [KNL]
3518                        Use expedited update-side primitives, if available.
3520        rcutorture.gp_normal= [KNL]
3521                        Use normal (non-expedited) asynchronous
3522                        update-side primitives, if available.
3524        rcutorture.gp_sync= [KNL]
3525                        Use normal (non-expedited) synchronous
3526                        update-side primitives, if available.  If all
3527                        of rcutorture.gp_cond=, rcutorture.gp_exp=,
3528                        rcutorture.gp_normal=, and rcutorture.gp_sync=
3529                        are zero, rcutorture acts as if is interpreted
3530                        they are all non-zero.
3532        rcutorture.n_barrier_cbs= [KNL]
3533                        Set callbacks/threads for rcu_barrier() testing.
3535        rcutorture.nfakewriters= [KNL]
3536                        Set number of concurrent RCU writers.  These just
3537                        stress RCU, they don't participate in the actual
3538                        test, hence the "fake".
3540        rcutorture.nreaders= [KNL]
3541                        Set number of RCU readers.  The value -1 selects
3542                        N-1, where N is the number of CPUs.  A value
3543                        "n" less than -1 selects N-n-2, where N is again
3544                        the number of CPUs.  For example, -2 selects N
3545                        (the number of CPUs), -3 selects N+1, and so on.
3547        rcutorture.object_debug= [KNL]
3548                        Enable debug-object double-call_rcu() testing.
3550        rcutorture.onoff_holdoff= [KNL]
3551                        Set time (s) after boot for CPU-hotplug testing.
3553        rcutorture.onoff_interval= [KNL]
3554                        Set time (s) between CPU-hotplug operations, or
3555                        zero to disable CPU-hotplug testing.
3557        rcutorture.shuffle_interval= [KNL]
3558                        Set task-shuffle interval (s).  Shuffling tasks
3559                        allows some CPUs to go into dyntick-idle mode
3560                        during the rcutorture test.
3562        rcutorture.shutdown_secs= [KNL]
3563                        Set time (s) after boot system shutdown.  This
3564                        is useful for hands-off automated testing.
3566        rcutorture.stall_cpu= [KNL]
3567                        Duration of CPU stall (s) to test RCU CPU stall
3568                        warnings, zero to disable.
3570        rcutorture.stall_cpu_holdoff= [KNL]
3571                        Time to wait (s) after boot before inducing stall.
3573        rcutorture.stat_interval= [KNL]
3574                        Time (s) between statistics printk()s.
3576        rcutorture.stutter= [KNL]
3577                        Time (s) to stutter testing, for example, specifying
3578                        five seconds causes the test to run for five seconds,
3579                        wait for five seconds, and so on.  This tests RCU's
3580                        ability to transition abruptly to and from idle.
3582        rcutorture.test_boost= [KNL]
3583                        Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
3584                        "Maybe" means test if the RCU implementation
3585                        under test support RCU priority boosting.
3587        rcutorture.test_boost_duration= [KNL]
3588                        Duration (s) of each individual boost test.
3590        rcutorture.test_boost_interval= [KNL]
3591                        Interval (s) between each boost test.
3593        rcutorture.test_no_idle_hz= [KNL]
3594                        Test RCU's dyntick-idle handling.  See also the
3595                        rcutorture.shuffle_interval parameter.
3597        rcutorture.torture_runnable= [BOOT]
3598                        Start rcutorture running at boot time.
3600        rcutorture.torture_type= [KNL]
3601                        Specify the RCU implementation to test.
3603        rcutorture.verbose= [KNL]
3604                        Enable additional printk() statements.
3606        rcupdate.rcu_cpu_stall_suppress= [KNL]
3607                        Suppress RCU CPU stall warning messages.
3609        rcupdate.rcu_cpu_stall_timeout= [KNL]
3610                        Set timeout for RCU CPU stall warning messages.
3612        rcupdate.rcu_expedited= [KNL]
3613                        Use expedited grace-period primitives, for
3614                        example, synchronize_rcu_expedited() instead
3615                        of synchronize_rcu().  This reduces latency,
3616                        but can increase CPU utilization, degrade
3617                        real-time latency, and degrade energy efficiency.
3618                        No effect on CONFIG_TINY_RCU kernels.
3620        rcupdate.rcu_normal= [KNL]
3621                        Use only normal grace-period primitives,
3622                        for example, synchronize_rcu() instead of
3623                        synchronize_rcu_expedited().  This improves
3624                        real-time latency, CPU utilization, and
3625                        energy efficiency, but can expose users to
3626                        increased grace-period latency.  This parameter
3627                        overrides rcupdate.rcu_expedited.  No effect on
3628                        CONFIG_TINY_RCU kernels.
3630        rcupdate.rcu_normal_after_boot= [KNL]
3631                        Once boot has completed (that is, after
3632                        rcu_end_inkernel_boot() has been invoked), use
3633                        only normal grace-period primitives.  No effect
3634                        on CONFIG_TINY_RCU kernels.
3636        rcupdate.rcu_task_stall_timeout= [KNL]
3637                        Set timeout in jiffies for RCU task stall warning
3638                        messages.  Disable with a value less than or equal
3639                        to zero.
3641        rcupdate.rcu_self_test= [KNL]
3642                        Run the RCU early boot self tests
3644        rcupdate.rcu_self_test_bh= [KNL]
3645                        Run the RCU bh early boot self tests
3647        rcupdate.rcu_self_test_sched= [KNL]
3648                        Run the RCU sched early boot self tests
3650        rdinit=         [KNL]
3651                        Format: <full_path>
3652                        Run specified binary instead of /init from the ramdisk,
3653                        used for early userspace startup. See initrd.
3655        reboot=         [KNL]
3656                        Format (x86 or x86_64):
3657                                [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3658                                [[,]s[mp]#### \
3659                                [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3660                                [[,]f[orce]
3661                        Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3662                              reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3663                              reboot_force is either force or not specified,
3664                              reboot_cpu is s[mp]#### with #### being the processor
3665                                        to be used for rebooting.
3667        relax_domain_level=
3668                        [KNL, SMP] Set scheduler's default relax_domain_level.
3669                        See Documentation/cgroup-v1/cpusets.txt.
3671        relative_sleep_states=
3672                        [SUSPEND] Use sleep state labeling where the deepest
3673                        state available other than hibernation is always "mem".
3674                        Format: { "0" | "1" }
3675                        0 -- Traditional sleep state labels.
3676                        1 -- Relative sleep state labels.
3678        reserve=        [KNL,BUGS] Force the kernel to ignore some iomem area
3680        reservetop=     [X86-32]
3681                        Format: nn[KMG]
3682                        Reserves a hole at the top of the kernel virtual
3683                        address space.
3685        reservelow=     [X86]
3686                        Format: nn[K]
3687                        Set the amount of memory to reserve for BIOS at
3688                        the bottom of the address space.
3690        reset_devices   [KNL] Force drivers to reset the underlying device
3691                        during initialization.
3693        resume=         [SWSUSP]
3694                        Specify the partition device for software suspend
3695                        Format:
3696                        {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3698        resume_offset=  [SWSUSP]
3699                        Specify the offset from the beginning of the partition
3700                        given by "resume=" at which the swap header is located,
3701                        in <PAGE_SIZE> units (needed only for swap files).
3702                        See  Documentation/power/swsusp-and-swap-files.txt
3704        resumedelay=    [HIBERNATION] Delay (in seconds) to pause before attempting to
3705                        read the resume files
3707        resumewait      [HIBERNATION] Wait (indefinitely) for resume device to show up.
3708                        Useful for devices that are detected asynchronously
3709                        (e.g. USB and MMC devices).
3711        hibernate=      [HIBERNATION]
3712                noresume        Don't check if there's a hibernation image
3713                                present during boot.
3714                nocompress      Don't compress/decompress hibernation images.
3715                no              Disable hibernation and resume.
3716                protect_image   Turn on image protection during restoration
3717                                (that will set all pages holding image data
3718                                during restoration read-only).
3720        retain_initrd   [RAM] Keep initrd memory after extraction
3722        rfkill.default_state=
3723                0       "airplane mode".  All wifi, bluetooth, wimax, gps, fm,
3724                        etc. communication is blocked by default.
3725                1       Unblocked.
3727        rfkill.master_switch_mode=
3728                0       The "airplane mode" button does nothing.
3729                1       The "airplane mode" button toggles between everything
3730                        blocked and the previous configuration.
3731                2       The "airplane mode" button toggles between everything
3732                        blocked and everything unblocked.
3734        rhash_entries=  [KNL,NET]
3735                        Set number of hash buckets for route cache
3737        ro              [KNL] Mount root device read-only on boot
3739        rodata=         [KNL]
3740                on      Mark read-only kernel memory as read-only (default).
3741                off     Leave read-only kernel memory writable for debugging.
3743        rockchip.usb_uart
3744                        Enable the uart passthrough on the designated usb port
3745                        on Rockchip SoCs. When active, the signals of the
3746                        debug-uart get routed to the D+ and D- pins of the usb
3747                        port and the regular usb controller gets disabled.
3749        root=           [KNL] Root filesystem
3750                        See name_to_dev_t comment in init/do_mounts.c.
3752        rootdelay=      [KNL] Delay (in seconds) to pause before attempting to
3753                        mount the root filesystem
3755        rootflags=      [KNL] Set root filesystem mount option string
3757        rootfstype=     [KNL] Set root filesystem type
3759        rootwait        [KNL] Wait (indefinitely) for root device to show up.
3760                        Useful for devices that are detected asynchronously
3761                        (e.g. USB and MMC devices).
3763        rproc_mem=nn[KMG][@address]
3764                        [KNL,ARM,CMA] Remoteproc physical memory block.
3765                        Memory area to be used by remote processor image,
3766                        managed by CMA.
3768        rw              [KNL] Mount root device read-write on boot
3770        S               [KNL] Run init in single mode
3772        s390_iommu=     [HW,S390]
3773                        Set s390 IOTLB flushing mode
3774                strict
3775                        With strict flushing every unmap operation will result in
3776                        an IOTLB flush. Default is lazy flushing before reuse,
3777                        which is faster.
3779        sa1100ir        [NET]
3780                        See drivers/net/irda/sa1100_ir.c.
3782        sbni=           [NET] Granch SBNI12 leased line adapter
3784        sched_debug     [KNL] Enables verbose scheduler debug messages.
3786        schedstats=     [KNL,X86] Enable or disable scheduled statistics.
3787                        Allowed values are enable and disable. This feature
3788                        incurs a small amount of overhead in the scheduler
3789                        but is useful for debugging and performance tuning.
3791        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
3792                        xtime_lock contention on larger systems, and/or RCU lock
3793                        contention on all systems with CONFIG_MAXSMP set.
3794                        Format: { "0" | "1" }
3795                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3796                        1 -- enable.
3797                        Note: increases power consumption, thus should only be
3798                        enabled if running jitter sensitive (HPC/RT) workloads.
3800        security=       [SECURITY] Choose a security module to enable at boot.
3801                        If this boot parameter is not specified, only the first
3802                        security module asking for security registration will be
3803                        loaded. An invalid security module name will be treated
3804                        as if no module has been chosen.
3806        selinux=        [SELINUX] Disable or enable SELinux at boot time.
3807                        Format: { "0" | "1" }
3808                        See security/selinux/Kconfig help text.
3809                        0 -- disable.
3810                        1 -- enable.
3811                        Default value is set via kernel config option.
3812                        If enabled at boot time, /selinux/disable can be used
3813                        later to disable prior to initial policy load.
3815        apparmor=       [APPARMOR] Disable or enable AppArmor at boot time
3816                        Format: { "0" | "1" }
3817                        See security/apparmor/Kconfig help text
3818                        0 -- disable.
3819                        1 -- enable.
3820                        Default value is set via kernel config option.
3822        serialnumber    [BUGS=X86-32]
3824        shapers=        [NET]
3825                        Maximal number of shapers.
3827        show_msr=       [x86] show boot-time MSR settings
3828                        Format: { <integer> }
3829                        Show boot-time (BIOS-initialized) MSR settings.
3830                        The parameter means the number of CPUs to show,
3831                        for example 1 means boot CPU only.
3833        simeth=         [IA-64]
3834        simscsi=
3836        slram=          [HW,MTD]
3838        slab_nomerge    [MM]
3839                        Disable merging of slabs with similar size. May be
3840                        necessary if there is some reason to distinguish
3841                        allocs to different slabs. Debug options disable
3842                        merging on their own.
3843                        For more information see Documentation/vm/slub.txt.
3845        slab_max_order= [MM, SLAB]
3846                        Determines the maximum allowed order for slabs.
3847                        A high setting may cause OOMs due to memory
3848                        fragmentation.  Defaults to 1 for systems with
3849                        more than 32MB of RAM, 0 otherwise.
3851        slub_debug[=options[,slabs]]    [MM, SLUB]
3852                        Enabling slub_debug allows one to determine the
3853                        culprit if slab objects become corrupted. Enabling
3854                        slub_debug can create guard zones around objects and
3855                        may poison objects when not in use. Also tracks the
3856                        last alloc / free. For more information see
3857                        Documentation/vm/slub.txt.
3859        slub_max_order= [MM, SLUB]
3860                        Determines the maximum allowed order for slabs.
3861                        A high setting may cause OOMs due to memory
3862                        fragmentation. For more information see
3863                        Documentation/vm/slub.txt.
3865        slub_min_objects=       [MM, SLUB]
3866                        The minimum number of objects per slab. SLUB will
3867                        increase the slab order up to slub_max_order to
3868                        generate a sufficiently large slab able to contain
3869                        the number of objects indicated. The higher the number
3870                        of objects the smaller the overhead of tracking slabs
3871                        and the less frequently locks need to be acquired.
3872                        For more information see Documentation/vm/slub.txt.
3874        slub_min_order= [MM, SLUB]
3875                        Determines the minimum page order for slabs. Must be
3876                        lower than slub_max_order.
3877                        For more information see Documentation/vm/slub.txt.
3879        slub_nomerge    [MM, SLUB]
3880                        Same with slab_nomerge. This is supported for legacy.
3881                        See slab_nomerge for more information.
3883        smart2=         [HW]
3884                        Format: <io1>[,<io2>[,...,<io8>]]
3886        smsc-ircc2.nopnp        [HW] Don't use PNP to discover SMC devices
3887        smsc-ircc2.ircc_cfg=    [HW] Device configuration I/O port
3888        smsc-ircc2.ircc_sir=    [HW] SIR base I/O port
3889        smsc-ircc2.ircc_fir=    [HW] FIR base I/O port
3890        smsc-ircc2.ircc_irq=    [HW] IRQ line
3891        smsc-ircc2.ircc_dma=    [HW] DMA channel
3892        smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3893                                0: Toshiba Satellite 1800 (GP data pin select)
3894                                1: Fast pin select (default)
3895                                2: ATC IRMode
3897        smt             [KNL,S390] Set the maximum number of threads (logical
3898                        CPUs) to use per physical CPU on systems capable of
3899                        symmetric multithreading (SMT). Will be capped to the
3900                        actual hardware limit.
3901                        Format: <integer>
3902                        Default: -1 (no limit)
3904        softlockup_panic=
3905                        [KNL] Should the soft-lockup detector generate panics.
3906                        Format: <integer>
3908        softlockup_all_cpu_backtrace=
3909                        [KNL] Should the soft-lockup detector generate
3910                        backtraces on all cpus.
3911                        Format: <integer>
3913        sonypi.*=       [HW] Sony Programmable I/O Control Device driver
3914                        See Documentation/laptops/sonypi.txt
3916        spia_io_base=   [HW,MTD]
3917        spia_fio_base=
3918        spia_pedr=
3919        spia_peddr=
3921        stacktrace      [FTRACE]
3922                        Enabled the stack tracer on boot up.
3924        stacktrace_filter=[function-list]
3925                        [FTRACE] Limit the functions that the stack tracer
3926                        will trace at boot up. function-list is a comma separated
3927                        list of functions. This list can be changed at run
3928                        time by the stack_trace_filter file in the debugfs
3929                        tracing directory. Note, this enables stack tracing
3930                        and the stacktrace above is not needed.
3932        sti=            [PARISC,HW]
3933                        Format: <num>
3934                        Set the STI (builtin display/keyboard on the HP-PARISC
3935                        machines) console (graphic card) which should be used
3936                        as the initial boot-console.
3937                        See also comment in drivers/video/console/sticore.c.
3939        sti_font=       [HW]
3940                        See comment in drivers/video/console/sticore.c.
3942        stifb=          [HW]
3943                        Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3945        sunrpc.min_resvport=
3946        sunrpc.max_resvport=
3947                        [NFS,SUNRPC]
3948                        SunRPC servers often require that client requests
3949                        originate from a privileged port (i.e. a port in the
3950                        range 0 < portnr < 1024).
3951                        An administrator who wishes to reserve some of these
3952                        ports for other uses may adjust the range that the
3953                        kernel's sunrpc client considers to be privileged
3954                        using these two parameters to set the minimum and
3955                        maximum port values.
3957        sunrpc.svc_rpc_per_connection_limit=
3958                        [NFS,SUNRPC]
3959                        Limit the number of requests that the server will
3960                        process in parallel from a single connection.
3961                        The default value is 0 (no limit).
3963        sunrpc.pool_mode=
3964                        [NFS]
3965                        Control how the NFS server code allocates CPUs to
3966                        service thread pools.  Depending on how many NICs
3967                        you have and where their interrupts are bound, this
3968                        option will affect which CPUs will do NFS serving.
3969                        Note: this parameter cannot be changed while the
3970                        NFS server is running.
3972                        auto        the server chooses an appropriate mode
3973                                    automatically using heuristics
3974                        global      a single global pool contains all CPUs
3975                        percpu      one pool for each CPU
3976                        pernode     one pool for each NUMA node (equivalent
3977                                    to global on non-NUMA machines)
3979        sunrpc.tcp_slot_table_entries=
3980        sunrpc.udp_slot_table_entries=
3981                        [NFS,SUNRPC]
3982                        Sets the upper limit on the number of simultaneous
3983                        RPC calls that can be sent from the client to a
3984                        server. Increasing these values may allow you to
3985                        improve throughput, but will also increase the
3986                        amount of memory reserved for use by the client.
3988        suspend.pm_test_delay=
3989                        [SUSPEND]
3990                        Sets the number of seconds to remain in a suspend test
3991                        mode before resuming the system (see
3992                        /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3993                        is set. Default value is 5.
3995        swapaccount=[0|1]
3996                        [KNL] Enable accounting of swap in memory resource
3997                        controller if no parameter or 1 is given or disable
3998                        it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4000        swiotlb=        [ARM,IA-64,PPC,MIPS,X86]
4001                        Format: { <int> | force }
4002                        <int> -- Number of I/O TLB slabs
4003                        force -- force using of bounce buffers even if they
4004                                 wouldn't be automatically used by the kernel
4006        switches=       [HW,M68k]
4008        sysfs.deprecated=0|1 [KNL]
4009                        Enable/disable old style sysfs layout for old udev
4010                        on older distributions. When this option is enabled
4011                        very new udev will not work anymore. When this option
4012                        is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4013                        in older udev will not work anymore.
4014                        Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4015                        the kernel configuration.
4017        sysrq_always_enabled
4018                        [KNL]
4019                        Ignore sysrq setting - this boot parameter will
4020                        neutralize any effect of /proc/sys/kernel/sysrq.
4021                        Useful for debugging.
4023        tcpmhash_entries= [KNL,NET]
4024                        Set the number of tcp_metrics_hash slots.
4025                        Default value is 8192 or 16384 depending on total
4026                        ram pages. This is used to specify the TCP metrics
4027                        cache size. See Documentation/networking/ip-sysctl.txt
4028                        "tcp_no_metrics_save" section for more details.
4030        tdfx=           [HW,DRM]
4032        test_suspend=   [SUSPEND][,N]
4033                        Specify "mem" (for Suspend-to-RAM) or "standby" (for
4034                        standby suspend) or "freeze" (for suspend type freeze)
4035                        as the system sleep state during system startup with
4036                        the optional capability to repeat N number of times.
4037                        The system is woken from this state using a
4038                        wakeup-capable RTC alarm.
4040        thash_entries=  [KNL,NET]
4041                        Set number of hash buckets for TCP connection
4043        thermal.act=    [HW,ACPI]
4044                        -1: disable all active trip points in all thermal zones
4045                        <degrees C>: override all lowest active trip points
4047        thermal.crt=    [HW,ACPI]
4048                        -1: disable all critical trip points in all thermal zones
4049                        <degrees C>: override all critical trip points
4051        thermal.nocrt=  [HW,ACPI]
4052                        Set to disable actions on ACPI thermal zone
4053                        critical and hot trip points.
4055    [HW,ACPI]
4056                        1: disable ACPI thermal control
4058        thermal.psv=    [HW,ACPI]
4059                        -1: disable all passive trip points
4060                        <degrees C>: override all passive trip points to this
4061                        value
4063        thermal.tzp=    [HW,ACPI]
4064                        Specify global default ACPI thermal zone polling rate
4065                        <deci-seconds>: poll all this frequency
4066                        0: no polling (default)
4068        threadirqs      [KNL]
4069                        Force threading of all interrupt handlers except those
4070                        marked explicitly IRQF_NO_THREAD.
4072        tmem            [KNL,XEN]
4073                        Enable the Transcendent memory driver if built-in.
4075        tmem.cleancache=0|1 [KNL, XEN]
4076                        Default is on (1). Disable the usage of the cleancache
4077                        API to send anonymous pages to the hypervisor.
4079        tmem.frontswap=0|1 [KNL, XEN]
4080                        Default is on (1). Disable the usage of the frontswap
4081                        API to send swap pages to the hypervisor. If disabled
4082                        the selfballooning and selfshrinking are force disabled.
4084        tmem.selfballooning=0|1 [KNL, XEN]
4085                        Default is on (1). Disable the driving of swap pages
4086                        to the hypervisor.
4088        tmem.selfshrinking=0|1 [KNL, XEN]
4089                        Default is on (1). Partial swapoff that immediately
4090                        transfers pages from Xen hypervisor back to the
4091                        kernel based on different criteria.
4093        topology=       [S390]
4094                        Format: {off | on}
4095                        Specify if the kernel should make use of the cpu
4096                        topology information if the hardware supports this.
4097                        The scheduler will make use of this information and
4098                        e.g. base its process migration decisions on it.
4099                        Default is on.
4101        topology_updates= [KNL, PPC, NUMA]
4102                        Format: {off}
4103                        Specify if the kernel should ignore (off)
4104                        topology updates sent by the hypervisor to this
4105                        LPAR.
4107        tp720=          [HW,PS2]
4109        tpm_suspend_pcr=[HW,TPM]
4110                        Format: integer pcr id
4111                        Specify that at suspend time, the tpm driver
4112                        should extend the specified pcr with zeros,
4113                        as a workaround for some chips which fail to
4114                        flush the last written pcr on TPM_SaveState.
4115                        This will guarantee that all the other pcrs
4116                        are saved.
4118        trace_buf_size=nn[KMG]
4119                        [FTRACE] will set tracing buffer size on each cpu.
4121        trace_event=[event-list]
4122                        [FTRACE] Set and start specified trace events in order
4123                        to facilitate early boot debugging. The event-list is a
4124                        comma separated list of trace events to enable. See
4125                        also Documentation/trace/events.txt
4127        trace_options=[option-list]
4128                        [FTRACE] Enable or disable tracer options at boot.
4129                        The option-list is a comma delimited list of options
4130                        that can be enabled or disabled just as if you were
4131                        to echo the option name into
4133                            /sys/kernel/debug/tracing/trace_options
4135                        For example, to enable stacktrace option (to dump the
4136                        stack trace of each event), add to the command line:
4138                              trace_options=stacktrace
4140                        See also Documentation/trace/ftrace.txt "trace options"
4141                        section.
4143        tp_printk[FTRACE]
4144                        Have the tracepoints sent to printk as well as the
4145                        tracing ring buffer. This is useful for early boot up
4146                        where the system hangs or reboots and does not give the
4147                        option for reading the tracing buffer or performing a
4148                        ftrace_dump_on_oops.
4150                        To turn off having tracepoints sent to printk,
4151                         echo 0 > /proc/sys/kernel/tracepoint_printk
4152                        Note, echoing 1 into this file without the
4153                        tracepoint_printk kernel cmdline option has no effect.
4155                        ** CAUTION **
4157                        Having tracepoints sent to printk() and activating high
4158                        frequency tracepoints such as irq or sched, can cause
4159                        the system to live lock.
4161        traceoff_on_warning
4162                        [FTRACE] enable this option to disable tracing when a
4163                        warning is hit. This turns off "tracing_on". Tracing can
4164                        be enabled again by echoing '1' into the "tracing_on"
4165                        file located in /sys/kernel/debug/tracing/
4167                        This option is useful, as it disables the trace before
4168                        the WARNING dump is called, which prevents the trace to
4169                        be filled with content caused by the warning output.
4171                        This option can also be set at run time via the sysctl
4172                        option:  kernel/traceoff_on_warning
4174        transparent_hugepage=
4175                        [KNL]
4176                        Format: [always|madvise|never]
4177                        Can be used to control the default behavior of the system
4178                        with respect to transparent hugepages.
4179                        See Documentation/vm/transhuge.txt for more details.
4181        tsc=            Disable clocksource stability checks for TSC.
4182                        Format: <string>
4183                        [x86] reliable: mark tsc clocksource as reliable, this
4184                        disables clocksource verification at runtime, as well
4185                        as the stability checks done at bootup. Used to enable
4186                        high-resolution timer mode on older hardware, and in
4187                        virtualized environment.
4188                        [x86] noirqtime: Do not use TSC to do irq accounting.
4189                        Used to run time disable IRQ_TIME_ACCOUNTING on any
4190                        platforms where RDTSC is slow and this accounting
4191                        can add overhead.
4193[2|3]=    [HW,JOY]
4194                        TurboGraFX parallel port interface
4195                        Format:
4196                        <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4197                        See also Documentation/input/joystick-parport.txt
4199        udbg-immortal   [PPC] When debugging early kernel crashes that
4200                        happen after console_init() and before a proper 
4201                        console driver takes over, this boot options might
4202                        help "seeing" what's going on.
4204        uhash_entries=  [KNL,NET]
4205                        Set number of hash buckets for UDP/UDP-Lite connections
4207        uhci-hcd.ignore_oc=
4208                        [USB] Ignore overcurrent events (default N).
4209                        Some badly-designed motherboards generate lots of
4210                        bogus events, for ports that aren't wired to
4211                        anything.  Set this parameter to avoid log spamming.
4212                        Note that genuine overcurrent events won't be
4213                        reported either.
4215        unknown_nmi_panic
4216                        [X86] Cause panic on unknown NMI.
4218        usbcore.authorized_default=
4219                        [USB] Default USB device authorization:
4220                        (default -1 = authorized except for wireless USB,
4221                        0 = not authorized, 1 = authorized)
4223        usbcore.autosuspend=
4224                        [USB] The autosuspend time delay (in seconds) used
4225                        for newly-detected USB devices (default 2).  This
4226                        is the time required before an idle device will be
4227                        autosuspended.  Devices for which the delay is set
4228                        to a negative value won't be autosuspended at all.
4230        usbcore.usbfs_snoop=
4231                        [USB] Set to log all usbfs traffic (default 0 = off).
4233        usbcore.usbfs_snoop_max=
4234                        [USB] Maximum number of bytes to snoop in each URB
4235                        (default = 65536).
4237        usbcore.blinkenlights=
4238                        [USB] Set to cycle leds on hubs (default 0 = off).
4240        usbcore.old_scheme_first=
4241                        [USB] Start with the old device initialization
4242                        scheme (default 0 = off).
4244        usbcore.usbfs_memory_mb=
4245                        [USB] Memory limit (in MB) for buffers allocated by
4246                        usbfs (default = 16, 0 = max = 2047).
4248        usbcore.use_both_schemes=
4249                        [USB] Try the other device initialization scheme
4250                        if the first one fails (default 1 = enabled).
4252        usbcore.initial_descriptor_timeout=
4253                        [USB] Specifies timeout for the initial 64-byte
4254                        USB_REQ_GET_DESCRIPTOR request in milliseconds
4255                        (default 5000 = 5.0 seconds).
4257        usbcore.nousb   [USB] Disable the USB subsystem
4259        usbhid.mousepoll=
4260                        [USBHID] The interval which mice are to be polled at.
4262        usb-storage.delay_use=
4263                        [UMS] The delay in seconds before a new device is
4264                        scanned for Logical Units (default 1).
4266        usb-storage.quirks=
4267                        [UMS] A list of quirks entries to supplement or
4268                        override the built-in unusual_devs list.  List
4269                        entries are separated by commas.  Each entry has
4270                        the form VID:PID:Flags where VID and PID are Vendor
4271                        and Product ID values (4-digit hex numbers) and
4272                        Flags is a set of characters, each corresponding
4273                        to a common usb-storage quirk flag as follows:
4274                                a = SANE_SENSE (collect more than 18 bytes
4275                                        of sense data);
4276                                b = BAD_SENSE (don't collect more than 18
4277                                        bytes of sense data);
4278                                c = FIX_CAPACITY (decrease the reported
4279                                        device capacity by one sector);
4280                                d = NO_READ_DISC_INFO (don't use
4281                                        READ_DISC_INFO command);
4282                                e = NO_READ_CAPACITY_16 (don't use
4283                                        READ_CAPACITY_16 command);
4284                                f = NO_REPORT_OPCODES (don't use report opcodes
4285                                        command, uas only);
4286                                g = MAX_SECTORS_240 (don't transfer more than
4287                                        240 sectors at a time, uas only);
4288                                h = CAPACITY_HEURISTICS (decrease the
4289                                        reported device capacity by one
4290                                        sector if the number is odd);
4291                                i = IGNORE_DEVICE (don't bind to this
4292                                        device);
4293                                j = NO_REPORT_LUNS (don't use report luns
4294                                        command, uas only);
4295                                l = NOT_LOCKABLE (don't try to lock and
4296                                        unlock ejectable media);
4297                                m = MAX_SECTORS_64 (don't transfer more
4298                                        than 64 sectors = 32 KB at a time);
4299                                n = INITIAL_READ10 (force a retry of the
4300                                        initial READ(10) command);
4301                                o = CAPACITY_OK (accept the capacity
4302                                        reported by the device);
4303                                p = WRITE_CACHE (the device cache is ON
4304                                        by default);
4305                                r = IGNORE_RESIDUE (the device reports
4306                                        bogus residue values);
4307                                s = SINGLE_LUN (the device has only one
4308                                        Logical Unit);
4309                                t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4310                                        commands, uas only);
4311                                u = IGNORE_UAS (don't bind to the uas driver);
4312                                w = NO_WP_DETECT (don't test whether the
4313                                        medium is write-protected).
4314                                y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4315                                        even if the device claims no cache)
4316                        Example: quirks=0419:aaf5:rl,0421:0433:rc
4318        user_debug=     [KNL,ARM]
4319                        Format: <int>
4320                        See arch/arm/Kconfig.debug help text.
4321                                 1 - undefined instruction events
4322                                 2 - system calls
4323                                 4 - invalid data aborts
4324                                 8 - SIGSEGV faults
4325                                16 - SIGBUS faults
4326                        Example: user_debug=31
4328        userpte=
4329                        [X86] Flags controlling user PTE allocations.
4331                                nohigh = do not allocate PTE pages in
4332                                        HIGHMEM regardless of setting
4333                                        of CONFIG_HIGHPTE.
4335        vdso=           [X86,SH]
4336                        On X86_32, this is an alias for vdso32=.  Otherwise:
4338                        vdso=1: enable VDSO (the default)
4339                        vdso=0: disable VDSO mapping
4341        vdso32=         [X86] Control the 32-bit vDSO
4342                        vdso32=1: enable 32-bit VDSO
4343                        vdso32=0 or vdso32=2: disable 32-bit VDSO
4345                        See the help text for CONFIG_COMPAT_VDSO for more
4346                        details.  If CONFIG_COMPAT_VDSO is set, the default is
4347                        vdso32=0; otherwise, the default is vdso32=1.
4349                        For compatibility with older kernels, vdso32=2 is an
4350                        alias for vdso32=0.
4352                        Try vdso32=0 if you encounter an error that says:
4353                        dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4355        vector=         [IA-64,SMP]
4356                        vector=percpu: enable percpu vector domain
4358        video=          [FB] Frame buffer configuration
4359                        See Documentation/fb/modedb.txt.
4361        video.brightness_switch_enabled= [0,1]
4362                        If set to 1, on receiving an ACPI notify event
4363                        generated by hotkey, video driver will adjust brightness
4364                        level and then send out the event to user space through
4365                        the allocated input device; If set to 0, video driver
4366                        will only send out the event without touching backlight
4367                        brightness level.
4368                        default: 1
4370        virtio_mmio.device=
4371                        [VMMIO] Memory mapped virtio (platform) device.
4373                                <size>@<baseaddr>:<irq>[:<id>]
4374                        where:
4375                                <size>     := size (can use standard suffixes
4376                                                like K, M and G)
4377                                <baseaddr> := physical base address
4378                                <irq>      := interrupt number (as passed to
4379                                                request_irq())
4380                                <id>       := (optional) platform device id
4381                        example:
4382                                virtio_mmio.device=1K@0x100b0000:48:7
4384                        Can be used multiple times for multiple devices.
4386        vga=            [BOOT,X86-32] Select a particular video mode
4387                        See Documentation/x86/boot.txt and
4388                        Documentation/svga.txt.
4389                        Use vga=ask for menu.
4390                        This is actually a boot loader parameter; the value is
4391                        passed to the kernel using a special protocol.
4393        vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4394                        size of <nn>. This can be used to increase the
4395                        minimum size (128MB on x86). It can also be used to
4396                        decrease the size and leave more room for directly
4397                        mapped kernel RAM.
4399        vmhalt=         [KNL,S390] Perform z/VM CP command after system halt.
4400                        Format: <command>
4402        vmpanic=        [KNL,S390] Perform z/VM CP command after kernel panic.
4403                        Format: <command>
4405        vmpoff=         [KNL,S390] Perform z/VM CP command after power off.
4406                        Format: <command>
4408        vsyscall=       [X86-64]
4409                        Controls the behavior of vsyscalls (i.e. calls to
4410                        fixed addresses of 0xffffffffff600x00 from legacy
4411                        code).  Most statically-linked binaries and older
4412                        versions of glibc use these calls.  Because these
4413                        functions are at fixed addresses, they make nice
4414                        targets for exploits that can control RIP.
4416                        emulate     [default] Vsyscalls turn into traps and are
4417                                    emulated reasonably safely.
4419                        native      Vsyscalls are native syscall instructions.
4420                                    This is a little bit faster than trapping
4421                                    and makes a few dynamic recompilers work
4422                                    better than they would in emulation mode.
4423                                    It also makes exploits much easier to write.
4425                        none        Vsyscalls don't work at all.  This makes
4426                                    them quite hard to use for exploits but
4427                                    might break your system.
4429        vt.color=       [VT] Default text color.
4430                        Format: 0xYX, X = foreground, Y = background.
4431                        Default: 0x07 = light gray on black.
4433        vt.cur_default= [VT] Default cursor shape.
4434                        Format: 0xCCBBAA, where AA, BB, and CC are the same as
4435                        the parameters of the <Esc>[?A;B;Cc escape sequence;
4436                        see VGA-softcursor.txt. Default: 2 = underline.
4438        vt.default_blu= [VT]
4439                        Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4440                        Change the default blue palette of the console.
4441                        This is a 16-member array composed of values
4442                        ranging from 0-255.
4444        vt.default_grn= [VT]
4445                        Format: <green0>,<green1>,<green2>,...,<green15>
4446                        Change the default green palette of the console.
4447                        This is a 16-member array composed of values
4448                        ranging from 0-255.
4450        vt.default_red= [VT]
4451                        Format: <red0>,<red1>,<red2>,...,<red15>
4452                        Change the default red palette of the console.
4453                        This is a 16-member array composed of values
4454                        ranging from 0-255.
4456        vt.default_utf8=
4457                        [VT]
4458                        Format=<0|1>
4459                        Set system-wide default UTF-8 mode for all tty's.
4460                        Default is 1, i.e. UTF-8 mode is enabled for all
4461                        newly opened terminals.
4463        vt.global_cursor_default=
4464                        [VT]
4465                        Format=<-1|0|1>
4466                        Set system-wide default for whether a cursor
4467                        is shown on new VTs. Default is -1,
4468                        i.e. cursors will be created by default unless
4469                        overridden by individual drivers. 0 will hide
4470                        cursors, 1 will display them.
4472        vt.italic=      [VT] Default color for italic text; 0-15.
4473                        Default: 2 = green.
4475        vt.underline=   [VT] Default color for underlined text; 0-15.
4476                        Default: 3 = cyan.
4478        watchdog timers [HW,WDT] For information on watchdog timers,
4479                        see Documentation/watchdog/watchdog-parameters.txt
4480                        or other driver-specific files in the
4481                        Documentation/watchdog/ directory.
4483        workqueue.watchdog_thresh=
4484                        If CONFIG_WQ_WATCHDOG is configured, workqueue can
4485                        warn stall conditions and dump internal state to
4486                        help debugging.  0 disables workqueue stall
4487                        detection; otherwise, it's the stall threshold
4488                        duration in seconds.  The default value is 30 and
4489                        it can be updated at runtime by writing to the
4490                        corresponding sysfs file.
4492        workqueue.disable_numa
4493                        By default, all work items queued to unbound
4494                        workqueues are affine to the NUMA nodes they're
4495                        issued on, which results in better behavior in
4496                        general.  If NUMA affinity needs to be disabled for
4497                        whatever reason, this option can be used.  Note
4498                        that this also can be controlled per-workqueue for
4499                        workqueues visible under /sys/bus/workqueue/.
4501        workqueue.power_efficient
4502                        Per-cpu workqueues are generally preferred because
4503                        they show better performance thanks to cache
4504                        locality; unfortunately, per-cpu workqueues tend to
4505                        be more power hungry than unbound workqueues.
4507                        Enabling this makes the per-cpu workqueues which
4508                        were observed to contribute significantly to power
4509                        consumption unbound, leading to measurably lower
4510                        power usage at the cost of small performance
4511                        overhead.
4513                        The default value of this parameter is determined by
4514                        the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4516        workqueue.debug_force_rr_cpu
4517                        Workqueue used to implicitly guarantee that work
4518                        items queued without explicit CPU specified are put
4519                        on the local CPU.  This guarantee is no longer true
4520                        and while local CPU is still preferred work items
4521                        may be put on foreign CPUs.  This debug option
4522                        forces round-robin CPU selection to flush out
4523                        usages which depend on the now broken guarantee.
4524                        When enabled, memory and cache locality will be
4525                        impacted.
4527        x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
4528                        default x2apic cluster mode on platforms
4529                        supporting x2apic.
4531        x86_intel_mid_timer= [X86-32,APBT]
4532                        Choose timer option for x86 Intel MID platform.
4533                        Two valid options are apbt timer only and lapic timer
4534                        plus one apbt timer for broadcast timer.
4535                        x86_intel_mid_timer=apbt_only | lapic_and_apbt
4537        xen_512gb_limit         [KNL,X86-64,XEN]
4538                        Restricts the kernel running paravirtualized under Xen
4539                        to use only up to 512 GB of RAM. The reason to do so is
4540                        crash analysis tools and Xen tools for doing domain
4541                        save/restore/migration must be enabled to handle larger
4542                        domains.
4544        xen_emul_unplug=                [HW,X86,XEN]
4545                        Unplug Xen emulated devices
4546                        Format: [unplug0,][unplug1]
4547                        ide-disks -- unplug primary master IDE devices
4548                        aux-ide-disks -- unplug non-primary-master IDE devices
4549                        nics -- unplug network devices
4550                        all -- unplug all emulated devices (NICs and IDE disks)
4551                        unnecessary -- unplugging emulated devices is
4552                                unnecessary even if the host did not respond to
4553                                the unplug protocol
4554                        never -- do not unplug even if version check succeeds
4556        xen_nopvspin    [X86,XEN]
4557                        Disables the ticketlock slowpath using Xen PV
4558                        optimizations.
4560        xen_nopv        [X86]
4561                        Disables the PV optimizations forcing the HVM guest to
4562                        run as generic HVM guest with no PV drivers.
4564        xirc2ps_cs=     [NET,PCMCIA]
4565                        Format:
4566                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4572        Add more DRM drivers.