linux/Documentation/kernel-parameters.txt
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   1                          Kernel Parameters
   2                          ~~~~~~~~~~~~~~~~~
   3
   4The following is a consolidated list of the kernel parameters as implemented
   5(mostly) by the __setup() macro and sorted into English Dictionary order
   6(defined as ignoring all punctuation and sorting digits before letters in a
   7case insensitive manner), and with descriptions where known.
   8
   9Module parameters for loadable modules are specified only as the
  10parameter name with optional '=' and value as appropriate, such as:
  11
  12        modprobe usbcore blinkenlights=1
  13
  14Module parameters for modules that are built into the kernel image
  15are specified on the kernel command line with the module name plus
  16'.' plus parameter name, with '=' and value if appropriate, such as:
  17
  18        usbcore.blinkenlights=1
  19
  20Hyphens (dashes) and underscores are equivalent in parameter names, so
  21        log_buf_len=1M print-fatal-signals=1
  22can also be entered as
  23        log-buf-len=1M print_fatal_signals=1
  24
  25
  26This document may not be entirely up to date and comprehensive. The command
  27"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
  28module. Loadable modules, after being loaded into the running kernel, also
  29reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
  30parameters may be changed at runtime by the command
  31"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
  32
  33The parameters listed below are only valid if certain kernel build options were
  34enabled and if respective hardware is present. The text in square brackets at
  35the beginning of each description states the restrictions within which a
  36parameter is applicable:
  37
  38        ACPI    ACPI support is enabled.
  39        AGP     AGP (Accelerated Graphics Port) is enabled.
  40        ALSA    ALSA sound support is enabled.
  41        APIC    APIC support is enabled.
  42        APM     Advanced Power Management support is enabled.
  43        ARM     ARM architecture is enabled.
  44        AVR32   AVR32 architecture is enabled.
  45        AX25    Appropriate AX.25 support is enabled.
  46        BLACKFIN Blackfin architecture is enabled.
  47        CLK     Common clock infrastructure is enabled.
  48        CMA     Contiguous Memory Area support is enabled.
  49        DRM     Direct Rendering Management support is enabled.
  50        DYNAMIC_DEBUG Build in debug messages and enable them at runtime
  51        EDD     BIOS Enhanced Disk Drive Services (EDD) is enabled
  52        EFI     EFI Partitioning (GPT) is enabled
  53        EIDE    EIDE/ATAPI support is enabled.
  54        EVM     Extended Verification Module
  55        FB      The frame buffer device is enabled.
  56        FTRACE  Function tracing enabled.
  57        GCOV    GCOV profiling is enabled.
  58        HW      Appropriate hardware is enabled.
  59        IA-64   IA-64 architecture is enabled.
  60        IMA     Integrity measurement architecture is enabled.
  61        IOSCHED More than one I/O scheduler is enabled.
  62        IP_PNP  IP DHCP, BOOTP, or RARP is enabled.
  63        IPV6    IPv6 support is enabled.
  64        ISAPNP  ISA PnP code is enabled.
  65        ISDN    Appropriate ISDN support is enabled.
  66        JOY     Appropriate joystick support is enabled.
  67        KGDB    Kernel debugger support is enabled.
  68        KVM     Kernel Virtual Machine support is enabled.
  69        LIBATA  Libata driver is enabled
  70        LP      Printer support is enabled.
  71        LOOP    Loopback device support is enabled.
  72        M68k    M68k architecture is enabled.
  73                        These options have more detailed description inside of
  74                        Documentation/m68k/kernel-options.txt.
  75        MDA     MDA console support is enabled.
  76        MIPS    MIPS architecture is enabled.
  77        MOUSE   Appropriate mouse support is enabled.
  78        MSI     Message Signaled Interrupts (PCI).
  79        MTD     MTD (Memory Technology Device) support is enabled.
  80        NET     Appropriate network support is enabled.
  81        NUMA    NUMA support is enabled.
  82        NFS     Appropriate NFS support is enabled.
  83        OSS     OSS sound support is enabled.
  84        PV_OPS  A paravirtualized kernel is enabled.
  85        PARIDE  The ParIDE (parallel port IDE) subsystem is enabled.
  86        PARISC  The PA-RISC architecture is enabled.
  87        PCI     PCI bus support is enabled.
  88        PCIE    PCI Express support is enabled.
  89        PCMCIA  The PCMCIA subsystem is enabled.
  90        PNP     Plug & Play support is enabled.
  91        PPC     PowerPC architecture is enabled.
  92        PPT     Parallel port support is enabled.
  93        PS2     Appropriate PS/2 support is enabled.
  94        RAM     RAM disk support is enabled.
  95        S390    S390 architecture is enabled.
  96        SCSI    Appropriate SCSI support is enabled.
  97                        A lot of drivers have their options described inside
  98                        the Documentation/scsi/ sub-directory.
  99        SECURITY Different security models are enabled.
 100        SELINUX SELinux support is enabled.
 101        APPARMOR AppArmor support is enabled.
 102        SERIAL  Serial support is enabled.
 103        SH      SuperH architecture is enabled.
 104        SMP     The kernel is an SMP kernel.
 105        SPARC   Sparc architecture is enabled.
 106        SWSUSP  Software suspend (hibernation) is enabled.
 107        SUSPEND System suspend states are enabled.
 108        TPM     TPM drivers are enabled.
 109        TS      Appropriate touchscreen support is enabled.
 110        UMS     USB Mass Storage support is enabled.
 111        USB     USB support is enabled.
 112        USBHID  USB Human Interface Device support is enabled.
 113        V4L     Video For Linux support is enabled.
 114        VMMIO   Driver for memory mapped virtio devices is enabled.
 115        VGA     The VGA console has been enabled.
 116        VT      Virtual terminal support is enabled.
 117        WDT     Watchdog support is enabled.
 118        XT      IBM PC/XT MFM hard disk support is enabled.
 119        X86-32  X86-32, aka i386 architecture is enabled.
 120        X86-64  X86-64 architecture is enabled.
 121                        More X86-64 boot options can be found in
 122                        Documentation/x86/x86_64/boot-options.txt .
 123        X86     Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
 124        XEN     Xen support is enabled
 125
 126In addition, the following text indicates that the option:
 127
 128        BUGS=   Relates to possible processor bugs on the said processor.
 129        KNL     Is a kernel start-up parameter.
 130        BOOT    Is a boot loader parameter.
 131
 132Parameters denoted with BOOT are actually interpreted by the boot
 133loader, and have no meaning to the kernel directly.
 134Do not modify the syntax of boot loader parameters without extreme
 135need or coordination with <Documentation/x86/boot.txt>.
 136
 137There are also arch-specific kernel-parameters not documented here.
 138See for example <Documentation/x86/x86_64/boot-options.txt>.
 139
 140Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
 141a trailing = on the name of any parameter states that that parameter will
 142be entered as an environment variable, whereas its absence indicates that
 143it will appear as a kernel argument readable via /proc/cmdline by programs
 144running once the system is up.
 145
 146The number of kernel parameters is not limited, but the length of the
 147complete command line (parameters including spaces etc.) is limited to
 148a fixed number of characters. This limit depends on the architecture
 149and is between 256 and 4096 characters. It is defined in the file
 150./include/asm/setup.h as COMMAND_LINE_SIZE.
 151
 152Finally, the [KMG] suffix is commonly described after a number of kernel
 153parameter values. These 'K', 'M', and 'G' letters represent the _binary_
 154multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
 155bytes respectively. Such letter suffixes can also be entirely omitted.
 156
 157
 158        acpi=           [HW,ACPI,X86]
 159                        Advanced Configuration and Power Interface
 160                        Format: { force | off | strict | noirq | rsdt }
 161                        force -- enable ACPI if default was off
 162                        off -- disable ACPI if default was on
 163                        noirq -- do not use ACPI for IRQ routing
 164                        strict -- Be less tolerant of platforms that are not
 165                                strictly ACPI specification compliant.
 166                        rsdt -- prefer RSDT over (default) XSDT
 167                        copy_dsdt -- copy DSDT to memory
 168
 169                        See also Documentation/power/runtime_pm.txt, pci=noacpi
 170
 171        acpi_rsdp=      [ACPI,EFI,KEXEC]
 172                        Pass the RSDP address to the kernel, mostly used
 173                        on machines running EFI runtime service to boot the
 174                        second kernel for kdump.
 175
 176        acpi_apic_instance=     [ACPI, IOAPIC]
 177                        Format: <int>
 178                        2: use 2nd APIC table, if available
 179                        1,0: use 1st APIC table
 180                        default: 0
 181
 182        acpi_backlight= [HW,ACPI]
 183                        acpi_backlight=vendor
 184                        acpi_backlight=video
 185                        If set to vendor, prefer vendor specific driver
 186                        (e.g. thinkpad_acpi, sony_acpi, etc.) instead
 187                        of the ACPI video.ko driver.
 188
 189        acpi.debug_layer=       [HW,ACPI,ACPI_DEBUG]
 190        acpi.debug_level=       [HW,ACPI,ACPI_DEBUG]
 191                        Format: <int>
 192                        CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
 193                        debug output.  Bits in debug_layer correspond to a
 194                        _COMPONENT in an ACPI source file, e.g.,
 195                            #define _COMPONENT ACPI_PCI_COMPONENT
 196                        Bits in debug_level correspond to a level in
 197                        ACPI_DEBUG_PRINT statements, e.g.,
 198                            ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
 199                        The debug_level mask defaults to "info".  See
 200                        Documentation/acpi/debug.txt for more information about
 201                        debug layers and levels.
 202
 203                        Enable processor driver info messages:
 204                            acpi.debug_layer=0x20000000
 205                        Enable PCI/PCI interrupt routing info messages:
 206                            acpi.debug_layer=0x400000
 207                        Enable AML "Debug" output, i.e., stores to the Debug
 208                        object while interpreting AML:
 209                            acpi.debug_layer=0xffffffff acpi.debug_level=0x2
 210                        Enable all messages related to ACPI hardware:
 211                            acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
 212
 213                        Some values produce so much output that the system is
 214                        unusable.  The "log_buf_len" parameter may be useful
 215                        if you need to capture more output.
 216
 217        acpi_irq_balance [HW,ACPI]
 218                        ACPI will balance active IRQs
 219                        default in APIC mode
 220
 221        acpi_irq_nobalance [HW,ACPI]
 222                        ACPI will not move active IRQs (default)
 223                        default in PIC mode
 224
 225        acpi_irq_isa=   [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
 226                        Format: <irq>,<irq>...
 227
 228        acpi_irq_pci=   [HW,ACPI] If irq_balance, clear listed IRQs for
 229                        use by PCI
 230                        Format: <irq>,<irq>...
 231
 232        acpi_no_auto_ssdt       [HW,ACPI] Disable automatic loading of SSDT
 233
 234        acpi_os_name=   [HW,ACPI] Tell ACPI BIOS the name of the OS
 235                        Format: To spoof as Windows 98: ="Microsoft Windows"
 236
 237        acpi_osi=       [HW,ACPI] Modify list of supported OS interface strings
 238                        acpi_osi="string1"      # add string1
 239                        acpi_osi="!string2"     # remove string2
 240                        acpi_osi=!*             # remove all strings
 241                        acpi_osi=!              # disable all built-in OS vendor
 242                                                  strings
 243                        acpi_osi=               # disable all strings
 244
 245                        'acpi_osi=!' can be used in combination with single or
 246                        multiple 'acpi_osi="string1"' to support specific OS
 247                        vendor string(s).  Note that such command can only
 248                        affect the default state of the OS vendor strings, thus
 249                        it cannot affect the default state of the feature group
 250                        strings and the current state of the OS vendor strings,
 251                        specifying it multiple times through kernel command line
 252                        is meaningless.  This command is useful when one do not
 253                        care about the state of the feature group strings which
 254                        should be controlled by the OSPM.
 255                        Examples:
 256                          1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
 257                             to 'acpi_osi="Windows 2000" acpi_osi=!', they all
 258                             can make '_OSI("Windows 2000")' TRUE.
 259
 260                        'acpi_osi=' cannot be used in combination with other
 261                        'acpi_osi=' command lines, the _OSI method will not
 262                        exist in the ACPI namespace.  NOTE that such command can
 263                        only affect the _OSI support state, thus specifying it
 264                        multiple times through kernel command line is also
 265                        meaningless.
 266                        Examples:
 267                          1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
 268                             FALSE.
 269
 270                        'acpi_osi=!*' can be used in combination with single or
 271                        multiple 'acpi_osi="string1"' to support specific
 272                        string(s).  Note that such command can affect the
 273                        current state of both the OS vendor strings and the
 274                        feature group strings, thus specifying it multiple times
 275                        through kernel command line is meaningful.  But it may
 276                        still not able to affect the final state of a string if
 277                        there are quirks related to this string.  This command
 278                        is useful when one want to control the state of the
 279                        feature group strings to debug BIOS issues related to
 280                        the OSPM features.
 281                        Examples:
 282                          1. 'acpi_osi="Module Device" acpi_osi=!*' can make
 283                             '_OSI("Module Device")' FALSE.
 284                          2. 'acpi_osi=!* acpi_osi="Module Device"' can make
 285                             '_OSI("Module Device")' TRUE.
 286                          3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
 287                             equivalent to
 288                             'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
 289                             and
 290                             'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
 291                             they all will make '_OSI("Windows 2000")' TRUE.
 292
 293        acpi_pm_good    [X86]
 294                        Override the pmtimer bug detection: force the kernel
 295                        to assume that this machine's pmtimer latches its value
 296                        and always returns good values.
 297
 298        acpi_sci=       [HW,ACPI] ACPI System Control Interrupt trigger mode
 299                        Format: { level | edge | high | low }
 300
 301        acpi_serialize  [HW,ACPI] force serialization of AML methods
 302
 303        acpi_skip_timer_override [HW,ACPI]
 304                        Recognize and ignore IRQ0/pin2 Interrupt Override.
 305                        For broken nForce2 BIOS resulting in XT-PIC timer.
 306
 307        acpi_sleep=     [HW,ACPI] Sleep options
 308                        Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
 309                                  old_ordering, nonvs, sci_force_enable }
 310                        See Documentation/power/video.txt for information on
 311                        s3_bios and s3_mode.
 312                        s3_beep is for debugging; it makes the PC's speaker beep
 313                        as soon as the kernel's real-mode entry point is called.
 314                        s4_nohwsig prevents ACPI hardware signature from being
 315                        used during resume from hibernation.
 316                        old_ordering causes the ACPI 1.0 ordering of the _PTS
 317                        control method, with respect to putting devices into
 318                        low power states, to be enforced (the ACPI 2.0 ordering
 319                        of _PTS is used by default).
 320                        nonvs prevents the kernel from saving/restoring the
 321                        ACPI NVS memory during suspend/hibernation and resume.
 322                        sci_force_enable causes the kernel to set SCI_EN directly
 323                        on resume from S1/S3 (which is against the ACPI spec,
 324                        but some broken systems don't work without it).
 325
 326        acpi_use_timer_override [HW,ACPI]
 327                        Use timer override. For some broken Nvidia NF5 boards
 328                        that require a timer override, but don't have HPET
 329
 330        acpi_enforce_resources= [ACPI]
 331                        { strict | lax | no }
 332                        Check for resource conflicts between native drivers
 333                        and ACPI OperationRegions (SystemIO and SystemMemory
 334                        only). IO ports and memory declared in ACPI might be
 335                        used by the ACPI subsystem in arbitrary AML code and
 336                        can interfere with legacy drivers.
 337                        strict (default): access to resources claimed by ACPI
 338                        is denied; legacy drivers trying to access reserved
 339                        resources will fail to bind to device using them.
 340                        lax: access to resources claimed by ACPI is allowed;
 341                        legacy drivers trying to access reserved resources
 342                        will bind successfully but a warning message is logged.
 343                        no: ACPI OperationRegions are not marked as reserved,
 344                        no further checks are performed.
 345
 346        add_efi_memmap  [EFI; X86] Include EFI memory map in
 347                        kernel's map of available physical RAM.
 348
 349        agp=            [AGP]
 350                        { off | try_unsupported }
 351                        off: disable AGP support
 352                        try_unsupported: try to drive unsupported chipsets
 353                                (may crash computer or cause data corruption)
 354
 355        ALSA            [HW,ALSA]
 356                        See Documentation/sound/alsa/alsa-parameters.txt
 357
 358        alignment=      [KNL,ARM]
 359                        Allow the default userspace alignment fault handler
 360                        behaviour to be specified.  Bit 0 enables warnings,
 361                        bit 1 enables fixups, and bit 2 sends a segfault.
 362
 363        align_va_addr=  [X86-64]
 364                        Align virtual addresses by clearing slice [14:12] when
 365                        allocating a VMA at process creation time. This option
 366                        gives you up to 3% performance improvement on AMD F15h
 367                        machines (where it is enabled by default) for a
 368                        CPU-intensive style benchmark, and it can vary highly in
 369                        a microbenchmark depending on workload and compiler.
 370
 371                        32: only for 32-bit processes
 372                        64: only for 64-bit processes
 373                        on: enable for both 32- and 64-bit processes
 374                        off: disable for both 32- and 64-bit processes
 375
 376        alloc_snapshot  [FTRACE]
 377                        Allocate the ftrace snapshot buffer on boot up when the
 378                        main buffer is allocated. This is handy if debugging
 379                        and you need to use tracing_snapshot() on boot up, and
 380                        do not want to use tracing_snapshot_alloc() as it needs
 381                        to be done where GFP_KERNEL allocations are allowed.
 382
 383        amd_iommu=      [HW,X86-64]
 384                        Pass parameters to the AMD IOMMU driver in the system.
 385                        Possible values are:
 386                        fullflush - enable flushing of IO/TLB entries when
 387                                    they are unmapped. Otherwise they are
 388                                    flushed before they will be reused, which
 389                                    is a lot of faster
 390                        off       - do not initialize any AMD IOMMU found in
 391                                    the system
 392                        force_isolation - Force device isolation for all
 393                                          devices. The IOMMU driver is not
 394                                          allowed anymore to lift isolation
 395                                          requirements as needed. This option
 396                                          does not override iommu=pt
 397
 398        amd_iommu_dump= [HW,X86-64]
 399                        Enable AMD IOMMU driver option to dump the ACPI table
 400                        for AMD IOMMU. With this option enabled, AMD IOMMU
 401                        driver will print ACPI tables for AMD IOMMU during
 402                        IOMMU initialization.
 403
 404        amijoy.map=     [HW,JOY] Amiga joystick support
 405                        Map of devices attached to JOY0DAT and JOY1DAT
 406                        Format: <a>,<b>
 407                        See also Documentation/input/joystick.txt
 408
 409        analog.map=     [HW,JOY] Analog joystick and gamepad support
 410                        Specifies type or capabilities of an analog joystick
 411                        connected to one of 16 gameports
 412                        Format: <type1>,<type2>,..<type16>
 413
 414        apc=            [HW,SPARC]
 415                        Power management functions (SPARCstation-4/5 + deriv.)
 416                        Format: noidle
 417                        Disable APC CPU standby support. SPARCstation-Fox does
 418                        not play well with APC CPU idle - disable it if you have
 419                        APC and your system crashes randomly.
 420
 421        apic=           [APIC,X86-32] Advanced Programmable Interrupt Controller
 422                        Change the output verbosity whilst booting
 423                        Format: { quiet (default) | verbose | debug }
 424                        Change the amount of debugging information output
 425                        when initialising the APIC and IO-APIC components.
 426
 427        autoconf=       [IPV6]
 428                        See Documentation/networking/ipv6.txt.
 429
 430        show_lapic=     [APIC,X86] Advanced Programmable Interrupt Controller
 431                        Limit apic dumping. The parameter defines the maximal
 432                        number of local apics being dumped. Also it is possible
 433                        to set it to "all" by meaning -- no limit here.
 434                        Format: { 1 (default) | 2 | ... | all }.
 435                        The parameter valid if only apic=debug or
 436                        apic=verbose is specified.
 437                        Example: apic=debug show_lapic=all
 438
 439        apm=            [APM] Advanced Power Management
 440                        See header of arch/x86/kernel/apm_32.c.
 441
 442        arcrimi=        [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
 443                        Format: <io>,<irq>,<nodeID>
 444
 445        ataflop=        [HW,M68k]
 446
 447        atarimouse=     [HW,MOUSE] Atari Mouse
 448
 449        atkbd.extra=    [HW] Enable extra LEDs and keys on IBM RapidAccess,
 450                        EzKey and similar keyboards
 451
 452        atkbd.reset=    [HW] Reset keyboard during initialization
 453
 454        atkbd.set=      [HW] Select keyboard code set
 455                        Format: <int> (2 = AT (default), 3 = PS/2)
 456
 457        atkbd.scroll=   [HW] Enable scroll wheel on MS Office and similar
 458                        keyboards
 459
 460        atkbd.softraw=  [HW] Choose between synthetic and real raw mode
 461                        Format: <bool> (0 = real, 1 = synthetic (default))
 462
 463        atkbd.softrepeat= [HW]
 464                        Use software keyboard repeat
 465
 466        baycom_epp=     [HW,AX25]
 467                        Format: <io>,<mode>
 468
 469        baycom_par=     [HW,AX25] BayCom Parallel Port AX.25 Modem
 470                        Format: <io>,<mode>
 471                        See header of drivers/net/hamradio/baycom_par.c.
 472
 473        baycom_ser_fdx= [HW,AX25]
 474                        BayCom Serial Port AX.25 Modem (Full Duplex Mode)
 475                        Format: <io>,<irq>,<mode>[,<baud>]
 476                        See header of drivers/net/hamradio/baycom_ser_fdx.c.
 477
 478        baycom_ser_hdx= [HW,AX25]
 479                        BayCom Serial Port AX.25 Modem (Half Duplex Mode)
 480                        Format: <io>,<irq>,<mode>
 481                        See header of drivers/net/hamradio/baycom_ser_hdx.c.
 482
 483        blkdevparts=    Manual partition parsing of block device(s) for
 484                        embedded devices based on command line input.
 485                        See Documentation/block/cmdline-partition.txt
 486
 487        boot_delay=     Milliseconds to delay each printk during boot.
 488                        Values larger than 10 seconds (10000) are changed to
 489                        no delay (0).
 490                        Format: integer
 491
 492        bootmem_debug   [KNL] Enable bootmem allocator debug messages.
 493
 494        bttv.card=      [HW,V4L] bttv (bt848 + bt878 based grabber cards)
 495        bttv.radio=     Most important insmod options are available as
 496                        kernel args too.
 497        bttv.pll=       See Documentation/video4linux/bttv/Insmod-options
 498        bttv.tuner=
 499
 500        bulk_remove=off [PPC]  This parameter disables the use of the pSeries
 501                        firmware feature for flushing multiple hpte entries
 502                        at a time.
 503
 504        c101=           [NET] Moxa C101 synchronous serial card
 505
 506        cachesize=      [BUGS=X86-32] Override level 2 CPU cache size detection.
 507                        Sometimes CPU hardware bugs make them report the cache
 508                        size incorrectly. The kernel will attempt work arounds
 509                        to fix known problems, but for some CPUs it is not
 510                        possible to determine what the correct size should be.
 511                        This option provides an override for these situations.
 512
 513        ccw_timeout_log [S390]
 514                        See Documentation/s390/CommonIO for details.
 515
 516        cgroup_disable= [KNL] Disable a particular controller
 517                        Format: {name of the controller(s) to disable}
 518                                {Currently supported controllers - "memory"}
 519
 520        checkreqprot    [SELINUX] Set initial checkreqprot flag value.
 521                        Format: { "0" | "1" }
 522                        See security/selinux/Kconfig help text.
 523                        0 -- check protection applied by kernel (includes
 524                                any implied execute protection).
 525                        1 -- check protection requested by application.
 526                        Default value is set via a kernel config option.
 527                        Value can be changed at runtime via
 528                                /selinux/checkreqprot.
 529
 530        cio_ignore=     [S390]
 531                        See Documentation/s390/CommonIO for details.
 532        clk_ignore_unused
 533                        [CLK]
 534                        Keep all clocks already enabled by bootloader on,
 535                        even if no driver has claimed them. This is useful
 536                        for debug and development, but should not be
 537                        needed on a platform with proper driver support.
 538                        For more information, see Documentation/clk.txt.
 539
 540        clock=          [BUGS=X86-32, HW] gettimeofday clocksource override.
 541                        [Deprecated]
 542                        Forces specified clocksource (if available) to be used
 543                        when calculating gettimeofday(). If specified
 544                        clocksource is not available, it defaults to PIT.
 545                        Format: { pit | tsc | cyclone | pmtmr }
 546
 547        clocksource=    Override the default clocksource
 548                        Format: <string>
 549                        Override the default clocksource and use the clocksource
 550                        with the name specified.
 551                        Some clocksource names to choose from, depending on
 552                        the platform:
 553                        [all] jiffies (this is the base, fallback clocksource)
 554                        [ACPI] acpi_pm
 555                        [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
 556                                pxa_timer,timer3,32k_counter,timer0_1
 557                        [AVR32] avr32
 558                        [X86-32] pit,hpet,tsc;
 559                                scx200_hrt on Geode; cyclone on IBM x440
 560                        [MIPS] MIPS
 561                        [PARISC] cr16
 562                        [S390] tod
 563                        [SH] SuperH
 564                        [SPARC64] tick
 565                        [X86-64] hpet,tsc
 566
 567        clearcpuid=BITNUM [X86]
 568                        Disable CPUID feature X for the kernel. See
 569                        arch/x86/include/asm/cpufeature.h for the valid bit
 570                        numbers. Note the Linux specific bits are not necessarily
 571                        stable over kernel options, but the vendor specific
 572                        ones should be.
 573                        Also note that user programs calling CPUID directly
 574                        or using the feature without checking anything
 575                        will still see it. This just prevents it from
 576                        being used by the kernel or shown in /proc/cpuinfo.
 577                        Also note the kernel might malfunction if you disable
 578                        some critical bits.
 579
 580        cma=nn[MG]      [ARM,KNL]
 581                        Sets the size of kernel global memory area for contiguous
 582                        memory allocations. For more information, see
 583                        include/linux/dma-contiguous.h
 584
 585        cmo_free_hint=  [PPC] Format: { yes | no }
 586                        Specify whether pages are marked as being inactive
 587                        when they are freed.  This is used in CMO environments
 588                        to determine OS memory pressure for page stealing by
 589                        a hypervisor.
 590                        Default: yes
 591
 592        coherent_pool=nn[KMG]   [ARM,KNL]
 593                        Sets the size of memory pool for coherent, atomic dma
 594                        allocations, by default set to 256K.
 595
 596        code_bytes      [X86] How many bytes of object code to print
 597                        in an oops report.
 598                        Range: 0 - 8192
 599                        Default: 64
 600
 601        com20020=       [HW,NET] ARCnet - COM20020 chipset
 602                        Format:
 603                        <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
 604
 605        com90io=        [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
 606                        Format: <io>[,<irq>]
 607
 608        com90xx=        [HW,NET]
 609                        ARCnet - COM90xx chipset (memory-mapped buffers)
 610                        Format: <io>[,<irq>[,<memstart>]]
 611
 612        condev=         [HW,S390] console device
 613        conmode=
 614
 615        console=        [KNL] Output console device and options.
 616
 617                tty<n>  Use the virtual console device <n>.
 618
 619                ttyS<n>[,options]
 620                ttyUSB0[,options]
 621                        Use the specified serial port.  The options are of
 622                        the form "bbbbpnf", where "bbbb" is the baud rate,
 623                        "p" is parity ("n", "o", or "e"), "n" is number of
 624                        bits, and "f" is flow control ("r" for RTS or
 625                        omit it).  Default is "9600n8".
 626
 627                        See Documentation/serial-console.txt for more
 628                        information.  See
 629                        Documentation/networking/netconsole.txt for an
 630                        alternative.
 631
 632                uart[8250],io,<addr>[,options]
 633                uart[8250],mmio,<addr>[,options]
 634                        Start an early, polled-mode console on the 8250/16550
 635                        UART at the specified I/O port or MMIO address,
 636                        switching to the matching ttyS device later.  The
 637                        options are the same as for ttyS, above.
 638                hvc<n>  Use the hypervisor console device <n>. This is for
 639                        both Xen and PowerPC hypervisors.
 640
 641                If the device connected to the port is not a TTY but a braille
 642                device, prepend "brl," before the device type, for instance
 643                        console=brl,ttyS0
 644                For now, only VisioBraille is supported.
 645
 646        consoleblank=   [KNL] The console blank (screen saver) timeout in
 647                        seconds. Defaults to 10*60 = 10mins. A value of 0
 648                        disables the blank timer.
 649
 650        coredump_filter=
 651                        [KNL] Change the default value for
 652                        /proc/<pid>/coredump_filter.
 653                        See also Documentation/filesystems/proc.txt.
 654
 655        cpuidle.off=1   [CPU_IDLE]
 656                        disable the cpuidle sub-system
 657
 658        cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
 659                        Format:
 660                        <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
 661
 662        crashkernel=size[KMG][@offset[KMG]]
 663                        [KNL] Using kexec, Linux can switch to a 'crash kernel'
 664                        upon panic. This parameter reserves the physical
 665                        memory region [offset, offset + size] for that kernel
 666                        image. If '@offset' is omitted, then a suitable offset
 667                        is selected automatically. Check
 668                        Documentation/kdump/kdump.txt for further details.
 669
 670        crashkernel=range1:size1[,range2:size2,...][@offset]
 671                        [KNL] Same as above, but depends on the memory
 672                        in the running system. The syntax of range is
 673                        start-[end] where start and end are both
 674                        a memory unit (amount[KMG]). See also
 675                        Documentation/kdump/kdump.txt for an example.
 676
 677        crashkernel=size[KMG],high
 678                        [KNL, x86_64] range could be above 4G. Allow kernel
 679                        to allocate physical memory region from top, so could
 680                        be above 4G if system have more than 4G ram installed.
 681                        Otherwise memory region will be allocated below 4G, if
 682                        available.
 683                        It will be ignored if crashkernel=X is specified.
 684        crashkernel=size[KMG],low
 685                        [KNL, x86_64] range under 4G. When crashkernel=X,high
 686                        is passed, kernel could allocate physical memory region
 687                        above 4G, that cause second kernel crash on system
 688                        that require some amount of low memory, e.g. swiotlb
 689                        requires at least 64M+32K low memory.  Kernel would
 690                        try to allocate 72M below 4G automatically.
 691                        This one let user to specify own low range under 4G
 692                        for second kernel instead.
 693                        0: to disable low allocation.
 694                        It will be ignored when crashkernel=X,high is not used
 695                        or memory reserved is below 4G.
 696
 697        cs89x0_dma=     [HW,NET]
 698                        Format: <dma>
 699
 700        cs89x0_media=   [HW,NET]
 701                        Format: { rj45 | aui | bnc }
 702
 703        dasd=           [HW,NET]
 704                        See header of drivers/s390/block/dasd_devmap.c.
 705
 706        db9.dev[2|3]=   [HW,JOY] Multisystem joystick support via parallel port
 707                        (one device per port)
 708                        Format: <port#>,<type>
 709                        See also Documentation/input/joystick-parport.txt
 710
 711        ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
 712                        time. See Documentation/dynamic-debug-howto.txt for
 713                        details.  Deprecated, see dyndbg.
 714
 715        debug           [KNL] Enable kernel debugging (events log level).
 716
 717        debug_locks_verbose=
 718                        [KNL] verbose self-tests
 719                        Format=<0|1>
 720                        Print debugging info while doing the locking API
 721                        self-tests.
 722                        We default to 0 (no extra messages), setting it to
 723                        1 will print _a lot_ more information - normally
 724                        only useful to kernel developers.
 725
 726        debug_objects   [KNL] Enable object debugging
 727
 728        no_debug_objects
 729                        [KNL] Disable object debugging
 730
 731        debug_guardpage_minorder=
 732                        [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
 733                        parameter allows control of the order of pages that will
 734                        be intentionally kept free (and hence protected) by the
 735                        buddy allocator. Bigger value increase the probability
 736                        of catching random memory corruption, but reduce the
 737                        amount of memory for normal system use. The maximum
 738                        possible value is MAX_ORDER/2.  Setting this parameter
 739                        to 1 or 2 should be enough to identify most random
 740                        memory corruption problems caused by bugs in kernel or
 741                        driver code when a CPU writes to (or reads from) a
 742                        random memory location. Note that there exists a class
 743                        of memory corruptions problems caused by buggy H/W or
 744                        F/W or by drivers badly programing DMA (basically when
 745                        memory is written at bus level and the CPU MMU is
 746                        bypassed) which are not detectable by
 747                        CONFIG_DEBUG_PAGEALLOC, hence this option will not help
 748                        tracking down these problems.
 749
 750        debugpat        [X86] Enable PAT debugging
 751
 752        decnet.addr=    [HW,NET]
 753                        Format: <area>[,<node>]
 754                        See also Documentation/networking/decnet.txt.
 755
 756        default_hugepagesz=
 757                        [same as hugepagesz=] The size of the default
 758                        HugeTLB page size. This is the size represented by
 759                        the legacy /proc/ hugepages APIs, used for SHM, and
 760                        default size when mounting hugetlbfs filesystems.
 761                        Defaults to the default architecture's huge page size
 762                        if not specified.
 763
 764        dhash_entries=  [KNL]
 765                        Set number of hash buckets for dentry cache.
 766
 767        digi=           [HW,SERIAL]
 768                        IO parameters + enable/disable command.
 769
 770        digiepca=       [HW,SERIAL]
 771                        See drivers/char/README.epca and
 772                        Documentation/serial/digiepca.txt.
 773
 774        disable=        [IPV6]
 775                        See Documentation/networking/ipv6.txt.
 776
 777        disable_ddw     [PPC/PSERIES]
 778                        Disable Dynamic DMA Window support. Use this if
 779                        to workaround buggy firmware.
 780
 781        disable_ipv6=   [IPV6]
 782                        See Documentation/networking/ipv6.txt.
 783
 784        disable_mtrr_cleanup [X86]
 785                        The kernel tries to adjust MTRR layout from continuous
 786                        to discrete, to make X server driver able to add WB
 787                        entry later. This parameter disables that.
 788
 789        disable_mtrr_trim [X86, Intel and AMD only]
 790                        By default the kernel will trim any uncacheable
 791                        memory out of your available memory pool based on
 792                        MTRR settings.  This parameter disables that behavior,
 793                        possibly causing your machine to run very slowly.
 794
 795        disable_timer_pin_1 [X86]
 796                        Disable PIN 1 of APIC timer
 797                        Can be useful to work around chipset bugs.
 798
 799        dma_debug=off   If the kernel is compiled with DMA_API_DEBUG support,
 800                        this option disables the debugging code at boot.
 801
 802        dma_debug_entries=<number>
 803                        This option allows to tune the number of preallocated
 804                        entries for DMA-API debugging code. One entry is
 805                        required per DMA-API allocation. Use this if the
 806                        DMA-API debugging code disables itself because the
 807                        architectural default is too low.
 808
 809        dma_debug_driver=<driver_name>
 810                        With this option the DMA-API debugging driver
 811                        filter feature can be enabled at boot time. Just
 812                        pass the driver to filter for as the parameter.
 813                        The filter can be disabled or changed to another
 814                        driver later using sysfs.
 815
 816        drm_kms_helper.edid_firmware=[<connector>:]<file>
 817                        Broken monitors, graphic adapters and KVMs may
 818                        send no or incorrect EDID data sets. This parameter
 819                        allows to specify an EDID data set in the
 820                        /lib/firmware directory that is used instead.
 821                        Generic built-in EDID data sets are used, if one of
 822                        edid/1024x768.bin, edid/1280x1024.bin,
 823                        edid/1680x1050.bin, or edid/1920x1080.bin is given
 824                        and no file with the same name exists. Details and
 825                        instructions how to build your own EDID data are
 826                        available in Documentation/EDID/HOWTO.txt. An EDID
 827                        data set will only be used for a particular connector,
 828                        if its name and a colon are prepended to the EDID
 829                        name.
 830
 831        dscc4.setup=    [NET]
 832
 833        dyndbg[="val"]          [KNL,DYNAMIC_DEBUG]
 834        module.dyndbg[="val"]
 835                        Enable debug messages at boot time.  See
 836                        Documentation/dynamic-debug-howto.txt for details.
 837
 838        earlycon=       [KNL] Output early console device and options.
 839                uart[8250],io,<addr>[,options]
 840                uart[8250],mmio,<addr>[,options]
 841                uart[8250],mmio32,<addr>[,options]
 842                        Start an early, polled-mode console on the 8250/16550
 843                        UART at the specified I/O port or MMIO address.
 844                        MMIO inter-register address stride is either 8-bit
 845                        (mmio) or 32-bit (mmio32).
 846                        The options are the same as for ttyS, above.
 847
 848        earlyprintk=    [X86,SH,BLACKFIN,ARM]
 849                        earlyprintk=vga
 850                        earlyprintk=xen
 851                        earlyprintk=serial[,ttySn[,baudrate]]
 852                        earlyprintk=serial[,0x...[,baudrate]]
 853                        earlyprintk=ttySn[,baudrate]
 854                        earlyprintk=dbgp[debugController#]
 855
 856                        earlyprintk is useful when the kernel crashes before
 857                        the normal console is initialized. It is not enabled by
 858                        default because it has some cosmetic problems.
 859
 860                        Append ",keep" to not disable it when the real console
 861                        takes over.
 862
 863                        Only vga or serial or usb debug port at a time.
 864
 865                        Currently only ttyS0 and ttyS1 may be specified by
 866                        name.  Other I/O ports may be explicitly specified
 867                        on some architectures (x86 and arm at least) by
 868                        replacing ttySn with an I/O port address, like this:
 869                                earlyprintk=serial,0x1008,115200
 870                        You can find the port for a given device in
 871                        /proc/tty/driver/serial:
 872                                2: uart:ST16650V2 port:00001008 irq:18 ...
 873
 874                        Interaction with the standard serial driver is not
 875                        very good.
 876
 877                        The VGA output is eventually overwritten by the real
 878                        console.
 879
 880                        The xen output can only be used by Xen PV guests.
 881
 882        ekgdboc=        [X86,KGDB] Allow early kernel console debugging
 883                        ekgdboc=kbd
 884
 885                        This is designed to be used in conjunction with
 886                        the boot argument: earlyprintk=vga
 887
 888        edd=            [EDD]
 889                        Format: {"off" | "on" | "skip[mbr]"}
 890
 891        efi_no_storage_paranoia [EFI; X86]
 892                        Using this parameter you can use more than 50% of
 893                        your efi variable storage. Use this parameter only if
 894                        you are really sure that your UEFI does sane gc and
 895                        fulfills the spec otherwise your board may brick.
 896
 897        eisa_irq_edge=  [PARISC,HW]
 898                        See header of drivers/parisc/eisa.c.
 899
 900        elanfreq=       [X86-32]
 901                        See comment before function elanfreq_setup() in
 902                        arch/x86/kernel/cpu/cpufreq/elanfreq.c.
 903
 904        elevator=       [IOSCHED]
 905                        Format: {"cfq" | "deadline" | "noop"}
 906                        See Documentation/block/cfq-iosched.txt and
 907                        Documentation/block/deadline-iosched.txt for details.
 908
 909        elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
 910                        Specifies physical address of start of kernel core
 911                        image elf header and optionally the size. Generally
 912                        kexec loader will pass this option to capture kernel.
 913                        See Documentation/kdump/kdump.txt for details.
 914
 915        enable_mtrr_cleanup [X86]
 916                        The kernel tries to adjust MTRR layout from continuous
 917                        to discrete, to make X server driver able to add WB
 918                        entry later. This parameter enables that.
 919
 920        enable_timer_pin_1 [X86]
 921                        Enable PIN 1 of APIC timer
 922                        Can be useful to work around chipset bugs
 923                        (in particular on some ATI chipsets).
 924                        The kernel tries to set a reasonable default.
 925
 926        enforcing       [SELINUX] Set initial enforcing status.
 927                        Format: {"0" | "1"}
 928                        See security/selinux/Kconfig help text.
 929                        0 -- permissive (log only, no denials).
 930                        1 -- enforcing (deny and log).
 931                        Default value is 0.
 932                        Value can be changed at runtime via /selinux/enforce.
 933
 934        erst_disable    [ACPI]
 935                        Disable Error Record Serialization Table (ERST)
 936                        support.
 937
 938        ether=          [HW,NET] Ethernet cards parameters
 939                        This option is obsoleted by the "netdev=" option, which
 940                        has equivalent usage. See its documentation for details.
 941
 942        evm=            [EVM]
 943                        Format: { "fix" }
 944                        Permit 'security.evm' to be updated regardless of
 945                        current integrity status.
 946
 947        failslab=
 948        fail_page_alloc=
 949        fail_make_request=[KNL]
 950                        General fault injection mechanism.
 951                        Format: <interval>,<probability>,<space>,<times>
 952                        See also Documentation/fault-injection/.
 953
 954        floppy=         [HW]
 955                        See Documentation/blockdev/floppy.txt.
 956
 957        force_pal_cache_flush
 958                        [IA-64] Avoid check_sal_cache_flush which may hang on
 959                        buggy SAL_CACHE_FLUSH implementations. Using this
 960                        parameter will force ia64_sal_cache_flush to call
 961                        ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
 962
 963        ftrace=[tracer]
 964                        [FTRACE] will set and start the specified tracer
 965                        as early as possible in order to facilitate early
 966                        boot debugging.
 967
 968        ftrace_dump_on_oops[=orig_cpu]
 969                        [FTRACE] will dump the trace buffers on oops.
 970                        If no parameter is passed, ftrace will dump
 971                        buffers of all CPUs, but if you pass orig_cpu, it will
 972                        dump only the buffer of the CPU that triggered the
 973                        oops.
 974
 975        ftrace_filter=[function-list]
 976                        [FTRACE] Limit the functions traced by the function
 977                        tracer at boot up. function-list is a comma separated
 978                        list of functions. This list can be changed at run
 979                        time by the set_ftrace_filter file in the debugfs
 980                        tracing directory.
 981
 982        ftrace_notrace=[function-list]
 983                        [FTRACE] Do not trace the functions specified in
 984                        function-list. This list can be changed at run time
 985                        by the set_ftrace_notrace file in the debugfs
 986                        tracing directory.
 987
 988        ftrace_graph_filter=[function-list]
 989                        [FTRACE] Limit the top level callers functions traced
 990                        by the function graph tracer at boot up.
 991                        function-list is a comma separated list of functions
 992                        that can be changed at run time by the
 993                        set_graph_function file in the debugfs tracing directory.
 994
 995        gamecon.map[2|3]=
 996                        [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
 997                        support via parallel port (up to 5 devices per port)
 998                        Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
 999                        See also Documentation/input/joystick-parport.txt
1000
1001        gamma=          [HW,DRM]
1002
1003        gart_fix_e820=  [X86_64] disable the fix e820 for K8 GART
1004                        Format: off | on
1005                        default: on
1006
1007        gcov_persist=   [GCOV] When non-zero (default), profiling data for
1008                        kernel modules is saved and remains accessible via
1009                        debugfs, even when the module is unloaded/reloaded.
1010                        When zero, profiling data is discarded and associated
1011                        debugfs files are removed at module unload time.
1012
1013        gpt             [EFI] Forces disk with valid GPT signature but
1014                        invalid Protective MBR to be treated as GPT.
1015
1016        grcan.enable0=  [HW] Configuration of physical interface 0. Determines
1017                        the "Enable 0" bit of the configuration register.
1018                        Format: 0 | 1
1019                        Default: 0
1020        grcan.enable1=  [HW] Configuration of physical interface 1. Determines
1021                        the "Enable 0" bit of the configuration register.
1022                        Format: 0 | 1
1023                        Default: 0
1024        grcan.select=   [HW] Select which physical interface to use.
1025                        Format: 0 | 1
1026                        Default: 0
1027        grcan.txsize=   [HW] Sets the size of the tx buffer.
1028                        Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1029                        Default: 1024
1030        grcan.rxsize=   [HW] Sets the size of the rx buffer.
1031                        Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1032                        Default: 1024
1033
1034        hashdist=       [KNL,NUMA] Large hashes allocated during boot
1035                        are distributed across NUMA nodes.  Defaults on
1036                        for 64-bit NUMA, off otherwise.
1037                        Format: 0 | 1 (for off | on)
1038
1039        hcl=            [IA-64] SGI's Hardware Graph compatibility layer
1040
1041        hd=             [EIDE] (E)IDE hard drive subsystem geometry
1042                        Format: <cyl>,<head>,<sect>
1043
1044        hest_disable    [ACPI]
1045                        Disable Hardware Error Source Table (HEST) support;
1046                        corresponding firmware-first mode error processing
1047                        logic will be disabled.
1048
1049        highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1050                        size of <nn>. This works even on boxes that have no
1051                        highmem otherwise. This also works to reduce highmem
1052                        size on bigger boxes.
1053
1054        highres=        [KNL] Enable/disable high resolution timer mode.
1055                        Valid parameters: "on", "off"
1056                        Default: "on"
1057
1058        hisax=          [HW,ISDN]
1059                        See Documentation/isdn/README.HiSax.
1060
1061        hlt             [BUGS=ARM,SH]
1062
1063        hpet=           [X86-32,HPET] option to control HPET usage
1064                        Format: { enable (default) | disable | force |
1065                                verbose }
1066                        disable: disable HPET and use PIT instead
1067                        force: allow force enabled of undocumented chips (ICH4,
1068                                VIA, nVidia)
1069                        verbose: show contents of HPET registers during setup
1070
1071        hugepages=      [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1072        hugepagesz=     [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1073                        On x86-64 and powerpc, this option can be specified
1074                        multiple times interleaved with hugepages= to reserve
1075                        huge pages of different sizes. Valid pages sizes on
1076                        x86-64 are 2M (when the CPU supports "pse") and 1G
1077                        (when the CPU supports the "pdpe1gb" cpuinfo flag)
1078                        Note that 1GB pages can only be allocated at boot time
1079                        using hugepages= and not freed afterwards.
1080
1081        hvc_iucv=       [S390] Number of z/VM IUCV hypervisor console (HVC)
1082                               terminal devices. Valid values: 0..8
1083        hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1084                               If specified, z/VM IUCV HVC accepts connections
1085                               from listed z/VM user IDs only.
1086
1087        hwthread_map=   [METAG] Comma-separated list of Linux cpu id to
1088                                hardware thread id mappings.
1089                                Format: <cpu>:<hwthread>
1090
1091        keep_bootcon    [KNL]
1092                        Do not unregister boot console at start. This is only
1093                        useful for debugging when something happens in the window
1094                        between unregistering the boot console and initializing
1095                        the real console.
1096
1097        i2c_bus=        [HW] Override the default board specific I2C bus speed
1098                             or register an additional I2C bus that is not
1099                             registered from board initialization code.
1100                             Format:
1101                             <bus_id>,<clkrate>
1102
1103        i8042.debug     [HW] Toggle i8042 debug mode
1104        i8042.direct    [HW] Put keyboard port into non-translated mode
1105        i8042.dumbkbd   [HW] Pretend that controller can only read data from
1106                             keyboard and cannot control its state
1107                             (Don't attempt to blink the leds)
1108        i8042.noaux     [HW] Don't check for auxiliary (== mouse) port
1109        i8042.nokbd     [HW] Don't check/create keyboard port
1110        i8042.noloop    [HW] Disable the AUX Loopback command while probing
1111                             for the AUX port
1112        i8042.nomux     [HW] Don't check presence of an active multiplexing
1113                             controller
1114        i8042.nopnp     [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1115                             controllers
1116        i8042.notimeout [HW] Ignore timeout condition signalled by controller
1117        i8042.reset     [HW] Reset the controller during init and cleanup
1118        i8042.unlock    [HW] Unlock (ignore) the keylock
1119
1120        i810=           [HW,DRM]
1121
1122        i8k.ignore_dmi  [HW] Continue probing hardware even if DMI data
1123                        indicates that the driver is running on unsupported
1124                        hardware.
1125        i8k.force       [HW] Activate i8k driver even if SMM BIOS signature
1126                        does not match list of supported models.
1127        i8k.power_status
1128                        [HW] Report power status in /proc/i8k
1129                        (disabled by default)
1130        i8k.restricted  [HW] Allow controlling fans only if SYS_ADMIN
1131                        capability is set.
1132
1133        i915.invert_brightness=
1134                        [DRM] Invert the sense of the variable that is used to
1135                        set the brightness of the panel backlight. Normally a
1136                        brightness value of 0 indicates backlight switched off,
1137                        and the maximum of the brightness value sets the backlight
1138                        to maximum brightness. If this parameter is set to 0
1139                        (default) and the machine requires it, or this parameter
1140                        is set to 1, a brightness value of 0 sets the backlight
1141                        to maximum brightness, and the maximum of the brightness
1142                        value switches the backlight off.
1143                        -1 -- never invert brightness
1144                         0 -- machine default
1145                         1 -- force brightness inversion
1146
1147        icn=            [HW,ISDN]
1148                        Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1149
1150        ide-core.nodma= [HW] (E)IDE subsystem
1151                        Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1152                        .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1153                        .cdrom .chs .ignore_cable are additional options
1154                        See Documentation/ide/ide.txt.
1155
1156        ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1157                        Claim all unknown PCI IDE storage controllers.
1158
1159        idle=           [X86]
1160                        Format: idle=poll, idle=halt, idle=nomwait
1161                        Poll forces a polling idle loop that can slightly
1162                        improve the performance of waking up a idle CPU, but
1163                        will use a lot of power and make the system run hot.
1164                        Not recommended.
1165                        idle=halt: Halt is forced to be used for CPU idle.
1166                        In such case C2/C3 won't be used again.
1167                        idle=nomwait: Disable mwait for CPU C-states
1168
1169        ignore_loglevel [KNL]
1170                        Ignore loglevel setting - this will print /all/
1171                        kernel messages to the console. Useful for debugging.
1172                        We also add it as printk module parameter, so users
1173                        could change it dynamically, usually by
1174                        /sys/module/printk/parameters/ignore_loglevel.
1175
1176        ihash_entries=  [KNL]
1177                        Set number of hash buckets for inode cache.
1178
1179        ima_appraise=   [IMA] appraise integrity measurements
1180                        Format: { "off" | "enforce" | "fix" }
1181                        default: "enforce"
1182
1183        ima_appraise_tcb [IMA]
1184                        The builtin appraise policy appraises all files
1185                        owned by uid=0.
1186
1187        ima_hash=       [IMA]
1188                        Format: { "sha1" | "md5" }
1189                        default: "sha1"
1190
1191        ima_tcb         [IMA]
1192                        Load a policy which meets the needs of the Trusted
1193                        Computing Base.  This means IMA will measure all
1194                        programs exec'd, files mmap'd for exec, and all files
1195                        opened for read by uid=0.
1196
1197        init=           [KNL]
1198                        Format: <full_path>
1199                        Run specified binary instead of /sbin/init as init
1200                        process.
1201
1202        initcall_debug  [KNL] Trace initcalls as they are executed.  Useful
1203                        for working out where the kernel is dying during
1204                        startup.
1205
1206        initrd=         [BOOT] Specify the location of the initial ramdisk
1207
1208        inport.irq=     [HW] Inport (ATI XL and Microsoft) busmouse driver
1209                        Format: <irq>
1210
1211        int_pln_enable  [x86] Enable power limit notification interrupt
1212
1213        integrity_audit=[IMA]
1214                        Format: { "0" | "1" }
1215                        0 -- basic integrity auditing messages. (Default)
1216                        1 -- additional integrity auditing messages.
1217
1218        intel_iommu=    [DMAR] Intel IOMMU driver (DMAR) option
1219                on
1220                        Enable intel iommu driver.
1221                off
1222                        Disable intel iommu driver.
1223                igfx_off [Default Off]
1224                        By default, gfx is mapped as normal device. If a gfx
1225                        device has a dedicated DMAR unit, the DMAR unit is
1226                        bypassed by not enabling DMAR with this option. In
1227                        this case, gfx device will use physical address for
1228                        DMA.
1229                forcedac [x86_64]
1230                        With this option iommu will not optimize to look
1231                        for io virtual address below 32-bit forcing dual
1232                        address cycle on pci bus for cards supporting greater
1233                        than 32-bit addressing. The default is to look
1234                        for translation below 32-bit and if not available
1235                        then look in the higher range.
1236                strict [Default Off]
1237                        With this option on every unmap_single operation will
1238                        result in a hardware IOTLB flush operation as opposed
1239                        to batching them for performance.
1240                sp_off [Default Off]
1241                        By default, super page will be supported if Intel IOMMU
1242                        has the capability. With this option, super page will
1243                        not be supported.
1244
1245        intel_idle.max_cstate=  [KNL,HW,ACPI,X86]
1246                        0       disables intel_idle and fall back on acpi_idle.
1247                        1 to 6  specify maximum depth of C-state.
1248
1249        intel_pstate=  [X86]
1250                       disable
1251                         Do not enable intel_pstate as the default
1252                         scaling driver for the supported processors
1253
1254        intremap=       [X86-64, Intel-IOMMU]
1255                        on      enable Interrupt Remapping (default)
1256                        off     disable Interrupt Remapping
1257                        nosid   disable Source ID checking
1258                        no_x2apic_optout
1259                                BIOS x2APIC opt-out request will be ignored
1260
1261        iomem=          Disable strict checking of access to MMIO memory
1262                strict  regions from userspace.
1263                relaxed
1264
1265        iommu=          [x86]
1266                off
1267                force
1268                noforce
1269                biomerge
1270                panic
1271                nopanic
1272                merge
1273                nomerge
1274                forcesac
1275                soft
1276                pt              [x86, IA-64]
1277
1278
1279        io7=            [HW] IO7 for Marvel based alpha systems
1280                        See comment before marvel_specify_io7 in
1281                        arch/alpha/kernel/core_marvel.c.
1282
1283        io_delay=       [X86] I/O delay method
1284                0x80
1285                        Standard port 0x80 based delay
1286                0xed
1287                        Alternate port 0xed based delay (needed on some systems)
1288                udelay
1289                        Simple two microseconds delay
1290                none
1291                        No delay
1292
1293        ip=             [IP_PNP]
1294                        See Documentation/filesystems/nfs/nfsroot.txt.
1295
1296        ip2=            [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1297                        See comment before ip2_setup() in
1298                        drivers/char/ip2/ip2base.c.
1299
1300        irqfixup        [HW]
1301                        When an interrupt is not handled search all handlers
1302                        for it. Intended to get systems with badly broken
1303                        firmware running.
1304
1305        irqpoll         [HW]
1306                        When an interrupt is not handled search all handlers
1307                        for it. Also check all handlers each timer
1308                        interrupt. Intended to get systems with badly broken
1309                        firmware running.
1310
1311        isapnp=         [ISAPNP]
1312                        Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1313
1314        isolcpus=       [KNL,SMP] Isolate CPUs from the general scheduler.
1315                        Format:
1316                        <cpu number>,...,<cpu number>
1317                        or
1318                        <cpu number>-<cpu number>
1319                        (must be a positive range in ascending order)
1320                        or a mixture
1321                        <cpu number>,...,<cpu number>-<cpu number>
1322
1323                        This option can be used to specify one or more CPUs
1324                        to isolate from the general SMP balancing and scheduling
1325                        algorithms. You can move a process onto or off an
1326                        "isolated" CPU via the CPU affinity syscalls or cpuset.
1327                        <cpu number> begins at 0 and the maximum value is
1328                        "number of CPUs in system - 1".
1329
1330                        This option is the preferred way to isolate CPUs. The
1331                        alternative -- manually setting the CPU mask of all
1332                        tasks in the system -- can cause problems and
1333                        suboptimal load balancer performance.
1334
1335        iucv=           [HW,NET]
1336
1337        ivrs_ioapic     [HW,X86_64]
1338                        Provide an override to the IOAPIC-ID<->DEVICE-ID
1339                        mapping provided in the IVRS ACPI table. For
1340                        example, to map IOAPIC-ID decimal 10 to
1341                        PCI device 00:14.0 write the parameter as:
1342                                ivrs_ioapic[10]=00:14.0
1343
1344        ivrs_hpet       [HW,X86_64]
1345                        Provide an override to the HPET-ID<->DEVICE-ID
1346                        mapping provided in the IVRS ACPI table. For
1347                        example, to map HPET-ID decimal 0 to
1348                        PCI device 00:14.0 write the parameter as:
1349                                ivrs_hpet[0]=00:14.0
1350
1351        js=             [HW,JOY] Analog joystick
1352                        See Documentation/input/joystick.txt.
1353
1354        keepinitrd      [HW,ARM]
1355
1356        kernelcore=nn[KMG]      [KNL,X86,IA-64,PPC] This parameter
1357                        specifies the amount of memory usable by the kernel
1358                        for non-movable allocations.  The requested amount is
1359                        spread evenly throughout all nodes in the system. The
1360                        remaining memory in each node is used for Movable
1361                        pages. In the event, a node is too small to have both
1362                        kernelcore and Movable pages, kernelcore pages will
1363                        take priority and other nodes will have a larger number
1364                        of Movable pages.  The Movable zone is used for the
1365                        allocation of pages that may be reclaimed or moved
1366                        by the page migration subsystem.  This means that
1367                        HugeTLB pages may not be allocated from this zone.
1368                        Note that allocations like PTEs-from-HighMem still
1369                        use the HighMem zone if it exists, and the Normal
1370                        zone if it does not.
1371
1372        kgdbdbgp=       [KGDB,HW] kgdb over EHCI usb debug port.
1373                        Format: <Controller#>[,poll interval]
1374                        The controller # is the number of the ehci usb debug
1375                        port as it is probed via PCI.  The poll interval is
1376                        optional and is the number seconds in between
1377                        each poll cycle to the debug port in case you need
1378                        the functionality for interrupting the kernel with
1379                        gdb or control-c on the dbgp connection.  When
1380                        not using this parameter you use sysrq-g to break into
1381                        the kernel debugger.
1382
1383        kgdboc=         [KGDB,HW] kgdb over consoles.
1384                        Requires a tty driver that supports console polling,
1385                        or a supported polling keyboard driver (non-usb).
1386                         Serial only format: <serial_device>[,baud]
1387                         keyboard only format: kbd
1388                         keyboard and serial format: kbd,<serial_device>[,baud]
1389                        Optional Kernel mode setting:
1390                         kms, kbd format: kms,kbd
1391                         kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1392
1393        kgdbwait        [KGDB] Stop kernel execution and enter the
1394                        kernel debugger at the earliest opportunity.
1395
1396        kmac=           [MIPS] korina ethernet MAC address.
1397                        Configure the RouterBoard 532 series on-chip
1398                        Ethernet adapter MAC address.
1399
1400        kmemleak=       [KNL] Boot-time kmemleak enable/disable
1401                        Valid arguments: on, off
1402                        Default: on
1403
1404        kstack=N        [X86] Print N words from the kernel stack
1405                        in oops dumps.
1406
1407        kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1408                        Default is 0 (don't ignore, but inject #GP)
1409
1410        kvm.mmu_audit=  [KVM] This is a R/W parameter which allows audit
1411                        KVM MMU at runtime.
1412                        Default is 0 (off)
1413
1414        kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1415                        Default is 1 (enabled)
1416
1417        kvm-amd.npt=    [KVM,AMD] Disable nested paging (virtualized MMU)
1418                        for all guests.
1419                        Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1420
1421        kvm-intel.ept=  [KVM,Intel] Disable extended page tables
1422                        (virtualized MMU) support on capable Intel chips.
1423                        Default is 1 (enabled)
1424
1425        kvm-intel.emulate_invalid_guest_state=
1426                        [KVM,Intel] Enable emulation of invalid guest states
1427                        Default is 0 (disabled)
1428
1429        kvm-intel.flexpriority=
1430                        [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1431                        Default is 1 (enabled)
1432
1433        kvm-intel.nested=
1434                        [KVM,Intel] Enable VMX nesting (nVMX).
1435                        Default is 0 (disabled)
1436
1437        kvm-intel.unrestricted_guest=
1438                        [KVM,Intel] Disable unrestricted guest feature
1439                        (virtualized real and unpaged mode) on capable
1440                        Intel chips. Default is 1 (enabled)
1441
1442        kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1443                        feature (tagged TLBs) on capable Intel chips.
1444                        Default is 1 (enabled)
1445
1446        l2cr=           [PPC]
1447
1448        l3cr=           [PPC]
1449
1450        lapic           [X86-32,APIC] Enable the local APIC even if BIOS
1451                        disabled it.
1452
1453        lapic=          [x86,APIC] "notscdeadline" Do not use TSC deadline
1454                        value for LAPIC timer one-shot implementation. Default
1455                        back to the programmable timer unit in the LAPIC.
1456
1457        lapic_timer_c2_ok       [X86,APIC] trust the local apic timer
1458                        in C2 power state.
1459
1460        libata.dma=     [LIBATA] DMA control
1461                        libata.dma=0      Disable all PATA and SATA DMA
1462                        libata.dma=1      PATA and SATA Disk DMA only
1463                        libata.dma=2      ATAPI (CDROM) DMA only
1464                        libata.dma=4      Compact Flash DMA only
1465                        Combinations also work, so libata.dma=3 enables DMA
1466                        for disks and CDROMs, but not CFs.
1467
1468        libata.ignore_hpa=      [LIBATA] Ignore HPA limit
1469                        libata.ignore_hpa=0       keep BIOS limits (default)
1470                        libata.ignore_hpa=1       ignore limits, using full disk
1471
1472        libata.noacpi   [LIBATA] Disables use of ACPI in libata suspend/resume
1473                        when set.
1474                        Format: <int>
1475
1476        libata.force=   [LIBATA] Force configurations.  The format is comma
1477                        separated list of "[ID:]VAL" where ID is
1478                        PORT[.DEVICE].  PORT and DEVICE are decimal numbers
1479                        matching port, link or device.  Basically, it matches
1480                        the ATA ID string printed on console by libata.  If
1481                        the whole ID part is omitted, the last PORT and DEVICE
1482                        values are used.  If ID hasn't been specified yet, the
1483                        configuration applies to all ports, links and devices.
1484
1485                        If only DEVICE is omitted, the parameter applies to
1486                        the port and all links and devices behind it.  DEVICE
1487                        number of 0 either selects the first device or the
1488                        first fan-out link behind PMP device.  It does not
1489                        select the host link.  DEVICE number of 15 selects the
1490                        host link and device attached to it.
1491
1492                        The VAL specifies the configuration to force.  As long
1493                        as there's no ambiguity shortcut notation is allowed.
1494                        For example, both 1.5 and 1.5G would work for 1.5Gbps.
1495                        The following configurations can be forced.
1496
1497                        * Cable type: 40c, 80c, short40c, unk, ign or sata.
1498                          Any ID with matching PORT is used.
1499
1500                        * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1501
1502                        * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1503                          udma[/][16,25,33,44,66,100,133] notation is also
1504                          allowed.
1505
1506                        * [no]ncq: Turn on or off NCQ.
1507
1508                        * nohrst, nosrst, norst: suppress hard, soft
1509                          and both resets.
1510
1511                        * rstonce: only attempt one reset during
1512                          hot-unplug link recovery
1513
1514                        * dump_id: dump IDENTIFY data.
1515
1516                        * atapi_dmadir: Enable ATAPI DMADIR bridge support
1517
1518                        If there are multiple matching configurations changing
1519                        the same attribute, the last one is used.
1520
1521        memblock=debug  [KNL] Enable memblock debug messages.
1522
1523        load_ramdisk=   [RAM] List of ramdisks to load from floppy
1524                        See Documentation/blockdev/ramdisk.txt.
1525
1526        lockd.nlm_grace_period=P  [NFS] Assign grace period.
1527                        Format: <integer>
1528
1529        lockd.nlm_tcpport=N     [NFS] Assign TCP port.
1530                        Format: <integer>
1531
1532        lockd.nlm_timeout=T     [NFS] Assign timeout value.
1533                        Format: <integer>
1534
1535        lockd.nlm_udpport=M     [NFS] Assign UDP port.
1536                        Format: <integer>
1537
1538        logibm.irq=     [HW,MOUSE] Logitech Bus Mouse Driver
1539                        Format: <irq>
1540
1541        loglevel=       All Kernel Messages with a loglevel smaller than the
1542                        console loglevel will be printed to the console. It can
1543                        also be changed with klogd or other programs. The
1544                        loglevels are defined as follows:
1545
1546                        0 (KERN_EMERG)          system is unusable
1547                        1 (KERN_ALERT)          action must be taken immediately
1548                        2 (KERN_CRIT)           critical conditions
1549                        3 (KERN_ERR)            error conditions
1550                        4 (KERN_WARNING)        warning conditions
1551                        5 (KERN_NOTICE)         normal but significant condition
1552                        6 (KERN_INFO)           informational
1553                        7 (KERN_DEBUG)          debug-level messages
1554
1555        log_buf_len=n[KMG]      Sets the size of the printk ring buffer,
1556                        in bytes.  n must be a power of two.  The default
1557                        size is set in the kernel config file.
1558
1559        logo.nologo     [FB] Disables display of the built-in Linux logo.
1560                        This may be used to provide more screen space for
1561                        kernel log messages and is useful when debugging
1562                        kernel boot problems.
1563
1564        lp=0            [LP]    Specify parallel ports to use, e.g,
1565        lp=port[,port...]       lp=none,parport0 (lp0 not configured, lp1 uses
1566        lp=reset                first parallel port). 'lp=0' disables the
1567        lp=auto                 printer driver. 'lp=reset' (which can be
1568                                specified in addition to the ports) causes
1569                                attached printers to be reset. Using
1570                                lp=port1,port2,... specifies the parallel ports
1571                                to associate lp devices with, starting with
1572                                lp0. A port specification may be 'none' to skip
1573                                that lp device, or a parport name such as
1574                                'parport0'. Specifying 'lp=auto' instead of a
1575                                port specification list means that device IDs
1576                                from each port should be examined, to see if
1577                                an IEEE 1284-compliant printer is attached; if
1578                                so, the driver will manage that printer.
1579                                See also header of drivers/char/lp.c.
1580
1581        lpj=n           [KNL]
1582                        Sets loops_per_jiffy to given constant, thus avoiding
1583                        time-consuming boot-time autodetection (up to 250 ms per
1584                        CPU). 0 enables autodetection (default). To determine
1585                        the correct value for your kernel, boot with normal
1586                        autodetection and see what value is printed. Note that
1587                        on SMP systems the preset will be applied to all CPUs,
1588                        which is likely to cause problems if your CPUs need
1589                        significantly divergent settings. An incorrect value
1590                        will cause delays in the kernel to be wrong, leading to
1591                        unpredictable I/O errors and other breakage. Although
1592                        unlikely, in the extreme case this might damage your
1593                        hardware.
1594
1595        ltpc=           [NET]
1596                        Format: <io>,<irq>,<dma>
1597
1598        machvec=        [IA-64] Force the use of a particular machine-vector
1599                        (machvec) in a generic kernel.
1600                        Example: machvec=hpzx1_swiotlb
1601
1602        machtype=       [Loongson] Share the same kernel image file between different
1603                         yeeloong laptop.
1604                        Example: machtype=lemote-yeeloong-2f-7inch
1605
1606        max_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory greater
1607                        than or equal to this physical address is ignored.
1608
1609        maxcpus=        [SMP] Maximum number of processors that an SMP kernel
1610                        should make use of.  maxcpus=n : n >= 0 limits the
1611                        kernel to using 'n' processors.  n=0 is a special case,
1612                        it is equivalent to "nosmp", which also disables
1613                        the IO APIC.
1614
1615        max_loop=       [LOOP] The number of loop block devices that get
1616        (loop.max_loop) unconditionally pre-created at init time. The default
1617                        number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1618                        of statically allocating a predefined number, loop
1619                        devices can be requested on-demand with the
1620                        /dev/loop-control interface.
1621
1622        mce             [X86-32] Machine Check Exception
1623
1624        mce=option      [X86-64] See Documentation/x86/x86_64/boot-options.txt
1625
1626        md=             [HW] RAID subsystems devices and level
1627                        See Documentation/md.txt.
1628
1629        mdacon=         [MDA]
1630                        Format: <first>,<last>
1631                        Specifies range of consoles to be captured by the MDA.
1632
1633        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
1634                        Amount of memory to be used when the kernel is not able
1635                        to see the whole system memory or for test.
1636                        [X86] Work as limiting max address. Use together
1637                        with memmap= to avoid physical address space collisions.
1638                        Without memmap= PCI devices could be placed at addresses
1639                        belonging to unused RAM.
1640
1641        mem=nopentium   [BUGS=X86-32] Disable usage of 4MB pages for kernel
1642                        memory.
1643
1644        memchunk=nn[KMG]
1645                        [KNL,SH] Allow user to override the default size for
1646                        per-device physically contiguous DMA buffers.
1647
1648        memmap=exactmap [KNL,X86] Enable setting of an exact
1649                        E820 memory map, as specified by the user.
1650                        Such memmap=exactmap lines can be constructed based on
1651                        BIOS output or other requirements. See the memmap=nn@ss
1652                        option description.
1653
1654        memmap=nn[KMG]@ss[KMG]
1655                        [KNL] Force usage of a specific region of memory
1656                        Region of memory to be used, from ss to ss+nn.
1657
1658        memmap=nn[KMG]#ss[KMG]
1659                        [KNL,ACPI] Mark specific memory as ACPI data.
1660                        Region of memory to be used, from ss to ss+nn.
1661
1662        memmap=nn[KMG]$ss[KMG]
1663                        [KNL,ACPI] Mark specific memory as reserved.
1664                        Region of memory to be used, from ss to ss+nn.
1665                        Example: Exclude memory from 0x18690000-0x1869ffff
1666                                 memmap=64K$0x18690000
1667                                 or
1668                                 memmap=0x10000$0x18690000
1669
1670        memory_corruption_check=0/1 [X86]
1671                        Some BIOSes seem to corrupt the first 64k of
1672                        memory when doing things like suspend/resume.
1673                        Setting this option will scan the memory
1674                        looking for corruption.  Enabling this will
1675                        both detect corruption and prevent the kernel
1676                        from using the memory being corrupted.
1677                        However, its intended as a diagnostic tool; if
1678                        repeatable BIOS-originated corruption always
1679                        affects the same memory, you can use memmap=
1680                        to prevent the kernel from using that memory.
1681
1682        memory_corruption_check_size=size [X86]
1683                        By default it checks for corruption in the low
1684                        64k, making this memory unavailable for normal
1685                        use.  Use this parameter to scan for
1686                        corruption in more or less memory.
1687
1688        memory_corruption_check_period=seconds [X86]
1689                        By default it checks for corruption every 60
1690                        seconds.  Use this parameter to check at some
1691                        other rate.  0 disables periodic checking.
1692
1693        memtest=        [KNL,X86] Enable memtest
1694                        Format: <integer>
1695                        default : 0 <disable>
1696                        Specifies the number of memtest passes to be
1697                        performed. Each pass selects another test
1698                        pattern from a given set of patterns. Memtest
1699                        fills the memory with this pattern, validates
1700                        memory contents and reserves bad memory
1701                        regions that are detected.
1702
1703        meye.*=         [HW] Set MotionEye Camera parameters
1704                        See Documentation/video4linux/meye.txt.
1705
1706        mfgpt_irq=      [IA-32] Specify the IRQ to use for the
1707                        Multi-Function General Purpose Timers on AMD Geode
1708                        platforms.
1709
1710        mfgptfix        [X86-32] Fix MFGPT timers on AMD Geode platforms when
1711                        the BIOS has incorrectly applied a workaround. TinyBIOS
1712                        version 0.98 is known to be affected, 0.99 fixes the
1713                        problem by letting the user disable the workaround.
1714
1715        mga=            [HW,DRM]
1716
1717        min_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory below this
1718                        physical address is ignored.
1719
1720        mini2440=       [ARM,HW,KNL]
1721                        Format:[0..2][b][c][t]
1722                        Default: "0tb"
1723                        MINI2440 configuration specification:
1724                        0 - The attached screen is the 3.5" TFT
1725                        1 - The attached screen is the 7" TFT
1726                        2 - The VGA Shield is attached (1024x768)
1727                        Leaving out the screen size parameter will not load
1728                        the TFT driver, and the framebuffer will be left
1729                        unconfigured.
1730                        b - Enable backlight. The TFT backlight pin will be
1731                        linked to the kernel VESA blanking code and a GPIO
1732                        LED. This parameter is not necessary when using the
1733                        VGA shield.
1734                        c - Enable the s3c camera interface.
1735                        t - Reserved for enabling touchscreen support. The
1736                        touchscreen support is not enabled in the mainstream
1737                        kernel as of 2.6.30, a preliminary port can be found
1738                        in the "bleeding edge" mini2440 support kernel at
1739                        http://repo.or.cz/w/linux-2.6/mini2440.git
1740
1741        mminit_loglevel=
1742                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1743                        parameter allows control of the logging verbosity for
1744                        the additional memory initialisation checks. A value
1745                        of 0 disables mminit logging and a level of 4 will
1746                        log everything. Information is printed at KERN_DEBUG
1747                        so loglevel=8 may also need to be specified.
1748
1749        module.sig_enforce
1750                        [KNL] When CONFIG_MODULE_SIG is set, this means that
1751                        modules without (valid) signatures will fail to load.
1752                        Note that if CONFIG_MODULE_SIG_FORCE is set, that
1753                        is always true, so this option does nothing.
1754
1755        mousedev.tap_time=
1756                        [MOUSE] Maximum time between finger touching and
1757                        leaving touchpad surface for touch to be considered
1758                        a tap and be reported as a left button click (for
1759                        touchpads working in absolute mode only).
1760                        Format: <msecs>
1761        mousedev.xres=  [MOUSE] Horizontal screen resolution, used for devices
1762                        reporting absolute coordinates, such as tablets
1763        mousedev.yres=  [MOUSE] Vertical screen resolution, used for devices
1764                        reporting absolute coordinates, such as tablets
1765
1766        movablecore=nn[KMG]     [KNL,X86,IA-64,PPC] This parameter
1767                        is similar to kernelcore except it specifies the
1768                        amount of memory used for migratable allocations.
1769                        If both kernelcore and movablecore is specified,
1770                        then kernelcore will be at *least* the specified
1771                        value but may be more. If movablecore on its own
1772                        is specified, the administrator must be careful
1773                        that the amount of memory usable for all allocations
1774                        is not too small.
1775
1776        MTD_Partition=  [MTD]
1777                        Format: <name>,<region-number>,<size>,<offset>
1778
1779        MTD_Region=     [MTD] Format:
1780                        <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1781
1782        mtdparts=       [MTD]
1783                        See drivers/mtd/cmdlinepart.c.
1784
1785        multitce=off    [PPC]  This parameter disables the use of the pSeries
1786                        firmware feature for updating multiple TCE entries
1787                        at a time.
1788
1789        onenand.bdry=   [HW,MTD] Flex-OneNAND Boundary Configuration
1790
1791                        Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1792
1793                        boundary - index of last SLC block on Flex-OneNAND.
1794                                   The remaining blocks are configured as MLC blocks.
1795                        lock     - Configure if Flex-OneNAND boundary should be locked.
1796                                   Once locked, the boundary cannot be changed.
1797                                   1 indicates lock status, 0 indicates unlock status.
1798
1799        mtdset=         [ARM]
1800                        ARM/S3C2412 JIVE boot control
1801
1802                        See arch/arm/mach-s3c2412/mach-jive.c
1803
1804        mtouchusb.raw_coordinates=
1805                        [HW] Make the MicroTouch USB driver use raw coordinates
1806                        ('y', default) or cooked coordinates ('n')
1807
1808        mtrr_chunk_size=nn[KMG] [X86]
1809                        used for mtrr cleanup. It is largest continuous chunk
1810                        that could hold holes aka. UC entries.
1811
1812        mtrr_gran_size=nn[KMG] [X86]
1813                        Used for mtrr cleanup. It is granularity of mtrr block.
1814                        Default is 1.
1815                        Large value could prevent small alignment from
1816                        using up MTRRs.
1817
1818        mtrr_spare_reg_nr=n [X86]
1819                        Format: <integer>
1820                        Range: 0,7 : spare reg number
1821                        Default : 1
1822                        Used for mtrr cleanup. It is spare mtrr entries number.
1823                        Set to 2 or more if your graphical card needs more.
1824
1825        n2=             [NET] SDL Inc. RISCom/N2 synchronous serial card
1826
1827        netdev=         [NET] Network devices parameters
1828                        Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1829                        Note that mem_start is often overloaded to mean
1830                        something different and driver-specific.
1831                        This usage is only documented in each driver source
1832                        file if at all.
1833
1834        nf_conntrack.acct=
1835                        [NETFILTER] Enable connection tracking flow accounting
1836                        0 to disable accounting
1837                        1 to enable accounting
1838                        Default value is 0.
1839
1840        nfsaddrs=       [NFS] Deprecated.  Use ip= instead.
1841                        See Documentation/filesystems/nfs/nfsroot.txt.
1842
1843        nfsroot=        [NFS] nfs root filesystem for disk-less boxes.
1844                        See Documentation/filesystems/nfs/nfsroot.txt.
1845
1846        nfsrootdebug    [NFS] enable nfsroot debugging messages.
1847                        See Documentation/filesystems/nfs/nfsroot.txt.
1848
1849        nfs.callback_tcpport=
1850                        [NFS] set the TCP port on which the NFSv4 callback
1851                        channel should listen.
1852
1853        nfs.cache_getent=
1854                        [NFS] sets the pathname to the program which is used
1855                        to update the NFS client cache entries.
1856
1857        nfs.cache_getent_timeout=
1858                        [NFS] sets the timeout after which an attempt to
1859                        update a cache entry is deemed to have failed.
1860
1861        nfs.idmap_cache_timeout=
1862                        [NFS] set the maximum lifetime for idmapper cache
1863                        entries.
1864
1865        nfs.enable_ino64=
1866                        [NFS] enable 64-bit inode numbers.
1867                        If zero, the NFS client will fake up a 32-bit inode
1868                        number for the readdir() and stat() syscalls instead
1869                        of returning the full 64-bit number.
1870                        The default is to return 64-bit inode numbers.
1871
1872        nfs.max_session_slots=
1873                        [NFSv4.1] Sets the maximum number of session slots
1874                        the client will attempt to negotiate with the server.
1875                        This limits the number of simultaneous RPC requests
1876                        that the client can send to the NFSv4.1 server.
1877                        Note that there is little point in setting this
1878                        value higher than the max_tcp_slot_table_limit.
1879
1880        nfs.nfs4_disable_idmapping=
1881                        [NFSv4] When set to the default of '1', this option
1882                        ensures that both the RPC level authentication
1883                        scheme and the NFS level operations agree to use
1884                        numeric uids/gids if the mount is using the
1885                        'sec=sys' security flavour. In effect it is
1886                        disabling idmapping, which can make migration from
1887                        legacy NFSv2/v3 systems to NFSv4 easier.
1888                        Servers that do not support this mode of operation
1889                        will be autodetected by the client, and it will fall
1890                        back to using the idmapper.
1891                        To turn off this behaviour, set the value to '0'.
1892        nfs.nfs4_unique_id=
1893                        [NFS4] Specify an additional fixed unique ident-
1894                        ification string that NFSv4 clients can insert into
1895                        their nfs_client_id4 string.  This is typically a
1896                        UUID that is generated at system install time.
1897
1898        nfs.send_implementation_id =
1899                        [NFSv4.1] Send client implementation identification
1900                        information in exchange_id requests.
1901                        If zero, no implementation identification information
1902                        will be sent.
1903                        The default is to send the implementation identification
1904                        information.
1905        
1906        nfs.recover_lost_locks =
1907                        [NFSv4] Attempt to recover locks that were lost due
1908                        to a lease timeout on the server. Please note that
1909                        doing this risks data corruption, since there are
1910                        no guarantees that the file will remain unchanged
1911                        after the locks are lost.
1912                        If you want to enable the kernel legacy behaviour of
1913                        attempting to recover these locks, then set this
1914                        parameter to '1'.
1915                        The default parameter value of '0' causes the kernel
1916                        not to attempt recovery of lost locks.
1917
1918        nfsd.nfs4_disable_idmapping=
1919                        [NFSv4] When set to the default of '1', the NFSv4
1920                        server will return only numeric uids and gids to
1921                        clients using auth_sys, and will accept numeric uids
1922                        and gids from such clients.  This is intended to ease
1923                        migration from NFSv2/v3.
1924
1925        objlayoutdriver.osd_login_prog=
1926                        [NFS] [OBJLAYOUT] sets the pathname to the program which
1927                        is used to automatically discover and login into new
1928                        osd-targets. Please see:
1929                        Documentation/filesystems/pnfs.txt for more explanations
1930
1931        nmi_debug=      [KNL,AVR32,SH] Specify one or more actions to take
1932                        when a NMI is triggered.
1933                        Format: [state][,regs][,debounce][,die]
1934
1935        nmi_watchdog=   [KNL,BUGS=X86] Debugging features for SMP kernels
1936                        Format: [panic,][nopanic,][num]
1937                        Valid num: 0
1938                        0 - turn nmi_watchdog off
1939                        When panic is specified, panic when an NMI watchdog
1940                        timeout occurs (or 'nopanic' to override the opposite
1941                        default).
1942                        This is useful when you use a panic=... timeout and
1943                        need the box quickly up again.
1944
1945        netpoll.carrier_timeout=
1946                        [NET] Specifies amount of time (in seconds) that
1947                        netpoll should wait for a carrier. By default netpoll
1948                        waits 4 seconds.
1949
1950        no387           [BUGS=X86-32] Tells the kernel to use the 387 maths
1951                        emulation library even if a 387 maths coprocessor
1952                        is present.
1953
1954        no_console_suspend
1955                        [HW] Never suspend the console
1956                        Disable suspending of consoles during suspend and
1957                        hibernate operations.  Once disabled, debugging
1958                        messages can reach various consoles while the rest
1959                        of the system is being put to sleep (ie, while
1960                        debugging driver suspend/resume hooks).  This may
1961                        not work reliably with all consoles, but is known
1962                        to work with serial and VGA consoles.
1963                        To facilitate more flexible debugging, we also add
1964                        console_suspend, a printk module parameter to control
1965                        it. Users could use console_suspend (usually
1966                        /sys/module/printk/parameters/console_suspend) to
1967                        turn on/off it dynamically.
1968
1969        noaliencache    [MM, NUMA, SLAB] Disables the allocation of alien
1970                        caches in the slab allocator.  Saves per-node memory,
1971                        but will impact performance.
1972
1973        noalign         [KNL,ARM]
1974
1975        noapic          [SMP,APIC] Tells the kernel to not make use of any
1976                        IOAPICs that may be present in the system.
1977
1978        noautogroup     Disable scheduler automatic task group creation.
1979
1980        nobats          [PPC] Do not use BATs for mapping kernel lowmem
1981                        on "Classic" PPC cores.
1982
1983        nocache         [ARM]
1984
1985        noclflush       [BUGS=X86] Don't use the CLFLUSH instruction
1986
1987        nodelayacct     [KNL] Disable per-task delay accounting
1988
1989        nodisconnect    [HW,SCSI,M68K] Disables SCSI disconnects.
1990
1991        nodsp           [SH] Disable hardware DSP at boot time.
1992
1993        noefi           [X86] Disable EFI runtime services support.
1994
1995        noexec          [IA-64]
1996
1997        noexec          [X86]
1998                        On X86-32 available only on PAE configured kernels.
1999                        noexec=on: enable non-executable mappings (default)
2000                        noexec=off: disable non-executable mappings
2001
2002        nosmap          [X86]
2003                        Disable SMAP (Supervisor Mode Access Prevention)
2004                        even if it is supported by processor.
2005
2006        nosmep          [X86]
2007                        Disable SMEP (Supervisor Mode Execution Prevention)
2008                        even if it is supported by processor.
2009
2010        noexec32        [X86-64]
2011                        This affects only 32-bit executables.
2012                        noexec32=on: enable non-executable mappings (default)
2013                                read doesn't imply executable mappings
2014                        noexec32=off: disable non-executable mappings
2015                                read implies executable mappings
2016
2017        nofpu           [SH] Disable hardware FPU at boot time.
2018
2019        nofxsr          [BUGS=X86-32] Disables x86 floating point extended
2020                        register save and restore. The kernel will only save
2021                        legacy floating-point registers on task switch.
2022
2023        noxsave         [BUGS=X86] Disables x86 extended register state save
2024                        and restore using xsave. The kernel will fallback to
2025                        enabling legacy floating-point and sse state.
2026
2027        eagerfpu=       [X86]
2028                        on      enable eager fpu restore
2029                        off     disable eager fpu restore
2030                        auto    selects the default scheme, which automatically
2031                                enables eagerfpu restore for xsaveopt.
2032
2033        nohlt           [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2034                        wfi(ARM) instruction doesn't work correctly and not to
2035                        use it. This is also useful when using JTAG debugger.
2036
2037        no_file_caps    Tells the kernel not to honor file capabilities.  The
2038                        only way then for a file to be executed with privilege
2039                        is to be setuid root or executed by root.
2040
2041        nohalt          [IA-64] Tells the kernel not to use the power saving
2042                        function PAL_HALT_LIGHT when idle. This increases
2043                        power-consumption. On the positive side, it reduces
2044                        interrupt wake-up latency, which may improve performance
2045                        in certain environments such as networked servers or
2046                        real-time systems.
2047
2048        nohz=           [KNL] Boottime enable/disable dynamic ticks
2049                        Valid arguments: on, off
2050                        Default: on
2051
2052        nohz_full=      [KNL,BOOT]
2053                        In kernels built with CONFIG_NO_HZ_FULL=y, set
2054                        the specified list of CPUs whose tick will be stopped
2055                        whenever possible. The boot CPU will be forced outside
2056                        the range to maintain the timekeeping.
2057                        The CPUs in this range must also be included in the
2058                        rcu_nocbs= set.
2059
2060        noiotrap        [SH] Disables trapped I/O port accesses.
2061
2062        noirqdebug      [X86-32] Disables the code which attempts to detect and
2063                        disable unhandled interrupt sources.
2064
2065        no_timer_check  [X86,APIC] Disables the code which tests for
2066                        broken timer IRQ sources.
2067
2068        noisapnp        [ISAPNP] Disables ISA PnP code.
2069
2070        noinitrd        [RAM] Tells the kernel not to load any configured
2071                        initial RAM disk.
2072
2073        nointremap      [X86-64, Intel-IOMMU] Do not enable interrupt
2074                        remapping.
2075                        [Deprecated - use intremap=off]
2076
2077        nointroute      [IA-64]
2078
2079        nojitter        [IA-64] Disables jitter checking for ITC timers.
2080
2081        no-kvmclock     [X86,KVM] Disable paravirtualized KVM clock driver
2082
2083        no-kvmapf       [X86,KVM] Disable paravirtualized asynchronous page
2084                        fault handling.
2085
2086        no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
2087                        steal time is computed, but won't influence scheduler
2088                        behaviour
2089
2090        nolapic         [X86-32,APIC] Do not enable or use the local APIC.
2091
2092        nolapic_timer   [X86-32,APIC] Do not use the local APIC timer.
2093
2094        noltlbs         [PPC] Do not use large page/tlb entries for kernel
2095                        lowmem mapping on PPC40x.
2096
2097        nomca           [IA-64] Disable machine check abort handling
2098
2099        nomce           [X86-32] Machine Check Exception
2100
2101        nomfgpt         [X86-32] Disable Multi-Function General Purpose
2102                        Timer usage (for AMD Geode machines).
2103
2104        nonmi_ipi       [X86] Disable using NMI IPIs during panic/reboot to
2105                        shutdown the other cpus.  Instead use the REBOOT_VECTOR
2106                        irq.
2107
2108        nomodule        Disable module load
2109
2110        nopat           [X86] Disable PAT (page attribute table extension of
2111                        pagetables) support.
2112
2113        norandmaps      Don't use address space randomization.  Equivalent to
2114                        echo 0 > /proc/sys/kernel/randomize_va_space
2115
2116        noreplace-paravirt      [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2117
2118        noreplace-smp   [X86-32,SMP] Don't replace SMP instructions
2119                        with UP alternatives
2120
2121        nordrand        [X86] Disable the direct use of the RDRAND
2122                        instruction even if it is supported by the
2123                        processor.  RDRAND is still available to user
2124                        space applications.
2125
2126        noresume        [SWSUSP] Disables resume and restores original swap
2127                        space.
2128
2129        no-scroll       [VGA] Disables scrollback.
2130                        This is required for the Braillex ib80-piezo Braille
2131                        reader made by F.H. Papenmeier (Germany).
2132
2133        nosbagart       [IA-64]
2134
2135        nosep           [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2136
2137        nosmp           [SMP] Tells an SMP kernel to act as a UP kernel,
2138                        and disable the IO APIC.  legacy for "maxcpus=0".
2139
2140        nosoftlockup    [KNL] Disable the soft-lockup detector.
2141
2142        nosync          [HW,M68K] Disables sync negotiation for all devices.
2143
2144        notsc           [BUGS=X86-32] Disable Time Stamp Counter
2145
2146        nousb           [USB] Disable the USB subsystem
2147
2148        nowatchdog      [KNL] Disable the lockup detector (NMI watchdog).
2149
2150        nowb            [ARM]
2151
2152        nox2apic        [X86-64,APIC] Do not enable x2APIC mode.
2153
2154        cpu0_hotplug    [X86] Turn on CPU0 hotplug feature when
2155                        CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2156                        Some features depend on CPU0. Known dependencies are:
2157                        1. Resume from suspend/hibernate depends on CPU0.
2158                        Suspend/hibernate will fail if CPU0 is offline and you
2159                        need to online CPU0 before suspend/hibernate.
2160                        2. PIC interrupts also depend on CPU0. CPU0 can't be
2161                        removed if a PIC interrupt is detected.
2162                        It's said poweroff/reboot may depend on CPU0 on some
2163                        machines although I haven't seen such issues so far
2164                        after CPU0 is offline on a few tested machines.
2165                        If the dependencies are under your control, you can
2166                        turn on cpu0_hotplug.
2167
2168        nptcg=          [IA-64] Override max number of concurrent global TLB
2169                        purges which is reported from either PAL_VM_SUMMARY or
2170                        SAL PALO.
2171
2172        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
2173                        could support.  nr_cpus=n : n >= 1 limits the kernel to
2174                        supporting 'n' processors. Later in runtime you can not
2175                        use hotplug cpu feature to put more cpu back to online.
2176                        just like you compile the kernel NR_CPUS=n
2177
2178        nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
2179
2180        numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2181                        Allowed values are enable and disable
2182
2183        numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2184                        one of ['zone', 'node', 'default'] can be specified
2185                        This can be set from sysctl after boot.
2186                        See Documentation/sysctl/vm.txt for details.
2187
2188        ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
2189                        See Documentation/debugging-via-ohci1394.txt for more
2190                        info.
2191
2192        olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2193                        Rather than timing out after 20 ms if an EC
2194                        command is not properly ACKed, override the length
2195                        of the timeout.  We have interrupts disabled while
2196                        waiting for the ACK, so if this is set too high
2197                        interrupts *may* be lost!
2198
2199        omap_mux=       [OMAP] Override bootloader pin multiplexing.
2200                        Format: <mux_mode0.mode_name=value>...
2201                        For example, to override I2C bus2:
2202                        omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2203
2204        oprofile.timer= [HW]
2205                        Use timer interrupt instead of performance counters
2206
2207        oprofile.cpu_type=      Force an oprofile cpu type
2208                        This might be useful if you have an older oprofile
2209                        userland or if you want common events.
2210                        Format: { arch_perfmon }
2211                        arch_perfmon: [X86] Force use of architectural
2212                                perfmon on Intel CPUs instead of the
2213                                CPU specific event set.
2214                        timer: [X86] Force use of architectural NMI
2215                                timer mode (see also oprofile.timer
2216                                for generic hr timer mode)
2217                                [s390] Force legacy basic mode sampling
2218                                (report cpu_type "timer")
2219
2220        oops=panic      Always panic on oopses. Default is to just kill the
2221                        process, but there is a small probability of
2222                        deadlocking the machine.
2223                        This will also cause panics on machine check exceptions.
2224                        Useful together with panic=30 to trigger a reboot.
2225
2226        OSS             [HW,OSS]
2227                        See Documentation/sound/oss/oss-parameters.txt
2228
2229        panic=          [KNL] Kernel behaviour on panic: delay <timeout>
2230                        timeout > 0: seconds before rebooting
2231                        timeout = 0: wait forever
2232                        timeout < 0: reboot immediately
2233                        Format: <timeout>
2234
2235        parkbd.port=    [HW] Parallel port number the keyboard adapter is
2236                        connected to, default is 0.
2237                        Format: <parport#>
2238        parkbd.mode=    [HW] Parallel port keyboard adapter mode of operation,
2239                        0 for XT, 1 for AT (default is AT).
2240                        Format: <mode>
2241
2242        parport=        [HW,PPT] Specify parallel ports. 0 disables.
2243                        Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2244                        Use 'auto' to force the driver to use any
2245                        IRQ/DMA settings detected (the default is to
2246                        ignore detected IRQ/DMA settings because of
2247                        possible conflicts). You can specify the base
2248                        address, IRQ, and DMA settings; IRQ and DMA
2249                        should be numbers, or 'auto' (for using detected
2250                        settings on that particular port), or 'nofifo'
2251                        (to avoid using a FIFO even if it is detected).
2252                        Parallel ports are assigned in the order they
2253                        are specified on the command line, starting
2254                        with parport0.
2255
2256        parport_init_mode=      [HW,PPT]
2257                        Configure VIA parallel port to operate in
2258                        a specific mode. This is necessary on Pegasos
2259                        computer where firmware has no options for setting
2260                        up parallel port mode and sets it to spp.
2261                        Currently this function knows 686a and 8231 chips.
2262                        Format: [spp|ps2|epp|ecp|ecpepp]
2263
2264        pause_on_oops=
2265                        Halt all CPUs after the first oops has been printed for
2266                        the specified number of seconds.  This is to be used if
2267                        your oopses keep scrolling off the screen.
2268
2269        pcbit=          [HW,ISDN]
2270
2271        pcd.            [PARIDE]
2272                        See header of drivers/block/paride/pcd.c.
2273                        See also Documentation/blockdev/paride.txt.
2274
2275        pci=option[,option...]  [PCI] various PCI subsystem options:
2276                earlydump       [X86] dump PCI config space before the kernel
2277                                changes anything
2278                off             [X86] don't probe for the PCI bus
2279                bios            [X86-32] force use of PCI BIOS, don't access
2280                                the hardware directly. Use this if your machine
2281                                has a non-standard PCI host bridge.
2282                nobios          [X86-32] disallow use of PCI BIOS, only direct
2283                                hardware access methods are allowed. Use this
2284                                if you experience crashes upon bootup and you
2285                                suspect they are caused by the BIOS.
2286                conf1           [X86] Force use of PCI Configuration
2287                                Mechanism 1.
2288                conf2           [X86] Force use of PCI Configuration
2289                                Mechanism 2.
2290                noaer           [PCIE] If the PCIEAER kernel config parameter is
2291                                enabled, this kernel boot option can be used to
2292                                disable the use of PCIE advanced error reporting.
2293                nodomains       [PCI] Disable support for multiple PCI
2294                                root domains (aka PCI segments, in ACPI-speak).
2295                nommconf        [X86] Disable use of MMCONFIG for PCI
2296                                Configuration
2297                check_enable_amd_mmconf [X86] check for and enable
2298                                properly configured MMIO access to PCI
2299                                config space on AMD family 10h CPU
2300                nomsi           [MSI] If the PCI_MSI kernel config parameter is
2301                                enabled, this kernel boot option can be used to
2302                                disable the use of MSI interrupts system-wide.
2303                noioapicquirk   [APIC] Disable all boot interrupt quirks.
2304                                Safety option to keep boot IRQs enabled. This
2305                                should never be necessary.
2306                ioapicreroute   [APIC] Enable rerouting of boot IRQs to the
2307                                primary IO-APIC for bridges that cannot disable
2308                                boot IRQs. This fixes a source of spurious IRQs
2309                                when the system masks IRQs.
2310                noioapicreroute [APIC] Disable workaround that uses the
2311                                boot IRQ equivalent of an IRQ that connects to
2312                                a chipset where boot IRQs cannot be disabled.
2313                                The opposite of ioapicreroute.
2314                biosirq         [X86-32] Use PCI BIOS calls to get the interrupt
2315                                routing table. These calls are known to be buggy
2316                                on several machines and they hang the machine
2317                                when used, but on other computers it's the only
2318                                way to get the interrupt routing table. Try
2319                                this option if the kernel is unable to allocate
2320                                IRQs or discover secondary PCI buses on your
2321                                motherboard.
2322                rom             [X86] Assign address space to expansion ROMs.
2323                                Use with caution as certain devices share
2324                                address decoders between ROMs and other
2325                                resources.
2326                norom           [X86] Do not assign address space to
2327                                expansion ROMs that do not already have
2328                                BIOS assigned address ranges.
2329                nobar           [X86] Do not assign address space to the
2330                                BARs that weren't assigned by the BIOS.
2331                irqmask=0xMMMM  [X86] Set a bit mask of IRQs allowed to be
2332                                assigned automatically to PCI devices. You can
2333                                make the kernel exclude IRQs of your ISA cards
2334                                this way.
2335                pirqaddr=0xAAAAA        [X86] Specify the physical address
2336                                of the PIRQ table (normally generated
2337                                by the BIOS) if it is outside the
2338                                F0000h-100000h range.
2339                lastbus=N       [X86] Scan all buses thru bus #N. Can be
2340                                useful if the kernel is unable to find your
2341                                secondary buses and you want to tell it
2342                                explicitly which ones they are.
2343                assign-busses   [X86] Always assign all PCI bus
2344                                numbers ourselves, overriding
2345                                whatever the firmware may have done.
2346                usepirqmask     [X86] Honor the possible IRQ mask stored
2347                                in the BIOS $PIR table. This is needed on
2348                                some systems with broken BIOSes, notably
2349                                some HP Pavilion N5400 and Omnibook XE3
2350                                notebooks. This will have no effect if ACPI
2351                                IRQ routing is enabled.
2352                noacpi          [X86] Do not use ACPI for IRQ routing
2353                                or for PCI scanning.
2354                use_crs         [X86] Use PCI host bridge window information
2355                                from ACPI.  On BIOSes from 2008 or later, this
2356                                is enabled by default.  If you need to use this,
2357                                please report a bug.
2358                nocrs           [X86] Ignore PCI host bridge windows from ACPI.
2359                                If you need to use this, please report a bug.
2360                routeirq        Do IRQ routing for all PCI devices.
2361                                This is normally done in pci_enable_device(),
2362                                so this option is a temporary workaround
2363                                for broken drivers that don't call it.
2364                skip_isa_align  [X86] do not align io start addr, so can
2365                                handle more pci cards
2366                firmware        [ARM] Do not re-enumerate the bus but instead
2367                                just use the configuration from the
2368                                bootloader. This is currently used on
2369                                IXP2000 systems where the bus has to be
2370                                configured a certain way for adjunct CPUs.
2371                noearly         [X86] Don't do any early type 1 scanning.
2372                                This might help on some broken boards which
2373                                machine check when some devices' config space
2374                                is read. But various workarounds are disabled
2375                                and some IOMMU drivers will not work.
2376                bfsort          Sort PCI devices into breadth-first order.
2377                                This sorting is done to get a device
2378                                order compatible with older (<= 2.4) kernels.
2379                nobfsort        Don't sort PCI devices into breadth-first order.
2380                pcie_bus_tune_off       Disable PCIe MPS (Max Payload Size)
2381                                tuning and use the BIOS-configured MPS defaults.
2382                pcie_bus_safe   Set every device's MPS to the largest value
2383                                supported by all devices below the root complex.
2384                pcie_bus_perf   Set device MPS to the largest allowable MPS
2385                                based on its parent bus. Also set MRRS (Max
2386                                Read Request Size) to the largest supported
2387                                value (no larger than the MPS that the device
2388                                or bus can support) for best performance.
2389                pcie_bus_peer2peer      Set every device's MPS to 128B, which
2390                                every device is guaranteed to support. This
2391                                configuration allows peer-to-peer DMA between
2392                                any pair of devices, possibly at the cost of
2393                                reduced performance.  This also guarantees
2394                                that hot-added devices will work.
2395                cbiosize=nn[KMG]        The fixed amount of bus space which is
2396                                reserved for the CardBus bridge's IO window.
2397                                The default value is 256 bytes.
2398                cbmemsize=nn[KMG]       The fixed amount of bus space which is
2399                                reserved for the CardBus bridge's memory
2400                                window. The default value is 64 megabytes.
2401                resource_alignment=
2402                                Format:
2403                                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2404                                Specifies alignment and device to reassign
2405                                aligned memory resources.
2406                                If <order of align> is not specified,
2407                                PAGE_SIZE is used as alignment.
2408                                PCI-PCI bridge can be specified, if resource
2409                                windows need to be expanded.
2410                ecrc=           Enable/disable PCIe ECRC (transaction layer
2411                                end-to-end CRC checking).
2412                                bios: Use BIOS/firmware settings. This is the
2413                                the default.
2414                                off: Turn ECRC off
2415                                on: Turn ECRC on.
2416                hpiosize=nn[KMG]        The fixed amount of bus space which is
2417                                reserved for hotplug bridge's IO window.
2418                                Default size is 256 bytes.
2419                hpmemsize=nn[KMG]       The fixed amount of bus space which is
2420                                reserved for hotplug bridge's memory window.
2421                                Default size is 2 megabytes.
2422                realloc=        Enable/disable reallocating PCI bridge resources
2423                                if allocations done by BIOS are too small to
2424                                accommodate resources required by all child
2425                                devices.
2426                                off: Turn realloc off
2427                                on: Turn realloc on
2428                realloc         same as realloc=on
2429                noari           do not use PCIe ARI.
2430                pcie_scan_all   Scan all possible PCIe devices.  Otherwise we
2431                                only look for one device below a PCIe downstream
2432                                port.
2433
2434        pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
2435                        Management.
2436                off     Disable ASPM.
2437                force   Enable ASPM even on devices that claim not to support it.
2438                        WARNING: Forcing ASPM on may cause system lockups.
2439
2440        pcie_hp=        [PCIE] PCI Express Hotplug driver options:
2441                nomsi   Do not use MSI for PCI Express Native Hotplug (this
2442                        makes all PCIe ports use INTx for hotplug services).
2443
2444        pcie_ports=     [PCIE] PCIe ports handling:
2445                auto    Ask the BIOS whether or not to use native PCIe services
2446                        associated with PCIe ports (PME, hot-plug, AER).  Use
2447                        them only if that is allowed by the BIOS.
2448                native  Use native PCIe services associated with PCIe ports
2449                        unconditionally.
2450                compat  Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2451                        ports driver.
2452
2453        pcie_pme=       [PCIE,PM] Native PCIe PME signaling options:
2454                nomsi   Do not use MSI for native PCIe PME signaling (this makes
2455                        all PCIe root ports use INTx for all services).
2456
2457        pcmv=           [HW,PCMCIA] BadgePAD 4
2458
2459        pd.             [PARIDE]
2460                        See Documentation/blockdev/paride.txt.
2461
2462        pdcchassis=     [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2463                        boot time.
2464                        Format: { 0 | 1 }
2465                        See arch/parisc/kernel/pdc_chassis.c
2466
2467        percpu_alloc=   Select which percpu first chunk allocator to use.
2468                        Currently supported values are "embed" and "page".
2469                        Archs may support subset or none of the selections.
2470                        See comments in mm/percpu.c for details on each
2471                        allocator.  This parameter is primarily for debugging
2472                        and performance comparison.
2473
2474        pf.             [PARIDE]
2475                        See Documentation/blockdev/paride.txt.
2476
2477        pg.             [PARIDE]
2478                        See Documentation/blockdev/paride.txt.
2479
2480        pirq=           [SMP,APIC] Manual mp-table setup
2481                        See Documentation/x86/i386/IO-APIC.txt.
2482
2483        plip=           [PPT,NET] Parallel port network link
2484                        Format: { parport<nr> | timid | 0 }
2485                        See also Documentation/parport.txt.
2486
2487        pmtmr=          [X86] Manual setup of pmtmr I/O Port.
2488                        Override pmtimer IOPort with a hex value.
2489                        e.g. pmtmr=0x508
2490
2491        pnp.debug=1     [PNP]
2492                        Enable PNP debug messages (depends on the
2493                        CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
2494                        via /sys/module/pnp/parameters/debug.  We always show
2495                        current resource usage; turning this on also shows
2496                        possible settings and some assignment information.
2497
2498        pnpacpi=        [ACPI]
2499                        { off }
2500
2501        pnpbios=        [ISAPNP]
2502                        { on | off | curr | res | no-curr | no-res }
2503
2504        pnp_reserve_irq=
2505                        [ISAPNP] Exclude IRQs for the autoconfiguration
2506
2507        pnp_reserve_dma=
2508                        [ISAPNP] Exclude DMAs for the autoconfiguration
2509
2510        pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2511                        Ranges are in pairs (I/O port base and size).
2512
2513        pnp_reserve_mem=
2514                        [ISAPNP] Exclude memory regions for the
2515                        autoconfiguration.
2516                        Ranges are in pairs (memory base and size).
2517
2518        ports=          [IP_VS_FTP] IPVS ftp helper module
2519                        Default is 21.
2520                        Up to 8 (IP_VS_APP_MAX_PORTS) ports
2521                        may be specified.
2522                        Format: <port>,<port>....
2523
2524        print-fatal-signals=
2525                        [KNL] debug: print fatal signals
2526
2527                        If enabled, warn about various signal handling
2528                        related application anomalies: too many signals,
2529                        too many POSIX.1 timers, fatal signals causing a
2530                        coredump - etc.
2531
2532                        If you hit the warning due to signal overflow,
2533                        you might want to try "ulimit -i unlimited".
2534
2535                        default: off.
2536
2537        printk.always_kmsg_dump=
2538                        Trigger kmsg_dump for cases other than kernel oops or
2539                        panics
2540                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2541                        default: disabled
2542
2543        printk.time=    Show timing data prefixed to each printk message line
2544                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2545
2546        processor.max_cstate=   [HW,ACPI]
2547                        Limit processor to maximum C-state
2548                        max_cstate=9 overrides any DMI blacklist limit.
2549
2550        processor.nocst [HW,ACPI]
2551                        Ignore the _CST method to determine C-states,
2552                        instead using the legacy FADT method
2553
2554        profile=        [KNL] Enable kernel profiling via /proc/profile
2555                        Format: [schedule,]<number>
2556                        Param: "schedule" - profile schedule points.
2557                        Param: <number> - step/bucket size as a power of 2 for
2558                                statistical time based profiling.
2559                        Param: "sleep" - profile D-state sleeping (millisecs).
2560                                Requires CONFIG_SCHEDSTATS
2561                        Param: "kvm" - profile VM exits.
2562
2563        prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2564                        before loading.
2565                        See Documentation/blockdev/ramdisk.txt.
2566
2567        psmouse.proto=  [HW,MOUSE] Highest PS2 mouse protocol extension to
2568                        probe for; one of (bare|imps|exps|lifebook|any).
2569        psmouse.rate=   [HW,MOUSE] Set desired mouse report rate, in reports
2570                        per second.
2571        psmouse.resetafter=     [HW,MOUSE]
2572                        Try to reset the device after so many bad packets
2573                        (0 = never).
2574        psmouse.resolution=
2575                        [HW,MOUSE] Set desired mouse resolution, in dpi.
2576        psmouse.smartscroll=
2577                        [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2578                        0 = disabled, 1 = enabled (default).
2579
2580        pstore.backend= Specify the name of the pstore backend to use
2581
2582        pt.             [PARIDE]
2583                        See Documentation/blockdev/paride.txt.
2584
2585        pty.legacy_count=
2586                        [KNL] Number of legacy pty's. Overwrites compiled-in
2587                        default number.
2588
2589        quiet           [KNL] Disable most log messages
2590
2591        r128=           [HW,DRM]
2592
2593        raid=           [HW,RAID]
2594                        See Documentation/md.txt.
2595
2596        ramdisk_blocksize=      [RAM]
2597                        See Documentation/blockdev/ramdisk.txt.
2598
2599        ramdisk_size=   [RAM] Sizes of RAM disks in kilobytes
2600                        See Documentation/blockdev/ramdisk.txt.
2601
2602        rcu_nocbs=      [KNL,BOOT]
2603                        In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2604                        the specified list of CPUs to be no-callback CPUs.
2605                        Invocation of these CPUs' RCU callbacks will
2606                        be offloaded to "rcuox/N" kthreads created for
2607                        that purpose, where "x" is "b" for RCU-bh, "p"
2608                        for RCU-preempt, and "s" for RCU-sched, and "N"
2609                        is the CPU number.  This reduces OS jitter on the
2610                        offloaded CPUs, which can be useful for HPC and
2611
2612                        real-time workloads.  It can also improve energy
2613                        efficiency for asymmetric multiprocessors.
2614
2615        rcu_nocb_poll   [KNL,BOOT]
2616                        Rather than requiring that offloaded CPUs
2617                        (specified by rcu_nocbs= above) explicitly
2618                        awaken the corresponding "rcuoN" kthreads,
2619                        make these kthreads poll for callbacks.
2620                        This improves the real-time response for the
2621                        offloaded CPUs by relieving them of the need to
2622                        wake up the corresponding kthread, but degrades
2623                        energy efficiency by requiring that the kthreads
2624                        periodically wake up to do the polling.
2625
2626        rcutree.blimit= [KNL,BOOT]
2627                        Set maximum number of finished RCU callbacks to process
2628                        in one batch.
2629
2630        rcutree.fanout_leaf=    [KNL,BOOT]
2631                        Increase the number of CPUs assigned to each
2632                        leaf rcu_node structure.  Useful for very large
2633                        systems.
2634
2635        rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2636                        Set delay from grace-period initialization to
2637                        first attempt to force quiescent states.
2638                        Units are jiffies, minimum value is zero,
2639                        and maximum value is HZ.
2640
2641        rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2642                        Set delay between subsequent attempts to force
2643                        quiescent states.  Units are jiffies, minimum
2644                        value is one, and maximum value is HZ.
2645
2646        rcutree.qhimark=        [KNL,BOOT]
2647                        Set threshold of queued
2648                        RCU callbacks over which batch limiting is disabled.
2649
2650        rcutree.qlowmark=       [KNL,BOOT]
2651                        Set threshold of queued RCU callbacks below which
2652                        batch limiting is re-enabled.
2653
2654        rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2655                        Suppress RCU CPU stall warning messages.
2656
2657        rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2658                        Set timeout for RCU CPU stall warning messages.
2659
2660        rcutree.rcu_idle_gp_delay=      [KNL,BOOT]
2661                        Set wakeup interval for idle CPUs that have
2662                        RCU callbacks (RCU_FAST_NO_HZ=y).
2663
2664        rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2665                        Set wakeup interval for idle CPUs that have
2666                        only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2667                        Lazy RCU callbacks are those which RCU can
2668                        prove do nothing more than free memory.
2669
2670        rcutorture.fqs_duration= [KNL,BOOT]
2671                        Set duration of force_quiescent_state bursts.
2672
2673        rcutorture.fqs_holdoff= [KNL,BOOT]
2674                        Set holdoff time within force_quiescent_state bursts.
2675
2676        rcutorture.fqs_stutter= [KNL,BOOT]
2677                        Set wait time between force_quiescent_state bursts.
2678
2679        rcutorture.irqreader= [KNL,BOOT]
2680                        Test RCU readers from irq handlers.
2681
2682        rcutorture.n_barrier_cbs= [KNL,BOOT]
2683                        Set callbacks/threads for rcu_barrier() testing.
2684
2685        rcutorture.nfakewriters= [KNL,BOOT]
2686                        Set number of concurrent RCU writers.  These just
2687                        stress RCU, they don't participate in the actual
2688                        test, hence the "fake".
2689
2690        rcutorture.nreaders= [KNL,BOOT]
2691                        Set number of RCU readers.
2692
2693        rcutorture.onoff_holdoff= [KNL,BOOT]
2694                        Set time (s) after boot for CPU-hotplug testing.
2695
2696        rcutorture.onoff_interval= [KNL,BOOT]
2697                        Set time (s) between CPU-hotplug operations, or
2698                        zero to disable CPU-hotplug testing.
2699
2700        rcutorture.shuffle_interval= [KNL,BOOT]
2701                        Set task-shuffle interval (s).  Shuffling tasks
2702                        allows some CPUs to go into dyntick-idle mode
2703                        during the rcutorture test.
2704
2705        rcutorture.shutdown_secs= [KNL,BOOT]
2706                        Set time (s) after boot system shutdown.  This
2707                        is useful for hands-off automated testing.
2708
2709        rcutorture.stall_cpu= [KNL,BOOT]
2710                        Duration of CPU stall (s) to test RCU CPU stall
2711                        warnings, zero to disable.
2712
2713        rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2714                        Time to wait (s) after boot before inducing stall.
2715
2716        rcutorture.stat_interval= [KNL,BOOT]
2717                        Time (s) between statistics printk()s.
2718
2719        rcutorture.stutter= [KNL,BOOT]
2720                        Time (s) to stutter testing, for example, specifying
2721                        five seconds causes the test to run for five seconds,
2722                        wait for five seconds, and so on.  This tests RCU's
2723                        ability to transition abruptly to and from idle.
2724
2725        rcutorture.test_boost= [KNL,BOOT]
2726                        Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
2727                        "Maybe" means test if the RCU implementation
2728                        under test support RCU priority boosting.
2729
2730        rcutorture.test_boost_duration= [KNL,BOOT]
2731                        Duration (s) of each individual boost test.
2732
2733        rcutorture.test_boost_interval= [KNL,BOOT]
2734                        Interval (s) between each boost test.
2735
2736        rcutorture.test_no_idle_hz= [KNL,BOOT]
2737                        Test RCU's dyntick-idle handling.  See also the
2738                        rcutorture.shuffle_interval parameter.
2739
2740        rcutorture.torture_type= [KNL,BOOT]
2741                        Specify the RCU implementation to test.
2742
2743        rcutorture.verbose= [KNL,BOOT]
2744                        Enable additional printk() statements.
2745
2746        rdinit=         [KNL]
2747                        Format: <full_path>
2748                        Run specified binary instead of /init from the ramdisk,
2749                        used for early userspace startup. See initrd.
2750
2751        reboot=         [KNL]
2752                        Format (x86 or x86_64):
2753                                [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2754                                [[,]s[mp]#### \
2755                                [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2756                                [[,]f[orce]
2757                        Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2758                              reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2759                              reboot_force is either force or not specified,
2760                              reboot_cpu is s[mp]#### with #### being the processor
2761                                        to be used for rebooting.
2762
2763        relax_domain_level=
2764                        [KNL, SMP] Set scheduler's default relax_domain_level.
2765                        See Documentation/cgroups/cpusets.txt.
2766
2767        reserve=        [KNL,BUGS] Force the kernel to ignore some iomem area
2768
2769        reservetop=     [X86-32]
2770                        Format: nn[KMG]
2771                        Reserves a hole at the top of the kernel virtual
2772                        address space.
2773
2774        reservelow=     [X86]
2775                        Format: nn[K]
2776                        Set the amount of memory to reserve for BIOS at
2777                        the bottom of the address space.
2778
2779        reset_devices   [KNL] Force drivers to reset the underlying device
2780                        during initialization.
2781
2782        resume=         [SWSUSP]
2783                        Specify the partition device for software suspend
2784                        Format:
2785                        {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2786
2787        resume_offset=  [SWSUSP]
2788                        Specify the offset from the beginning of the partition
2789                        given by "resume=" at which the swap header is located,
2790                        in <PAGE_SIZE> units (needed only for swap files).
2791                        See  Documentation/power/swsusp-and-swap-files.txt
2792
2793        resumedelay=    [HIBERNATION] Delay (in seconds) to pause before attempting to
2794                        read the resume files
2795
2796        resumewait      [HIBERNATION] Wait (indefinitely) for resume device to show up.
2797                        Useful for devices that are detected asynchronously
2798                        (e.g. USB and MMC devices).
2799
2800        hibernate=      [HIBERNATION]
2801                noresume        Don't check if there's a hibernation image
2802                                present during boot.
2803                nocompress      Don't compress/decompress hibernation images.
2804
2805        retain_initrd   [RAM] Keep initrd memory after extraction
2806
2807        rhash_entries=  [KNL,NET]
2808                        Set number of hash buckets for route cache
2809
2810        riscom8=        [HW,SERIAL]
2811                        Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2812
2813        ro              [KNL] Mount root device read-only on boot
2814
2815        root=           [KNL] Root filesystem
2816                        See name_to_dev_t comment in init/do_mounts.c.
2817
2818        rootdelay=      [KNL] Delay (in seconds) to pause before attempting to
2819                        mount the root filesystem
2820
2821        rootflags=      [KNL] Set root filesystem mount option string
2822
2823        rootfstype=     [KNL] Set root filesystem type
2824
2825        rootwait        [KNL] Wait (indefinitely) for root device to show up.
2826                        Useful for devices that are detected asynchronously
2827                        (e.g. USB and MMC devices).
2828
2829        rproc_mem=nn[KMG][@address]
2830                        [KNL,ARM,CMA] Remoteproc physical memory block.
2831                        Memory area to be used by remote processor image,
2832                        managed by CMA.
2833
2834        rw              [KNL] Mount root device read-write on boot
2835
2836        S               [KNL] Run init in single mode
2837
2838        sa1100ir        [NET]
2839                        See drivers/net/irda/sa1100_ir.c.
2840
2841        sbni=           [NET] Granch SBNI12 leased line adapter
2842
2843        sched_debug     [KNL] Enables verbose scheduler debug messages.
2844
2845        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
2846                        xtime_lock contention on larger systems, and/or RCU lock
2847                        contention on all systems with CONFIG_MAXSMP set.
2848                        Format: { "0" | "1" }
2849                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2850                        1 -- enable.
2851                        Note: increases power consumption, thus should only be
2852                        enabled if running jitter sensitive (HPC/RT) workloads.
2853
2854        security=       [SECURITY] Choose a security module to enable at boot.
2855                        If this boot parameter is not specified, only the first
2856                        security module asking for security registration will be
2857                        loaded. An invalid security module name will be treated
2858                        as if no module has been chosen.
2859
2860        selinux=        [SELINUX] Disable or enable SELinux at boot time.
2861                        Format: { "0" | "1" }
2862                        See security/selinux/Kconfig help text.
2863                        0 -- disable.
2864                        1 -- enable.
2865                        Default value is set via kernel config option.
2866                        If enabled at boot time, /selinux/disable can be used
2867                        later to disable prior to initial policy load.
2868
2869        apparmor=       [APPARMOR] Disable or enable AppArmor at boot time
2870                        Format: { "0" | "1" }
2871                        See security/apparmor/Kconfig help text
2872                        0 -- disable.
2873                        1 -- enable.
2874                        Default value is set via kernel config option.
2875
2876        serialnumber    [BUGS=X86-32]
2877
2878        shapers=        [NET]
2879                        Maximal number of shapers.
2880
2881        show_msr=       [x86] show boot-time MSR settings
2882                        Format: { <integer> }
2883                        Show boot-time (BIOS-initialized) MSR settings.
2884                        The parameter means the number of CPUs to show,
2885                        for example 1 means boot CPU only.
2886
2887        simeth=         [IA-64]
2888        simscsi=
2889
2890        slram=          [HW,MTD]
2891
2892        slab_max_order= [MM, SLAB]
2893                        Determines the maximum allowed order for slabs.
2894                        A high setting may cause OOMs due to memory
2895                        fragmentation.  Defaults to 1 for systems with
2896                        more than 32MB of RAM, 0 otherwise.
2897
2898        slub_debug[=options[,slabs]]    [MM, SLUB]
2899                        Enabling slub_debug allows one to determine the
2900                        culprit if slab objects become corrupted. Enabling
2901                        slub_debug can create guard zones around objects and
2902                        may poison objects when not in use. Also tracks the
2903                        last alloc / free. For more information see
2904                        Documentation/vm/slub.txt.
2905
2906        slub_max_order= [MM, SLUB]
2907                        Determines the maximum allowed order for slabs.
2908                        A high setting may cause OOMs due to memory
2909                        fragmentation. For more information see
2910                        Documentation/vm/slub.txt.
2911
2912        slub_min_objects=       [MM, SLUB]
2913                        The minimum number of objects per slab. SLUB will
2914                        increase the slab order up to slub_max_order to
2915                        generate a sufficiently large slab able to contain
2916                        the number of objects indicated. The higher the number
2917                        of objects the smaller the overhead of tracking slabs
2918                        and the less frequently locks need to be acquired.
2919                        For more information see Documentation/vm/slub.txt.
2920
2921        slub_min_order= [MM, SLUB]
2922                        Determines the minimum page order for slabs. Must be
2923                        lower than slub_max_order.
2924                        For more information see Documentation/vm/slub.txt.
2925
2926        slub_nomerge    [MM, SLUB]
2927                        Disable merging of slabs with similar size. May be
2928                        necessary if there is some reason to distinguish
2929                        allocs to different slabs. Debug options disable
2930                        merging on their own.
2931                        For more information see Documentation/vm/slub.txt.
2932
2933        smart2=         [HW]
2934                        Format: <io1>[,<io2>[,...,<io8>]]
2935
2936        smsc-ircc2.nopnp        [HW] Don't use PNP to discover SMC devices
2937        smsc-ircc2.ircc_cfg=    [HW] Device configuration I/O port
2938        smsc-ircc2.ircc_sir=    [HW] SIR base I/O port
2939        smsc-ircc2.ircc_fir=    [HW] FIR base I/O port
2940        smsc-ircc2.ircc_irq=    [HW] IRQ line
2941        smsc-ircc2.ircc_dma=    [HW] DMA channel
2942        smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2943                                0: Toshiba Satellite 1800 (GP data pin select)
2944                                1: Fast pin select (default)
2945                                2: ATC IRMode
2946
2947        softlockup_panic=
2948                        [KNL] Should the soft-lockup detector generate panics.
2949                        Format: <integer>
2950
2951        sonypi.*=       [HW] Sony Programmable I/O Control Device driver
2952                        See Documentation/laptops/sonypi.txt
2953
2954        specialix=      [HW,SERIAL] Specialix multi-serial port adapter
2955                        See Documentation/serial/specialix.txt.
2956
2957        spia_io_base=   [HW,MTD]
2958        spia_fio_base=
2959        spia_pedr=
2960        spia_peddr=
2961
2962        stacktrace      [FTRACE]
2963                        Enabled the stack tracer on boot up.
2964
2965        stacktrace_filter=[function-list]
2966                        [FTRACE] Limit the functions that the stack tracer
2967                        will trace at boot up. function-list is a comma separated
2968                        list of functions. This list can be changed at run
2969                        time by the stack_trace_filter file in the debugfs
2970                        tracing directory. Note, this enables stack tracing
2971                        and the stacktrace above is not needed.
2972
2973        sti=            [PARISC,HW]
2974                        Format: <num>
2975                        Set the STI (builtin display/keyboard on the HP-PARISC
2976                        machines) console (graphic card) which should be used
2977                        as the initial boot-console.
2978                        See also comment in drivers/video/console/sticore.c.
2979
2980        sti_font=       [HW]
2981                        See comment in drivers/video/console/sticore.c.
2982
2983        stifb=          [HW]
2984                        Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2985
2986        sunrpc.min_resvport=
2987        sunrpc.max_resvport=
2988                        [NFS,SUNRPC]
2989                        SunRPC servers often require that client requests
2990                        originate from a privileged port (i.e. a port in the
2991                        range 0 < portnr < 1024).
2992                        An administrator who wishes to reserve some of these
2993                        ports for other uses may adjust the range that the
2994                        kernel's sunrpc client considers to be privileged
2995                        using these two parameters to set the minimum and
2996                        maximum port values.
2997
2998        sunrpc.pool_mode=
2999                        [NFS]
3000                        Control how the NFS server code allocates CPUs to
3001                        service thread pools.  Depending on how many NICs
3002                        you have and where their interrupts are bound, this
3003                        option will affect which CPUs will do NFS serving.
3004                        Note: this parameter cannot be changed while the
3005                        NFS server is running.
3006
3007                        auto        the server chooses an appropriate mode
3008                                    automatically using heuristics
3009                        global      a single global pool contains all CPUs
3010                        percpu      one pool for each CPU
3011                        pernode     one pool for each NUMA node (equivalent
3012                                    to global on non-NUMA machines)
3013
3014        sunrpc.tcp_slot_table_entries=
3015        sunrpc.udp_slot_table_entries=
3016                        [NFS,SUNRPC]
3017                        Sets the upper limit on the number of simultaneous
3018                        RPC calls that can be sent from the client to a
3019                        server. Increasing these values may allow you to
3020                        improve throughput, but will also increase the
3021                        amount of memory reserved for use by the client.
3022
3023        swapaccount=[0|1]
3024                        [KNL] Enable accounting of swap in memory resource
3025                        controller if no parameter or 1 is given or disable
3026                        it if 0 is given (See Documentation/cgroups/memory.txt)
3027
3028        swiotlb=        [IA-64] Number of I/O TLB slabs
3029
3030        switches=       [HW,M68k]
3031
3032        sysfs.deprecated=0|1 [KNL]
3033                        Enable/disable old style sysfs layout for old udev
3034                        on older distributions. When this option is enabled
3035                        very new udev will not work anymore. When this option
3036                        is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3037                        in older udev will not work anymore.
3038                        Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3039                        the kernel configuration.
3040
3041        sysrq_always_enabled
3042                        [KNL]
3043                        Ignore sysrq setting - this boot parameter will
3044                        neutralize any effect of /proc/sys/kernel/sysrq.
3045                        Useful for debugging.
3046
3047        tdfx=           [HW,DRM]
3048
3049        test_suspend=   [SUSPEND]
3050                        Specify "mem" (for Suspend-to-RAM) or "standby" (for
3051                        standby suspend) as the system sleep state to briefly
3052                        enter during system startup.  The system is woken from
3053                        this state using a wakeup-capable RTC alarm.
3054
3055        thash_entries=  [KNL,NET]
3056                        Set number of hash buckets for TCP connection
3057
3058        thermal.act=    [HW,ACPI]
3059                        -1: disable all active trip points in all thermal zones
3060                        <degrees C>: override all lowest active trip points
3061
3062        thermal.crt=    [HW,ACPI]
3063                        -1: disable all critical trip points in all thermal zones
3064                        <degrees C>: override all critical trip points
3065
3066        thermal.nocrt=  [HW,ACPI]
3067                        Set to disable actions on ACPI thermal zone
3068                        critical and hot trip points.
3069
3070        thermal.off=    [HW,ACPI]
3071                        1: disable ACPI thermal control
3072
3073        thermal.psv=    [HW,ACPI]
3074                        -1: disable all passive trip points
3075                        <degrees C>: override all passive trip points to this
3076                        value
3077
3078        thermal.tzp=    [HW,ACPI]
3079                        Specify global default ACPI thermal zone polling rate
3080                        <deci-seconds>: poll all this frequency
3081                        0: no polling (default)
3082
3083        threadirqs      [KNL]
3084                        Force threading of all interrupt handlers except those
3085                        marked explicitly IRQF_NO_THREAD.
3086
3087        tmem            [KNL,XEN]
3088                        Enable the Transcendent memory driver if built-in.
3089
3090        tmem.cleancache=0|1 [KNL, XEN]
3091                        Default is on (1). Disable the usage of the cleancache
3092                        API to send anonymous pages to the hypervisor.
3093
3094        tmem.frontswap=0|1 [KNL, XEN]
3095                        Default is on (1). Disable the usage of the frontswap
3096                        API to send swap pages to the hypervisor. If disabled
3097                        the selfballooning and selfshrinking are force disabled.
3098
3099        tmem.selfballooning=0|1 [KNL, XEN]
3100                        Default is on (1). Disable the driving of swap pages
3101                        to the hypervisor.
3102
3103        tmem.selfshrinking=0|1 [KNL, XEN]
3104                        Default is on (1). Partial swapoff that immediately
3105                        transfers pages from Xen hypervisor back to the
3106                        kernel based on different criteria.
3107
3108        topology=       [S390]
3109                        Format: {off | on}
3110                        Specify if the kernel should make use of the cpu
3111                        topology information if the hardware supports this.
3112                        The scheduler will make use of this information and
3113                        e.g. base its process migration decisions on it.
3114                        Default is on.
3115
3116        tp720=          [HW,PS2]
3117
3118        tpm_suspend_pcr=[HW,TPM]
3119                        Format: integer pcr id
3120                        Specify that at suspend time, the tpm driver
3121                        should extend the specified pcr with zeros,
3122                        as a workaround for some chips which fail to
3123                        flush the last written pcr on TPM_SaveState.
3124                        This will guarantee that all the other pcrs
3125                        are saved.
3126
3127        trace_buf_size=nn[KMG]
3128                        [FTRACE] will set tracing buffer size.
3129
3130        trace_event=[event-list]
3131                        [FTRACE] Set and start specified trace events in order
3132                        to facilitate early boot debugging.
3133                        See also Documentation/trace/events.txt
3134
3135        trace_options=[option-list]
3136                        [FTRACE] Enable or disable tracer options at boot.
3137                        The option-list is a comma delimited list of options
3138                        that can be enabled or disabled just as if you were
3139                        to echo the option name into
3140
3141                            /sys/kernel/debug/tracing/trace_options
3142
3143                        For example, to enable stacktrace option (to dump the
3144                        stack trace of each event), add to the command line:
3145
3146                              trace_options=stacktrace
3147
3148                        See also Documentation/trace/ftrace.txt "trace options"
3149                        section.
3150
3151        traceoff_on_warning
3152                        [FTRACE] enable this option to disable tracing when a
3153                        warning is hit. This turns off "tracing_on". Tracing can
3154                        be enabled again by echoing '1' into the "tracing_on"
3155                        file located in /sys/kernel/debug/tracing/
3156
3157                        This option is useful, as it disables the trace before
3158                        the WARNING dump is called, which prevents the trace to
3159                        be filled with content caused by the warning output.
3160
3161                        This option can also be set at run time via the sysctl
3162                        option:  kernel/traceoff_on_warning
3163
3164        transparent_hugepage=
3165                        [KNL]
3166                        Format: [always|madvise|never]
3167                        Can be used to control the default behavior of the system
3168                        with respect to transparent hugepages.
3169                        See Documentation/vm/transhuge.txt for more details.
3170
3171        tsc=            Disable clocksource stability checks for TSC.
3172                        Format: <string>
3173                        [x86] reliable: mark tsc clocksource as reliable, this
3174                        disables clocksource verification at runtime, as well
3175                        as the stability checks done at bootup. Used to enable
3176                        high-resolution timer mode on older hardware, and in
3177                        virtualized environment.
3178                        [x86] noirqtime: Do not use TSC to do irq accounting.
3179                        Used to run time disable IRQ_TIME_ACCOUNTING on any
3180                        platforms where RDTSC is slow and this accounting
3181                        can add overhead.
3182
3183        turbografx.map[2|3]=    [HW,JOY]
3184                        TurboGraFX parallel port interface
3185                        Format:
3186                        <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3187                        See also Documentation/input/joystick-parport.txt
3188
3189        udbg-immortal   [PPC] When debugging early kernel crashes that
3190                        happen after console_init() and before a proper 
3191                        console driver takes over, this boot options might
3192                        help "seeing" what's going on.
3193
3194        uhash_entries=  [KNL,NET]
3195                        Set number of hash buckets for UDP/UDP-Lite connections
3196
3197        uhci-hcd.ignore_oc=
3198                        [USB] Ignore overcurrent events (default N).
3199                        Some badly-designed motherboards generate lots of
3200                        bogus events, for ports that aren't wired to
3201                        anything.  Set this parameter to avoid log spamming.
3202                        Note that genuine overcurrent events won't be
3203                        reported either.
3204
3205        unknown_nmi_panic
3206                        [X86] Cause panic on unknown NMI.
3207
3208        usbcore.authorized_default=
3209                        [USB] Default USB device authorization:
3210                        (default -1 = authorized except for wireless USB,
3211                        0 = not authorized, 1 = authorized)
3212
3213        usbcore.autosuspend=
3214                        [USB] The autosuspend time delay (in seconds) used
3215                        for newly-detected USB devices (default 2).  This
3216                        is the time required before an idle device will be
3217                        autosuspended.  Devices for which the delay is set
3218                        to a negative value won't be autosuspended at all.
3219
3220        usbcore.usbfs_snoop=
3221                        [USB] Set to log all usbfs traffic (default 0 = off).
3222
3223        usbcore.blinkenlights=
3224                        [USB] Set to cycle leds on hubs (default 0 = off).
3225
3226        usbcore.old_scheme_first=
3227                        [USB] Start with the old device initialization
3228                        scheme (default 0 = off).
3229
3230        usbcore.usbfs_memory_mb=
3231                        [USB] Memory limit (in MB) for buffers allocated by
3232                        usbfs (default = 16, 0 = max = 2047).
3233
3234        usbcore.use_both_schemes=
3235                        [USB] Try the other device initialization scheme
3236                        if the first one fails (default 1 = enabled).
3237
3238        usbcore.initial_descriptor_timeout=
3239                        [USB] Specifies timeout for the initial 64-byte
3240                        USB_REQ_GET_DESCRIPTOR request in milliseconds
3241                        (default 5000 = 5.0 seconds).
3242
3243        usbhid.mousepoll=
3244                        [USBHID] The interval which mice are to be polled at.
3245
3246        usb-storage.delay_use=
3247                        [UMS] The delay in seconds before a new device is
3248                        scanned for Logical Units (default 5).
3249
3250        usb-storage.quirks=
3251                        [UMS] A list of quirks entries to supplement or
3252                        override the built-in unusual_devs list.  List
3253                        entries are separated by commas.  Each entry has
3254                        the form VID:PID:Flags where VID and PID are Vendor
3255                        and Product ID values (4-digit hex numbers) and
3256                        Flags is a set of characters, each corresponding
3257                        to a common usb-storage quirk flag as follows:
3258                                a = SANE_SENSE (collect more than 18 bytes
3259                                        of sense data);
3260                                b = BAD_SENSE (don't collect more than 18
3261                                        bytes of sense data);
3262                                c = FIX_CAPACITY (decrease the reported
3263                                        device capacity by one sector);
3264                                d = NO_READ_DISC_INFO (don't use
3265                                        READ_DISC_INFO command);
3266                                e = NO_READ_CAPACITY_16 (don't use
3267                                        READ_CAPACITY_16 command);
3268                                h = CAPACITY_HEURISTICS (decrease the
3269                                        reported device capacity by one
3270                                        sector if the number is odd);
3271                                i = IGNORE_DEVICE (don't bind to this
3272                                        device);
3273                                l = NOT_LOCKABLE (don't try to lock and
3274                                        unlock ejectable media);
3275                                m = MAX_SECTORS_64 (don't transfer more
3276                                        than 64 sectors = 32 KB at a time);
3277                                n = INITIAL_READ10 (force a retry of the
3278                                        initial READ(10) command);
3279                                o = CAPACITY_OK (accept the capacity
3280                                        reported by the device);
3281                                p = WRITE_CACHE (the device cache is ON
3282                                        by default);
3283                                r = IGNORE_RESIDUE (the device reports
3284                                        bogus residue values);
3285                                s = SINGLE_LUN (the device has only one
3286                                        Logical Unit);
3287                                w = NO_WP_DETECT (don't test whether the
3288                                        medium is write-protected).
3289                        Example: quirks=0419:aaf5:rl,0421:0433:rc
3290
3291        user_debug=     [KNL,ARM]
3292                        Format: <int>
3293                        See arch/arm/Kconfig.debug help text.
3294                                 1 - undefined instruction events
3295                                 2 - system calls
3296                                 4 - invalid data aborts
3297                                 8 - SIGSEGV faults
3298                                16 - SIGBUS faults
3299                        Example: user_debug=31
3300
3301        userpte=
3302                        [X86] Flags controlling user PTE allocations.
3303
3304                                nohigh = do not allocate PTE pages in
3305                                        HIGHMEM regardless of setting
3306                                        of CONFIG_HIGHPTE.
3307
3308        vdso=           [X86,SH]
3309                        vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3310                        vdso=1: enable VDSO (default)
3311                        vdso=0: disable VDSO mapping
3312
3313        vdso32=         [X86]
3314                        vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3315                        vdso32=1: enable 32-bit VDSO (default)
3316                        vdso32=0: disable 32-bit VDSO mapping
3317
3318        vector=         [IA-64,SMP]
3319                        vector=percpu: enable percpu vector domain
3320
3321        video=          [FB] Frame buffer configuration
3322                        See Documentation/fb/modedb.txt.
3323
3324        video.brightness_switch_enabled= [0,1]
3325                        If set to 1, on receiving an ACPI notify event
3326                        generated by hotkey, video driver will adjust brightness
3327                        level and then send out the event to user space through
3328                        the allocated input device; If set to 0, video driver
3329                        will only send out the event without touching backlight
3330                        brightness level.
3331                        default: 1
3332
3333        virtio_mmio.device=
3334                        [VMMIO] Memory mapped virtio (platform) device.
3335
3336                                <size>@<baseaddr>:<irq>[:<id>]
3337                        where:
3338                                <size>     := size (can use standard suffixes
3339                                                like K, M and G)
3340                                <baseaddr> := physical base address
3341                                <irq>      := interrupt number (as passed to
3342                                                request_irq())
3343                                <id>       := (optional) platform device id
3344                        example:
3345                                virtio_mmio.device=1K@0x100b0000:48:7
3346
3347                        Can be used multiple times for multiple devices.
3348
3349        vga=            [BOOT,X86-32] Select a particular video mode
3350                        See Documentation/x86/boot.txt and
3351                        Documentation/svga.txt.
3352                        Use vga=ask for menu.
3353                        This is actually a boot loader parameter; the value is
3354                        passed to the kernel using a special protocol.
3355
3356        vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3357                        size of <nn>. This can be used to increase the
3358                        minimum size (128MB on x86). It can also be used to
3359                        decrease the size and leave more room for directly
3360                        mapped kernel RAM.
3361
3362        vmhalt=         [KNL,S390] Perform z/VM CP command after system halt.
3363                        Format: <command>
3364
3365        vmpanic=        [KNL,S390] Perform z/VM CP command after kernel panic.
3366                        Format: <command>
3367
3368        vmpoff=         [KNL,S390] Perform z/VM CP command after power off.
3369                        Format: <command>
3370
3371        vsyscall=       [X86-64]
3372                        Controls the behavior of vsyscalls (i.e. calls to
3373                        fixed addresses of 0xffffffffff600x00 from legacy
3374                        code).  Most statically-linked binaries and older
3375                        versions of glibc use these calls.  Because these
3376                        functions are at fixed addresses, they make nice
3377                        targets for exploits that can control RIP.
3378
3379                        emulate     [default] Vsyscalls turn into traps and are
3380                                    emulated reasonably safely.
3381
3382                        native      Vsyscalls are native syscall instructions.
3383                                    This is a little bit faster than trapping
3384                                    and makes a few dynamic recompilers work
3385                                    better than they would in emulation mode.
3386                                    It also makes exploits much easier to write.
3387
3388                        none        Vsyscalls don't work at all.  This makes
3389                                    them quite hard to use for exploits but
3390                                    might break your system.
3391
3392        vt.color=       [VT] Default text color.
3393                        Format: 0xYX, X = foreground, Y = background.
3394                        Default: 0x07 = light gray on black.
3395
3396        vt.cur_default= [VT] Default cursor shape.
3397                        Format: 0xCCBBAA, where AA, BB, and CC are the same as
3398                        the parameters of the <Esc>[?A;B;Cc escape sequence;
3399                        see VGA-softcursor.txt. Default: 2 = underline.
3400
3401        vt.default_blu= [VT]
3402                        Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3403                        Change the default blue palette of the console.
3404                        This is a 16-member array composed of values
3405                        ranging from 0-255.
3406
3407        vt.default_grn= [VT]
3408                        Format: <green0>,<green1>,<green2>,...,<green15>
3409                        Change the default green palette of the console.
3410                        This is a 16-member array composed of values
3411                        ranging from 0-255.
3412
3413        vt.default_red= [VT]
3414                        Format: <red0>,<red1>,<red2>,...,<red15>
3415                        Change the default red palette of the console.
3416                        This is a 16-member array composed of values
3417                        ranging from 0-255.
3418
3419        vt.default_utf8=
3420                        [VT]
3421                        Format=<0|1>
3422                        Set system-wide default UTF-8 mode for all tty's.
3423                        Default is 1, i.e. UTF-8 mode is enabled for all
3424                        newly opened terminals.
3425
3426        vt.global_cursor_default=
3427                        [VT]
3428                        Format=<-1|0|1>
3429                        Set system-wide default for whether a cursor
3430                        is shown on new VTs. Default is -1,
3431                        i.e. cursors will be created by default unless
3432                        overridden by individual drivers. 0 will hide
3433                        cursors, 1 will display them.
3434
3435        vt.italic=      [VT] Default color for italic text; 0-15.
3436                        Default: 2 = green.
3437
3438        vt.underline=   [VT] Default color for underlined text; 0-15.
3439                        Default: 3 = cyan.
3440
3441        watchdog timers [HW,WDT] For information on watchdog timers,
3442                        see Documentation/watchdog/watchdog-parameters.txt
3443                        or other driver-specific files in the
3444                        Documentation/watchdog/ directory.
3445
3446        workqueue.disable_numa
3447                        By default, all work items queued to unbound
3448                        workqueues are affine to the NUMA nodes they're
3449                        issued on, which results in better behavior in
3450                        general.  If NUMA affinity needs to be disabled for
3451                        whatever reason, this option can be used.  Note
3452                        that this also can be controlled per-workqueue for
3453                        workqueues visible under /sys/bus/workqueue/.
3454
3455        workqueue.power_efficient
3456                        Per-cpu workqueues are generally preferred because
3457                        they show better performance thanks to cache
3458                        locality; unfortunately, per-cpu workqueues tend to
3459                        be more power hungry than unbound workqueues.
3460
3461                        Enabling this makes the per-cpu workqueues which
3462                        were observed to contribute significantly to power
3463                        consumption unbound, leading to measurably lower
3464                        power usage at the cost of small performance
3465                        overhead.
3466
3467                        The default value of this parameter is determined by
3468                        the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3469
3470        x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
3471                        default x2apic cluster mode on platforms
3472                        supporting x2apic.
3473
3474        x86_mrst_timer= [X86-32,APBT]
3475                        Choose timer option for x86 Moorestown MID platform.
3476                        Two valid options are apbt timer only and lapic timer
3477                        plus one apbt timer for broadcast timer.
3478                        x86_mrst_timer=apbt_only | lapic_and_apbt
3479
3480        xen_emul_unplug=                [HW,X86,XEN]
3481                        Unplug Xen emulated devices
3482                        Format: [unplug0,][unplug1]
3483                        ide-disks -- unplug primary master IDE devices
3484                        aux-ide-disks -- unplug non-primary-master IDE devices
3485                        nics -- unplug network devices
3486                        all -- unplug all emulated devices (NICs and IDE disks)
3487                        unnecessary -- unplugging emulated devices is
3488                                unnecessary even if the host did not respond to
3489                                the unplug protocol
3490                        never -- do not unplug even if version check succeeds
3491
3492        xen_nopvspin    [X86,XEN]
3493                        Disables the ticketlock slowpath using Xen PV
3494                        optimizations.
3495
3496        xirc2ps_cs=     [NET,PCMCIA]
3497                        Format:
3498                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3499
3500______________________________________________________________________
3501
3502TODO:
3503
3504        Add more DRM drivers.
3505
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