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        DRM     Direct Rendering Management support is enabled.
  48        DYNAMIC_DEBUG Build in debug messages and enable them at runtime
  49        EDD     BIOS Enhanced Disk Drive Services (EDD) is enabled
  50        EFI     EFI Partitioning (GPT) is enabled
  51        EIDE    EIDE/ATAPI support is enabled.
  52        EVM     Extended Verification Module
  53        FB      The frame buffer device is enabled.
  54        FTRACE  Function tracing enabled.
  55        GCOV    GCOV profiling is enabled.
  56        HW      Appropriate hardware is enabled.
  57        IA-64   IA-64 architecture is enabled.
  58        IMA     Integrity measurement architecture is enabled.
  59        IOSCHED More than one I/O scheduler is enabled.
  60        IP_PNP  IP DHCP, BOOTP, or RARP is enabled.
  61        IPV6    IPv6 support is enabled.
  62        ISAPNP  ISA PnP code is enabled.
  63        ISDN    Appropriate ISDN support is enabled.
  64        JOY     Appropriate joystick support is enabled.
  65        KGDB    Kernel debugger support is enabled.
  66        KVM     Kernel Virtual Machine support is enabled.
  67        LIBATA  Libata driver is enabled
  68        LP      Printer support is enabled.
  69        LOOP    Loopback device support is enabled.
  70        M68k    M68k architecture is enabled.
  71                        These options have more detailed description inside of
  72                        Documentation/m68k/kernel-options.txt.
  73        MDA     MDA console support is enabled.
  74        MIPS    MIPS architecture is enabled.
  75        MOUSE   Appropriate mouse support is enabled.
  76        MSI     Message Signaled Interrupts (PCI).
  77        MTD     MTD (Memory Technology Device) support is enabled.
  78        NET     Appropriate network support is enabled.
  79        NUMA    NUMA support is enabled.
  80        NFS     Appropriate NFS support is enabled.
  81        OSS     OSS sound support is enabled.
  82        PV_OPS  A paravirtualized kernel is enabled.
  83        PARIDE  The ParIDE (parallel port IDE) subsystem is enabled.
  84        PARISC  The PA-RISC architecture is enabled.
  85        PCI     PCI bus support is enabled.
  86        PCIE    PCI Express support is enabled.
  87        PCMCIA  The PCMCIA subsystem is enabled.
  88        PNP     Plug & Play support is enabled.
  89        PPC     PowerPC architecture is enabled.
  90        PPT     Parallel port support is enabled.
  91        PS2     Appropriate PS/2 support is enabled.
  92        RAM     RAM disk support is enabled.
  93        S390    S390 architecture is enabled.
  94        SCSI    Appropriate SCSI support is enabled.
  95                        A lot of drivers have their options described inside
  96                        the Documentation/scsi/ sub-directory.
  97        SECURITY Different security models are enabled.
  98        SELINUX SELinux support is enabled.
  99        APPARMOR AppArmor support is enabled.
 100        SERIAL  Serial support is enabled.
 101        SH      SuperH architecture is enabled.
 102        SMP     The kernel is an SMP kernel.
 103        SPARC   Sparc architecture is enabled.
 104        SWSUSP  Software suspend (hibernation) is enabled.
 105        SUSPEND System suspend states are enabled.
 106        TPM     TPM drivers are enabled.
 107        TS      Appropriate touchscreen support is enabled.
 108        UMS     USB Mass Storage support is enabled.
 109        USB     USB support is enabled.
 110        USBHID  USB Human Interface Device support is enabled.
 111        V4L     Video For Linux support is enabled.
 112        VMMIO   Driver for memory mapped virtio devices is enabled.
 113        VGA     The VGA console has been enabled.
 114        VT      Virtual terminal support is enabled.
 115        WDT     Watchdog support is enabled.
 116        XT      IBM PC/XT MFM hard disk support is enabled.
 117        X86-32  X86-32, aka i386 architecture is enabled.
 118        X86-64  X86-64 architecture is enabled.
 119                        More X86-64 boot options can be found in
 120                        Documentation/x86/x86_64/boot-options.txt .
 121        X86     Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
 122        XEN     Xen support is enabled
 123
 124In addition, the following text indicates that the option:
 125
 126        BUGS=   Relates to possible processor bugs on the said processor.
 127        KNL     Is a kernel start-up parameter.
 128        BOOT    Is a boot loader parameter.
 129
 130Parameters denoted with BOOT are actually interpreted by the boot
 131loader, and have no meaning to the kernel directly.
 132Do not modify the syntax of boot loader parameters without extreme
 133need or coordination with <Documentation/x86/boot.txt>.
 134
 135There are also arch-specific kernel-parameters not documented here.
 136See for example <Documentation/x86/x86_64/boot-options.txt>.
 137
 138Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
 139a trailing = on the name of any parameter states that that parameter will
 140be entered as an environment variable, whereas its absence indicates that
 141it will appear as a kernel argument readable via /proc/cmdline by programs
 142running once the system is up.
 143
 144The number of kernel parameters is not limited, but the length of the
 145complete command line (parameters including spaces etc.) is limited to
 146a fixed number of characters. This limit depends on the architecture
 147and is between 256 and 4096 characters. It is defined in the file
 148./include/asm/setup.h as COMMAND_LINE_SIZE.
 149
 150Finally, the [KMG] suffix is commonly described after a number of kernel
 151parameter values. These 'K', 'M', and 'G' letters represent the _binary_
 152multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
 153bytes respectively. Such letter suffixes can also be entirely omitted.
 154
 155
 156        acpi=           [HW,ACPI,X86]
 157                        Advanced Configuration and Power Interface
 158                        Format: { force | off | strict | noirq | rsdt }
 159                        force -- enable ACPI if default was off
 160                        off -- disable ACPI if default was on
 161                        noirq -- do not use ACPI for IRQ routing
 162                        strict -- Be less tolerant of platforms that are not
 163                                strictly ACPI specification compliant.
 164                        rsdt -- prefer RSDT over (default) XSDT
 165                        copy_dsdt -- copy DSDT to memory
 166
 167                        See also Documentation/power/runtime_pm.txt, pci=noacpi
 168
 169        acpi_rsdp=      [ACPI,EFI,KEXEC]
 170                        Pass the RSDP address to the kernel, mostly used
 171                        on machines running EFI runtime service to boot the
 172                        second kernel for kdump.
 173
 174        acpi_apic_instance=     [ACPI, IOAPIC]
 175                        Format: <int>
 176                        2: use 2nd APIC table, if available
 177                        1,0: use 1st APIC table
 178                        default: 0
 179
 180        acpi_backlight= [HW,ACPI]
 181                        acpi_backlight=vendor
 182                        acpi_backlight=video
 183                        If set to vendor, prefer vendor specific driver
 184                        (e.g. thinkpad_acpi, sony_acpi, etc.) instead
 185                        of the ACPI video.ko driver.
 186
 187        acpi.debug_layer=       [HW,ACPI,ACPI_DEBUG]
 188        acpi.debug_level=       [HW,ACPI,ACPI_DEBUG]
 189                        Format: <int>
 190                        CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
 191                        debug output.  Bits in debug_layer correspond to a
 192                        _COMPONENT in an ACPI source file, e.g.,
 193                            #define _COMPONENT ACPI_PCI_COMPONENT
 194                        Bits in debug_level correspond to a level in
 195                        ACPI_DEBUG_PRINT statements, e.g.,
 196                            ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
 197                        The debug_level mask defaults to "info".  See
 198                        Documentation/acpi/debug.txt for more information about
 199                        debug layers and levels.
 200
 201                        Enable processor driver info messages:
 202                            acpi.debug_layer=0x20000000
 203                        Enable PCI/PCI interrupt routing info messages:
 204                            acpi.debug_layer=0x400000
 205                        Enable AML "Debug" output, i.e., stores to the Debug
 206                        object while interpreting AML:
 207                            acpi.debug_layer=0xffffffff acpi.debug_level=0x2
 208                        Enable all messages related to ACPI hardware:
 209                            acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
 210
 211                        Some values produce so much output that the system is
 212                        unusable.  The "log_buf_len" parameter may be useful
 213                        if you need to capture more output.
 214
 215        acpi_irq_balance [HW,ACPI]
 216                        ACPI will balance active IRQs
 217                        default in APIC mode
 218
 219        acpi_irq_nobalance [HW,ACPI]
 220                        ACPI will not move active IRQs (default)
 221                        default in PIC mode
 222
 223        acpi_irq_isa=   [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
 224                        Format: <irq>,<irq>...
 225
 226        acpi_irq_pci=   [HW,ACPI] If irq_balance, clear listed IRQs for
 227                        use by PCI
 228                        Format: <irq>,<irq>...
 229
 230        acpi_no_auto_ssdt       [HW,ACPI] Disable automatic loading of SSDT
 231
 232        acpi_os_name=   [HW,ACPI] Tell ACPI BIOS the name of the OS
 233                        Format: To spoof as Windows 98: ="Microsoft Windows"
 234
 235        acpi_osi=       [HW,ACPI] Modify list of supported OS interface strings
 236                        acpi_osi="string1"      # add string1 -- only one string
 237                        acpi_osi="!string2"     # remove built-in string2
 238                        acpi_osi=               # disable all strings
 239
 240        acpi_pm_good    [X86]
 241                        Override the pmtimer bug detection: force the kernel
 242                        to assume that this machine's pmtimer latches its value
 243                        and always returns good values.
 244
 245        acpi_sci=       [HW,ACPI] ACPI System Control Interrupt trigger mode
 246                        Format: { level | edge | high | low }
 247
 248        acpi_serialize  [HW,ACPI] force serialization of AML methods
 249
 250        acpi_skip_timer_override [HW,ACPI]
 251                        Recognize and ignore IRQ0/pin2 Interrupt Override.
 252                        For broken nForce2 BIOS resulting in XT-PIC timer.
 253
 254        acpi_sleep=     [HW,ACPI] Sleep options
 255                        Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
 256                                  old_ordering, nonvs, sci_force_enable }
 257                        See Documentation/power/video.txt for information on
 258                        s3_bios and s3_mode.
 259                        s3_beep is for debugging; it makes the PC's speaker beep
 260                        as soon as the kernel's real-mode entry point is called.
 261                        s4_nohwsig prevents ACPI hardware signature from being
 262                        used during resume from hibernation.
 263                        old_ordering causes the ACPI 1.0 ordering of the _PTS
 264                        control method, with respect to putting devices into
 265                        low power states, to be enforced (the ACPI 2.0 ordering
 266                        of _PTS is used by default).
 267                        nonvs prevents the kernel from saving/restoring the
 268                        ACPI NVS memory during suspend/hibernation and resume.
 269                        sci_force_enable causes the kernel to set SCI_EN directly
 270                        on resume from S1/S3 (which is against the ACPI spec,
 271                        but some broken systems don't work without it).
 272
 273        acpi_use_timer_override [HW,ACPI]
 274                        Use timer override. For some broken Nvidia NF5 boards
 275                        that require a timer override, but don't have HPET
 276
 277        acpi_enforce_resources= [ACPI]
 278                        { strict | lax | no }
 279                        Check for resource conflicts between native drivers
 280                        and ACPI OperationRegions (SystemIO and SystemMemory
 281                        only). IO ports and memory declared in ACPI might be
 282                        used by the ACPI subsystem in arbitrary AML code and
 283                        can interfere with legacy drivers.
 284                        strict (default): access to resources claimed by ACPI
 285                        is denied; legacy drivers trying to access reserved
 286                        resources will fail to bind to device using them.
 287                        lax: access to resources claimed by ACPI is allowed;
 288                        legacy drivers trying to access reserved resources
 289                        will bind successfully but a warning message is logged.
 290                        no: ACPI OperationRegions are not marked as reserved,
 291                        no further checks are performed.
 292
 293        add_efi_memmap  [EFI; X86] Include EFI memory map in
 294                        kernel's map of available physical RAM.
 295
 296        agp=            [AGP]
 297                        { off | try_unsupported }
 298                        off: disable AGP support
 299                        try_unsupported: try to drive unsupported chipsets
 300                                (may crash computer or cause data corruption)
 301
 302        ALSA            [HW,ALSA]
 303                        See Documentation/sound/alsa/alsa-parameters.txt
 304
 305        alignment=      [KNL,ARM]
 306                        Allow the default userspace alignment fault handler
 307                        behaviour to be specified.  Bit 0 enables warnings,
 308                        bit 1 enables fixups, and bit 2 sends a segfault.
 309
 310        align_va_addr=  [X86-64]
 311                        Align virtual addresses by clearing slice [14:12] when
 312                        allocating a VMA at process creation time. This option
 313                        gives you up to 3% performance improvement on AMD F15h
 314                        machines (where it is enabled by default) for a
 315                        CPU-intensive style benchmark, and it can vary highly in
 316                        a microbenchmark depending on workload and compiler.
 317
 318                        32: only for 32-bit processes
 319                        64: only for 64-bit processes
 320                        on: enable for both 32- and 64-bit processes
 321                        off: disable for both 32- and 64-bit processes
 322
 323        amd_iommu=      [HW,X86-64]
 324                        Pass parameters to the AMD IOMMU driver in the system.
 325                        Possible values are:
 326                        fullflush - enable flushing of IO/TLB entries when
 327                                    they are unmapped. Otherwise they are
 328                                    flushed before they will be reused, which
 329                                    is a lot of faster
 330                        off       - do not initialize any AMD IOMMU found in
 331                                    the system
 332                        force_isolation - Force device isolation for all
 333                                          devices. The IOMMU driver is not
 334                                          allowed anymore to lift isolation
 335                                          requirements as needed. This option
 336                                          does not override iommu=pt
 337
 338        amd_iommu_dump= [HW,X86-64]
 339                        Enable AMD IOMMU driver option to dump the ACPI table
 340                        for AMD IOMMU. With this option enabled, AMD IOMMU
 341                        driver will print ACPI tables for AMD IOMMU during
 342                        IOMMU initialization.
 343
 344        amijoy.map=     [HW,JOY] Amiga joystick support
 345                        Map of devices attached to JOY0DAT and JOY1DAT
 346                        Format: <a>,<b>
 347                        See also Documentation/input/joystick.txt
 348
 349        analog.map=     [HW,JOY] Analog joystick and gamepad support
 350                        Specifies type or capabilities of an analog joystick
 351                        connected to one of 16 gameports
 352                        Format: <type1>,<type2>,..<type16>
 353
 354        apc=            [HW,SPARC]
 355                        Power management functions (SPARCstation-4/5 + deriv.)
 356                        Format: noidle
 357                        Disable APC CPU standby support. SPARCstation-Fox does
 358                        not play well with APC CPU idle - disable it if you have
 359                        APC and your system crashes randomly.
 360
 361        apic=           [APIC,X86-32] Advanced Programmable Interrupt Controller
 362                        Change the output verbosity whilst booting
 363                        Format: { quiet (default) | verbose | debug }
 364                        Change the amount of debugging information output
 365                        when initialising the APIC and IO-APIC components.
 366
 367        autoconf=       [IPV6]
 368                        See Documentation/networking/ipv6.txt.
 369
 370        show_lapic=     [APIC,X86] Advanced Programmable Interrupt Controller
 371                        Limit apic dumping. The parameter defines the maximal
 372                        number of local apics being dumped. Also it is possible
 373                        to set it to "all" by meaning -- no limit here.
 374                        Format: { 1 (default) | 2 | ... | all }.
 375                        The parameter valid if only apic=debug or
 376                        apic=verbose is specified.
 377                        Example: apic=debug show_lapic=all
 378
 379        apm=            [APM] Advanced Power Management
 380                        See header of arch/x86/kernel/apm_32.c.
 381
 382        arcrimi=        [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
 383                        Format: <io>,<irq>,<nodeID>
 384
 385        ataflop=        [HW,M68k]
 386
 387        atarimouse=     [HW,MOUSE] Atari Mouse
 388
 389        atkbd.extra=    [HW] Enable extra LEDs and keys on IBM RapidAccess,
 390                        EzKey and similar keyboards
 391
 392        atkbd.reset=    [HW] Reset keyboard during initialization
 393
 394        atkbd.set=      [HW] Select keyboard code set
 395                        Format: <int> (2 = AT (default), 3 = PS/2)
 396
 397        atkbd.scroll=   [HW] Enable scroll wheel on MS Office and similar
 398                        keyboards
 399
 400        atkbd.softraw=  [HW] Choose between synthetic and real raw mode
 401                        Format: <bool> (0 = real, 1 = synthetic (default))
 402
 403        atkbd.softrepeat= [HW]
 404                        Use software keyboard repeat
 405
 406        baycom_epp=     [HW,AX25]
 407                        Format: <io>,<mode>
 408
 409        baycom_par=     [HW,AX25] BayCom Parallel Port AX.25 Modem
 410                        Format: <io>,<mode>
 411                        See header of drivers/net/hamradio/baycom_par.c.
 412
 413        baycom_ser_fdx= [HW,AX25]
 414                        BayCom Serial Port AX.25 Modem (Full Duplex Mode)
 415                        Format: <io>,<irq>,<mode>[,<baud>]
 416                        See header of drivers/net/hamradio/baycom_ser_fdx.c.
 417
 418        baycom_ser_hdx= [HW,AX25]
 419                        BayCom Serial Port AX.25 Modem (Half Duplex Mode)
 420                        Format: <io>,<irq>,<mode>
 421                        See header of drivers/net/hamradio/baycom_ser_hdx.c.
 422
 423        boot_delay=     Milliseconds to delay each printk during boot.
 424                        Values larger than 10 seconds (10000) are changed to
 425                        no delay (0).
 426                        Format: integer
 427
 428        bootmem_debug   [KNL] Enable bootmem allocator debug messages.
 429
 430        bttv.card=      [HW,V4L] bttv (bt848 + bt878 based grabber cards)
 431        bttv.radio=     Most important insmod options are available as
 432                        kernel args too.
 433        bttv.pll=       See Documentation/video4linux/bttv/Insmod-options
 434        bttv.tuner=
 435
 436        bulk_remove=off [PPC]  This parameter disables the use of the pSeries
 437                        firmware feature for flushing multiple hpte entries
 438                        at a time.
 439
 440        c101=           [NET] Moxa C101 synchronous serial card
 441
 442        cachesize=      [BUGS=X86-32] Override level 2 CPU cache size detection.
 443                        Sometimes CPU hardware bugs make them report the cache
 444                        size incorrectly. The kernel will attempt work arounds
 445                        to fix known problems, but for some CPUs it is not
 446                        possible to determine what the correct size should be.
 447                        This option provides an override for these situations.
 448
 449        capability.disable=
 450                        [SECURITY] Disable capabilities.  This would normally
 451                        be used only if an alternative security model is to be
 452                        configured.  Potentially dangerous and should only be
 453                        used if you are entirely sure of the consequences.
 454
 455        ccw_timeout_log [S390]
 456                        See Documentation/s390/CommonIO for details.
 457
 458        cgroup_disable= [KNL] Disable a particular controller
 459                        Format: {name of the controller(s) to disable}
 460                                {Currently supported controllers - "memory"}
 461
 462        checkreqprot    [SELINUX] Set initial checkreqprot flag value.
 463                        Format: { "0" | "1" }
 464                        See security/selinux/Kconfig help text.
 465                        0 -- check protection applied by kernel (includes
 466                                any implied execute protection).
 467                        1 -- check protection requested by application.
 468                        Default value is set via a kernel config option.
 469                        Value can be changed at runtime via
 470                                /selinux/checkreqprot.
 471
 472        cio_ignore=     [S390]
 473                        See Documentation/s390/CommonIO for details.
 474
 475        clock=          [BUGS=X86-32, HW] gettimeofday clocksource override.
 476                        [Deprecated]
 477                        Forces specified clocksource (if available) to be used
 478                        when calculating gettimeofday(). If specified
 479                        clocksource is not available, it defaults to PIT.
 480                        Format: { pit | tsc | cyclone | pmtmr }
 481
 482        clocksource=    Override the default clocksource
 483                        Format: <string>
 484                        Override the default clocksource and use the clocksource
 485                        with the name specified.
 486                        Some clocksource names to choose from, depending on
 487                        the platform:
 488                        [all] jiffies (this is the base, fallback clocksource)
 489                        [ACPI] acpi_pm
 490                        [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
 491                                pxa_timer,timer3,32k_counter,timer0_1
 492                        [AVR32] avr32
 493                        [X86-32] pit,hpet,tsc;
 494                                scx200_hrt on Geode; cyclone on IBM x440
 495                        [MIPS] MIPS
 496                        [PARISC] cr16
 497                        [S390] tod
 498                        [SH] SuperH
 499                        [SPARC64] tick
 500                        [X86-64] hpet,tsc
 501
 502        clearcpuid=BITNUM [X86]
 503                        Disable CPUID feature X for the kernel. See
 504                        arch/x86/include/asm/cpufeature.h for the valid bit
 505                        numbers. Note the Linux specific bits are not necessarily
 506                        stable over kernel options, but the vendor specific
 507                        ones should be.
 508                        Also note that user programs calling CPUID directly
 509                        or using the feature without checking anything
 510                        will still see it. This just prevents it from
 511                        being used by the kernel or shown in /proc/cpuinfo.
 512                        Also note the kernel might malfunction if you disable
 513                        some critical bits.
 514
 515        cma=nn[MG]      [ARM,KNL]
 516                        Sets the size of kernel global memory area for contiguous
 517                        memory allocations. For more information, see
 518                        include/linux/dma-contiguous.h
 519
 520        cmo_free_hint=  [PPC] Format: { yes | no }
 521                        Specify whether pages are marked as being inactive
 522                        when they are freed.  This is used in CMO environments
 523                        to determine OS memory pressure for page stealing by
 524                        a hypervisor.
 525                        Default: yes
 526
 527        coherent_pool=nn[KMG]   [ARM,KNL]
 528                        Sets the size of memory pool for coherent, atomic dma
 529                        allocations, by default set to 256K.
 530
 531        code_bytes      [X86] How many bytes of object code to print
 532                        in an oops report.
 533                        Range: 0 - 8192
 534                        Default: 64
 535
 536        com20020=       [HW,NET] ARCnet - COM20020 chipset
 537                        Format:
 538                        <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
 539
 540        com90io=        [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
 541                        Format: <io>[,<irq>]
 542
 543        com90xx=        [HW,NET]
 544                        ARCnet - COM90xx chipset (memory-mapped buffers)
 545                        Format: <io>[,<irq>[,<memstart>]]
 546
 547        condev=         [HW,S390] console device
 548        conmode=
 549
 550        console=        [KNL] Output console device and options.
 551
 552                tty<n>  Use the virtual console device <n>.
 553
 554                ttyS<n>[,options]
 555                ttyUSB0[,options]
 556                        Use the specified serial port.  The options are of
 557                        the form "bbbbpnf", where "bbbb" is the baud rate,
 558                        "p" is parity ("n", "o", or "e"), "n" is number of
 559                        bits, and "f" is flow control ("r" for RTS or
 560                        omit it).  Default is "9600n8".
 561
 562                        See Documentation/serial-console.txt for more
 563                        information.  See
 564                        Documentation/networking/netconsole.txt for an
 565                        alternative.
 566
 567                uart[8250],io,<addr>[,options]
 568                uart[8250],mmio,<addr>[,options]
 569                        Start an early, polled-mode console on the 8250/16550
 570                        UART at the specified I/O port or MMIO address,
 571                        switching to the matching ttyS device later.  The
 572                        options are the same as for ttyS, above.
 573
 574                If the device connected to the port is not a TTY but a braille
 575                device, prepend "brl," before the device type, for instance
 576                        console=brl,ttyS0
 577                For now, only VisioBraille is supported.
 578
 579        consoleblank=   [KNL] The console blank (screen saver) timeout in
 580                        seconds. Defaults to 10*60 = 10mins. A value of 0
 581                        disables the blank timer.
 582
 583        coredump_filter=
 584                        [KNL] Change the default value for
 585                        /proc/<pid>/coredump_filter.
 586                        See also Documentation/filesystems/proc.txt.
 587
 588        cpuidle.off=1   [CPU_IDLE]
 589                        disable the cpuidle sub-system
 590
 591        cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
 592                        Format:
 593                        <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
 594
 595        crashkernel=size[KMG][@offset[KMG]]
 596                        [KNL] Using kexec, Linux can switch to a 'crash kernel'
 597                        upon panic. This parameter reserves the physical
 598                        memory region [offset, offset + size] for that kernel
 599                        image. If '@offset' is omitted, then a suitable offset
 600                        is selected automatically. Check
 601                        Documentation/kdump/kdump.txt for further details.
 602
 603        crashkernel=range1:size1[,range2:size2,...][@offset]
 604                        [KNL] Same as above, but depends on the memory
 605                        in the running system. The syntax of range is
 606                        start-[end] where start and end are both
 607                        a memory unit (amount[KMG]). See also
 608                        Documentation/kdump/kdump.txt for an example.
 609
 610        cs89x0_dma=     [HW,NET]
 611                        Format: <dma>
 612
 613        cs89x0_media=   [HW,NET]
 614                        Format: { rj45 | aui | bnc }
 615
 616        dasd=           [HW,NET]
 617                        See header of drivers/s390/block/dasd_devmap.c.
 618
 619        db9.dev[2|3]=   [HW,JOY] Multisystem joystick support via parallel port
 620                        (one device per port)
 621                        Format: <port#>,<type>
 622                        See also Documentation/input/joystick-parport.txt
 623
 624        ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
 625                        time. See Documentation/dynamic-debug-howto.txt for
 626                        details.  Deprecated, see dyndbg.
 627
 628        debug           [KNL] Enable kernel debugging (events log level).
 629
 630        debug_locks_verbose=
 631                        [KNL] verbose self-tests
 632                        Format=<0|1>
 633                        Print debugging info while doing the locking API
 634                        self-tests.
 635                        We default to 0 (no extra messages), setting it to
 636                        1 will print _a lot_ more information - normally
 637                        only useful to kernel developers.
 638
 639        debug_objects   [KNL] Enable object debugging
 640
 641        no_debug_objects
 642                        [KNL] Disable object debugging
 643
 644        debug_guardpage_minorder=
 645                        [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
 646                        parameter allows control of the order of pages that will
 647                        be intentionally kept free (and hence protected) by the
 648                        buddy allocator. Bigger value increase the probability
 649                        of catching random memory corruption, but reduce the
 650                        amount of memory for normal system use. The maximum
 651                        possible value is MAX_ORDER/2.  Setting this parameter
 652                        to 1 or 2 should be enough to identify most random
 653                        memory corruption problems caused by bugs in kernel or
 654                        driver code when a CPU writes to (or reads from) a
 655                        random memory location. Note that there exists a class
 656                        of memory corruptions problems caused by buggy H/W or
 657                        F/W or by drivers badly programing DMA (basically when
 658                        memory is written at bus level and the CPU MMU is
 659                        bypassed) which are not detectable by
 660                        CONFIG_DEBUG_PAGEALLOC, hence this option will not help
 661                        tracking down these problems.
 662
 663        debugpat        [X86] Enable PAT debugging
 664
 665        decnet.addr=    [HW,NET]
 666                        Format: <area>[,<node>]
 667                        See also Documentation/networking/decnet.txt.
 668
 669        default_hugepagesz=
 670                        [same as hugepagesz=] The size of the default
 671                        HugeTLB page size. This is the size represented by
 672                        the legacy /proc/ hugepages APIs, used for SHM, and
 673                        default size when mounting hugetlbfs filesystems.
 674                        Defaults to the default architecture's huge page size
 675                        if not specified.
 676
 677        dhash_entries=  [KNL]
 678                        Set number of hash buckets for dentry cache.
 679
 680        digi=           [HW,SERIAL]
 681                        IO parameters + enable/disable command.
 682
 683        digiepca=       [HW,SERIAL]
 684                        See drivers/char/README.epca and
 685                        Documentation/serial/digiepca.txt.
 686
 687        disable=        [IPV6]
 688                        See Documentation/networking/ipv6.txt.
 689
 690        disable_ddw     [PPC/PSERIES]
 691                        Disable Dynamic DMA Window support. Use this if
 692                        to workaround buggy firmware.
 693
 694        disable_ipv6=   [IPV6]
 695                        See Documentation/networking/ipv6.txt.
 696
 697        disable_mtrr_cleanup [X86]
 698                        The kernel tries to adjust MTRR layout from continuous
 699                        to discrete, to make X server driver able to add WB
 700                        entry later. This parameter disables that.
 701
 702        disable_mtrr_trim [X86, Intel and AMD only]
 703                        By default the kernel will trim any uncacheable
 704                        memory out of your available memory pool based on
 705                        MTRR settings.  This parameter disables that behavior,
 706                        possibly causing your machine to run very slowly.
 707
 708        disable_timer_pin_1 [X86]
 709                        Disable PIN 1 of APIC timer
 710                        Can be useful to work around chipset bugs.
 711
 712        dma_debug=off   If the kernel is compiled with DMA_API_DEBUG support,
 713                        this option disables the debugging code at boot.
 714
 715        dma_debug_entries=<number>
 716                        This option allows to tune the number of preallocated
 717                        entries for DMA-API debugging code. One entry is
 718                        required per DMA-API allocation. Use this if the
 719                        DMA-API debugging code disables itself because the
 720                        architectural default is too low.
 721
 722        dma_debug_driver=<driver_name>
 723                        With this option the DMA-API debugging driver
 724                        filter feature can be enabled at boot time. Just
 725                        pass the driver to filter for as the parameter.
 726                        The filter can be disabled or changed to another
 727                        driver later using sysfs.
 728
 729        drm_kms_helper.edid_firmware=[<connector>:]<file>
 730                        Broken monitors, graphic adapters and KVMs may
 731                        send no or incorrect EDID data sets. This parameter
 732                        allows to specify an EDID data set in the
 733                        /lib/firmware directory that is used instead.
 734                        Generic built-in EDID data sets are used, if one of
 735                        edid/1024x768.bin, edid/1280x1024.bin,
 736                        edid/1680x1050.bin, or edid/1920x1080.bin is given
 737                        and no file with the same name exists. Details and
 738                        instructions how to build your own EDID data are
 739                        available in Documentation/EDID/HOWTO.txt. An EDID
 740                        data set will only be used for a particular connector,
 741                        if its name and a colon are prepended to the EDID
 742                        name.
 743
 744        dscc4.setup=    [NET]
 745
 746        dyndbg[="val"]          [KNL,DYNAMIC_DEBUG]
 747        module.dyndbg[="val"]
 748                        Enable debug messages at boot time.  See
 749                        Documentation/dynamic-debug-howto.txt for details.
 750
 751        earlycon=       [KNL] Output early console device and options.
 752                uart[8250],io,<addr>[,options]
 753                uart[8250],mmio,<addr>[,options]
 754                uart[8250],mmio32,<addr>[,options]
 755                        Start an early, polled-mode console on the 8250/16550
 756                        UART at the specified I/O port or MMIO address.
 757                        MMIO inter-register address stride is either 8-bit
 758                        (mmio) or 32-bit (mmio32).
 759                        The options are the same as for ttyS, above.
 760
 761        earlyprintk=    [X86,SH,BLACKFIN]
 762                        earlyprintk=vga
 763                        earlyprintk=serial[,ttySn[,baudrate]]
 764                        earlyprintk=ttySn[,baudrate]
 765                        earlyprintk=dbgp[debugController#]
 766
 767                        Append ",keep" to not disable it when the real console
 768                        takes over.
 769
 770                        Only vga or serial or usb debug port at a time.
 771
 772                        Currently only ttyS0 and ttyS1 are supported.
 773
 774                        Interaction with the standard serial driver is not
 775                        very good.
 776
 777                        The VGA output is eventually overwritten by the real
 778                        console.
 779
 780        ekgdboc=        [X86,KGDB] Allow early kernel console debugging
 781                        ekgdboc=kbd
 782
 783                        This is designed to be used in conjunction with
 784                        the boot argument: earlyprintk=vga
 785
 786        edd=            [EDD]
 787                        Format: {"off" | "on" | "skip[mbr]"}
 788
 789        eisa_irq_edge=  [PARISC,HW]
 790                        See header of drivers/parisc/eisa.c.
 791
 792        elanfreq=       [X86-32]
 793                        See comment before function elanfreq_setup() in
 794                        arch/x86/kernel/cpu/cpufreq/elanfreq.c.
 795
 796        elevator=       [IOSCHED]
 797                        Format: {"cfq" | "deadline" | "noop"}
 798                        See Documentation/block/cfq-iosched.txt and
 799                        Documentation/block/deadline-iosched.txt for details.
 800
 801        elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
 802                        Specifies physical address of start of kernel core
 803                        image elf header and optionally the size. Generally
 804                        kexec loader will pass this option to capture kernel.
 805                        See Documentation/kdump/kdump.txt for details.
 806
 807        enable_mtrr_cleanup [X86]
 808                        The kernel tries to adjust MTRR layout from continuous
 809                        to discrete, to make X server driver able to add WB
 810                        entry later. This parameter enables that.
 811
 812        enable_timer_pin_1 [X86]
 813                        Enable PIN 1 of APIC timer
 814                        Can be useful to work around chipset bugs
 815                        (in particular on some ATI chipsets).
 816                        The kernel tries to set a reasonable default.
 817
 818        enforcing       [SELINUX] Set initial enforcing status.
 819                        Format: {"0" | "1"}
 820                        See security/selinux/Kconfig help text.
 821                        0 -- permissive (log only, no denials).
 822                        1 -- enforcing (deny and log).
 823                        Default value is 0.
 824                        Value can be changed at runtime via /selinux/enforce.
 825
 826        erst_disable    [ACPI]
 827                        Disable Error Record Serialization Table (ERST)
 828                        support.
 829
 830        ether=          [HW,NET] Ethernet cards parameters
 831                        This option is obsoleted by the "netdev=" option, which
 832                        has equivalent usage. See its documentation for details.
 833
 834        evm=            [EVM]
 835                        Format: { "fix" }
 836                        Permit 'security.evm' to be updated regardless of
 837                        current integrity status.
 838
 839        failslab=
 840        fail_page_alloc=
 841        fail_make_request=[KNL]
 842                        General fault injection mechanism.
 843                        Format: <interval>,<probability>,<space>,<times>
 844                        See also Documentation/fault-injection/.
 845
 846        floppy=         [HW]
 847                        See Documentation/blockdev/floppy.txt.
 848
 849        force_pal_cache_flush
 850                        [IA-64] Avoid check_sal_cache_flush which may hang on
 851                        buggy SAL_CACHE_FLUSH implementations. Using this
 852                        parameter will force ia64_sal_cache_flush to call
 853                        ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
 854
 855        ftrace=[tracer]
 856                        [FTRACE] will set and start the specified tracer
 857                        as early as possible in order to facilitate early
 858                        boot debugging.
 859
 860        ftrace_dump_on_oops[=orig_cpu]
 861                        [FTRACE] will dump the trace buffers on oops.
 862                        If no parameter is passed, ftrace will dump
 863                        buffers of all CPUs, but if you pass orig_cpu, it will
 864                        dump only the buffer of the CPU that triggered the
 865                        oops.
 866
 867        ftrace_filter=[function-list]
 868                        [FTRACE] Limit the functions traced by the function
 869                        tracer at boot up. function-list is a comma separated
 870                        list of functions. This list can be changed at run
 871                        time by the set_ftrace_filter file in the debugfs
 872                        tracing directory.
 873
 874        ftrace_notrace=[function-list]
 875                        [FTRACE] Do not trace the functions specified in
 876                        function-list. This list can be changed at run time
 877                        by the set_ftrace_notrace file in the debugfs
 878                        tracing directory.
 879
 880        ftrace_graph_filter=[function-list]
 881                        [FTRACE] Limit the top level callers functions traced
 882                        by the function graph tracer at boot up.
 883                        function-list is a comma separated list of functions
 884                        that can be changed at run time by the
 885                        set_graph_function file in the debugfs tracing directory.
 886
 887        gamecon.map[2|3]=
 888                        [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
 889                        support via parallel port (up to 5 devices per port)
 890                        Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
 891                        See also Documentation/input/joystick-parport.txt
 892
 893        gamma=          [HW,DRM]
 894
 895        gart_fix_e820=  [X86_64] disable the fix e820 for K8 GART
 896                        Format: off | on
 897                        default: on
 898
 899        gcov_persist=   [GCOV] When non-zero (default), profiling data for
 900                        kernel modules is saved and remains accessible via
 901                        debugfs, even when the module is unloaded/reloaded.
 902                        When zero, profiling data is discarded and associated
 903                        debugfs files are removed at module unload time.
 904
 905        gpt             [EFI] Forces disk with valid GPT signature but
 906                        invalid Protective MBR to be treated as GPT.
 907
 908        hashdist=       [KNL,NUMA] Large hashes allocated during boot
 909                        are distributed across NUMA nodes.  Defaults on
 910                        for 64-bit NUMA, off otherwise.
 911                        Format: 0 | 1 (for off | on)
 912
 913        hcl=            [IA-64] SGI's Hardware Graph compatibility layer
 914
 915        hd=             [EIDE] (E)IDE hard drive subsystem geometry
 916                        Format: <cyl>,<head>,<sect>
 917
 918        hest_disable    [ACPI]
 919                        Disable Hardware Error Source Table (HEST) support;
 920                        corresponding firmware-first mode error processing
 921                        logic will be disabled.
 922
 923        highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
 924                        size of <nn>. This works even on boxes that have no
 925                        highmem otherwise. This also works to reduce highmem
 926                        size on bigger boxes.
 927
 928        highres=        [KNL] Enable/disable high resolution timer mode.
 929                        Valid parameters: "on", "off"
 930                        Default: "on"
 931
 932        hisax=          [HW,ISDN]
 933                        See Documentation/isdn/README.HiSax.
 934
 935        hlt             [BUGS=ARM,SH]
 936
 937        hpet=           [X86-32,HPET] option to control HPET usage
 938                        Format: { enable (default) | disable | force |
 939                                verbose }
 940                        disable: disable HPET and use PIT instead
 941                        force: allow force enabled of undocumented chips (ICH4,
 942                                VIA, nVidia)
 943                        verbose: show contents of HPET registers during setup
 944
 945        hugepages=      [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
 946        hugepagesz=     [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
 947                        On x86-64 and powerpc, this option can be specified
 948                        multiple times interleaved with hugepages= to reserve
 949                        huge pages of different sizes. Valid pages sizes on
 950                        x86-64 are 2M (when the CPU supports "pse") and 1G
 951                        (when the CPU supports the "pdpe1gb" cpuinfo flag)
 952                        Note that 1GB pages can only be allocated at boot time
 953                        using hugepages= and not freed afterwards.
 954
 955        hvc_iucv=       [S390] Number of z/VM IUCV hypervisor console (HVC)
 956                               terminal devices. Valid values: 0..8
 957        hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
 958                               If specified, z/VM IUCV HVC accepts connections
 959                               from listed z/VM user IDs only.
 960
 961        keep_bootcon    [KNL]
 962                        Do not unregister boot console at start. This is only
 963                        useful for debugging when something happens in the window
 964                        between unregistering the boot console and initializing
 965                        the real console.
 966
 967        i2c_bus=        [HW] Override the default board specific I2C bus speed
 968                             or register an additional I2C bus that is not
 969                             registered from board initialization code.
 970                             Format:
 971                             <bus_id>,<clkrate>
 972
 973        i8042.debug     [HW] Toggle i8042 debug mode
 974        i8042.direct    [HW] Put keyboard port into non-translated mode
 975        i8042.dumbkbd   [HW] Pretend that controller can only read data from
 976                             keyboard and cannot control its state
 977                             (Don't attempt to blink the leds)
 978        i8042.noaux     [HW] Don't check for auxiliary (== mouse) port
 979        i8042.nokbd     [HW] Don't check/create keyboard port
 980        i8042.noloop    [HW] Disable the AUX Loopback command while probing
 981                             for the AUX port
 982        i8042.nomux     [HW] Don't check presence of an active multiplexing
 983                             controller
 984        i8042.nopnp     [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
 985                             controllers
 986        i8042.notimeout [HW] Ignore timeout condition signalled by controller
 987        i8042.reset     [HW] Reset the controller during init and cleanup
 988        i8042.unlock    [HW] Unlock (ignore) the keylock
 989
 990        i810=           [HW,DRM]
 991
 992        i8k.ignore_dmi  [HW] Continue probing hardware even if DMI data
 993                        indicates that the driver is running on unsupported
 994                        hardware.
 995        i8k.force       [HW] Activate i8k driver even if SMM BIOS signature
 996                        does not match list of supported models.
 997        i8k.power_status
 998                        [HW] Report power status in /proc/i8k
 999                        (disabled by default)
1000        i8k.restricted  [HW] Allow controlling fans only if SYS_ADMIN
1001                        capability is set.
1002
1003        i915.invert_brightness=
1004                        [DRM] Invert the sense of the variable that is used to
1005                        set the brightness of the panel backlight. Normally a
1006                        brightness value of 0 indicates backlight switched off,
1007                        and the maximum of the brightness value sets the backlight
1008                        to maximum brightness. If this parameter is set to 0
1009                        (default) and the machine requires it, or this parameter
1010                        is set to 1, a brightness value of 0 sets the backlight
1011                        to maximum brightness, and the maximum of the brightness
1012                        value switches the backlight off.
1013                        -1 -- never invert brightness
1014                         0 -- machine default
1015                         1 -- force brightness inversion
1016
1017        icn=            [HW,ISDN]
1018                        Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1019
1020        ide-core.nodma= [HW] (E)IDE subsystem
1021                        Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1022                        .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1023                        .cdrom .chs .ignore_cable are additional options
1024                        See Documentation/ide/ide.txt.
1025
1026        ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1027                        Claim all unknown PCI IDE storage controllers.
1028
1029        idle=           [X86]
1030                        Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
1031                        Poll forces a polling idle loop that can slightly
1032                        improve the performance of waking up a idle CPU, but
1033                        will use a lot of power and make the system run hot.
1034                        Not recommended.
1035                        idle=mwait: On systems which support MONITOR/MWAIT but
1036                        the kernel chose to not use it because it doesn't save
1037                        as much power as a normal idle loop, use the
1038                        MONITOR/MWAIT idle loop anyways. Performance should be
1039                        the same as idle=poll.
1040                        idle=halt: Halt is forced to be used for CPU idle.
1041                        In such case C2/C3 won't be used again.
1042                        idle=nomwait: Disable mwait for CPU C-states
1043
1044        ignore_loglevel [KNL]
1045                        Ignore loglevel setting - this will print /all/
1046                        kernel messages to the console. Useful for debugging.
1047                        We also add it as printk module parameter, so users
1048                        could change it dynamically, usually by
1049                        /sys/module/printk/parameters/ignore_loglevel.
1050
1051        ihash_entries=  [KNL]
1052                        Set number of hash buckets for inode cache.
1053
1054        ima_appraise=   [IMA] appraise integrity measurements
1055                        Format: { "off" | "enforce" | "fix" }
1056                        default: "enforce"
1057
1058        ima_appraise_tcb [IMA]
1059                        The builtin appraise policy appraises all files
1060                        owned by uid=0.
1061
1062        ima_audit=      [IMA]
1063                        Format: { "0" | "1" }
1064                        0 -- integrity auditing messages. (Default)
1065                        1 -- enable informational integrity auditing messages.
1066
1067        ima_hash=       [IMA]
1068                        Format: { "sha1" | "md5" }
1069                        default: "sha1"
1070
1071        ima_tcb         [IMA]
1072                        Load a policy which meets the needs of the Trusted
1073                        Computing Base.  This means IMA will measure all
1074                        programs exec'd, files mmap'd for exec, and all files
1075                        opened for read by uid=0.
1076
1077        init=           [KNL]
1078                        Format: <full_path>
1079                        Run specified binary instead of /sbin/init as init
1080                        process.
1081
1082        initcall_debug  [KNL] Trace initcalls as they are executed.  Useful
1083                        for working out where the kernel is dying during
1084                        startup.
1085
1086        initrd=         [BOOT] Specify the location of the initial ramdisk
1087
1088        inport.irq=     [HW] Inport (ATI XL and Microsoft) busmouse driver
1089                        Format: <irq>
1090
1091        intel_iommu=    [DMAR] Intel IOMMU driver (DMAR) option
1092                on
1093                        Enable intel iommu driver.
1094                off
1095                        Disable intel iommu driver.
1096                igfx_off [Default Off]
1097                        By default, gfx is mapped as normal device. If a gfx
1098                        device has a dedicated DMAR unit, the DMAR unit is
1099                        bypassed by not enabling DMAR with this option. In
1100                        this case, gfx device will use physical address for
1101                        DMA.
1102                forcedac [x86_64]
1103                        With this option iommu will not optimize to look
1104                        for io virtual address below 32-bit forcing dual
1105                        address cycle on pci bus for cards supporting greater
1106                        than 32-bit addressing. The default is to look
1107                        for translation below 32-bit and if not available
1108                        then look in the higher range.
1109                strict [Default Off]
1110                        With this option on every unmap_single operation will
1111                        result in a hardware IOTLB flush operation as opposed
1112                        to batching them for performance.
1113                sp_off [Default Off]
1114                        By default, super page will be supported if Intel IOMMU
1115                        has the capability. With this option, super page will
1116                        not be supported.
1117
1118        intel_idle.max_cstate=  [KNL,HW,ACPI,X86]
1119                        0       disables intel_idle and fall back on acpi_idle.
1120                        1 to 6  specify maximum depth of C-state.
1121
1122        intremap=       [X86-64, Intel-IOMMU]
1123                        on      enable Interrupt Remapping (default)
1124                        off     disable Interrupt Remapping
1125                        nosid   disable Source ID checking
1126                        no_x2apic_optout
1127                                BIOS x2APIC opt-out request will be ignored
1128
1129        iomem=          Disable strict checking of access to MMIO memory
1130                strict  regions from userspace.
1131                relaxed
1132
1133        iommu=          [x86]
1134                off
1135                force
1136                noforce
1137                biomerge
1138                panic
1139                nopanic
1140                merge
1141                nomerge
1142                forcesac
1143                soft
1144                pt              [x86, IA-64]
1145
1146
1147        io7=            [HW] IO7 for Marvel based alpha systems
1148                        See comment before marvel_specify_io7 in
1149                        arch/alpha/kernel/core_marvel.c.
1150
1151        io_delay=       [X86] I/O delay method
1152                0x80
1153                        Standard port 0x80 based delay
1154                0xed
1155                        Alternate port 0xed based delay (needed on some systems)
1156                udelay
1157                        Simple two microseconds delay
1158                none
1159                        No delay
1160
1161        ip=             [IP_PNP]
1162                        See Documentation/filesystems/nfs/nfsroot.txt.
1163
1164        ip2=            [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1165                        See comment before ip2_setup() in
1166                        drivers/char/ip2/ip2base.c.
1167
1168        irqfixup        [HW]
1169                        When an interrupt is not handled search all handlers
1170                        for it. Intended to get systems with badly broken
1171                        firmware running.
1172
1173        irqpoll         [HW]
1174                        When an interrupt is not handled search all handlers
1175                        for it. Also check all handlers each timer
1176                        interrupt. Intended to get systems with badly broken
1177                        firmware running.
1178
1179        isapnp=         [ISAPNP]
1180                        Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1181
1182        isolcpus=       [KNL,SMP] Isolate CPUs from the general scheduler.
1183                        Format:
1184                        <cpu number>,...,<cpu number>
1185                        or
1186                        <cpu number>-<cpu number>
1187                        (must be a positive range in ascending order)
1188                        or a mixture
1189                        <cpu number>,...,<cpu number>-<cpu number>
1190
1191                        This option can be used to specify one or more CPUs
1192                        to isolate from the general SMP balancing and scheduling
1193                        algorithms. You can move a process onto or off an
1194                        "isolated" CPU via the CPU affinity syscalls or cpuset.
1195                        <cpu number> begins at 0 and the maximum value is
1196                        "number of CPUs in system - 1".
1197
1198                        This option is the preferred way to isolate CPUs. The
1199                        alternative -- manually setting the CPU mask of all
1200                        tasks in the system -- can cause problems and
1201                        suboptimal load balancer performance.
1202
1203        iucv=           [HW,NET]
1204
1205        js=             [HW,JOY] Analog joystick
1206                        See Documentation/input/joystick.txt.
1207
1208        keepinitrd      [HW,ARM]
1209
1210        kernelcore=nn[KMG]      [KNL,X86,IA-64,PPC] This parameter
1211                        specifies the amount of memory usable by the kernel
1212                        for non-movable allocations.  The requested amount is
1213                        spread evenly throughout all nodes in the system. The
1214                        remaining memory in each node is used for Movable
1215                        pages. In the event, a node is too small to have both
1216                        kernelcore and Movable pages, kernelcore pages will
1217                        take priority and other nodes will have a larger number
1218                        of kernelcore pages.  The Movable zone is used for the
1219                        allocation of pages that may be reclaimed or moved
1220                        by the page migration subsystem.  This means that
1221                        HugeTLB pages may not be allocated from this zone.
1222                        Note that allocations like PTEs-from-HighMem still
1223                        use the HighMem zone if it exists, and the Normal
1224                        zone if it does not.
1225
1226        kgdbdbgp=       [KGDB,HW] kgdb over EHCI usb debug port.
1227                        Format: <Controller#>[,poll interval]
1228                        The controller # is the number of the ehci usb debug
1229                        port as it is probed via PCI.  The poll interval is
1230                        optional and is the number seconds in between
1231                        each poll cycle to the debug port in case you need
1232                        the functionality for interrupting the kernel with
1233                        gdb or control-c on the dbgp connection.  When
1234                        not using this parameter you use sysrq-g to break into
1235                        the kernel debugger.
1236
1237        kgdboc=         [KGDB,HW] kgdb over consoles.
1238                        Requires a tty driver that supports console polling,
1239                        or a supported polling keyboard driver (non-usb).
1240                         Serial only format: <serial_device>[,baud]
1241                         keyboard only format: kbd
1242                         keyboard and serial format: kbd,<serial_device>[,baud]
1243                        Optional Kernel mode setting:
1244                         kms, kbd format: kms,kbd
1245                         kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1246
1247        kgdbwait        [KGDB] Stop kernel execution and enter the
1248                        kernel debugger at the earliest opportunity.
1249
1250        kmac=           [MIPS] korina ethernet MAC address.
1251                        Configure the RouterBoard 532 series on-chip
1252                        Ethernet adapter MAC address.
1253
1254        kmemleak=       [KNL] Boot-time kmemleak enable/disable
1255                        Valid arguments: on, off
1256                        Default: on
1257
1258        kstack=N        [X86] Print N words from the kernel stack
1259                        in oops dumps.
1260
1261        kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1262                        Default is 0 (don't ignore, but inject #GP)
1263
1264        kvm.mmu_audit=  [KVM] This is a R/W parameter which allows audit
1265                        KVM MMU at runtime.
1266                        Default is 0 (off)
1267
1268        kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1269                        Default is 1 (enabled)
1270
1271        kvm-amd.npt=    [KVM,AMD] Disable nested paging (virtualized MMU)
1272                        for all guests.
1273                        Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1274
1275        kvm-intel.ept=  [KVM,Intel] Disable extended page tables
1276                        (virtualized MMU) support on capable Intel chips.
1277                        Default is 1 (enabled)
1278
1279        kvm-intel.emulate_invalid_guest_state=
1280                        [KVM,Intel] Enable emulation of invalid guest states
1281                        Default is 0 (disabled)
1282
1283        kvm-intel.flexpriority=
1284                        [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1285                        Default is 1 (enabled)
1286
1287        kvm-intel.nested=
1288                        [KVM,Intel] Enable VMX nesting (nVMX).
1289                        Default is 0 (disabled)
1290
1291        kvm-intel.unrestricted_guest=
1292                        [KVM,Intel] Disable unrestricted guest feature
1293                        (virtualized real and unpaged mode) on capable
1294                        Intel chips. Default is 1 (enabled)
1295
1296        kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1297                        feature (tagged TLBs) on capable Intel chips.
1298                        Default is 1 (enabled)
1299
1300        l2cr=           [PPC]
1301
1302        l3cr=           [PPC]
1303
1304        lapic           [X86-32,APIC] Enable the local APIC even if BIOS
1305                        disabled it.
1306
1307        lapic_timer_c2_ok       [X86,APIC] trust the local apic timer
1308                        in C2 power state.
1309
1310        libata.dma=     [LIBATA] DMA control
1311                        libata.dma=0      Disable all PATA and SATA DMA
1312                        libata.dma=1      PATA and SATA Disk DMA only
1313                        libata.dma=2      ATAPI (CDROM) DMA only
1314                        libata.dma=4      Compact Flash DMA only
1315                        Combinations also work, so libata.dma=3 enables DMA
1316                        for disks and CDROMs, but not CFs.
1317
1318        libata.ignore_hpa=      [LIBATA] Ignore HPA limit
1319                        libata.ignore_hpa=0       keep BIOS limits (default)
1320                        libata.ignore_hpa=1       ignore limits, using full disk
1321
1322        libata.noacpi   [LIBATA] Disables use of ACPI in libata suspend/resume
1323                        when set.
1324                        Format: <int>
1325
1326        libata.force=   [LIBATA] Force configurations.  The format is comma
1327                        separated list of "[ID:]VAL" where ID is
1328                        PORT[.DEVICE].  PORT and DEVICE are decimal numbers
1329                        matching port, link or device.  Basically, it matches
1330                        the ATA ID string printed on console by libata.  If
1331                        the whole ID part is omitted, the last PORT and DEVICE
1332                        values are used.  If ID hasn't been specified yet, the
1333                        configuration applies to all ports, links and devices.
1334
1335                        If only DEVICE is omitted, the parameter applies to
1336                        the port and all links and devices behind it.  DEVICE
1337                        number of 0 either selects the first device or the
1338                        first fan-out link behind PMP device.  It does not
1339                        select the host link.  DEVICE number of 15 selects the
1340                        host link and device attached to it.
1341
1342                        The VAL specifies the configuration to force.  As long
1343                        as there's no ambiguity shortcut notation is allowed.
1344                        For example, both 1.5 and 1.5G would work for 1.5Gbps.
1345                        The following configurations can be forced.
1346
1347                        * Cable type: 40c, 80c, short40c, unk, ign or sata.
1348                          Any ID with matching PORT is used.
1349
1350                        * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1351
1352                        * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1353                          udma[/][16,25,33,44,66,100,133] notation is also
1354                          allowed.
1355
1356                        * [no]ncq: Turn on or off NCQ.
1357
1358                        * nohrst, nosrst, norst: suppress hard, soft
1359                          and both resets.
1360
1361                        * rstonce: only attempt one reset during
1362                          hot-unplug link recovery
1363
1364                        * dump_id: dump IDENTIFY data.
1365
1366                        If there are multiple matching configurations changing
1367                        the same attribute, the last one is used.
1368
1369        memblock=debug  [KNL] Enable memblock debug messages.
1370
1371        load_ramdisk=   [RAM] List of ramdisks to load from floppy
1372                        See Documentation/blockdev/ramdisk.txt.
1373
1374        lockd.nlm_grace_period=P  [NFS] Assign grace period.
1375                        Format: <integer>
1376
1377        lockd.nlm_tcpport=N     [NFS] Assign TCP port.
1378                        Format: <integer>
1379
1380        lockd.nlm_timeout=T     [NFS] Assign timeout value.
1381                        Format: <integer>
1382
1383        lockd.nlm_udpport=M     [NFS] Assign UDP port.
1384                        Format: <integer>
1385
1386        logibm.irq=     [HW,MOUSE] Logitech Bus Mouse Driver
1387                        Format: <irq>
1388
1389        loglevel=       All Kernel Messages with a loglevel smaller than the
1390                        console loglevel will be printed to the console. It can
1391                        also be changed with klogd or other programs. The
1392                        loglevels are defined as follows:
1393
1394                        0 (KERN_EMERG)          system is unusable
1395                        1 (KERN_ALERT)          action must be taken immediately
1396                        2 (KERN_CRIT)           critical conditions
1397                        3 (KERN_ERR)            error conditions
1398                        4 (KERN_WARNING)        warning conditions
1399                        5 (KERN_NOTICE)         normal but significant condition
1400                        6 (KERN_INFO)           informational
1401                        7 (KERN_DEBUG)          debug-level messages
1402
1403        log_buf_len=n[KMG]      Sets the size of the printk ring buffer,
1404                        in bytes.  n must be a power of two.  The default
1405                        size is set in the kernel config file.
1406
1407        logo.nologo     [FB] Disables display of the built-in Linux logo.
1408                        This may be used to provide more screen space for
1409                        kernel log messages and is useful when debugging
1410                        kernel boot problems.
1411
1412        lp=0            [LP]    Specify parallel ports to use, e.g,
1413        lp=port[,port...]       lp=none,parport0 (lp0 not configured, lp1 uses
1414        lp=reset                first parallel port). 'lp=0' disables the
1415        lp=auto                 printer driver. 'lp=reset' (which can be
1416                                specified in addition to the ports) causes
1417                                attached printers to be reset. Using
1418                                lp=port1,port2,... specifies the parallel ports
1419                                to associate lp devices with, starting with
1420                                lp0. A port specification may be 'none' to skip
1421                                that lp device, or a parport name such as
1422                                'parport0'. Specifying 'lp=auto' instead of a
1423                                port specification list means that device IDs
1424                                from each port should be examined, to see if
1425                                an IEEE 1284-compliant printer is attached; if
1426                                so, the driver will manage that printer.
1427                                See also header of drivers/char/lp.c.
1428
1429        lpj=n           [KNL]
1430                        Sets loops_per_jiffy to given constant, thus avoiding
1431                        time-consuming boot-time autodetection (up to 250 ms per
1432                        CPU). 0 enables autodetection (default). To determine
1433                        the correct value for your kernel, boot with normal
1434                        autodetection and see what value is printed. Note that
1435                        on SMP systems the preset will be applied to all CPUs,
1436                        which is likely to cause problems if your CPUs need
1437                        significantly divergent settings. An incorrect value
1438                        will cause delays in the kernel to be wrong, leading to
1439                        unpredictable I/O errors and other breakage. Although
1440                        unlikely, in the extreme case this might damage your
1441                        hardware.
1442
1443        ltpc=           [NET]
1444                        Format: <io>,<irq>,<dma>
1445
1446        machvec=        [IA-64] Force the use of a particular machine-vector
1447                        (machvec) in a generic kernel.
1448                        Example: machvec=hpzx1_swiotlb
1449
1450        machtype=       [Loongson] Share the same kernel image file between different
1451                         yeeloong laptop.
1452                        Example: machtype=lemote-yeeloong-2f-7inch
1453
1454        max_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory greater
1455                        than or equal to this physical address is ignored.
1456
1457        maxcpus=        [SMP] Maximum number of processors that an SMP kernel
1458                        should make use of.  maxcpus=n : n >= 0 limits the
1459                        kernel to using 'n' processors.  n=0 is a special case,
1460                        it is equivalent to "nosmp", which also disables
1461                        the IO APIC.
1462
1463        max_loop=       [LOOP] The number of loop block devices that get
1464        (loop.max_loop) unconditionally pre-created at init time. The default
1465                        number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1466                        of statically allocating a predefined number, loop
1467                        devices can be requested on-demand with the
1468                        /dev/loop-control interface.
1469
1470        mce             [X86-32] Machine Check Exception
1471
1472        mce=option      [X86-64] See Documentation/x86/x86_64/boot-options.txt
1473
1474        md=             [HW] RAID subsystems devices and level
1475                        See Documentation/md.txt.
1476
1477        mdacon=         [MDA]
1478                        Format: <first>,<last>
1479                        Specifies range of consoles to be captured by the MDA.
1480
1481        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
1482                        Amount of memory to be used when the kernel is not able
1483                        to see the whole system memory or for test.
1484                        [X86-32] Use together with memmap= to avoid physical
1485                        address space collisions. Without memmap= PCI devices
1486                        could be placed at addresses belonging to unused RAM.
1487
1488        mem=nopentium   [BUGS=X86-32] Disable usage of 4MB pages for kernel
1489                        memory.
1490
1491        memchunk=nn[KMG]
1492                        [KNL,SH] Allow user to override the default size for
1493                        per-device physically contiguous DMA buffers.
1494
1495        memmap=exactmap [KNL,X86] Enable setting of an exact
1496                        E820 memory map, as specified by the user.
1497                        Such memmap=exactmap lines can be constructed based on
1498                        BIOS output or other requirements. See the memmap=nn@ss
1499                        option description.
1500
1501        memmap=nn[KMG]@ss[KMG]
1502                        [KNL] Force usage of a specific region of memory
1503                        Region of memory to be used, from ss to ss+nn.
1504
1505        memmap=nn[KMG]#ss[KMG]
1506                        [KNL,ACPI] Mark specific memory as ACPI data.
1507                        Region of memory to be used, from ss to ss+nn.
1508
1509        memmap=nn[KMG]$ss[KMG]
1510                        [KNL,ACPI] Mark specific memory as reserved.
1511                        Region of memory to be used, from ss to ss+nn.
1512                        Example: Exclude memory from 0x18690000-0x1869ffff
1513                                 memmap=64K$0x18690000
1514                                 or
1515                                 memmap=0x10000$0x18690000
1516
1517        memory_corruption_check=0/1 [X86]
1518                        Some BIOSes seem to corrupt the first 64k of
1519                        memory when doing things like suspend/resume.
1520                        Setting this option will scan the memory
1521                        looking for corruption.  Enabling this will
1522                        both detect corruption and prevent the kernel
1523                        from using the memory being corrupted.
1524                        However, its intended as a diagnostic tool; if
1525                        repeatable BIOS-originated corruption always
1526                        affects the same memory, you can use memmap=
1527                        to prevent the kernel from using that memory.
1528
1529        memory_corruption_check_size=size [X86]
1530                        By default it checks for corruption in the low
1531                        64k, making this memory unavailable for normal
1532                        use.  Use this parameter to scan for
1533                        corruption in more or less memory.
1534
1535        memory_corruption_check_period=seconds [X86]
1536                        By default it checks for corruption every 60
1537                        seconds.  Use this parameter to check at some
1538                        other rate.  0 disables periodic checking.
1539
1540        memtest=        [KNL,X86] Enable memtest
1541                        Format: <integer>
1542                        default : 0 <disable>
1543                        Specifies the number of memtest passes to be
1544                        performed. Each pass selects another test
1545                        pattern from a given set of patterns. Memtest
1546                        fills the memory with this pattern, validates
1547                        memory contents and reserves bad memory
1548                        regions that are detected.
1549
1550        meye.*=         [HW] Set MotionEye Camera parameters
1551                        See Documentation/video4linux/meye.txt.
1552
1553        mfgpt_irq=      [IA-32] Specify the IRQ to use for the
1554                        Multi-Function General Purpose Timers on AMD Geode
1555                        platforms.
1556
1557        mfgptfix        [X86-32] Fix MFGPT timers on AMD Geode platforms when
1558                        the BIOS has incorrectly applied a workaround. TinyBIOS
1559                        version 0.98 is known to be affected, 0.99 fixes the
1560                        problem by letting the user disable the workaround.
1561
1562        mga=            [HW,DRM]
1563
1564        min_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory below this
1565                        physical address is ignored.
1566
1567        mini2440=       [ARM,HW,KNL]
1568                        Format:[0..2][b][c][t]
1569                        Default: "0tb"
1570                        MINI2440 configuration specification:
1571                        0 - The attached screen is the 3.5" TFT
1572                        1 - The attached screen is the 7" TFT
1573                        2 - The VGA Shield is attached (1024x768)
1574                        Leaving out the screen size parameter will not load
1575                        the TFT driver, and the framebuffer will be left
1576                        unconfigured.
1577                        b - Enable backlight. The TFT backlight pin will be
1578                        linked to the kernel VESA blanking code and a GPIO
1579                        LED. This parameter is not necessary when using the
1580                        VGA shield.
1581                        c - Enable the s3c camera interface.
1582                        t - Reserved for enabling touchscreen support. The
1583                        touchscreen support is not enabled in the mainstream
1584                        kernel as of 2.6.30, a preliminary port can be found
1585                        in the "bleeding edge" mini2440 support kernel at
1586                        http://repo.or.cz/w/linux-2.6/mini2440.git
1587
1588        mminit_loglevel=
1589                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1590                        parameter allows control of the logging verbosity for
1591                        the additional memory initialisation checks. A value
1592                        of 0 disables mminit logging and a level of 4 will
1593                        log everything. Information is printed at KERN_DEBUG
1594                        so loglevel=8 may also need to be specified.
1595
1596        module.sig_enforce
1597                        [KNL] When CONFIG_MODULE_SIG is set, this means that
1598                        modules without (valid) signatures will fail to load.
1599                        Note that if CONFIG_MODULE_SIG_ENFORCE is set, that
1600                        is always true, so this option does nothing.
1601
1602        mousedev.tap_time=
1603                        [MOUSE] Maximum time between finger touching and
1604                        leaving touchpad surface for touch to be considered
1605                        a tap and be reported as a left button click (for
1606                        touchpads working in absolute mode only).
1607                        Format: <msecs>
1608        mousedev.xres=  [MOUSE] Horizontal screen resolution, used for devices
1609                        reporting absolute coordinates, such as tablets
1610        mousedev.yres=  [MOUSE] Vertical screen resolution, used for devices
1611                        reporting absolute coordinates, such as tablets
1612
1613        movablecore=nn[KMG]     [KNL,X86,IA-64,PPC] This parameter
1614                        is similar to kernelcore except it specifies the
1615                        amount of memory used for migratable allocations.
1616                        If both kernelcore and movablecore is specified,
1617                        then kernelcore will be at *least* the specified
1618                        value but may be more. If movablecore on its own
1619                        is specified, the administrator must be careful
1620                        that the amount of memory usable for all allocations
1621                        is not too small.
1622
1623        MTD_Partition=  [MTD]
1624                        Format: <name>,<region-number>,<size>,<offset>
1625
1626        MTD_Region=     [MTD] Format:
1627                        <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1628
1629        mtdparts=       [MTD]
1630                        See drivers/mtd/cmdlinepart.c.
1631
1632        multitce=off    [PPC]  This parameter disables the use of the pSeries
1633                        firmware feature for updating multiple TCE entries
1634                        at a time.
1635
1636        onenand.bdry=   [HW,MTD] Flex-OneNAND Boundary Configuration
1637
1638                        Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1639
1640                        boundary - index of last SLC block on Flex-OneNAND.
1641                                   The remaining blocks are configured as MLC blocks.
1642                        lock     - Configure if Flex-OneNAND boundary should be locked.
1643                                   Once locked, the boundary cannot be changed.
1644                                   1 indicates lock status, 0 indicates unlock status.
1645
1646        mtdset=         [ARM]
1647                        ARM/S3C2412 JIVE boot control
1648
1649                        See arch/arm/mach-s3c2412/mach-jive.c
1650
1651        mtouchusb.raw_coordinates=
1652                        [HW] Make the MicroTouch USB driver use raw coordinates
1653                        ('y', default) or cooked coordinates ('n')
1654
1655        mtrr_chunk_size=nn[KMG] [X86]
1656                        used for mtrr cleanup. It is largest continuous chunk
1657                        that could hold holes aka. UC entries.
1658
1659        mtrr_gran_size=nn[KMG] [X86]
1660                        Used for mtrr cleanup. It is granularity of mtrr block.
1661                        Default is 1.
1662                        Large value could prevent small alignment from
1663                        using up MTRRs.
1664
1665        mtrr_spare_reg_nr=n [X86]
1666                        Format: <integer>
1667                        Range: 0,7 : spare reg number
1668                        Default : 1
1669                        Used for mtrr cleanup. It is spare mtrr entries number.
1670                        Set to 2 or more if your graphical card needs more.
1671
1672        n2=             [NET] SDL Inc. RISCom/N2 synchronous serial card
1673
1674        netdev=         [NET] Network devices parameters
1675                        Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1676                        Note that mem_start is often overloaded to mean
1677                        something different and driver-specific.
1678                        This usage is only documented in each driver source
1679                        file if at all.
1680
1681        nf_conntrack.acct=
1682                        [NETFILTER] Enable connection tracking flow accounting
1683                        0 to disable accounting
1684                        1 to enable accounting
1685                        Default value is 0.
1686
1687        nfsaddrs=       [NFS] Deprecated.  Use ip= instead.
1688                        See Documentation/filesystems/nfs/nfsroot.txt.
1689
1690        nfsroot=        [NFS] nfs root filesystem for disk-less boxes.
1691                        See Documentation/filesystems/nfs/nfsroot.txt.
1692
1693        nfsrootdebug    [NFS] enable nfsroot debugging messages.
1694                        See Documentation/filesystems/nfs/nfsroot.txt.
1695
1696        nfs.callback_tcpport=
1697                        [NFS] set the TCP port on which the NFSv4 callback
1698                        channel should listen.
1699
1700        nfs.cache_getent=
1701                        [NFS] sets the pathname to the program which is used
1702                        to update the NFS client cache entries.
1703
1704        nfs.cache_getent_timeout=
1705                        [NFS] sets the timeout after which an attempt to
1706                        update a cache entry is deemed to have failed.
1707
1708        nfs.idmap_cache_timeout=
1709                        [NFS] set the maximum lifetime for idmapper cache
1710                        entries.
1711
1712        nfs.enable_ino64=
1713                        [NFS] enable 64-bit inode numbers.
1714                        If zero, the NFS client will fake up a 32-bit inode
1715                        number for the readdir() and stat() syscalls instead
1716                        of returning the full 64-bit number.
1717                        The default is to return 64-bit inode numbers.
1718
1719        nfs.max_session_slots=
1720                        [NFSv4.1] Sets the maximum number of session slots
1721                        the client will attempt to negotiate with the server.
1722                        This limits the number of simultaneous RPC requests
1723                        that the client can send to the NFSv4.1 server.
1724                        Note that there is little point in setting this
1725                        value higher than the max_tcp_slot_table_limit.
1726
1727        nfs.nfs4_disable_idmapping=
1728                        [NFSv4] When set to the default of '1', this option
1729                        ensures that both the RPC level authentication
1730                        scheme and the NFS level operations agree to use
1731                        numeric uids/gids if the mount is using the
1732                        'sec=sys' security flavour. In effect it is
1733                        disabling idmapping, which can make migration from
1734                        legacy NFSv2/v3 systems to NFSv4 easier.
1735                        Servers that do not support this mode of operation
1736                        will be autodetected by the client, and it will fall
1737                        back to using the idmapper.
1738                        To turn off this behaviour, set the value to '0'.
1739        nfs.nfs4_unique_id=
1740                        [NFS4] Specify an additional fixed unique ident-
1741                        ification string that NFSv4 clients can insert into
1742                        their nfs_client_id4 string.  This is typically a
1743                        UUID that is generated at system install time.
1744
1745        nfs.send_implementation_id =
1746                        [NFSv4.1] Send client implementation identification
1747                        information in exchange_id requests.
1748                        If zero, no implementation identification information
1749                        will be sent.
1750                        The default is to send the implementation identification
1751                        information.
1752
1753        nfsd.nfs4_disable_idmapping=
1754                        [NFSv4] When set to the default of '1', the NFSv4
1755                        server will return only numeric uids and gids to
1756                        clients using auth_sys, and will accept numeric uids
1757                        and gids from such clients.  This is intended to ease
1758                        migration from NFSv2/v3.
1759
1760        objlayoutdriver.osd_login_prog=
1761                        [NFS] [OBJLAYOUT] sets the pathname to the program which
1762                        is used to automatically discover and login into new
1763                        osd-targets. Please see:
1764                        Documentation/filesystems/pnfs.txt for more explanations
1765
1766        nmi_debug=      [KNL,AVR32,SH] Specify one or more actions to take
1767                        when a NMI is triggered.
1768                        Format: [state][,regs][,debounce][,die]
1769
1770        nmi_watchdog=   [KNL,BUGS=X86] Debugging features for SMP kernels
1771                        Format: [panic,][nopanic,][num]
1772                        Valid num: 0
1773                        0 - turn nmi_watchdog off
1774                        When panic is specified, panic when an NMI watchdog
1775                        timeout occurs (or 'nopanic' to override the opposite
1776                        default).
1777                        This is useful when you use a panic=... timeout and
1778                        need the box quickly up again.
1779
1780        netpoll.carrier_timeout=
1781                        [NET] Specifies amount of time (in seconds) that
1782                        netpoll should wait for a carrier. By default netpoll
1783                        waits 4 seconds.
1784
1785        no387           [BUGS=X86-32] Tells the kernel to use the 387 maths
1786                        emulation library even if a 387 maths coprocessor
1787                        is present.
1788
1789        no_console_suspend
1790                        [HW] Never suspend the console
1791                        Disable suspending of consoles during suspend and
1792                        hibernate operations.  Once disabled, debugging
1793                        messages can reach various consoles while the rest
1794                        of the system is being put to sleep (ie, while
1795                        debugging driver suspend/resume hooks).  This may
1796                        not work reliably with all consoles, but is known
1797                        to work with serial and VGA consoles.
1798                        To facilitate more flexible debugging, we also add
1799                        console_suspend, a printk module parameter to control
1800                        it. Users could use console_suspend (usually
1801                        /sys/module/printk/parameters/console_suspend) to
1802                        turn on/off it dynamically.
1803
1804        noaliencache    [MM, NUMA, SLAB] Disables the allocation of alien
1805                        caches in the slab allocator.  Saves per-node memory,
1806                        but will impact performance.
1807
1808        noalign         [KNL,ARM]
1809
1810        noapic          [SMP,APIC] Tells the kernel to not make use of any
1811                        IOAPICs that may be present in the system.
1812
1813        noautogroup     Disable scheduler automatic task group creation.
1814
1815        nobats          [PPC] Do not use BATs for mapping kernel lowmem
1816                        on "Classic" PPC cores.
1817
1818        nocache         [ARM]
1819
1820        noclflush       [BUGS=X86] Don't use the CLFLUSH instruction
1821
1822        nodelayacct     [KNL] Disable per-task delay accounting
1823
1824        nodisconnect    [HW,SCSI,M68K] Disables SCSI disconnects.
1825
1826        nodsp           [SH] Disable hardware DSP at boot time.
1827
1828        noefi           [X86] Disable EFI runtime services support.
1829
1830        noexec          [IA-64]
1831
1832        noexec          [X86]
1833                        On X86-32 available only on PAE configured kernels.
1834                        noexec=on: enable non-executable mappings (default)
1835                        noexec=off: disable non-executable mappings
1836
1837        nosmap          [X86]
1838                        Disable SMAP (Supervisor Mode Access Prevention)
1839                        even if it is supported by processor.
1840
1841        nosmep          [X86]
1842                        Disable SMEP (Supervisor Mode Execution Prevention)
1843                        even if it is supported by processor.
1844
1845        noexec32        [X86-64]
1846                        This affects only 32-bit executables.
1847                        noexec32=on: enable non-executable mappings (default)
1848                                read doesn't imply executable mappings
1849                        noexec32=off: disable non-executable mappings
1850                                read implies executable mappings
1851
1852        nofpu           [SH] Disable hardware FPU at boot time.
1853
1854        nofxsr          [BUGS=X86-32] Disables x86 floating point extended
1855                        register save and restore. The kernel will only save
1856                        legacy floating-point registers on task switch.
1857
1858        noxsave         [BUGS=X86] Disables x86 extended register state save
1859                        and restore using xsave. The kernel will fallback to
1860                        enabling legacy floating-point and sse state.
1861
1862        eagerfpu=       [X86]
1863                        on      enable eager fpu restore
1864                        off     disable eager fpu restore
1865                        auto    selects the default scheme, which automatically
1866                                enables eagerfpu restore for xsaveopt.
1867
1868        nohlt           [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1869                        wfi(ARM) instruction doesn't work correctly and not to
1870                        use it. This is also useful when using JTAG debugger.
1871
1872        no-hlt          [BUGS=X86-32] Tells the kernel that the hlt
1873                        instruction doesn't work correctly and not to
1874                        use it.
1875
1876        no_file_caps    Tells the kernel not to honor file capabilities.  The
1877                        only way then for a file to be executed with privilege
1878                        is to be setuid root or executed by root.
1879
1880        nohalt          [IA-64] Tells the kernel not to use the power saving
1881                        function PAL_HALT_LIGHT when idle. This increases
1882                        power-consumption. On the positive side, it reduces
1883                        interrupt wake-up latency, which may improve performance
1884                        in certain environments such as networked servers or
1885                        real-time systems.
1886
1887        nohz=           [KNL] Boottime enable/disable dynamic ticks
1888                        Valid arguments: on, off
1889                        Default: on
1890
1891        noiotrap        [SH] Disables trapped I/O port accesses.
1892
1893        noirqdebug      [X86-32] Disables the code which attempts to detect and
1894                        disable unhandled interrupt sources.
1895
1896        no_timer_check  [X86,APIC] Disables the code which tests for
1897                        broken timer IRQ sources.
1898
1899        noisapnp        [ISAPNP] Disables ISA PnP code.
1900
1901        noinitrd        [RAM] Tells the kernel not to load any configured
1902                        initial RAM disk.
1903
1904        nointremap      [X86-64, Intel-IOMMU] Do not enable interrupt
1905                        remapping.
1906                        [Deprecated - use intremap=off]
1907
1908        nointroute      [IA-64]
1909
1910        nojitter        [IA-64] Disables jitter checking for ITC timers.
1911
1912        no-kvmclock     [X86,KVM] Disable paravirtualized KVM clock driver
1913
1914        no-kvmapf       [X86,KVM] Disable paravirtualized asynchronous page
1915                        fault handling.
1916
1917        no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
1918                        steal time is computed, but won't influence scheduler
1919                        behaviour
1920
1921        nolapic         [X86-32,APIC] Do not enable or use the local APIC.
1922
1923        nolapic_timer   [X86-32,APIC] Do not use the local APIC timer.
1924
1925        noltlbs         [PPC] Do not use large page/tlb entries for kernel
1926                        lowmem mapping on PPC40x.
1927
1928        nomca           [IA-64] Disable machine check abort handling
1929
1930        nomce           [X86-32] Machine Check Exception
1931
1932        nomfgpt         [X86-32] Disable Multi-Function General Purpose
1933                        Timer usage (for AMD Geode machines).
1934
1935        nonmi_ipi       [X86] Disable using NMI IPIs during panic/reboot to
1936                        shutdown the other cpus.  Instead use the REBOOT_VECTOR
1937                        irq.
1938
1939        nomodule        Disable module load
1940
1941        nopat           [X86] Disable PAT (page attribute table extension of
1942                        pagetables) support.
1943
1944        norandmaps      Don't use address space randomization.  Equivalent to
1945                        echo 0 > /proc/sys/kernel/randomize_va_space
1946
1947        noreplace-paravirt      [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1948
1949        noreplace-smp   [X86-32,SMP] Don't replace SMP instructions
1950                        with UP alternatives
1951
1952        noresidual      [PPC] Don't use residual data on PReP machines.
1953
1954        nordrand        [X86] Disable the direct use of the RDRAND
1955                        instruction even if it is supported by the
1956                        processor.  RDRAND is still available to user
1957                        space applications.
1958
1959        noresume        [SWSUSP] Disables resume and restores original swap
1960                        space.
1961
1962        no-scroll       [VGA] Disables scrollback.
1963                        This is required for the Braillex ib80-piezo Braille
1964                        reader made by F.H. Papenmeier (Germany).
1965
1966        nosbagart       [IA-64]
1967
1968        nosep           [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1969
1970        nosmp           [SMP] Tells an SMP kernel to act as a UP kernel,
1971                        and disable the IO APIC.  legacy for "maxcpus=0".
1972
1973        nosoftlockup    [KNL] Disable the soft-lockup detector.
1974
1975        nosync          [HW,M68K] Disables sync negotiation for all devices.
1976
1977        notsc           [BUGS=X86-32] Disable Time Stamp Counter
1978
1979        nousb           [USB] Disable the USB subsystem
1980
1981        nowatchdog      [KNL] Disable the lockup detector (NMI watchdog).
1982
1983        nowb            [ARM]
1984
1985        nox2apic        [X86-64,APIC] Do not enable x2APIC mode.
1986
1987        nptcg=          [IA-64] Override max number of concurrent global TLB
1988                        purges which is reported from either PAL_VM_SUMMARY or
1989                        SAL PALO.
1990
1991        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
1992                        could support.  nr_cpus=n : n >= 1 limits the kernel to
1993                        supporting 'n' processors. Later in runtime you can not
1994                        use hotplug cpu feature to put more cpu back to online.
1995                        just like you compile the kernel NR_CPUS=n
1996
1997        nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
1998
1999        numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2000                        one of ['zone', 'node', 'default'] can be specified
2001                        This can be set from sysctl after boot.
2002                        See Documentation/sysctl/vm.txt for details.
2003
2004        ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
2005                        See Documentation/debugging-via-ohci1394.txt for more
2006                        info.
2007
2008        olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2009                        Rather than timing out after 20 ms if an EC
2010                        command is not properly ACKed, override the length
2011                        of the timeout.  We have interrupts disabled while
2012                        waiting for the ACK, so if this is set too high
2013                        interrupts *may* be lost!
2014
2015        omap_mux=       [OMAP] Override bootloader pin multiplexing.
2016                        Format: <mux_mode0.mode_name=value>...
2017                        For example, to override I2C bus2:
2018                        omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2019
2020        oprofile.timer= [HW]
2021                        Use timer interrupt instead of performance counters
2022
2023        oprofile.cpu_type=      Force an oprofile cpu type
2024                        This might be useful if you have an older oprofile
2025                        userland or if you want common events.
2026                        Format: { arch_perfmon }
2027                        arch_perfmon: [X86] Force use of architectural
2028                                perfmon on Intel CPUs instead of the
2029                                CPU specific event set.
2030                        timer: [X86] Force use of architectural NMI
2031                                timer mode (see also oprofile.timer
2032                                for generic hr timer mode)
2033                                [s390] Force legacy basic mode sampling
2034                                (report cpu_type "timer")
2035
2036        oops=panic      Always panic on oopses. Default is to just kill the
2037                        process, but there is a small probability of
2038                        deadlocking the machine.
2039                        This will also cause panics on machine check exceptions.
2040                        Useful together with panic=30 to trigger a reboot.
2041
2042        OSS             [HW,OSS]
2043                        See Documentation/sound/oss/oss-parameters.txt
2044
2045        panic=          [KNL] Kernel behaviour on panic: delay <timeout>
2046                        timeout > 0: seconds before rebooting
2047                        timeout = 0: wait forever
2048                        timeout < 0: reboot immediately
2049                        Format: <timeout>
2050
2051        parkbd.port=    [HW] Parallel port number the keyboard adapter is
2052                        connected to, default is 0.
2053                        Format: <parport#>
2054        parkbd.mode=    [HW] Parallel port keyboard adapter mode of operation,
2055                        0 for XT, 1 for AT (default is AT).
2056                        Format: <mode>
2057
2058        parport=        [HW,PPT] Specify parallel ports. 0 disables.
2059                        Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2060                        Use 'auto' to force the driver to use any
2061                        IRQ/DMA settings detected (the default is to
2062                        ignore detected IRQ/DMA settings because of
2063                        possible conflicts). You can specify the base
2064                        address, IRQ, and DMA settings; IRQ and DMA
2065                        should be numbers, or 'auto' (for using detected
2066                        settings on that particular port), or 'nofifo'
2067                        (to avoid using a FIFO even if it is detected).
2068                        Parallel ports are assigned in the order they
2069                        are specified on the command line, starting
2070                        with parport0.
2071
2072        parport_init_mode=      [HW,PPT]
2073                        Configure VIA parallel port to operate in
2074                        a specific mode. This is necessary on Pegasos
2075                        computer where firmware has no options for setting
2076                        up parallel port mode and sets it to spp.
2077                        Currently this function knows 686a and 8231 chips.
2078                        Format: [spp|ps2|epp|ecp|ecpepp]
2079
2080        pause_on_oops=
2081                        Halt all CPUs after the first oops has been printed for
2082                        the specified number of seconds.  This is to be used if
2083                        your oopses keep scrolling off the screen.
2084
2085        pcbit=          [HW,ISDN]
2086
2087        pcd.            [PARIDE]
2088                        See header of drivers/block/paride/pcd.c.
2089                        See also Documentation/blockdev/paride.txt.
2090
2091        pci=option[,option...]  [PCI] various PCI subsystem options:
2092                earlydump       [X86] dump PCI config space before the kernel
2093                                changes anything
2094                off             [X86] don't probe for the PCI bus
2095                bios            [X86-32] force use of PCI BIOS, don't access
2096                                the hardware directly. Use this if your machine
2097                                has a non-standard PCI host bridge.
2098                nobios          [X86-32] disallow use of PCI BIOS, only direct
2099                                hardware access methods are allowed. Use this
2100                                if you experience crashes upon bootup and you
2101                                suspect they are caused by the BIOS.
2102                conf1           [X86] Force use of PCI Configuration
2103                                Mechanism 1.
2104                conf2           [X86] Force use of PCI Configuration
2105                                Mechanism 2.
2106                noaer           [PCIE] If the PCIEAER kernel config parameter is
2107                                enabled, this kernel boot option can be used to
2108                                disable the use of PCIE advanced error reporting.
2109                nodomains       [PCI] Disable support for multiple PCI
2110                                root domains (aka PCI segments, in ACPI-speak).
2111                nommconf        [X86] Disable use of MMCONFIG for PCI
2112                                Configuration
2113                check_enable_amd_mmconf [X86] check for and enable
2114                                properly configured MMIO access to PCI
2115                                config space on AMD family 10h CPU
2116                nomsi           [MSI] If the PCI_MSI kernel config parameter is
2117                                enabled, this kernel boot option can be used to
2118                                disable the use of MSI interrupts system-wide.
2119                noioapicquirk   [APIC] Disable all boot interrupt quirks.
2120                                Safety option to keep boot IRQs enabled. This
2121                                should never be necessary.
2122                ioapicreroute   [APIC] Enable rerouting of boot IRQs to the
2123                                primary IO-APIC for bridges that cannot disable
2124                                boot IRQs. This fixes a source of spurious IRQs
2125                                when the system masks IRQs.
2126                noioapicreroute [APIC] Disable workaround that uses the
2127                                boot IRQ equivalent of an IRQ that connects to
2128                                a chipset where boot IRQs cannot be disabled.
2129                                The opposite of ioapicreroute.
2130                biosirq         [X86-32] Use PCI BIOS calls to get the interrupt
2131                                routing table. These calls are known to be buggy
2132                                on several machines and they hang the machine
2133                                when used, but on other computers it's the only
2134                                way to get the interrupt routing table. Try
2135                                this option if the kernel is unable to allocate
2136                                IRQs or discover secondary PCI buses on your
2137                                motherboard.
2138                rom             [X86] Assign address space to expansion ROMs.
2139                                Use with caution as certain devices share
2140                                address decoders between ROMs and other
2141                                resources.
2142                norom           [X86] Do not assign address space to
2143                                expansion ROMs that do not already have
2144                                BIOS assigned address ranges.
2145                nobar           [X86] Do not assign address space to the
2146                                BARs that weren't assigned by the BIOS.
2147                irqmask=0xMMMM  [X86] Set a bit mask of IRQs allowed to be
2148                                assigned automatically to PCI devices. You can
2149                                make the kernel exclude IRQs of your ISA cards
2150                                this way.
2151                pirqaddr=0xAAAAA        [X86] Specify the physical address
2152                                of the PIRQ table (normally generated
2153                                by the BIOS) if it is outside the
2154                                F0000h-100000h range.
2155                lastbus=N       [X86] Scan all buses thru bus #N. Can be
2156                                useful if the kernel is unable to find your
2157                                secondary buses and you want to tell it
2158                                explicitly which ones they are.
2159                assign-busses   [X86] Always assign all PCI bus
2160                                numbers ourselves, overriding
2161                                whatever the firmware may have done.
2162                usepirqmask     [X86] Honor the possible IRQ mask stored
2163                                in the BIOS $PIR table. This is needed on
2164                                some systems with broken BIOSes, notably
2165                                some HP Pavilion N5400 and Omnibook XE3
2166                                notebooks. This will have no effect if ACPI
2167                                IRQ routing is enabled.
2168                noacpi          [X86] Do not use ACPI for IRQ routing
2169                                or for PCI scanning.
2170                use_crs         [X86] Use PCI host bridge window information
2171                                from ACPI.  On BIOSes from 2008 or later, this
2172                                is enabled by default.  If you need to use this,
2173                                please report a bug.
2174                nocrs           [X86] Ignore PCI host bridge windows from ACPI.
2175                                If you need to use this, please report a bug.
2176                routeirq        Do IRQ routing for all PCI devices.
2177                                This is normally done in pci_enable_device(),
2178                                so this option is a temporary workaround
2179                                for broken drivers that don't call it.
2180                skip_isa_align  [X86] do not align io start addr, so can
2181                                handle more pci cards
2182                firmware        [ARM] Do not re-enumerate the bus but instead
2183                                just use the configuration from the
2184                                bootloader. This is currently used on
2185                                IXP2000 systems where the bus has to be
2186                                configured a certain way for adjunct CPUs.
2187                noearly         [X86] Don't do any early type 1 scanning.
2188                                This might help on some broken boards which
2189                                machine check when some devices' config space
2190                                is read. But various workarounds are disabled
2191                                and some IOMMU drivers will not work.
2192                bfsort          Sort PCI devices into breadth-first order.
2193                                This sorting is done to get a device
2194                                order compatible with older (<= 2.4) kernels.
2195                nobfsort        Don't sort PCI devices into breadth-first order.
2196                cbiosize=nn[KMG]        The fixed amount of bus space which is
2197                                reserved for the CardBus bridge's IO window.
2198                                The default value is 256 bytes.
2199                cbmemsize=nn[KMG]       The fixed amount of bus space which is
2200                                reserved for the CardBus bridge's memory
2201                                window. The default value is 64 megabytes.
2202                resource_alignment=
2203                                Format:
2204                                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2205                                Specifies alignment and device to reassign
2206                                aligned memory resources.
2207                                If <order of align> is not specified,
2208                                PAGE_SIZE is used as alignment.
2209                                PCI-PCI bridge can be specified, if resource
2210                                windows need to be expanded.
2211                ecrc=           Enable/disable PCIe ECRC (transaction layer
2212                                end-to-end CRC checking).
2213                                bios: Use BIOS/firmware settings. This is the
2214                                the default.
2215                                off: Turn ECRC off
2216                                on: Turn ECRC on.
2217                realloc=        Enable/disable reallocating PCI bridge resources
2218                                if allocations done by BIOS are too small to
2219                                accommodate resources required by all child
2220                                devices.
2221                                off: Turn realloc off
2222                                on: Turn realloc on
2223                realloc         same as realloc=on
2224                noari           do not use PCIe ARI.
2225                pcie_scan_all   Scan all possible PCIe devices.  Otherwise we
2226                                only look for one device below a PCIe downstream
2227                                port.
2228
2229        pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
2230                        Management.
2231                off     Disable ASPM.
2232                force   Enable ASPM even on devices that claim not to support it.
2233                        WARNING: Forcing ASPM on may cause system lockups.
2234
2235        pcie_hp=        [PCIE] PCI Express Hotplug driver options:
2236                nomsi   Do not use MSI for PCI Express Native Hotplug (this
2237                        makes all PCIe ports use INTx for hotplug services).
2238
2239        pcie_ports=     [PCIE] PCIe ports handling:
2240                auto    Ask the BIOS whether or not to use native PCIe services
2241                        associated with PCIe ports (PME, hot-plug, AER).  Use
2242                        them only if that is allowed by the BIOS.
2243                native  Use native PCIe services associated with PCIe ports
2244                        unconditionally.
2245                compat  Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2246                        ports driver.
2247
2248        pcie_pme=       [PCIE,PM] Native PCIe PME signaling options:
2249                nomsi   Do not use MSI for native PCIe PME signaling (this makes
2250                        all PCIe root ports use INTx for all services).
2251
2252        pcmv=           [HW,PCMCIA] BadgePAD 4
2253
2254        pd.             [PARIDE]
2255                        See Documentation/blockdev/paride.txt.
2256
2257        pdcchassis=     [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2258                        boot time.
2259                        Format: { 0 | 1 }
2260                        See arch/parisc/kernel/pdc_chassis.c
2261
2262        percpu_alloc=   Select which percpu first chunk allocator to use.
2263                        Currently supported values are "embed" and "page".
2264                        Archs may support subset or none of the selections.
2265                        See comments in mm/percpu.c for details on each
2266                        allocator.  This parameter is primarily for debugging
2267                        and performance comparison.
2268
2269        pf.             [PARIDE]
2270                        See Documentation/blockdev/paride.txt.
2271
2272        pg.             [PARIDE]
2273                        See Documentation/blockdev/paride.txt.
2274
2275        pirq=           [SMP,APIC] Manual mp-table setup
2276                        See Documentation/x86/i386/IO-APIC.txt.
2277
2278        plip=           [PPT,NET] Parallel port network link
2279                        Format: { parport<nr> | timid | 0 }
2280                        See also Documentation/parport.txt.
2281
2282        pmtmr=          [X86] Manual setup of pmtmr I/O Port.
2283                        Override pmtimer IOPort with a hex value.
2284                        e.g. pmtmr=0x508
2285
2286        pnp.debug=1     [PNP]
2287                        Enable PNP debug messages (depends on the
2288                        CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
2289                        via /sys/module/pnp/parameters/debug.  We always show
2290                        current resource usage; turning this on also shows
2291                        possible settings and some assignment information.
2292
2293        pnpacpi=        [ACPI]
2294                        { off }
2295
2296        pnpbios=        [ISAPNP]
2297                        { on | off | curr | res | no-curr | no-res }
2298
2299        pnp_reserve_irq=
2300                        [ISAPNP] Exclude IRQs for the autoconfiguration
2301
2302        pnp_reserve_dma=
2303                        [ISAPNP] Exclude DMAs for the autoconfiguration
2304
2305        pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2306                        Ranges are in pairs (I/O port base and size).
2307
2308        pnp_reserve_mem=
2309                        [ISAPNP] Exclude memory regions for the
2310                        autoconfiguration.
2311                        Ranges are in pairs (memory base and size).
2312
2313        ports=          [IP_VS_FTP] IPVS ftp helper module
2314                        Default is 21.
2315                        Up to 8 (IP_VS_APP_MAX_PORTS) ports
2316                        may be specified.
2317                        Format: <port>,<port>....
2318
2319        print-fatal-signals=
2320                        [KNL] debug: print fatal signals
2321
2322                        If enabled, warn about various signal handling
2323                        related application anomalies: too many signals,
2324                        too many POSIX.1 timers, fatal signals causing a
2325                        coredump - etc.
2326
2327                        If you hit the warning due to signal overflow,
2328                        you might want to try "ulimit -i unlimited".
2329
2330                        default: off.
2331
2332        printk.always_kmsg_dump=
2333                        Trigger kmsg_dump for cases other than kernel oops or
2334                        panics
2335                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2336                        default: disabled
2337
2338        printk.time=    Show timing data prefixed to each printk message line
2339                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2340
2341        processor.max_cstate=   [HW,ACPI]
2342                        Limit processor to maximum C-state
2343                        max_cstate=9 overrides any DMI blacklist limit.
2344
2345        processor.nocst [HW,ACPI]
2346                        Ignore the _CST method to determine C-states,
2347                        instead using the legacy FADT method
2348
2349        profile=        [KNL] Enable kernel profiling via /proc/profile
2350                        Format: [schedule,]<number>
2351                        Param: "schedule" - profile schedule points.
2352                        Param: <number> - step/bucket size as a power of 2 for
2353                                statistical time based profiling.
2354                        Param: "sleep" - profile D-state sleeping (millisecs).
2355                                Requires CONFIG_SCHEDSTATS
2356                        Param: "kvm" - profile VM exits.
2357
2358        prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2359                        before loading.
2360                        See Documentation/blockdev/ramdisk.txt.
2361
2362        psmouse.proto=  [HW,MOUSE] Highest PS2 mouse protocol extension to
2363                        probe for; one of (bare|imps|exps|lifebook|any).
2364        psmouse.rate=   [HW,MOUSE] Set desired mouse report rate, in reports
2365                        per second.
2366        psmouse.resetafter=     [HW,MOUSE]
2367                        Try to reset the device after so many bad packets
2368                        (0 = never).
2369        psmouse.resolution=
2370                        [HW,MOUSE] Set desired mouse resolution, in dpi.
2371        psmouse.smartscroll=
2372                        [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2373                        0 = disabled, 1 = enabled (default).
2374
2375        pstore.backend= Specify the name of the pstore backend to use
2376
2377        pt.             [PARIDE]
2378                        See Documentation/blockdev/paride.txt.
2379
2380        pty.legacy_count=
2381                        [KNL] Number of legacy pty's. Overwrites compiled-in
2382                        default number.
2383
2384        quiet           [KNL] Disable most log messages
2385
2386        r128=           [HW,DRM]
2387
2388        raid=           [HW,RAID]
2389                        See Documentation/md.txt.
2390
2391        ramdisk_blocksize=      [RAM]
2392                        See Documentation/blockdev/ramdisk.txt.
2393
2394        ramdisk_size=   [RAM] Sizes of RAM disks in kilobytes
2395                        See Documentation/blockdev/ramdisk.txt.
2396
2397        rcutree.blimit= [KNL,BOOT]
2398                        Set maximum number of finished RCU callbacks to process
2399                        in one batch.
2400
2401        rcutree.fanout_leaf=    [KNL,BOOT]
2402                        Increase the number of CPUs assigned to each
2403                        leaf rcu_node structure.  Useful for very large
2404                        systems.
2405
2406        rcutree.qhimark=        [KNL,BOOT]
2407                        Set threshold of queued
2408                        RCU callbacks over which batch limiting is disabled.
2409
2410        rcutree.qlowmark=       [KNL,BOOT]
2411                        Set threshold of queued RCU callbacks below which
2412                        batch limiting is re-enabled.
2413
2414        rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2415                        Suppress RCU CPU stall warning messages.
2416
2417        rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2418                        Set timeout for RCU CPU stall warning messages.
2419
2420        rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2421                        Set delay from grace-period initialization to
2422                        first attempt to force quiescent states.
2423                        Units are jiffies, minimum value is zero,
2424                        and maximum value is HZ.
2425
2426        rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2427                        Set delay between subsequent attempts to force
2428                        quiescent states.  Units are jiffies, minimum
2429                        value is one, and maximum value is HZ.
2430
2431        rcutorture.fqs_duration= [KNL,BOOT]
2432                        Set duration of force_quiescent_state bursts.
2433
2434        rcutorture.fqs_holdoff= [KNL,BOOT]
2435                        Set holdoff time within force_quiescent_state bursts.
2436
2437        rcutorture.fqs_stutter= [KNL,BOOT]
2438                        Set wait time between force_quiescent_state bursts.
2439
2440        rcutorture.irqreader= [KNL,BOOT]
2441                        Test RCU readers from irq handlers.
2442
2443        rcutorture.n_barrier_cbs= [KNL,BOOT]
2444                        Set callbacks/threads for rcu_barrier() testing.
2445
2446        rcutorture.nfakewriters= [KNL,BOOT]
2447                        Set number of concurrent RCU writers.  These just
2448                        stress RCU, they don't participate in the actual
2449                        test, hence the "fake".
2450
2451        rcutorture.nreaders= [KNL,BOOT]
2452                        Set number of RCU readers.
2453
2454        rcutorture.onoff_holdoff= [KNL,BOOT]
2455                        Set time (s) after boot for CPU-hotplug testing.
2456
2457        rcutorture.onoff_interval= [KNL,BOOT]
2458                        Set time (s) between CPU-hotplug operations, or
2459                        zero to disable CPU-hotplug testing.
2460
2461        rcutorture.shuffle_interval= [KNL,BOOT]
2462                        Set task-shuffle interval (s).  Shuffling tasks
2463                        allows some CPUs to go into dyntick-idle mode
2464                        during the rcutorture test.
2465
2466        rcutorture.shutdown_secs= [KNL,BOOT]
2467                        Set time (s) after boot system shutdown.  This
2468                        is useful for hands-off automated testing.
2469
2470        rcutorture.stall_cpu= [KNL,BOOT]
2471                        Duration of CPU stall (s) to test RCU CPU stall
2472                        warnings, zero to disable.
2473
2474        rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2475                        Time to wait (s) after boot before inducing stall.
2476
2477        rcutorture.stat_interval= [KNL,BOOT]
2478                        Time (s) between statistics printk()s.
2479
2480        rcutorture.stutter= [KNL,BOOT]
2481                        Time (s) to stutter testing, for example, specifying
2482                        five seconds causes the test to run for five seconds,
2483                        wait for five seconds, and so on.  This tests RCU's
2484                        ability to transition abruptly to and from idle.
2485
2486        rcutorture.test_boost= [KNL,BOOT]
2487                        Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
2488                        "Maybe" means test if the RCU implementation
2489                        under test support RCU priority boosting.
2490
2491        rcutorture.test_boost_duration= [KNL,BOOT]
2492                        Duration (s) of each individual boost test.
2493
2494        rcutorture.test_boost_interval= [KNL,BOOT]
2495                        Interval (s) between each boost test.
2496
2497        rcutorture.test_no_idle_hz= [KNL,BOOT]
2498                        Test RCU's dyntick-idle handling.  See also the
2499                        rcutorture.shuffle_interval parameter.
2500
2501        rcutorture.torture_type= [KNL,BOOT]
2502                        Specify the RCU implementation to test.
2503
2504        rcutorture.verbose= [KNL,BOOT]
2505                        Enable additional printk() statements.
2506
2507        rdinit=         [KNL]
2508                        Format: <full_path>
2509                        Run specified binary instead of /init from the ramdisk,
2510                        used for early userspace startup. See initrd.
2511
2512        reboot=         [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2513                        Format: <reboot_mode>[,<reboot_mode2>[,...]]
2514                        See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2515
2516        relax_domain_level=
2517                        [KNL, SMP] Set scheduler's default relax_domain_level.
2518                        See Documentation/cgroups/cpusets.txt.
2519
2520        reserve=        [KNL,BUGS] Force the kernel to ignore some iomem area
2521
2522        reservetop=     [X86-32]
2523                        Format: nn[KMG]
2524                        Reserves a hole at the top of the kernel virtual
2525                        address space.
2526
2527        reservelow=     [X86]
2528                        Format: nn[K]
2529                        Set the amount of memory to reserve for BIOS at
2530                        the bottom of the address space.
2531
2532        reset_devices   [KNL] Force drivers to reset the underlying device
2533                        during initialization.
2534
2535        resume=         [SWSUSP]
2536                        Specify the partition device for software suspend
2537                        Format:
2538                        {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2539
2540        resume_offset=  [SWSUSP]
2541                        Specify the offset from the beginning of the partition
2542                        given by "resume=" at which the swap header is located,
2543                        in <PAGE_SIZE> units (needed only for swap files).
2544                        See  Documentation/power/swsusp-and-swap-files.txt
2545
2546        resumedelay=    [HIBERNATION] Delay (in seconds) to pause before attempting to
2547                        read the resume files
2548
2549        resumewait      [HIBERNATION] Wait (indefinitely) for resume device to show up.
2550                        Useful for devices that are detected asynchronously
2551                        (e.g. USB and MMC devices).
2552
2553        hibernate=      [HIBERNATION]
2554                noresume        Don't check if there's a hibernation image
2555                                present during boot.
2556                nocompress      Don't compress/decompress hibernation images.
2557
2558        retain_initrd   [RAM] Keep initrd memory after extraction
2559
2560        rhash_entries=  [KNL,NET]
2561                        Set number of hash buckets for route cache
2562
2563        riscom8=        [HW,SERIAL]
2564                        Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2565
2566        ro              [KNL] Mount root device read-only on boot
2567
2568        root=           [KNL] Root filesystem
2569                        See name_to_dev_t comment in init/do_mounts.c.
2570
2571        rootdelay=      [KNL] Delay (in seconds) to pause before attempting to
2572                        mount the root filesystem
2573
2574        rootflags=      [KNL] Set root filesystem mount option string
2575
2576        rootfstype=     [KNL] Set root filesystem type
2577
2578        rootwait        [KNL] Wait (indefinitely) for root device to show up.
2579                        Useful for devices that are detected asynchronously
2580                        (e.g. USB and MMC devices).
2581
2582        rw              [KNL] Mount root device read-write on boot
2583
2584        S               [KNL] Run init in single mode
2585
2586        sa1100ir        [NET]
2587                        See drivers/net/irda/sa1100_ir.c.
2588
2589        sbni=           [NET] Granch SBNI12 leased line adapter
2590
2591        sched_debug     [KNL] Enables verbose scheduler debug messages.
2592
2593        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
2594                        xtime_lock contention on larger systems, and/or RCU lock
2595                        contention on all systems with CONFIG_MAXSMP set.
2596                        Format: { "0" | "1" }
2597                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2598                        1 -- enable.
2599                        Note: increases power consumption, thus should only be
2600                        enabled if running jitter sensitive (HPC/RT) workloads.
2601
2602        security=       [SECURITY] Choose a security module to enable at boot.
2603                        If this boot parameter is not specified, only the first
2604                        security module asking for security registration will be
2605                        loaded. An invalid security module name will be treated
2606                        as if no module has been chosen.
2607
2608        selinux=        [SELINUX] Disable or enable SELinux at boot time.
2609                        Format: { "0" | "1" }
2610                        See security/selinux/Kconfig help text.
2611                        0 -- disable.
2612                        1 -- enable.
2613                        Default value is set via kernel config option.
2614                        If enabled at boot time, /selinux/disable can be used
2615                        later to disable prior to initial policy load.
2616
2617        apparmor=       [APPARMOR] Disable or enable AppArmor at boot time
2618                        Format: { "0" | "1" }
2619                        See security/apparmor/Kconfig help text
2620                        0 -- disable.
2621                        1 -- enable.
2622                        Default value is set via kernel config option.
2623
2624        serialnumber    [BUGS=X86-32]
2625
2626        shapers=        [NET]
2627                        Maximal number of shapers.
2628
2629        show_msr=       [x86] show boot-time MSR settings
2630                        Format: { <integer> }
2631                        Show boot-time (BIOS-initialized) MSR settings.
2632                        The parameter means the number of CPUs to show,
2633                        for example 1 means boot CPU only.
2634
2635        simeth=         [IA-64]
2636        simscsi=
2637
2638        slram=          [HW,MTD]
2639
2640        slab_max_order= [MM, SLAB]
2641                        Determines the maximum allowed order for slabs.
2642                        A high setting may cause OOMs due to memory
2643                        fragmentation.  Defaults to 1 for systems with
2644                        more than 32MB of RAM, 0 otherwise.
2645
2646        slub_debug[=options[,slabs]]    [MM, SLUB]
2647                        Enabling slub_debug allows one to determine the
2648                        culprit if slab objects become corrupted. Enabling
2649                        slub_debug can create guard zones around objects and
2650                        may poison objects when not in use. Also tracks the
2651                        last alloc / free. For more information see
2652                        Documentation/vm/slub.txt.
2653
2654        slub_max_order= [MM, SLUB]
2655                        Determines the maximum allowed order for slabs.
2656                        A high setting may cause OOMs due to memory
2657                        fragmentation. For more information see
2658                        Documentation/vm/slub.txt.
2659
2660        slub_min_objects=       [MM, SLUB]
2661                        The minimum number of objects per slab. SLUB will
2662                        increase the slab order up to slub_max_order to
2663                        generate a sufficiently large slab able to contain
2664                        the number of objects indicated. The higher the number
2665                        of objects the smaller the overhead of tracking slabs
2666                        and the less frequently locks need to be acquired.
2667                        For more information see Documentation/vm/slub.txt.
2668
2669        slub_min_order= [MM, SLUB]
2670                        Determines the minimum page order for slabs. Must be
2671                        lower than slub_max_order.
2672                        For more information see Documentation/vm/slub.txt.
2673
2674        slub_nomerge    [MM, SLUB]
2675                        Disable merging of slabs with similar size. May be
2676                        necessary if there is some reason to distinguish
2677                        allocs to different slabs. Debug options disable
2678                        merging on their own.
2679                        For more information see Documentation/vm/slub.txt.
2680
2681        smart2=         [HW]
2682                        Format: <io1>[,<io2>[,...,<io8>]]
2683
2684        smsc-ircc2.nopnp        [HW] Don't use PNP to discover SMC devices
2685        smsc-ircc2.ircc_cfg=    [HW] Device configuration I/O port
2686        smsc-ircc2.ircc_sir=    [HW] SIR base I/O port
2687        smsc-ircc2.ircc_fir=    [HW] FIR base I/O port
2688        smsc-ircc2.ircc_irq=    [HW] IRQ line
2689        smsc-ircc2.ircc_dma=    [HW] DMA channel
2690        smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2691                                0: Toshiba Satellite 1800 (GP data pin select)
2692                                1: Fast pin select (default)
2693                                2: ATC IRMode
2694
2695        softlockup_panic=
2696                        [KNL] Should the soft-lockup detector generate panics.
2697                        Format: <integer>
2698
2699        sonypi.*=       [HW] Sony Programmable I/O Control Device driver
2700                        See Documentation/laptops/sonypi.txt
2701
2702        specialix=      [HW,SERIAL] Specialix multi-serial port adapter
2703                        See Documentation/serial/specialix.txt.
2704
2705        spia_io_base=   [HW,MTD]
2706        spia_fio_base=
2707        spia_pedr=
2708        spia_peddr=
2709
2710        stacktrace      [FTRACE]
2711                        Enabled the stack tracer on boot up.
2712
2713        stacktrace_filter=[function-list]
2714                        [FTRACE] Limit the functions that the stack tracer
2715                        will trace at boot up. function-list is a comma separated
2716                        list of functions. This list can be changed at run
2717                        time by the stack_trace_filter file in the debugfs
2718                        tracing directory. Note, this enables stack tracing
2719                        and the stacktrace above is not needed.
2720
2721        sti=            [PARISC,HW]
2722                        Format: <num>
2723                        Set the STI (builtin display/keyboard on the HP-PARISC
2724                        machines) console (graphic card) which should be used
2725                        as the initial boot-console.
2726                        See also comment in drivers/video/console/sticore.c.
2727
2728        sti_font=       [HW]
2729                        See comment in drivers/video/console/sticore.c.
2730
2731        stifb=          [HW]
2732                        Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2733
2734        sunrpc.min_resvport=
2735        sunrpc.max_resvport=
2736                        [NFS,SUNRPC]
2737                        SunRPC servers often require that client requests
2738                        originate from a privileged port (i.e. a port in the
2739                        range 0 < portnr < 1024).
2740                        An administrator who wishes to reserve some of these
2741                        ports for other uses may adjust the range that the
2742                        kernel's sunrpc client considers to be privileged
2743                        using these two parameters to set the minimum and
2744                        maximum port values.
2745
2746        sunrpc.pool_mode=
2747                        [NFS]
2748                        Control how the NFS server code allocates CPUs to
2749                        service thread pools.  Depending on how many NICs
2750                        you have and where their interrupts are bound, this
2751                        option will affect which CPUs will do NFS serving.
2752                        Note: this parameter cannot be changed while the
2753                        NFS server is running.
2754
2755                        auto        the server chooses an appropriate mode
2756                                    automatically using heuristics
2757                        global      a single global pool contains all CPUs
2758                        percpu      one pool for each CPU
2759                        pernode     one pool for each NUMA node (equivalent
2760                                    to global on non-NUMA machines)
2761
2762        sunrpc.tcp_slot_table_entries=
2763        sunrpc.udp_slot_table_entries=
2764                        [NFS,SUNRPC]
2765                        Sets the upper limit on the number of simultaneous
2766                        RPC calls that can be sent from the client to a
2767                        server. Increasing these values may allow you to
2768                        improve throughput, but will also increase the
2769                        amount of memory reserved for use by the client.
2770
2771        swapaccount[=0|1]
2772                        [KNL] Enable accounting of swap in memory resource
2773                        controller if no parameter or 1 is given or disable
2774                        it if 0 is given (See Documentation/cgroups/memory.txt)
2775
2776        swiotlb=        [IA-64] Number of I/O TLB slabs
2777
2778        switches=       [HW,M68k]
2779
2780        sysfs.deprecated=0|1 [KNL]
2781                        Enable/disable old style sysfs layout for old udev
2782                        on older distributions. When this option is enabled
2783                        very new udev will not work anymore. When this option
2784                        is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2785                        in older udev will not work anymore.
2786                        Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2787                        the kernel configuration.
2788
2789        sysrq_always_enabled
2790                        [KNL]
2791                        Ignore sysrq setting - this boot parameter will
2792                        neutralize any effect of /proc/sys/kernel/sysrq.
2793                        Useful for debugging.
2794
2795        tdfx=           [HW,DRM]
2796
2797        test_suspend=   [SUSPEND]
2798                        Specify "mem" (for Suspend-to-RAM) or "standby" (for
2799                        standby suspend) as the system sleep state to briefly
2800                        enter during system startup.  The system is woken from
2801                        this state using a wakeup-capable RTC alarm.
2802
2803        thash_entries=  [KNL,NET]
2804                        Set number of hash buckets for TCP connection
2805
2806        thermal.act=    [HW,ACPI]
2807                        -1: disable all active trip points in all thermal zones
2808                        <degrees C>: override all lowest active trip points
2809
2810        thermal.crt=    [HW,ACPI]
2811                        -1: disable all critical trip points in all thermal zones
2812                        <degrees C>: override all critical trip points
2813
2814        thermal.nocrt=  [HW,ACPI]
2815                        Set to disable actions on ACPI thermal zone
2816                        critical and hot trip points.
2817
2818        thermal.off=    [HW,ACPI]
2819                        1: disable ACPI thermal control
2820
2821        thermal.psv=    [HW,ACPI]
2822                        -1: disable all passive trip points
2823                        <degrees C>: override all passive trip points to this
2824                        value
2825
2826        thermal.tzp=    [HW,ACPI]
2827                        Specify global default ACPI thermal zone polling rate
2828                        <deci-seconds>: poll all this frequency
2829                        0: no polling (default)
2830
2831        threadirqs      [KNL]
2832                        Force threading of all interrupt handlers except those
2833                        marked explicitly IRQF_NO_THREAD.
2834
2835        topology=       [S390]
2836                        Format: {off | on}
2837                        Specify if the kernel should make use of the cpu
2838                        topology information if the hardware supports this.
2839                        The scheduler will make use of this information and
2840                        e.g. base its process migration decisions on it.
2841                        Default is on.
2842
2843        tp720=          [HW,PS2]
2844
2845        tpm_suspend_pcr=[HW,TPM]
2846                        Format: integer pcr id
2847                        Specify that at suspend time, the tpm driver
2848                        should extend the specified pcr with zeros,
2849                        as a workaround for some chips which fail to
2850                        flush the last written pcr on TPM_SaveState.
2851                        This will guarantee that all the other pcrs
2852                        are saved.
2853
2854        trace_buf_size=nn[KMG]
2855                        [FTRACE] will set tracing buffer size.
2856
2857        trace_event=[event-list]
2858                        [FTRACE] Set and start specified trace events in order
2859                        to facilitate early boot debugging.
2860                        See also Documentation/trace/events.txt
2861
2862        transparent_hugepage=
2863                        [KNL]
2864                        Format: [always|madvise|never]
2865                        Can be used to control the default behavior of the system
2866                        with respect to transparent hugepages.
2867                        See Documentation/vm/transhuge.txt for more details.
2868
2869        tsc=            Disable clocksource stability checks for TSC.
2870                        Format: <string>
2871                        [x86] reliable: mark tsc clocksource as reliable, this
2872                        disables clocksource verification at runtime, as well
2873                        as the stability checks done at bootup. Used to enable
2874                        high-resolution timer mode on older hardware, and in
2875                        virtualized environment.
2876                        [x86] noirqtime: Do not use TSC to do irq accounting.
2877                        Used to run time disable IRQ_TIME_ACCOUNTING on any
2878                        platforms where RDTSC is slow and this accounting
2879                        can add overhead.
2880
2881        turbografx.map[2|3]=    [HW,JOY]
2882                        TurboGraFX parallel port interface
2883                        Format:
2884                        <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2885                        See also Documentation/input/joystick-parport.txt
2886
2887        udbg-immortal   [PPC] When debugging early kernel crashes that
2888                        happen after console_init() and before a proper 
2889                        console driver takes over, this boot options might
2890                        help "seeing" what's going on.
2891
2892        uhash_entries=  [KNL,NET]
2893                        Set number of hash buckets for UDP/UDP-Lite connections
2894
2895        uhci-hcd.ignore_oc=
2896                        [USB] Ignore overcurrent events (default N).
2897                        Some badly-designed motherboards generate lots of
2898                        bogus events, for ports that aren't wired to
2899                        anything.  Set this parameter to avoid log spamming.
2900                        Note that genuine overcurrent events won't be
2901                        reported either.
2902
2903        unknown_nmi_panic
2904                        [X86] Cause panic on unknown NMI.
2905
2906        usbcore.authorized_default=
2907                        [USB] Default USB device authorization:
2908                        (default -1 = authorized except for wireless USB,
2909                        0 = not authorized, 1 = authorized)
2910
2911        usbcore.autosuspend=
2912                        [USB] The autosuspend time delay (in seconds) used
2913                        for newly-detected USB devices (default 2).  This
2914                        is the time required before an idle device will be
2915                        autosuspended.  Devices for which the delay is set
2916                        to a negative value won't be autosuspended at all.
2917
2918        usbcore.usbfs_snoop=
2919                        [USB] Set to log all usbfs traffic (default 0 = off).
2920
2921        usbcore.blinkenlights=
2922                        [USB] Set to cycle leds on hubs (default 0 = off).
2923
2924        usbcore.old_scheme_first=
2925                        [USB] Start with the old device initialization
2926                        scheme (default 0 = off).
2927
2928        usbcore.usbfs_memory_mb=
2929                        [USB] Memory limit (in MB) for buffers allocated by
2930                        usbfs (default = 16, 0 = max = 2047).
2931
2932        usbcore.use_both_schemes=
2933                        [USB] Try the other device initialization scheme
2934                        if the first one fails (default 1 = enabled).
2935
2936        usbcore.initial_descriptor_timeout=
2937                        [USB] Specifies timeout for the initial 64-byte
2938                        USB_REQ_GET_DESCRIPTOR request in milliseconds
2939                        (default 5000 = 5.0 seconds).
2940
2941        usbhid.mousepoll=
2942                        [USBHID] The interval which mice are to be polled at.
2943
2944        usb-storage.delay_use=
2945                        [UMS] The delay in seconds before a new device is
2946                        scanned for Logical Units (default 5).
2947
2948        usb-storage.quirks=
2949                        [UMS] A list of quirks entries to supplement or
2950                        override the built-in unusual_devs list.  List
2951                        entries are separated by commas.  Each entry has
2952                        the form VID:PID:Flags where VID and PID are Vendor
2953                        and Product ID values (4-digit hex numbers) and
2954                        Flags is a set of characters, each corresponding
2955                        to a common usb-storage quirk flag as follows:
2956                                a = SANE_SENSE (collect more than 18 bytes
2957                                        of sense data);
2958                                b = BAD_SENSE (don't collect more than 18
2959                                        bytes of sense data);
2960                                c = FIX_CAPACITY (decrease the reported
2961                                        device capacity by one sector);
2962                                d = NO_READ_DISC_INFO (don't use
2963                                        READ_DISC_INFO command);
2964                                e = NO_READ_CAPACITY_16 (don't use
2965                                        READ_CAPACITY_16 command);
2966                                h = CAPACITY_HEURISTICS (decrease the
2967                                        reported device capacity by one
2968                                        sector if the number is odd);
2969                                i = IGNORE_DEVICE (don't bind to this
2970                                        device);
2971                                l = NOT_LOCKABLE (don't try to lock and
2972                                        unlock ejectable media);
2973                                m = MAX_SECTORS_64 (don't transfer more
2974                                        than 64 sectors = 32 KB at a time);
2975                                n = INITIAL_READ10 (force a retry of the
2976                                        initial READ(10) command);
2977                                o = CAPACITY_OK (accept the capacity
2978                                        reported by the device);
2979                                p = WRITE_CACHE (the device cache is ON
2980                                        by default);
2981                                r = IGNORE_RESIDUE (the device reports
2982                                        bogus residue values);
2983                                s = SINGLE_LUN (the device has only one
2984                                        Logical Unit);
2985                                w = NO_WP_DETECT (don't test whether the
2986                                        medium is write-protected).
2987                        Example: quirks=0419:aaf5:rl,0421:0433:rc
2988
2989        user_debug=     [KNL,ARM]
2990                        Format: <int>
2991                        See arch/arm/Kconfig.debug help text.
2992                                 1 - undefined instruction events
2993                                 2 - system calls
2994                                 4 - invalid data aborts
2995                                 8 - SIGSEGV faults
2996                                16 - SIGBUS faults
2997                        Example: user_debug=31
2998
2999        userpte=
3000                        [X86] Flags controlling user PTE allocations.
3001
3002                                nohigh = do not allocate PTE pages in
3003                                        HIGHMEM regardless of setting
3004                                        of CONFIG_HIGHPTE.
3005
3006        vdso=           [X86,SH]
3007                        vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3008                        vdso=1: enable VDSO (default)
3009                        vdso=0: disable VDSO mapping
3010
3011        vdso32=         [X86]
3012                        vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3013                        vdso32=1: enable 32-bit VDSO (default)
3014                        vdso32=0: disable 32-bit VDSO mapping
3015
3016        vector=         [IA-64,SMP]
3017                        vector=percpu: enable percpu vector domain
3018
3019        video=          [FB] Frame buffer configuration
3020                        See Documentation/fb/modedb.txt.
3021
3022        virtio_mmio.device=
3023                        [VMMIO] Memory mapped virtio (platform) device.
3024
3025                                <size>@<baseaddr>:<irq>[:<id>]
3026                        where:
3027                                <size>     := size (can use standard suffixes
3028                                                like K, M and G)
3029                                <baseaddr> := physical base address
3030                                <irq>      := interrupt number (as passed to
3031                                                request_irq())
3032                                <id>       := (optional) platform device id
3033                        example:
3034                                virtio_mmio.device=1K@0x100b0000:48:7
3035
3036                        Can be used multiple times for multiple devices.
3037
3038        vga=            [BOOT,X86-32] Select a particular video mode
3039                        See Documentation/x86/boot.txt and
3040                        Documentation/svga.txt.
3041                        Use vga=ask for menu.
3042                        This is actually a boot loader parameter; the value is
3043                        passed to the kernel using a special protocol.
3044
3045        vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3046                        size of <nn>. This can be used to increase the
3047                        minimum size (128MB on x86). It can also be used to
3048                        decrease the size and leave more room for directly
3049                        mapped kernel RAM.
3050
3051        vmhalt=         [KNL,S390] Perform z/VM CP command after system halt.
3052                        Format: <command>
3053
3054        vmpanic=        [KNL,S390] Perform z/VM CP command after kernel panic.
3055                        Format: <command>
3056
3057        vmpoff=         [KNL,S390] Perform z/VM CP command after power off.
3058                        Format: <command>
3059
3060        vsyscall=       [X86-64]
3061                        Controls the behavior of vsyscalls (i.e. calls to
3062                        fixed addresses of 0xffffffffff600x00 from legacy
3063                        code).  Most statically-linked binaries and older
3064                        versions of glibc use these calls.  Because these
3065                        functions are at fixed addresses, they make nice
3066                        targets for exploits that can control RIP.
3067
3068                        emulate     [default] Vsyscalls turn into traps and are
3069                                    emulated reasonably safely.
3070
3071                        native      Vsyscalls are native syscall instructions.
3072                                    This is a little bit faster than trapping
3073                                    and makes a few dynamic recompilers work
3074                                    better than they would in emulation mode.
3075                                    It also makes exploits much easier to write.
3076
3077                        none        Vsyscalls don't work at all.  This makes
3078                                    them quite hard to use for exploits but
3079                                    might break your system.
3080
3081        vt.cur_default= [VT] Default cursor shape.
3082                        Format: 0xCCBBAA, where AA, BB, and CC are the same as
3083                        the parameters of the <Esc>[?A;B;Cc escape sequence;
3084                        see VGA-softcursor.txt. Default: 2 = underline.
3085
3086        vt.default_blu= [VT]
3087                        Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3088                        Change the default blue palette of the console.
3089                        This is a 16-member array composed of values
3090                        ranging from 0-255.
3091
3092        vt.default_grn= [VT]
3093                        Format: <green0>,<green1>,<green2>,...,<green15>
3094                        Change the default green palette of the console.
3095                        This is a 16-member array composed of values
3096                        ranging from 0-255.
3097
3098        vt.default_red= [VT]
3099                        Format: <red0>,<red1>,<red2>,...,<red15>
3100                        Change the default red palette of the console.
3101                        This is a 16-member array composed of values
3102                        ranging from 0-255.
3103
3104        vt.default_utf8=
3105                        [VT]
3106                        Format=<0|1>
3107                        Set system-wide default UTF-8 mode for all tty's.
3108                        Default is 1, i.e. UTF-8 mode is enabled for all
3109                        newly opened terminals.
3110
3111        vt.global_cursor_default=
3112                        [VT]
3113                        Format=<-1|0|1>
3114                        Set system-wide default for whether a cursor
3115                        is shown on new VTs. Default is -1,
3116                        i.e. cursors will be created by default unless
3117                        overridden by individual drivers. 0 will hide
3118                        cursors, 1 will display them.
3119
3120        watchdog timers [HW,WDT] For information on watchdog timers,
3121                        see Documentation/watchdog/watchdog-parameters.txt
3122                        or other driver-specific files in the
3123                        Documentation/watchdog/ directory.
3124
3125        x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
3126                        default x2apic cluster mode on platforms
3127                        supporting x2apic.
3128
3129        x86_mrst_timer= [X86-32,APBT]
3130                        Choose timer option for x86 Moorestown MID platform.
3131                        Two valid options are apbt timer only and lapic timer
3132                        plus one apbt timer for broadcast timer.
3133                        x86_mrst_timer=apbt_only | lapic_and_apbt
3134
3135        xd=             [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3136        xd_geo=         See header of drivers/block/xd.c.
3137
3138        xen_emul_unplug=                [HW,X86,XEN]
3139                        Unplug Xen emulated devices
3140                        Format: [unplug0,][unplug1]
3141                        ide-disks -- unplug primary master IDE devices
3142                        aux-ide-disks -- unplug non-primary-master IDE devices
3143                        nics -- unplug network devices
3144                        all -- unplug all emulated devices (NICs and IDE disks)
3145                        unnecessary -- unplugging emulated devices is
3146                                unnecessary even if the host did not respond to
3147                                the unplug protocol
3148                        never -- do not unplug even if version check succeeds
3149
3150        xirc2ps_cs=     [NET,PCMCIA]
3151                        Format:
3152                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3153
3154______________________________________________________________________
3155
3156TODO:
3157
3158        Add more DRM drivers.
3159
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