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