linux/Documentation/kernel-parameters.txt
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   1                          Kernel Parameters
   2                          ~~~~~~~~~~~~~~~~~
   3
   4The following is a consolidated list of the kernel parameters as implemented
   5(mostly) by the __setup() macro and sorted into English Dictionary order
   6(defined as ignoring all punctuation and sorting digits before letters in a
   7case insensitive manner), and with descriptions where known.
   8
   9Module parameters for loadable modules are specified only as the
  10parameter name with optional '=' and value as appropriate, such as:
  11
  12        modprobe usbcore blinkenlights=1
  13
  14Module parameters for modules that are built into the kernel image
  15are specified on the kernel command line with the module name plus
  16'.' plus parameter name, with '=' and value if appropriate, such as:
  17
  18        usbcore.blinkenlights=1
  19
  20Hyphens (dashes) and underscores are equivalent in parameter names, so
  21        log_buf_len=1M print-fatal-signals=1
  22can also be entered as
  23        log-buf-len=1M print_fatal_signals=1
  24
  25
  26This document may not be entirely up to date and comprehensive. The command
  27"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
  28module. Loadable modules, after being loaded into the running kernel, also
  29reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
  30parameters may be changed at runtime by the command
  31"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
  32
  33The parameters listed below are only valid if certain kernel build options were
  34enabled and if respective hardware is present. The text in square brackets at
  35the beginning of each description states the restrictions within which a
  36parameter is applicable:
  37
  38        ACPI    ACPI support is enabled.
  39        AGP     AGP (Accelerated Graphics Port) is enabled.
  40        ALSA    ALSA sound support is enabled.
  41        APIC    APIC support is enabled.
  42        APM     Advanced Power Management support is enabled.
  43        ARM     ARM architecture is enabled.
  44        AVR32   AVR32 architecture is enabled.
  45        AX25    Appropriate AX.25 support is enabled.
  46        BLACKFIN Blackfin architecture is enabled.
  47        DRM     Direct Rendering Management support is enabled.
  48        DYNAMIC_DEBUG Build in debug messages and enable them at runtime
  49        EDD     BIOS Enhanced Disk Drive Services (EDD) is enabled
  50        EFI     EFI Partitioning (GPT) is enabled
  51        EIDE    EIDE/ATAPI support is enabled.
  52        EVM     Extended Verification Module
  53        FB      The frame buffer device is enabled.
  54        FTRACE  Function tracing enabled.
  55        GCOV    GCOV profiling is enabled.
  56        HW      Appropriate hardware is enabled.
  57        IA-64   IA-64 architecture is enabled.
  58        IMA     Integrity measurement architecture is enabled.
  59        IOSCHED More than one I/O scheduler is enabled.
  60        IP_PNP  IP DHCP, BOOTP, or RARP is enabled.
  61        IPV6    IPv6 support is enabled.
  62        ISAPNP  ISA PnP code is enabled.
  63        ISDN    Appropriate ISDN support is enabled.
  64        JOY     Appropriate joystick support is enabled.
  65        KGDB    Kernel debugger support is enabled.
  66        KVM     Kernel Virtual Machine support is enabled.
  67        LIBATA  Libata driver is enabled
  68        LP      Printer support is enabled.
  69        LOOP    Loopback device support is enabled.
  70        M68k    M68k architecture is enabled.
  71                        These options have more detailed description inside of
  72                        Documentation/m68k/kernel-options.txt.
  73        MDA     MDA console support is enabled.
  74        MIPS    MIPS architecture is enabled.
  75        MOUSE   Appropriate mouse support is enabled.
  76        MSI     Message Signaled Interrupts (PCI).
  77        MTD     MTD (Memory Technology Device) support is enabled.
  78        NET     Appropriate network support is enabled.
  79        NUMA    NUMA support is enabled.
  80        NFS     Appropriate NFS support is enabled.
  81        OSS     OSS sound support is enabled.
  82        PV_OPS  A paravirtualized kernel is enabled.
  83        PARIDE  The ParIDE (parallel port IDE) subsystem is enabled.
  84        PARISC  The PA-RISC architecture is enabled.
  85        PCI     PCI bus support is enabled.
  86        PCIE    PCI Express support is enabled.
  87        PCMCIA  The PCMCIA subsystem is enabled.
  88        PNP     Plug & Play support is enabled.
  89        PPC     PowerPC architecture is enabled.
  90        PPT     Parallel port support is enabled.
  91        PS2     Appropriate PS/2 support is enabled.
  92        RAM     RAM disk support is enabled.
  93        S390    S390 architecture is enabled.
  94        SCSI    Appropriate SCSI support is enabled.
  95                        A lot of drivers have their options described inside
  96                        the Documentation/scsi/ sub-directory.
  97        SECURITY Different security models are enabled.
  98        SELINUX SELinux support is enabled.
  99        APPARMOR AppArmor support is enabled.
 100        SERIAL  Serial support is enabled.
 101        SH      SuperH architecture is enabled.
 102        SMP     The kernel is an SMP kernel.
 103        SPARC   Sparc architecture is enabled.
 104        SWSUSP  Software suspend (hibernation) is enabled.
 105        SUSPEND System suspend states are enabled.
 106        TPM     TPM drivers are enabled.
 107        TS      Appropriate touchscreen support is enabled.
 108        UMS     USB Mass Storage support is enabled.
 109        USB     USB support is enabled.
 110        USBHID  USB Human Interface Device support is enabled.
 111        V4L     Video For Linux support is enabled.
 112        VMMIO   Driver for memory mapped virtio devices is enabled.
 113        VGA     The VGA console has been enabled.
 114        VT      Virtual terminal support is enabled.
 115        WDT     Watchdog support is enabled.
 116        XT      IBM PC/XT MFM hard disk support is enabled.
 117        X86-32  X86-32, aka i386 architecture is enabled.
 118        X86-64  X86-64 architecture is enabled.
 119                        More X86-64 boot options can be found in
 120                        Documentation/x86/x86_64/boot-options.txt .
 121        X86     Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
 122        XEN     Xen support is enabled
 123
 124In addition, the following text indicates that the option:
 125
 126        BUGS=   Relates to possible processor bugs on the said processor.
 127        KNL     Is a kernel start-up parameter.
 128        BOOT    Is a boot loader parameter.
 129
 130Parameters denoted with BOOT are actually interpreted by the boot
 131loader, and have no meaning to the kernel directly.
 132Do not modify the syntax of boot loader parameters without extreme
 133need or coordination with <Documentation/x86/boot.txt>.
 134
 135There are also arch-specific kernel-parameters not documented here.
 136See for example <Documentation/x86/x86_64/boot-options.txt>.
 137
 138Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
 139a trailing = on the name of any parameter states that that parameter will
 140be entered as an environment variable, whereas its absence indicates that
 141it will appear as a kernel argument readable via /proc/cmdline by programs
 142running once the system is up.
 143
 144The number of kernel parameters is not limited, but the length of the
 145complete command line (parameters including spaces etc.) is limited to
 146a fixed number of characters. This limit depends on the architecture
 147and is between 256 and 4096 characters. It is defined in the file
 148./include/asm/setup.h as COMMAND_LINE_SIZE.
 149
 150Finally, the [KMG] suffix is commonly described after a number of kernel
 151parameter values. These 'K', 'M', and 'G' letters represent the _binary_
 152multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
 153bytes respectively. Such letter suffixes can also be entirely omitted.
 154
 155
 156        acpi=           [HW,ACPI,X86]
 157                        Advanced Configuration and Power Interface
 158                        Format: { force | off | strict | noirq | rsdt }
 159                        force -- enable ACPI if default was off
 160                        off -- disable ACPI if default was on
 161                        noirq -- do not use ACPI for IRQ routing
 162                        strict -- Be less tolerant of platforms that are not
 163                                strictly ACPI specification compliant.
 164                        rsdt -- prefer RSDT over (default) XSDT
 165                        copy_dsdt -- copy DSDT to memory
 166
 167                        See also Documentation/power/runtime_pm.txt, pci=noacpi
 168
 169        acpi_rsdp=      [ACPI,EFI,KEXEC]
 170                        Pass the RSDP address to the kernel, mostly used
 171                        on machines running EFI runtime service to boot the
 172                        second kernel for kdump.
 173
 174        acpi_apic_instance=     [ACPI, IOAPIC]
 175                        Format: <int>
 176                        2: use 2nd APIC table, if available
 177                        1,0: use 1st APIC table
 178                        default: 0
 179
 180        acpi_backlight= [HW,ACPI]
 181                        acpi_backlight=vendor
 182                        acpi_backlight=video
 183                        If set to vendor, prefer vendor specific driver
 184                        (e.g. thinkpad_acpi, sony_acpi, etc.) instead
 185                        of the ACPI video.ko driver.
 186
 187        acpi.debug_layer=       [HW,ACPI,ACPI_DEBUG]
 188        acpi.debug_level=       [HW,ACPI,ACPI_DEBUG]
 189                        Format: <int>
 190                        CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
 191                        debug output.  Bits in debug_layer correspond to a
 192                        _COMPONENT in an ACPI source file, e.g.,
 193                            #define _COMPONENT ACPI_PCI_COMPONENT
 194                        Bits in debug_level correspond to a level in
 195                        ACPI_DEBUG_PRINT statements, e.g.,
 196                            ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
 197                        The debug_level mask defaults to "info".  See
 198                        Documentation/acpi/debug.txt for more information about
 199                        debug layers and levels.
 200
 201                        Enable processor driver info messages:
 202                            acpi.debug_layer=0x20000000
 203                        Enable PCI/PCI interrupt routing info messages:
 204                            acpi.debug_layer=0x400000
 205                        Enable AML "Debug" output, i.e., stores to the Debug
 206                        object while interpreting AML:
 207                            acpi.debug_layer=0xffffffff acpi.debug_level=0x2
 208                        Enable all messages related to ACPI hardware:
 209                            acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
 210
 211                        Some values produce so much output that the system is
 212                        unusable.  The "log_buf_len" parameter may be useful
 213                        if you need to capture more output.
 214
 215        acpi_irq_balance [HW,ACPI]
 216                        ACPI will balance active IRQs
 217                        default in APIC mode
 218
 219        acpi_irq_nobalance [HW,ACPI]
 220                        ACPI will not move active IRQs (default)
 221                        default in PIC mode
 222
 223        acpi_irq_isa=   [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
 224                        Format: <irq>,<irq>...
 225
 226        acpi_irq_pci=   [HW,ACPI] If irq_balance, clear listed IRQs for
 227                        use by PCI
 228                        Format: <irq>,<irq>...
 229
 230        acpi_no_auto_ssdt       [HW,ACPI] Disable automatic loading of SSDT
 231
 232        acpi_os_name=   [HW,ACPI] Tell ACPI BIOS the name of the OS
 233                        Format: To spoof as Windows 98: ="Microsoft Windows"
 234
 235        acpi_osi=       [HW,ACPI] Modify list of supported OS interface strings
 236                        acpi_osi="string1"      # add string1 -- only one string
 237                        acpi_osi="!string2"     # remove built-in string2
 238                        acpi_osi=               # disable all strings
 239
 240        acpi_pm_good    [X86]
 241                        Override the pmtimer bug detection: force the kernel
 242                        to assume that this machine's pmtimer latches its value
 243                        and always returns good values.
 244
 245        acpi_sci=       [HW,ACPI] ACPI System Control Interrupt trigger mode
 246                        Format: { level | edge | high | low }
 247
 248        acpi_serialize  [HW,ACPI] force serialization of AML methods
 249
 250        acpi_skip_timer_override [HW,ACPI]
 251                        Recognize and ignore IRQ0/pin2 Interrupt Override.
 252                        For broken nForce2 BIOS resulting in XT-PIC timer.
 253
 254        acpi_sleep=     [HW,ACPI] Sleep options
 255                        Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
 256                                  old_ordering, nonvs, sci_force_enable }
 257                        See Documentation/power/video.txt for information on
 258                        s3_bios and s3_mode.
 259                        s3_beep is for debugging; it makes the PC's speaker beep
 260                        as soon as the kernel's real-mode entry point is called.
 261                        s4_nohwsig prevents ACPI hardware signature from being
 262                        used during resume from hibernation.
 263                        old_ordering causes the ACPI 1.0 ordering of the _PTS
 264                        control method, with respect to putting devices into
 265                        low power states, to be enforced (the ACPI 2.0 ordering
 266                        of _PTS is used by default).
 267                        nonvs prevents the kernel from saving/restoring the
 268                        ACPI NVS memory during suspend/hibernation and resume.
 269                        sci_force_enable causes the kernel to set SCI_EN directly
 270                        on resume from S1/S3 (which is against the ACPI spec,
 271                        but some broken systems don't work without it).
 272
 273        acpi_use_timer_override [HW,ACPI]
 274                        Use timer override. For some broken Nvidia NF5 boards
 275                        that require a timer override, but don't have HPET
 276
 277        acpi_enforce_resources= [ACPI]
 278                        { strict | lax | no }
 279                        Check for resource conflicts between native drivers
 280                        and ACPI OperationRegions (SystemIO and SystemMemory
 281                        only). IO ports and memory declared in ACPI might be
 282                        used by the ACPI subsystem in arbitrary AML code and
 283                        can interfere with legacy drivers.
 284                        strict (default): access to resources claimed by ACPI
 285                        is denied; legacy drivers trying to access reserved
 286                        resources will fail to bind to device using them.
 287                        lax: access to resources claimed by ACPI is allowed;
 288                        legacy drivers trying to access reserved resources
 289                        will bind successfully but a warning message is logged.
 290                        no: ACPI OperationRegions are not marked as reserved,
 291                        no further checks are performed.
 292
 293        add_efi_memmap  [EFI; X86] Include EFI memory map in
 294                        kernel's map of available physical RAM.
 295
 296        agp=            [AGP]
 297                        { off | try_unsupported }
 298                        off: disable AGP support
 299                        try_unsupported: try to drive unsupported chipsets
 300                                (may crash computer or cause data corruption)
 301
 302        ALSA            [HW,ALSA]
 303                        See Documentation/sound/alsa/alsa-parameters.txt
 304
 305        alignment=      [KNL,ARM]
 306                        Allow the default userspace alignment fault handler
 307                        behaviour to be specified.  Bit 0 enables warnings,
 308                        bit 1 enables fixups, and bit 2 sends a segfault.
 309
 310        align_va_addr=  [X86-64]
 311                        Align virtual addresses by clearing slice [14:12] when
 312                        allocating a VMA at process creation time. This option
 313                        gives you up to 3% performance improvement on AMD F15h
 314                        machines (where it is enabled by default) for a
 315                        CPU-intensive style benchmark, and it can vary highly in
 316                        a microbenchmark depending on workload and compiler.
 317
 318                        32: only for 32-bit processes
 319                        64: only for 64-bit processes
 320                        on: enable for both 32- and 64-bit processes
 321                        off: disable for both 32- and 64-bit processes
 322
 323        amd_iommu=      [HW,X86-64]
 324                        Pass parameters to the AMD IOMMU driver in the system.
 325                        Possible values are:
 326                        fullflush - enable flushing of IO/TLB entries when
 327                                    they are unmapped. Otherwise they are
 328                                    flushed before they will be reused, which
 329                                    is a lot of faster
 330                        off       - do not initialize any AMD IOMMU found in
 331                                    the system
 332                        force_isolation - Force device isolation for all
 333                                          devices. The IOMMU driver is not
 334                                          allowed anymore to lift isolation
 335                                          requirements as needed. This option
 336                                          does not override iommu=pt
 337
 338        amd_iommu_dump= [HW,X86-64]
 339                        Enable AMD IOMMU driver option to dump the ACPI table
 340                        for AMD IOMMU. With this option enabled, AMD IOMMU
 341                        driver will print ACPI tables for AMD IOMMU during
 342                        IOMMU initialization.
 343
 344        amijoy.map=     [HW,JOY] Amiga joystick support
 345                        Map of devices attached to JOY0DAT and JOY1DAT
 346                        Format: <a>,<b>
 347                        See also Documentation/input/joystick.txt
 348
 349        analog.map=     [HW,JOY] Analog joystick and gamepad support
 350                        Specifies type or capabilities of an analog joystick
 351                        connected to one of 16 gameports
 352                        Format: <type1>,<type2>,..<type16>
 353
 354        apc=            [HW,SPARC]
 355                        Power management functions (SPARCstation-4/5 + deriv.)
 356                        Format: noidle
 357                        Disable APC CPU standby support. SPARCstation-Fox does
 358                        not play well with APC CPU idle - disable it if you have
 359                        APC and your system crashes randomly.
 360
 361        apic=           [APIC,X86-32] Advanced Programmable Interrupt Controller
 362                        Change the output verbosity whilst booting
 363                        Format: { quiet (default) | verbose | debug }
 364                        Change the amount of debugging information output
 365                        when initialising the APIC and IO-APIC components.
 366
 367        autoconf=       [IPV6]
 368                        See Documentation/networking/ipv6.txt.
 369
 370        show_lapic=     [APIC,X86] Advanced Programmable Interrupt Controller
 371                        Limit apic dumping. The parameter defines the maximal
 372                        number of local apics being dumped. Also it is possible
 373                        to set it to "all" by meaning -- no limit here.
 374                        Format: { 1 (default) | 2 | ... | all }.
 375                        The parameter valid if only apic=debug or
 376                        apic=verbose is specified.
 377                        Example: apic=debug show_lapic=all
 378
 379        apm=            [APM] Advanced Power Management
 380                        See header of arch/x86/kernel/apm_32.c.
 381
 382        arcrimi=        [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
 383                        Format: <io>,<irq>,<nodeID>
 384
 385        ataflop=        [HW,M68k]
 386
 387        atarimouse=     [HW,MOUSE] Atari Mouse
 388
 389        atkbd.extra=    [HW] Enable extra LEDs and keys on IBM RapidAccess,
 390                        EzKey and similar keyboards
 391
 392        atkbd.reset=    [HW] Reset keyboard during initialization
 393
 394        atkbd.set=      [HW] Select keyboard code set
 395                        Format: <int> (2 = AT (default), 3 = PS/2)
 396
 397        atkbd.scroll=   [HW] Enable scroll wheel on MS Office and similar
 398                        keyboards
 399
 400        atkbd.softraw=  [HW] Choose between synthetic and real raw mode
 401                        Format: <bool> (0 = real, 1 = synthetic (default))
 402
 403        atkbd.softrepeat= [HW]
 404                        Use software keyboard repeat
 405
 406        baycom_epp=     [HW,AX25]
 407                        Format: <io>,<mode>
 408
 409        baycom_par=     [HW,AX25] BayCom Parallel Port AX.25 Modem
 410                        Format: <io>,<mode>
 411                        See header of drivers/net/hamradio/baycom_par.c.
 412
 413        baycom_ser_fdx= [HW,AX25]
 414                        BayCom Serial Port AX.25 Modem (Full Duplex Mode)
 415                        Format: <io>,<irq>,<mode>[,<baud>]
 416                        See header of drivers/net/hamradio/baycom_ser_fdx.c.
 417
 418        baycom_ser_hdx= [HW,AX25]
 419                        BayCom Serial Port AX.25 Modem (Half Duplex Mode)
 420                        Format: <io>,<irq>,<mode>
 421                        See header of drivers/net/hamradio/baycom_ser_hdx.c.
 422
 423        boot_delay=     Milliseconds to delay each printk during boot.
 424                        Values larger than 10 seconds (10000) are changed to
 425                        no delay (0).
 426                        Format: integer
 427
 428        bootmem_debug   [KNL] Enable bootmem allocator debug messages.
 429
 430        bttv.card=      [HW,V4L] bttv (bt848 + bt878 based grabber cards)
 431        bttv.radio=     Most important insmod options are available as
 432                        kernel args too.
 433        bttv.pll=       See Documentation/video4linux/bttv/Insmod-options
 434        bttv.tuner=
 435
 436        bulk_remove=off [PPC]  This parameter disables the use of the pSeries
 437                        firmware feature for flushing multiple hpte entries
 438                        at a time.
 439
 440        c101=           [NET] Moxa C101 synchronous serial card
 441
 442        cachesize=      [BUGS=X86-32] Override level 2 CPU cache size detection.
 443                        Sometimes CPU hardware bugs make them report the cache
 444                        size incorrectly. The kernel will attempt work arounds
 445                        to fix known problems, but for some CPUs it is not
 446                        possible to determine what the correct size should be.
 447                        This option provides an override for these situations.
 448
 449        ccw_timeout_log [S390]
 450                        See Documentation/s390/CommonIO for details.
 451
 452        cgroup_disable= [KNL] Disable a particular controller
 453                        Format: {name of the controller(s) to disable}
 454                                {Currently supported controllers - "memory"}
 455
 456        checkreqprot    [SELINUX] Set initial checkreqprot flag value.
 457                        Format: { "0" | "1" }
 458                        See security/selinux/Kconfig help text.
 459                        0 -- check protection applied by kernel (includes
 460                                any implied execute protection).
 461                        1 -- check protection requested by application.
 462                        Default value is set via a kernel config option.
 463                        Value can be changed at runtime via
 464                                /selinux/checkreqprot.
 465
 466        cio_ignore=     [S390]
 467                        See Documentation/s390/CommonIO for details.
 468
 469        clock=          [BUGS=X86-32, HW] gettimeofday clocksource override.
 470                        [Deprecated]
 471                        Forces specified clocksource (if available) to be used
 472                        when calculating gettimeofday(). If specified
 473                        clocksource is not available, it defaults to PIT.
 474                        Format: { pit | tsc | cyclone | pmtmr }
 475
 476        clocksource=    Override the default clocksource
 477                        Format: <string>
 478                        Override the default clocksource and use the clocksource
 479                        with the name specified.
 480                        Some clocksource names to choose from, depending on
 481                        the platform:
 482                        [all] jiffies (this is the base, fallback clocksource)
 483                        [ACPI] acpi_pm
 484                        [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
 485                                pxa_timer,timer3,32k_counter,timer0_1
 486                        [AVR32] avr32
 487                        [X86-32] pit,hpet,tsc;
 488                                scx200_hrt on Geode; cyclone on IBM x440
 489                        [MIPS] MIPS
 490                        [PARISC] cr16
 491                        [S390] tod
 492                        [SH] SuperH
 493                        [SPARC64] tick
 494                        [X86-64] hpet,tsc
 495
 496        clearcpuid=BITNUM [X86]
 497                        Disable CPUID feature X for the kernel. See
 498                        arch/x86/include/asm/cpufeature.h for the valid bit
 499                        numbers. Note the Linux specific bits are not necessarily
 500                        stable over kernel options, but the vendor specific
 501                        ones should be.
 502                        Also note that user programs calling CPUID directly
 503                        or using the feature without checking anything
 504                        will still see it. This just prevents it from
 505                        being used by the kernel or shown in /proc/cpuinfo.
 506                        Also note the kernel might malfunction if you disable
 507                        some critical bits.
 508
 509        cma=nn[MG]      [ARM,KNL]
 510                        Sets the size of kernel global memory area for contiguous
 511                        memory allocations. For more information, see
 512                        include/linux/dma-contiguous.h
 513
 514        cmo_free_hint=  [PPC] Format: { yes | no }
 515                        Specify whether pages are marked as being inactive
 516                        when they are freed.  This is used in CMO environments
 517                        to determine OS memory pressure for page stealing by
 518                        a hypervisor.
 519                        Default: yes
 520
 521        coherent_pool=nn[KMG]   [ARM,KNL]
 522                        Sets the size of memory pool for coherent, atomic dma
 523                        allocations, by default set to 256K.
 524
 525        code_bytes      [X86] How many bytes of object code to print
 526                        in an oops report.
 527                        Range: 0 - 8192
 528                        Default: 64
 529
 530        com20020=       [HW,NET] ARCnet - COM20020 chipset
 531                        Format:
 532                        <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
 533
 534        com90io=        [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
 535                        Format: <io>[,<irq>]
 536
 537        com90xx=        [HW,NET]
 538                        ARCnet - COM90xx chipset (memory-mapped buffers)
 539                        Format: <io>[,<irq>[,<memstart>]]
 540
 541        condev=         [HW,S390] console device
 542        conmode=
 543
 544        console=        [KNL] Output console device and options.
 545
 546                tty<n>  Use the virtual console device <n>.
 547
 548                ttyS<n>[,options]
 549                ttyUSB0[,options]
 550                        Use the specified serial port.  The options are of
 551                        the form "bbbbpnf", where "bbbb" is the baud rate,
 552                        "p" is parity ("n", "o", or "e"), "n" is number of
 553                        bits, and "f" is flow control ("r" for RTS or
 554                        omit it).  Default is "9600n8".
 555
 556                        See Documentation/serial-console.txt for more
 557                        information.  See
 558                        Documentation/networking/netconsole.txt for an
 559                        alternative.
 560
 561                uart[8250],io,<addr>[,options]
 562                uart[8250],mmio,<addr>[,options]
 563                        Start an early, polled-mode console on the 8250/16550
 564                        UART at the specified I/O port or MMIO address,
 565                        switching to the matching ttyS device later.  The
 566                        options are the same as for ttyS, above.
 567                hvc<n>  Use the hypervisor console device <n>. This is for
 568                        both Xen and PowerPC hypervisors.
 569
 570                If the device connected to the port is not a TTY but a braille
 571                device, prepend "brl," before the device type, for instance
 572                        console=brl,ttyS0
 573                For now, only VisioBraille is supported.
 574
 575        consoleblank=   [KNL] The console blank (screen saver) timeout in
 576                        seconds. Defaults to 10*60 = 10mins. A value of 0
 577                        disables the blank timer.
 578
 579        coredump_filter=
 580                        [KNL] Change the default value for
 581                        /proc/<pid>/coredump_filter.
 582                        See also Documentation/filesystems/proc.txt.
 583
 584        cpuidle.off=1   [CPU_IDLE]
 585                        disable the cpuidle sub-system
 586
 587        cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
 588                        Format:
 589                        <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
 590
 591        crashkernel=size[KMG][@offset[KMG]]
 592                        [KNL] Using kexec, Linux can switch to a 'crash kernel'
 593                        upon panic. This parameter reserves the physical
 594                        memory region [offset, offset + size] for that kernel
 595                        image. If '@offset' is omitted, then a suitable offset
 596                        is selected automatically. Check
 597                        Documentation/kdump/kdump.txt for further details.
 598
 599        crashkernel=range1:size1[,range2:size2,...][@offset]
 600                        [KNL] Same as above, but depends on the memory
 601                        in the running system. The syntax of range is
 602                        start-[end] where start and end are both
 603                        a memory unit (amount[KMG]). See also
 604                        Documentation/kdump/kdump.txt for an example.
 605
 606        cs89x0_dma=     [HW,NET]
 607                        Format: <dma>
 608
 609        cs89x0_media=   [HW,NET]
 610                        Format: { rj45 | aui | bnc }
 611
 612        dasd=           [HW,NET]
 613                        See header of drivers/s390/block/dasd_devmap.c.
 614
 615        db9.dev[2|3]=   [HW,JOY] Multisystem joystick support via parallel port
 616                        (one device per port)
 617                        Format: <port#>,<type>
 618                        See also Documentation/input/joystick-parport.txt
 619
 620        ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
 621                        time. See Documentation/dynamic-debug-howto.txt for
 622                        details.  Deprecated, see dyndbg.
 623
 624        debug           [KNL] Enable kernel debugging (events log level).
 625
 626        debug_locks_verbose=
 627                        [KNL] verbose self-tests
 628                        Format=<0|1>
 629                        Print debugging info while doing the locking API
 630                        self-tests.
 631                        We default to 0 (no extra messages), setting it to
 632                        1 will print _a lot_ more information - normally
 633                        only useful to kernel developers.
 634
 635        debug_objects   [KNL] Enable object debugging
 636
 637        no_debug_objects
 638                        [KNL] Disable object debugging
 639
 640        debug_guardpage_minorder=
 641                        [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
 642                        parameter allows control of the order of pages that will
 643                        be intentionally kept free (and hence protected) by the
 644                        buddy allocator. Bigger value increase the probability
 645                        of catching random memory corruption, but reduce the
 646                        amount of memory for normal system use. The maximum
 647                        possible value is MAX_ORDER/2.  Setting this parameter
 648                        to 1 or 2 should be enough to identify most random
 649                        memory corruption problems caused by bugs in kernel or
 650                        driver code when a CPU writes to (or reads from) a
 651                        random memory location. Note that there exists a class
 652                        of memory corruptions problems caused by buggy H/W or
 653                        F/W or by drivers badly programing DMA (basically when
 654                        memory is written at bus level and the CPU MMU is
 655                        bypassed) which are not detectable by
 656                        CONFIG_DEBUG_PAGEALLOC, hence this option will not help
 657                        tracking down these problems.
 658
 659        debugpat        [X86] Enable PAT debugging
 660
 661        decnet.addr=    [HW,NET]
 662                        Format: <area>[,<node>]
 663                        See also Documentation/networking/decnet.txt.
 664
 665        default_hugepagesz=
 666                        [same as hugepagesz=] The size of the default
 667                        HugeTLB page size. This is the size represented by
 668                        the legacy /proc/ hugepages APIs, used for SHM, and
 669                        default size when mounting hugetlbfs filesystems.
 670                        Defaults to the default architecture's huge page size
 671                        if not specified.
 672
 673        dhash_entries=  [KNL]
 674                        Set number of hash buckets for dentry cache.
 675
 676        digi=           [HW,SERIAL]
 677                        IO parameters + enable/disable command.
 678
 679        digiepca=       [HW,SERIAL]
 680                        See drivers/char/README.epca and
 681                        Documentation/serial/digiepca.txt.
 682
 683        disable=        [IPV6]
 684                        See Documentation/networking/ipv6.txt.
 685
 686        disable_ddw     [PPC/PSERIES]
 687                        Disable Dynamic DMA Window support. Use this if
 688                        to workaround buggy firmware.
 689
 690        disable_ipv6=   [IPV6]
 691                        See Documentation/networking/ipv6.txt.
 692
 693        disable_mtrr_cleanup [X86]
 694                        The kernel tries to adjust MTRR layout from continuous
 695                        to discrete, to make X server driver able to add WB
 696                        entry later. This parameter disables that.
 697
 698        disable_mtrr_trim [X86, Intel and AMD only]
 699                        By default the kernel will trim any uncacheable
 700                        memory out of your available memory pool based on
 701                        MTRR settings.  This parameter disables that behavior,
 702                        possibly causing your machine to run very slowly.
 703
 704        disable_timer_pin_1 [X86]
 705                        Disable PIN 1 of APIC timer
 706                        Can be useful to work around chipset bugs.
 707
 708        dma_debug=off   If the kernel is compiled with DMA_API_DEBUG support,
 709                        this option disables the debugging code at boot.
 710
 711        dma_debug_entries=<number>
 712                        This option allows to tune the number of preallocated
 713                        entries for DMA-API debugging code. One entry is
 714                        required per DMA-API allocation. Use this if the
 715                        DMA-API debugging code disables itself because the
 716                        architectural default is too low.
 717
 718        dma_debug_driver=<driver_name>
 719                        With this option the DMA-API debugging driver
 720                        filter feature can be enabled at boot time. Just
 721                        pass the driver to filter for as the parameter.
 722                        The filter can be disabled or changed to another
 723                        driver later using sysfs.
 724
 725        drm_kms_helper.edid_firmware=[<connector>:]<file>
 726                        Broken monitors, graphic adapters and KVMs may
 727                        send no or incorrect EDID data sets. This parameter
 728                        allows to specify an EDID data set in the
 729                        /lib/firmware directory that is used instead.
 730                        Generic built-in EDID data sets are used, if one of
 731                        edid/1024x768.bin, edid/1280x1024.bin,
 732                        edid/1680x1050.bin, or edid/1920x1080.bin is given
 733                        and no file with the same name exists. Details and
 734                        instructions how to build your own EDID data are
 735                        available in Documentation/EDID/HOWTO.txt. An EDID
 736                        data set will only be used for a particular connector,
 737                        if its name and a colon are prepended to the EDID
 738                        name.
 739
 740        dscc4.setup=    [NET]
 741
 742        dyndbg[="val"]          [KNL,DYNAMIC_DEBUG]
 743        module.dyndbg[="val"]
 744                        Enable debug messages at boot time.  See
 745                        Documentation/dynamic-debug-howto.txt for details.
 746
 747        earlycon=       [KNL] Output early console device and options.
 748                uart[8250],io,<addr>[,options]
 749                uart[8250],mmio,<addr>[,options]
 750                uart[8250],mmio32,<addr>[,options]
 751                        Start an early, polled-mode console on the 8250/16550
 752                        UART at the specified I/O port or MMIO address.
 753                        MMIO inter-register address stride is either 8-bit
 754                        (mmio) or 32-bit (mmio32).
 755                        The options are the same as for ttyS, above.
 756
 757        earlyprintk=    [X86,SH,BLACKFIN]
 758                        earlyprintk=vga
 759                        earlyprintk=xen
 760                        earlyprintk=serial[,ttySn[,baudrate]]
 761                        earlyprintk=ttySn[,baudrate]
 762                        earlyprintk=dbgp[debugController#]
 763
 764                        Append ",keep" to not disable it when the real console
 765                        takes over.
 766
 767                        Only vga or serial or usb debug port at a time.
 768
 769                        Currently only ttyS0 and ttyS1 are supported.
 770
 771                        Interaction with the standard serial driver is not
 772                        very good.
 773
 774                        The VGA output is eventually overwritten by the real
 775                        console.
 776
 777                        The xen output can only be used by Xen PV guests.
 778
 779        ekgdboc=        [X86,KGDB] Allow early kernel console debugging
 780                        ekgdboc=kbd
 781
 782                        This is designed to be used in conjunction with
 783                        the boot argument: earlyprintk=vga
 784
 785        edd=            [EDD]
 786                        Format: {"off" | "on" | "skip[mbr]"}
 787
 788        eisa_irq_edge=  [PARISC,HW]
 789                        See header of drivers/parisc/eisa.c.
 790
 791        elanfreq=       [X86-32]
 792                        See comment before function elanfreq_setup() in
 793                        arch/x86/kernel/cpu/cpufreq/elanfreq.c.
 794
 795        elevator=       [IOSCHED]
 796                        Format: {"cfq" | "deadline" | "noop"}
 797                        See Documentation/block/cfq-iosched.txt and
 798                        Documentation/block/deadline-iosched.txt for details.
 799
 800        elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
 801                        Specifies physical address of start of kernel core
 802                        image elf header and optionally the size. Generally
 803                        kexec loader will pass this option to capture kernel.
 804                        See Documentation/kdump/kdump.txt for details.
 805
 806        enable_mtrr_cleanup [X86]
 807                        The kernel tries to adjust MTRR layout from continuous
 808                        to discrete, to make X server driver able to add WB
 809                        entry later. This parameter enables that.
 810
 811        enable_timer_pin_1 [X86]
 812                        Enable PIN 1 of APIC timer
 813                        Can be useful to work around chipset bugs
 814                        (in particular on some ATI chipsets).
 815                        The kernel tries to set a reasonable default.
 816
 817        enforcing       [SELINUX] Set initial enforcing status.
 818                        Format: {"0" | "1"}
 819                        See security/selinux/Kconfig help text.
 820                        0 -- permissive (log only, no denials).
 821                        1 -- enforcing (deny and log).
 822                        Default value is 0.
 823                        Value can be changed at runtime via /selinux/enforce.
 824
 825        erst_disable    [ACPI]
 826                        Disable Error Record Serialization Table (ERST)
 827                        support.
 828
 829        ether=          [HW,NET] Ethernet cards parameters
 830                        This option is obsoleted by the "netdev=" option, which
 831                        has equivalent usage. See its documentation for details.
 832
 833        evm=            [EVM]
 834                        Format: { "fix" }
 835                        Permit 'security.evm' to be updated regardless of
 836                        current integrity status.
 837
 838        failslab=
 839        fail_page_alloc=
 840        fail_make_request=[KNL]
 841                        General fault injection mechanism.
 842                        Format: <interval>,<probability>,<space>,<times>
 843                        See also Documentation/fault-injection/.
 844
 845        floppy=         [HW]
 846                        See Documentation/blockdev/floppy.txt.
 847
 848        force_pal_cache_flush
 849                        [IA-64] Avoid check_sal_cache_flush which may hang on
 850                        buggy SAL_CACHE_FLUSH implementations. Using this
 851                        parameter will force ia64_sal_cache_flush to call
 852                        ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
 853
 854        ftrace=[tracer]
 855                        [FTRACE] will set and start the specified tracer
 856                        as early as possible in order to facilitate early
 857                        boot debugging.
 858
 859        ftrace_dump_on_oops[=orig_cpu]
 860                        [FTRACE] will dump the trace buffers on oops.
 861                        If no parameter is passed, ftrace will dump
 862                        buffers of all CPUs, but if you pass orig_cpu, it will
 863                        dump only the buffer of the CPU that triggered the
 864                        oops.
 865
 866        ftrace_filter=[function-list]
 867                        [FTRACE] Limit the functions traced by the function
 868                        tracer at boot up. function-list is a comma separated
 869                        list of functions. This list can be changed at run
 870                        time by the set_ftrace_filter file in the debugfs
 871                        tracing directory.
 872
 873        ftrace_notrace=[function-list]
 874                        [FTRACE] Do not trace the functions specified in
 875                        function-list. This list can be changed at run time
 876                        by the set_ftrace_notrace file in the debugfs
 877                        tracing directory.
 878
 879        ftrace_graph_filter=[function-list]
 880                        [FTRACE] Limit the top level callers functions traced
 881                        by the function graph tracer at boot up.
 882                        function-list is a comma separated list of functions
 883                        that can be changed at run time by the
 884                        set_graph_function file in the debugfs tracing directory.
 885
 886        gamecon.map[2|3]=
 887                        [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
 888                        support via parallel port (up to 5 devices per port)
 889                        Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
 890                        See also Documentation/input/joystick-parport.txt
 891
 892        gamma=          [HW,DRM]
 893
 894        gart_fix_e820=  [X86_64] disable the fix e820 for K8 GART
 895                        Format: off | on
 896                        default: on
 897
 898        gcov_persist=   [GCOV] When non-zero (default), profiling data for
 899                        kernel modules is saved and remains accessible via
 900                        debugfs, even when the module is unloaded/reloaded.
 901                        When zero, profiling data is discarded and associated
 902                        debugfs files are removed at module unload time.
 903
 904        gpt             [EFI] Forces disk with valid GPT signature but
 905                        invalid Protective MBR to be treated as GPT.
 906
 907        grcan.enable0=  [HW] Configuration of physical interface 0. Determines
 908                        the "Enable 0" bit of the configuration register.
 909                        Format: 0 | 1
 910                        Default: 0
 911        grcan.enable1=  [HW] Configuration of physical interface 1. Determines
 912                        the "Enable 0" bit of the configuration register.
 913                        Format: 0 | 1
 914                        Default: 0
 915        grcan.select=   [HW] Select which physical interface to use.
 916                        Format: 0 | 1
 917                        Default: 0
 918        grcan.txsize=   [HW] Sets the size of the tx buffer.
 919                        Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
 920                        Default: 1024
 921        grcan.rxsize=   [HW] Sets the size of the rx buffer.
 922                        Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
 923                        Default: 1024
 924
 925        hashdist=       [KNL,NUMA] Large hashes allocated during boot
 926                        are distributed across NUMA nodes.  Defaults on
 927                        for 64-bit NUMA, off otherwise.
 928                        Format: 0 | 1 (for off | on)
 929
 930        hcl=            [IA-64] SGI's Hardware Graph compatibility layer
 931
 932        hd=             [EIDE] (E)IDE hard drive subsystem geometry
 933                        Format: <cyl>,<head>,<sect>
 934
 935        hest_disable    [ACPI]
 936                        Disable Hardware Error Source Table (HEST) support;
 937                        corresponding firmware-first mode error processing
 938                        logic will be disabled.
 939
 940        highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
 941                        size of <nn>. This works even on boxes that have no
 942                        highmem otherwise. This also works to reduce highmem
 943                        size on bigger boxes.
 944
 945        highres=        [KNL] Enable/disable high resolution timer mode.
 946                        Valid parameters: "on", "off"
 947                        Default: "on"
 948
 949        hisax=          [HW,ISDN]
 950                        See Documentation/isdn/README.HiSax.
 951
 952        hlt             [BUGS=ARM,SH]
 953
 954        hpet=           [X86-32,HPET] option to control HPET usage
 955                        Format: { enable (default) | disable | force |
 956                                verbose }
 957                        disable: disable HPET and use PIT instead
 958                        force: allow force enabled of undocumented chips (ICH4,
 959                                VIA, nVidia)
 960                        verbose: show contents of HPET registers during setup
 961
 962        hugepages=      [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
 963        hugepagesz=     [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
 964                        On x86-64 and powerpc, this option can be specified
 965                        multiple times interleaved with hugepages= to reserve
 966                        huge pages of different sizes. Valid pages sizes on
 967                        x86-64 are 2M (when the CPU supports "pse") and 1G
 968                        (when the CPU supports the "pdpe1gb" cpuinfo flag)
 969                        Note that 1GB pages can only be allocated at boot time
 970                        using hugepages= and not freed afterwards.
 971
 972        hvc_iucv=       [S390] Number of z/VM IUCV hypervisor console (HVC)
 973                               terminal devices. Valid values: 0..8
 974        hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
 975                               If specified, z/VM IUCV HVC accepts connections
 976                               from listed z/VM user IDs only.
 977
 978        keep_bootcon    [KNL]
 979                        Do not unregister boot console at start. This is only
 980                        useful for debugging when something happens in the window
 981                        between unregistering the boot console and initializing
 982                        the real console.
 983
 984        i2c_bus=        [HW] Override the default board specific I2C bus speed
 985                             or register an additional I2C bus that is not
 986                             registered from board initialization code.
 987                             Format:
 988                             <bus_id>,<clkrate>
 989
 990        i8042.debug     [HW] Toggle i8042 debug mode
 991        i8042.direct    [HW] Put keyboard port into non-translated mode
 992        i8042.dumbkbd   [HW] Pretend that controller can only read data from
 993                             keyboard and cannot control its state
 994                             (Don't attempt to blink the leds)
 995        i8042.noaux     [HW] Don't check for auxiliary (== mouse) port
 996        i8042.nokbd     [HW] Don't check/create keyboard port
 997        i8042.noloop    [HW] Disable the AUX Loopback command while probing
 998                             for the AUX port
 999        i8042.nomux     [HW] Don't check presence of an active multiplexing
1000                             controller
1001        i8042.nopnp     [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1002                             controllers
1003        i8042.notimeout [HW] Ignore timeout condition signalled by controller
1004        i8042.reset     [HW] Reset the controller during init and cleanup
1005        i8042.unlock    [HW] Unlock (ignore) the keylock
1006
1007        i810=           [HW,DRM]
1008
1009        i8k.ignore_dmi  [HW] Continue probing hardware even if DMI data
1010                        indicates that the driver is running on unsupported
1011                        hardware.
1012        i8k.force       [HW] Activate i8k driver even if SMM BIOS signature
1013                        does not match list of supported models.
1014        i8k.power_status
1015                        [HW] Report power status in /proc/i8k
1016                        (disabled by default)
1017        i8k.restricted  [HW] Allow controlling fans only if SYS_ADMIN
1018                        capability is set.
1019
1020        i915.invert_brightness=
1021                        [DRM] Invert the sense of the variable that is used to
1022                        set the brightness of the panel backlight. Normally a
1023                        brightness value of 0 indicates backlight switched off,
1024                        and the maximum of the brightness value sets the backlight
1025                        to maximum brightness. If this parameter is set to 0
1026                        (default) and the machine requires it, or this parameter
1027                        is set to 1, a brightness value of 0 sets the backlight
1028                        to maximum brightness, and the maximum of the brightness
1029                        value switches the backlight off.
1030                        -1 -- never invert brightness
1031                         0 -- machine default
1032                         1 -- force brightness inversion
1033
1034        icn=            [HW,ISDN]
1035                        Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1036
1037        ide-core.nodma= [HW] (E)IDE subsystem
1038                        Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1039                        .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1040                        .cdrom .chs .ignore_cable are additional options
1041                        See Documentation/ide/ide.txt.
1042
1043        ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1044                        Claim all unknown PCI IDE storage controllers.
1045
1046        idle=           [X86]
1047                        Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
1048                        Poll forces a polling idle loop that can slightly
1049                        improve the performance of waking up a idle CPU, but
1050                        will use a lot of power and make the system run hot.
1051                        Not recommended.
1052                        idle=mwait: On systems which support MONITOR/MWAIT but
1053                        the kernel chose to not use it because it doesn't save
1054                        as much power as a normal idle loop, use the
1055                        MONITOR/MWAIT idle loop anyways. Performance should be
1056                        the same as idle=poll.
1057                        idle=halt: Halt is forced to be used for CPU idle.
1058                        In such case C2/C3 won't be used again.
1059                        idle=nomwait: Disable mwait for CPU C-states
1060
1061        ignore_loglevel [KNL]
1062                        Ignore loglevel setting - this will print /all/
1063                        kernel messages to the console. Useful for debugging.
1064                        We also add it as printk module parameter, so users
1065                        could change it dynamically, usually by
1066                        /sys/module/printk/parameters/ignore_loglevel.
1067
1068        ihash_entries=  [KNL]
1069                        Set number of hash buckets for inode cache.
1070
1071        ima_appraise=   [IMA] appraise integrity measurements
1072                        Format: { "off" | "enforce" | "fix" }
1073                        default: "enforce"
1074
1075        ima_appraise_tcb [IMA]
1076                        The builtin appraise policy appraises all files
1077                        owned by uid=0.
1078
1079        ima_audit=      [IMA]
1080                        Format: { "0" | "1" }
1081                        0 -- integrity auditing messages. (Default)
1082                        1 -- enable informational integrity auditing messages.
1083
1084        ima_hash=       [IMA]
1085                        Format: { "sha1" | "md5" }
1086                        default: "sha1"
1087
1088        ima_tcb         [IMA]
1089                        Load a policy which meets the needs of the Trusted
1090                        Computing Base.  This means IMA will measure all
1091                        programs exec'd, files mmap'd for exec, and all files
1092                        opened for read by uid=0.
1093
1094        init=           [KNL]
1095                        Format: <full_path>
1096                        Run specified binary instead of /sbin/init as init
1097                        process.
1098
1099        initcall_debug  [KNL] Trace initcalls as they are executed.  Useful
1100                        for working out where the kernel is dying during
1101                        startup.
1102
1103        initrd=         [BOOT] Specify the location of the initial ramdisk
1104
1105        inport.irq=     [HW] Inport (ATI XL and Microsoft) busmouse driver
1106                        Format: <irq>
1107
1108        intel_iommu=    [DMAR] Intel IOMMU driver (DMAR) option
1109                on
1110                        Enable intel iommu driver.
1111                off
1112                        Disable intel iommu driver.
1113                igfx_off [Default Off]
1114                        By default, gfx is mapped as normal device. If a gfx
1115                        device has a dedicated DMAR unit, the DMAR unit is
1116                        bypassed by not enabling DMAR with this option. In
1117                        this case, gfx device will use physical address for
1118                        DMA.
1119                forcedac [x86_64]
1120                        With this option iommu will not optimize to look
1121                        for io virtual address below 32-bit forcing dual
1122                        address cycle on pci bus for cards supporting greater
1123                        than 32-bit addressing. The default is to look
1124                        for translation below 32-bit and if not available
1125                        then look in the higher range.
1126                strict [Default Off]
1127                        With this option on every unmap_single operation will
1128                        result in a hardware IOTLB flush operation as opposed
1129                        to batching them for performance.
1130                sp_off [Default Off]
1131                        By default, super page will be supported if Intel IOMMU
1132                        has the capability. With this option, super page will
1133                        not be supported.
1134
1135        intel_idle.max_cstate=  [KNL,HW,ACPI,X86]
1136                        0       disables intel_idle and fall back on acpi_idle.
1137                        1 to 6  specify maximum depth of C-state.
1138
1139        intremap=       [X86-64, Intel-IOMMU]
1140                        on      enable Interrupt Remapping (default)
1141                        off     disable Interrupt Remapping
1142                        nosid   disable Source ID checking
1143                        no_x2apic_optout
1144                                BIOS x2APIC opt-out request will be ignored
1145
1146        iomem=          Disable strict checking of access to MMIO memory
1147                strict  regions from userspace.
1148                relaxed
1149
1150        iommu=          [x86]
1151                off
1152                force
1153                noforce
1154                biomerge
1155                panic
1156                nopanic
1157                merge
1158                nomerge
1159                forcesac
1160                soft
1161                pt              [x86, IA-64]
1162
1163
1164        io7=            [HW] IO7 for Marvel based alpha systems
1165                        See comment before marvel_specify_io7 in
1166                        arch/alpha/kernel/core_marvel.c.
1167
1168        io_delay=       [X86] I/O delay method
1169                0x80
1170                        Standard port 0x80 based delay
1171                0xed
1172                        Alternate port 0xed based delay (needed on some systems)
1173                udelay
1174                        Simple two microseconds delay
1175                none
1176                        No delay
1177
1178        ip=             [IP_PNP]
1179                        See Documentation/filesystems/nfs/nfsroot.txt.
1180
1181        ip2=            [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1182                        See comment before ip2_setup() in
1183                        drivers/char/ip2/ip2base.c.
1184
1185        irqfixup        [HW]
1186                        When an interrupt is not handled search all handlers
1187                        for it. Intended to get systems with badly broken
1188                        firmware running.
1189
1190        irqpoll         [HW]
1191                        When an interrupt is not handled search all handlers
1192                        for it. Also check all handlers each timer
1193                        interrupt. Intended to get systems with badly broken
1194                        firmware running.
1195
1196        isapnp=         [ISAPNP]
1197                        Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1198
1199        isolcpus=       [KNL,SMP] Isolate CPUs from the general scheduler.
1200                        Format:
1201                        <cpu number>,...,<cpu number>
1202                        or
1203                        <cpu number>-<cpu number>
1204                        (must be a positive range in ascending order)
1205                        or a mixture
1206                        <cpu number>,...,<cpu number>-<cpu number>
1207
1208                        This option can be used to specify one or more CPUs
1209                        to isolate from the general SMP balancing and scheduling
1210                        algorithms. You can move a process onto or off an
1211                        "isolated" CPU via the CPU affinity syscalls or cpuset.
1212                        <cpu number> begins at 0 and the maximum value is
1213                        "number of CPUs in system - 1".
1214
1215                        This option is the preferred way to isolate CPUs. The
1216                        alternative -- manually setting the CPU mask of all
1217                        tasks in the system -- can cause problems and
1218                        suboptimal load balancer performance.
1219
1220        iucv=           [HW,NET]
1221
1222        js=             [HW,JOY] Analog joystick
1223                        See Documentation/input/joystick.txt.
1224
1225        keepinitrd      [HW,ARM]
1226
1227        kernelcore=nn[KMG]      [KNL,X86,IA-64,PPC] This parameter
1228                        specifies the amount of memory usable by the kernel
1229                        for non-movable allocations.  The requested amount is
1230                        spread evenly throughout all nodes in the system. The
1231                        remaining memory in each node is used for Movable
1232                        pages. In the event, a node is too small to have both
1233                        kernelcore and Movable pages, kernelcore pages will
1234                        take priority and other nodes will have a larger number
1235                        of kernelcore pages.  The Movable zone is used for the
1236                        allocation of pages that may be reclaimed or moved
1237                        by the page migration subsystem.  This means that
1238                        HugeTLB pages may not be allocated from this zone.
1239                        Note that allocations like PTEs-from-HighMem still
1240                        use the HighMem zone if it exists, and the Normal
1241                        zone if it does not.
1242
1243        kgdbdbgp=       [KGDB,HW] kgdb over EHCI usb debug port.
1244                        Format: <Controller#>[,poll interval]
1245                        The controller # is the number of the ehci usb debug
1246                        port as it is probed via PCI.  The poll interval is
1247                        optional and is the number seconds in between
1248                        each poll cycle to the debug port in case you need
1249                        the functionality for interrupting the kernel with
1250                        gdb or control-c on the dbgp connection.  When
1251                        not using this parameter you use sysrq-g to break into
1252                        the kernel debugger.
1253
1254        kgdboc=         [KGDB,HW] kgdb over consoles.
1255                        Requires a tty driver that supports console polling,
1256                        or a supported polling keyboard driver (non-usb).
1257                         Serial only format: <serial_device>[,baud]
1258                         keyboard only format: kbd
1259                         keyboard and serial format: kbd,<serial_device>[,baud]
1260                        Optional Kernel mode setting:
1261                         kms, kbd format: kms,kbd
1262                         kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1263
1264        kgdbwait        [KGDB] Stop kernel execution and enter the
1265                        kernel debugger at the earliest opportunity.
1266
1267        kmac=           [MIPS] korina ethernet MAC address.
1268                        Configure the RouterBoard 532 series on-chip
1269                        Ethernet adapter MAC address.
1270
1271        kmemleak=       [KNL] Boot-time kmemleak enable/disable
1272                        Valid arguments: on, off
1273                        Default: on
1274
1275        kstack=N        [X86] Print N words from the kernel stack
1276                        in oops dumps.
1277
1278        kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1279                        Default is 0 (don't ignore, but inject #GP)
1280
1281        kvm.mmu_audit=  [KVM] This is a R/W parameter which allows audit
1282                        KVM MMU at runtime.
1283                        Default is 0 (off)
1284
1285        kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1286                        Default is 1 (enabled)
1287
1288        kvm-amd.npt=    [KVM,AMD] Disable nested paging (virtualized MMU)
1289                        for all guests.
1290                        Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1291
1292        kvm-intel.ept=  [KVM,Intel] Disable extended page tables
1293                        (virtualized MMU) support on capable Intel chips.
1294                        Default is 1 (enabled)
1295
1296        kvm-intel.emulate_invalid_guest_state=
1297                        [KVM,Intel] Enable emulation of invalid guest states
1298                        Default is 0 (disabled)
1299
1300        kvm-intel.flexpriority=
1301                        [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1302                        Default is 1 (enabled)
1303
1304        kvm-intel.nested=
1305                        [KVM,Intel] Enable VMX nesting (nVMX).
1306                        Default is 0 (disabled)
1307
1308        kvm-intel.unrestricted_guest=
1309                        [KVM,Intel] Disable unrestricted guest feature
1310                        (virtualized real and unpaged mode) on capable
1311                        Intel chips. Default is 1 (enabled)
1312
1313        kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1314                        feature (tagged TLBs) on capable Intel chips.
1315                        Default is 1 (enabled)
1316
1317        l2cr=           [PPC]
1318
1319        l3cr=           [PPC]
1320
1321        lapic           [X86-32,APIC] Enable the local APIC even if BIOS
1322                        disabled it.
1323
1324        lapic=          [x86,APIC] "notscdeadline" Do not use TSC deadline
1325                        value for LAPIC timer one-shot implementation. Default
1326                        back to the programmable timer unit in the LAPIC.
1327
1328        lapic_timer_c2_ok       [X86,APIC] trust the local apic timer
1329                        in C2 power state.
1330
1331        libata.dma=     [LIBATA] DMA control
1332                        libata.dma=0      Disable all PATA and SATA DMA
1333                        libata.dma=1      PATA and SATA Disk DMA only
1334                        libata.dma=2      ATAPI (CDROM) DMA only
1335                        libata.dma=4      Compact Flash DMA only
1336                        Combinations also work, so libata.dma=3 enables DMA
1337                        for disks and CDROMs, but not CFs.
1338
1339        libata.ignore_hpa=      [LIBATA] Ignore HPA limit
1340                        libata.ignore_hpa=0       keep BIOS limits (default)
1341                        libata.ignore_hpa=1       ignore limits, using full disk
1342
1343        libata.noacpi   [LIBATA] Disables use of ACPI in libata suspend/resume
1344                        when set.
1345                        Format: <int>
1346
1347        libata.force=   [LIBATA] Force configurations.  The format is comma
1348                        separated list of "[ID:]VAL" where ID is
1349                        PORT[.DEVICE].  PORT and DEVICE are decimal numbers
1350                        matching port, link or device.  Basically, it matches
1351                        the ATA ID string printed on console by libata.  If
1352                        the whole ID part is omitted, the last PORT and DEVICE
1353                        values are used.  If ID hasn't been specified yet, the
1354                        configuration applies to all ports, links and devices.
1355
1356                        If only DEVICE is omitted, the parameter applies to
1357                        the port and all links and devices behind it.  DEVICE
1358                        number of 0 either selects the first device or the
1359                        first fan-out link behind PMP device.  It does not
1360                        select the host link.  DEVICE number of 15 selects the
1361                        host link and device attached to it.
1362
1363                        The VAL specifies the configuration to force.  As long
1364                        as there's no ambiguity shortcut notation is allowed.
1365                        For example, both 1.5 and 1.5G would work for 1.5Gbps.
1366                        The following configurations can be forced.
1367
1368                        * Cable type: 40c, 80c, short40c, unk, ign or sata.
1369                          Any ID with matching PORT is used.
1370
1371                        * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1372
1373                        * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1374                          udma[/][16,25,33,44,66,100,133] notation is also
1375                          allowed.
1376
1377                        * [no]ncq: Turn on or off NCQ.
1378
1379                        * nohrst, nosrst, norst: suppress hard, soft
1380                          and both resets.
1381
1382                        * rstonce: only attempt one reset during
1383                          hot-unplug link recovery
1384
1385                        * dump_id: dump IDENTIFY data.
1386
1387                        If there are multiple matching configurations changing
1388                        the same attribute, the last one is used.
1389
1390        memblock=debug  [KNL] Enable memblock debug messages.
1391
1392        load_ramdisk=   [RAM] List of ramdisks to load from floppy
1393                        See Documentation/blockdev/ramdisk.txt.
1394
1395        lockd.nlm_grace_period=P  [NFS] Assign grace period.
1396                        Format: <integer>
1397
1398        lockd.nlm_tcpport=N     [NFS] Assign TCP port.
1399                        Format: <integer>
1400
1401        lockd.nlm_timeout=T     [NFS] Assign timeout value.
1402                        Format: <integer>
1403
1404        lockd.nlm_udpport=M     [NFS] Assign UDP port.
1405                        Format: <integer>
1406
1407        logibm.irq=     [HW,MOUSE] Logitech Bus Mouse Driver
1408                        Format: <irq>
1409
1410        loglevel=       All Kernel Messages with a loglevel smaller than the
1411                        console loglevel will be printed to the console. It can
1412                        also be changed with klogd or other programs. The
1413                        loglevels are defined as follows:
1414
1415                        0 (KERN_EMERG)          system is unusable
1416                        1 (KERN_ALERT)          action must be taken immediately
1417                        2 (KERN_CRIT)           critical conditions
1418                        3 (KERN_ERR)            error conditions
1419                        4 (KERN_WARNING)        warning conditions
1420                        5 (KERN_NOTICE)         normal but significant condition
1421                        6 (KERN_INFO)           informational
1422                        7 (KERN_DEBUG)          debug-level messages
1423
1424        log_buf_len=n[KMG]      Sets the size of the printk ring buffer,
1425                        in bytes.  n must be a power of two.  The default
1426                        size is set in the kernel config file.
1427
1428        logo.nologo     [FB] Disables display of the built-in Linux logo.
1429                        This may be used to provide more screen space for
1430                        kernel log messages and is useful when debugging
1431                        kernel boot problems.
1432
1433        lp=0            [LP]    Specify parallel ports to use, e.g,
1434        lp=port[,port...]       lp=none,parport0 (lp0 not configured, lp1 uses
1435        lp=reset                first parallel port). 'lp=0' disables the
1436        lp=auto                 printer driver. 'lp=reset' (which can be
1437                                specified in addition to the ports) causes
1438                                attached printers to be reset. Using
1439                                lp=port1,port2,... specifies the parallel ports
1440                                to associate lp devices with, starting with
1441                                lp0. A port specification may be 'none' to skip
1442                                that lp device, or a parport name such as
1443                                'parport0'. Specifying 'lp=auto' instead of a
1444                                port specification list means that device IDs
1445                                from each port should be examined, to see if
1446                                an IEEE 1284-compliant printer is attached; if
1447                                so, the driver will manage that printer.
1448                                See also header of drivers/char/lp.c.
1449
1450        lpj=n           [KNL]
1451                        Sets loops_per_jiffy to given constant, thus avoiding
1452                        time-consuming boot-time autodetection (up to 250 ms per
1453                        CPU). 0 enables autodetection (default). To determine
1454                        the correct value for your kernel, boot with normal
1455                        autodetection and see what value is printed. Note that
1456                        on SMP systems the preset will be applied to all CPUs,
1457                        which is likely to cause problems if your CPUs need
1458                        significantly divergent settings. An incorrect value
1459                        will cause delays in the kernel to be wrong, leading to
1460                        unpredictable I/O errors and other breakage. Although
1461                        unlikely, in the extreme case this might damage your
1462                        hardware.
1463
1464        ltpc=           [NET]
1465                        Format: <io>,<irq>,<dma>
1466
1467        machvec=        [IA-64] Force the use of a particular machine-vector
1468                        (machvec) in a generic kernel.
1469                        Example: machvec=hpzx1_swiotlb
1470
1471        machtype=       [Loongson] Share the same kernel image file between different
1472                         yeeloong laptop.
1473                        Example: machtype=lemote-yeeloong-2f-7inch
1474
1475        max_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory greater
1476                        than or equal to this physical address is ignored.
1477
1478        maxcpus=        [SMP] Maximum number of processors that an SMP kernel
1479                        should make use of.  maxcpus=n : n >= 0 limits the
1480                        kernel to using 'n' processors.  n=0 is a special case,
1481                        it is equivalent to "nosmp", which also disables
1482                        the IO APIC.
1483
1484        max_loop=       [LOOP] The number of loop block devices that get
1485        (loop.max_loop) unconditionally pre-created at init time. The default
1486                        number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1487                        of statically allocating a predefined number, loop
1488                        devices can be requested on-demand with the
1489                        /dev/loop-control interface.
1490
1491        mce             [X86-32] Machine Check Exception
1492
1493        mce=option      [X86-64] See Documentation/x86/x86_64/boot-options.txt
1494
1495        md=             [HW] RAID subsystems devices and level
1496                        See Documentation/md.txt.
1497
1498        mdacon=         [MDA]
1499                        Format: <first>,<last>
1500                        Specifies range of consoles to be captured by the MDA.
1501
1502        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
1503                        Amount of memory to be used when the kernel is not able
1504                        to see the whole system memory or for test.
1505                        [X86] Work as limiting max address. Use together
1506                        with memmap= to avoid physical address space collisions.
1507                        Without memmap= PCI devices could be placed at addresses
1508                        belonging to unused RAM.
1509
1510        mem=nopentium   [BUGS=X86-32] Disable usage of 4MB pages for kernel
1511                        memory.
1512
1513        memchunk=nn[KMG]
1514                        [KNL,SH] Allow user to override the default size for
1515                        per-device physically contiguous DMA buffers.
1516
1517        memmap=exactmap [KNL,X86] Enable setting of an exact
1518                        E820 memory map, as specified by the user.
1519                        Such memmap=exactmap lines can be constructed based on
1520                        BIOS output or other requirements. See the memmap=nn@ss
1521                        option description.
1522
1523        memmap=nn[KMG]@ss[KMG]
1524                        [KNL] Force usage of a specific region of memory
1525                        Region of memory to be used, from ss to ss+nn.
1526
1527        memmap=nn[KMG]#ss[KMG]
1528                        [KNL,ACPI] Mark specific memory as ACPI data.
1529                        Region of memory to be used, from ss to ss+nn.
1530
1531        memmap=nn[KMG]$ss[KMG]
1532                        [KNL,ACPI] Mark specific memory as reserved.
1533                        Region of memory to be used, from ss to ss+nn.
1534                        Example: Exclude memory from 0x18690000-0x1869ffff
1535                                 memmap=64K$0x18690000
1536                                 or
1537                                 memmap=0x10000$0x18690000
1538
1539        memory_corruption_check=0/1 [X86]
1540                        Some BIOSes seem to corrupt the first 64k of
1541                        memory when doing things like suspend/resume.
1542                        Setting this option will scan the memory
1543                        looking for corruption.  Enabling this will
1544                        both detect corruption and prevent the kernel
1545                        from using the memory being corrupted.
1546                        However, its intended as a diagnostic tool; if
1547                        repeatable BIOS-originated corruption always
1548                        affects the same memory, you can use memmap=
1549                        to prevent the kernel from using that memory.
1550
1551        memory_corruption_check_size=size [X86]
1552                        By default it checks for corruption in the low
1553                        64k, making this memory unavailable for normal
1554                        use.  Use this parameter to scan for
1555                        corruption in more or less memory.
1556
1557        memory_corruption_check_period=seconds [X86]
1558                        By default it checks for corruption every 60
1559                        seconds.  Use this parameter to check at some
1560                        other rate.  0 disables periodic checking.
1561
1562        memtest=        [KNL,X86] Enable memtest
1563                        Format: <integer>
1564                        default : 0 <disable>
1565                        Specifies the number of memtest passes to be
1566                        performed. Each pass selects another test
1567                        pattern from a given set of patterns. Memtest
1568                        fills the memory with this pattern, validates
1569                        memory contents and reserves bad memory
1570                        regions that are detected.
1571
1572        meye.*=         [HW] Set MotionEye Camera parameters
1573                        See Documentation/video4linux/meye.txt.
1574
1575        mfgpt_irq=      [IA-32] Specify the IRQ to use for the
1576                        Multi-Function General Purpose Timers on AMD Geode
1577                        platforms.
1578
1579        mfgptfix        [X86-32] Fix MFGPT timers on AMD Geode platforms when
1580                        the BIOS has incorrectly applied a workaround. TinyBIOS
1581                        version 0.98 is known to be affected, 0.99 fixes the
1582                        problem by letting the user disable the workaround.
1583
1584        mga=            [HW,DRM]
1585
1586        min_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory below this
1587                        physical address is ignored.
1588
1589        mini2440=       [ARM,HW,KNL]
1590                        Format:[0..2][b][c][t]
1591                        Default: "0tb"
1592                        MINI2440 configuration specification:
1593                        0 - The attached screen is the 3.5" TFT
1594                        1 - The attached screen is the 7" TFT
1595                        2 - The VGA Shield is attached (1024x768)
1596                        Leaving out the screen size parameter will not load
1597                        the TFT driver, and the framebuffer will be left
1598                        unconfigured.
1599                        b - Enable backlight. The TFT backlight pin will be
1600                        linked to the kernel VESA blanking code and a GPIO
1601                        LED. This parameter is not necessary when using the
1602                        VGA shield.
1603                        c - Enable the s3c camera interface.
1604                        t - Reserved for enabling touchscreen support. The
1605                        touchscreen support is not enabled in the mainstream
1606                        kernel as of 2.6.30, a preliminary port can be found
1607                        in the "bleeding edge" mini2440 support kernel at
1608                        http://repo.or.cz/w/linux-2.6/mini2440.git
1609
1610        mminit_loglevel=
1611                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1612                        parameter allows control of the logging verbosity for
1613                        the additional memory initialisation checks. A value
1614                        of 0 disables mminit logging and a level of 4 will
1615                        log everything. Information is printed at KERN_DEBUG
1616                        so loglevel=8 may also need to be specified.
1617
1618        module.sig_enforce
1619                        [KNL] When CONFIG_MODULE_SIG is set, this means that
1620                        modules without (valid) signatures will fail to load.
1621                        Note that if CONFIG_MODULE_SIG_ENFORCE is set, that
1622                        is always true, so this option does nothing.
1623
1624        mousedev.tap_time=
1625                        [MOUSE] Maximum time between finger touching and
1626                        leaving touchpad surface for touch to be considered
1627                        a tap and be reported as a left button click (for
1628                        touchpads working in absolute mode only).
1629                        Format: <msecs>
1630        mousedev.xres=  [MOUSE] Horizontal screen resolution, used for devices
1631                        reporting absolute coordinates, such as tablets
1632        mousedev.yres=  [MOUSE] Vertical screen resolution, used for devices
1633                        reporting absolute coordinates, such as tablets
1634
1635        movablecore=nn[KMG]     [KNL,X86,IA-64,PPC] This parameter
1636                        is similar to kernelcore except it specifies the
1637                        amount of memory used for migratable allocations.
1638                        If both kernelcore and movablecore is specified,
1639                        then kernelcore will be at *least* the specified
1640                        value but may be more. If movablecore on its own
1641                        is specified, the administrator must be careful
1642                        that the amount of memory usable for all allocations
1643                        is not too small.
1644
1645        MTD_Partition=  [MTD]
1646                        Format: <name>,<region-number>,<size>,<offset>
1647
1648        MTD_Region=     [MTD] Format:
1649                        <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1650
1651        mtdparts=       [MTD]
1652                        See drivers/mtd/cmdlinepart.c.
1653
1654        multitce=off    [PPC]  This parameter disables the use of the pSeries
1655                        firmware feature for updating multiple TCE entries
1656                        at a time.
1657
1658        onenand.bdry=   [HW,MTD] Flex-OneNAND Boundary Configuration
1659
1660                        Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1661
1662                        boundary - index of last SLC block on Flex-OneNAND.
1663                                   The remaining blocks are configured as MLC blocks.
1664                        lock     - Configure if Flex-OneNAND boundary should be locked.
1665                                   Once locked, the boundary cannot be changed.
1666                                   1 indicates lock status, 0 indicates unlock status.
1667
1668        mtdset=         [ARM]
1669                        ARM/S3C2412 JIVE boot control
1670
1671                        See arch/arm/mach-s3c2412/mach-jive.c
1672
1673        mtouchusb.raw_coordinates=
1674                        [HW] Make the MicroTouch USB driver use raw coordinates
1675                        ('y', default) or cooked coordinates ('n')
1676
1677        mtrr_chunk_size=nn[KMG] [X86]
1678                        used for mtrr cleanup. It is largest continuous chunk
1679                        that could hold holes aka. UC entries.
1680
1681        mtrr_gran_size=nn[KMG] [X86]
1682                        Used for mtrr cleanup. It is granularity of mtrr block.
1683                        Default is 1.
1684                        Large value could prevent small alignment from
1685                        using up MTRRs.
1686
1687        mtrr_spare_reg_nr=n [X86]
1688                        Format: <integer>
1689                        Range: 0,7 : spare reg number
1690                        Default : 1
1691                        Used for mtrr cleanup. It is spare mtrr entries number.
1692                        Set to 2 or more if your graphical card needs more.
1693
1694        n2=             [NET] SDL Inc. RISCom/N2 synchronous serial card
1695
1696        netdev=         [NET] Network devices parameters
1697                        Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1698                        Note that mem_start is often overloaded to mean
1699                        something different and driver-specific.
1700                        This usage is only documented in each driver source
1701                        file if at all.
1702
1703        nf_conntrack.acct=
1704                        [NETFILTER] Enable connection tracking flow accounting
1705                        0 to disable accounting
1706                        1 to enable accounting
1707                        Default value is 0.
1708
1709        nfsaddrs=       [NFS] Deprecated.  Use ip= instead.
1710                        See Documentation/filesystems/nfs/nfsroot.txt.
1711
1712        nfsroot=        [NFS] nfs root filesystem for disk-less boxes.
1713                        See Documentation/filesystems/nfs/nfsroot.txt.
1714
1715        nfsrootdebug    [NFS] enable nfsroot debugging messages.
1716                        See Documentation/filesystems/nfs/nfsroot.txt.
1717
1718        nfs.callback_tcpport=
1719                        [NFS] set the TCP port on which the NFSv4 callback
1720                        channel should listen.
1721
1722        nfs.cache_getent=
1723                        [NFS] sets the pathname to the program which is used
1724                        to update the NFS client cache entries.
1725
1726        nfs.cache_getent_timeout=
1727                        [NFS] sets the timeout after which an attempt to
1728                        update a cache entry is deemed to have failed.
1729
1730        nfs.idmap_cache_timeout=
1731                        [NFS] set the maximum lifetime for idmapper cache
1732                        entries.
1733
1734        nfs.enable_ino64=
1735                        [NFS] enable 64-bit inode numbers.
1736                        If zero, the NFS client will fake up a 32-bit inode
1737                        number for the readdir() and stat() syscalls instead
1738                        of returning the full 64-bit number.
1739                        The default is to return 64-bit inode numbers.
1740
1741        nfs.max_session_slots=
1742                        [NFSv4.1] Sets the maximum number of session slots
1743                        the client will attempt to negotiate with the server.
1744                        This limits the number of simultaneous RPC requests
1745                        that the client can send to the NFSv4.1 server.
1746                        Note that there is little point in setting this
1747                        value higher than the max_tcp_slot_table_limit.
1748
1749        nfs.nfs4_disable_idmapping=
1750                        [NFSv4] When set to the default of '1', this option
1751                        ensures that both the RPC level authentication
1752                        scheme and the NFS level operations agree to use
1753                        numeric uids/gids if the mount is using the
1754                        'sec=sys' security flavour. In effect it is
1755                        disabling idmapping, which can make migration from
1756                        legacy NFSv2/v3 systems to NFSv4 easier.
1757                        Servers that do not support this mode of operation
1758                        will be autodetected by the client, and it will fall
1759                        back to using the idmapper.
1760                        To turn off this behaviour, set the value to '0'.
1761        nfs.nfs4_unique_id=
1762                        [NFS4] Specify an additional fixed unique ident-
1763                        ification string that NFSv4 clients can insert into
1764                        their nfs_client_id4 string.  This is typically a
1765                        UUID that is generated at system install time.
1766
1767        nfs.send_implementation_id =
1768                        [NFSv4.1] Send client implementation identification
1769                        information in exchange_id requests.
1770                        If zero, no implementation identification information
1771                        will be sent.
1772                        The default is to send the implementation identification
1773                        information.
1774
1775        nfsd.nfs4_disable_idmapping=
1776                        [NFSv4] When set to the default of '1', the NFSv4
1777                        server will return only numeric uids and gids to
1778                        clients using auth_sys, and will accept numeric uids
1779                        and gids from such clients.  This is intended to ease
1780                        migration from NFSv2/v3.
1781
1782        objlayoutdriver.osd_login_prog=
1783                        [NFS] [OBJLAYOUT] sets the pathname to the program which
1784                        is used to automatically discover and login into new
1785                        osd-targets. Please see:
1786                        Documentation/filesystems/pnfs.txt for more explanations
1787
1788        nmi_debug=      [KNL,AVR32,SH] Specify one or more actions to take
1789                        when a NMI is triggered.
1790                        Format: [state][,regs][,debounce][,die]
1791
1792        nmi_watchdog=   [KNL,BUGS=X86] Debugging features for SMP kernels
1793                        Format: [panic,][nopanic,][num]
1794                        Valid num: 0
1795                        0 - turn nmi_watchdog off
1796                        When panic is specified, panic when an NMI watchdog
1797                        timeout occurs (or 'nopanic' to override the opposite
1798                        default).
1799                        This is useful when you use a panic=... timeout and
1800                        need the box quickly up again.
1801
1802        netpoll.carrier_timeout=
1803                        [NET] Specifies amount of time (in seconds) that
1804                        netpoll should wait for a carrier. By default netpoll
1805                        waits 4 seconds.
1806
1807        no387           [BUGS=X86-32] Tells the kernel to use the 387 maths
1808                        emulation library even if a 387 maths coprocessor
1809                        is present.
1810
1811        no_console_suspend
1812                        [HW] Never suspend the console
1813                        Disable suspending of consoles during suspend and
1814                        hibernate operations.  Once disabled, debugging
1815                        messages can reach various consoles while the rest
1816                        of the system is being put to sleep (ie, while
1817                        debugging driver suspend/resume hooks).  This may
1818                        not work reliably with all consoles, but is known
1819                        to work with serial and VGA consoles.
1820                        To facilitate more flexible debugging, we also add
1821                        console_suspend, a printk module parameter to control
1822                        it. Users could use console_suspend (usually
1823                        /sys/module/printk/parameters/console_suspend) to
1824                        turn on/off it dynamically.
1825
1826        noaliencache    [MM, NUMA, SLAB] Disables the allocation of alien
1827                        caches in the slab allocator.  Saves per-node memory,
1828                        but will impact performance.
1829
1830        noalign         [KNL,ARM]
1831
1832        noapic          [SMP,APIC] Tells the kernel to not make use of any
1833                        IOAPICs that may be present in the system.
1834
1835        noautogroup     Disable scheduler automatic task group creation.
1836
1837        nobats          [PPC] Do not use BATs for mapping kernel lowmem
1838                        on "Classic" PPC cores.
1839
1840        nocache         [ARM]
1841
1842        noclflush       [BUGS=X86] Don't use the CLFLUSH instruction
1843
1844        nodelayacct     [KNL] Disable per-task delay accounting
1845
1846        nodisconnect    [HW,SCSI,M68K] Disables SCSI disconnects.
1847
1848        nodsp           [SH] Disable hardware DSP at boot time.
1849
1850        noefi           [X86] Disable EFI runtime services support.
1851
1852        noexec          [IA-64]
1853
1854        noexec          [X86]
1855                        On X86-32 available only on PAE configured kernels.
1856                        noexec=on: enable non-executable mappings (default)
1857                        noexec=off: disable non-executable mappings
1858
1859        nosmap          [X86]
1860                        Disable SMAP (Supervisor Mode Access Prevention)
1861                        even if it is supported by processor.
1862
1863        nosmep          [X86]
1864                        Disable SMEP (Supervisor Mode Execution Prevention)
1865                        even if it is supported by processor.
1866
1867        noexec32        [X86-64]
1868                        This affects only 32-bit executables.
1869                        noexec32=on: enable non-executable mappings (default)
1870                                read doesn't imply executable mappings
1871                        noexec32=off: disable non-executable mappings
1872                                read implies executable mappings
1873
1874        nofpu           [SH] Disable hardware FPU at boot time.
1875
1876        nofxsr          [BUGS=X86-32] Disables x86 floating point extended
1877                        register save and restore. The kernel will only save
1878                        legacy floating-point registers on task switch.
1879
1880        noxsave         [BUGS=X86] Disables x86 extended register state save
1881                        and restore using xsave. The kernel will fallback to
1882                        enabling legacy floating-point and sse state.
1883
1884        eagerfpu=       [X86]
1885                        on      enable eager fpu restore
1886                        off     disable eager fpu restore
1887                        auto    selects the default scheme, which automatically
1888                                enables eagerfpu restore for xsaveopt.
1889
1890        nohlt           [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1891                        wfi(ARM) instruction doesn't work correctly and not to
1892                        use it. This is also useful when using JTAG debugger.
1893
1894        no-hlt          [BUGS=X86-32] Tells the kernel that the hlt
1895                        instruction doesn't work correctly and not to
1896                        use it.
1897
1898        no_file_caps    Tells the kernel not to honor file capabilities.  The
1899                        only way then for a file to be executed with privilege
1900                        is to be setuid root or executed by root.
1901
1902        nohalt          [IA-64] Tells the kernel not to use the power saving
1903                        function PAL_HALT_LIGHT when idle. This increases
1904                        power-consumption. On the positive side, it reduces
1905                        interrupt wake-up latency, which may improve performance
1906                        in certain environments such as networked servers or
1907                        real-time systems.
1908
1909        nohz=           [KNL] Boottime enable/disable dynamic ticks
1910                        Valid arguments: on, off
1911                        Default: on
1912
1913        noiotrap        [SH] Disables trapped I/O port accesses.
1914
1915        noirqdebug      [X86-32] Disables the code which attempts to detect and
1916                        disable unhandled interrupt sources.
1917
1918        no_timer_check  [X86,APIC] Disables the code which tests for
1919                        broken timer IRQ sources.
1920
1921        noisapnp        [ISAPNP] Disables ISA PnP code.
1922
1923        noinitrd        [RAM] Tells the kernel not to load any configured
1924                        initial RAM disk.
1925
1926        nointremap      [X86-64, Intel-IOMMU] Do not enable interrupt
1927                        remapping.
1928                        [Deprecated - use intremap=off]
1929
1930        nointroute      [IA-64]
1931
1932        nojitter        [IA-64] Disables jitter checking for ITC timers.
1933
1934        no-kvmclock     [X86,KVM] Disable paravirtualized KVM clock driver
1935
1936        no-kvmapf       [X86,KVM] Disable paravirtualized asynchronous page
1937                        fault handling.
1938
1939        no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
1940                        steal time is computed, but won't influence scheduler
1941                        behaviour
1942
1943        nolapic         [X86-32,APIC] Do not enable or use the local APIC.
1944
1945        nolapic_timer   [X86-32,APIC] Do not use the local APIC timer.
1946
1947        noltlbs         [PPC] Do not use large page/tlb entries for kernel
1948                        lowmem mapping on PPC40x.
1949
1950        nomca           [IA-64] Disable machine check abort handling
1951
1952        nomce           [X86-32] Machine Check Exception
1953
1954        nomfgpt         [X86-32] Disable Multi-Function General Purpose
1955                        Timer usage (for AMD Geode machines).
1956
1957        nonmi_ipi       [X86] Disable using NMI IPIs during panic/reboot to
1958                        shutdown the other cpus.  Instead use the REBOOT_VECTOR
1959                        irq.
1960
1961        nomodule        Disable module load
1962
1963        nopat           [X86] Disable PAT (page attribute table extension of
1964                        pagetables) support.
1965
1966        norandmaps      Don't use address space randomization.  Equivalent to
1967                        echo 0 > /proc/sys/kernel/randomize_va_space
1968
1969        noreplace-paravirt      [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1970
1971        noreplace-smp   [X86-32,SMP] Don't replace SMP instructions
1972                        with UP alternatives
1973
1974        noresidual      [PPC] Don't use residual data on PReP machines.
1975
1976        nordrand        [X86] Disable the direct use of the RDRAND
1977                        instruction even if it is supported by the
1978                        processor.  RDRAND is still available to user
1979                        space applications.
1980
1981        noresume        [SWSUSP] Disables resume and restores original swap
1982                        space.
1983
1984        no-scroll       [VGA] Disables scrollback.
1985                        This is required for the Braillex ib80-piezo Braille
1986                        reader made by F.H. Papenmeier (Germany).
1987
1988        nosbagart       [IA-64]
1989
1990        nosep           [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1991
1992        nosmp           [SMP] Tells an SMP kernel to act as a UP kernel,
1993                        and disable the IO APIC.  legacy for "maxcpus=0".
1994
1995        nosoftlockup    [KNL] Disable the soft-lockup detector.
1996
1997        nosync          [HW,M68K] Disables sync negotiation for all devices.
1998
1999        notsc           [BUGS=X86-32] Disable Time Stamp Counter
2000
2001        nousb           [USB] Disable the USB subsystem
2002
2003        nowatchdog      [KNL] Disable the lockup detector (NMI watchdog).
2004
2005        nowb            [ARM]
2006
2007        nox2apic        [X86-64,APIC] Do not enable x2APIC mode.
2008
2009        cpu0_hotplug    [X86] Turn on CPU0 hotplug feature when
2010                        CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2011                        Some features depend on CPU0. Known dependencies are:
2012                        1. Resume from suspend/hibernate depends on CPU0.
2013                        Suspend/hibernate will fail if CPU0 is offline and you
2014                        need to online CPU0 before suspend/hibernate.
2015                        2. PIC interrupts also depend on CPU0. CPU0 can't be
2016                        removed if a PIC interrupt is detected.
2017                        It's said poweroff/reboot may depend on CPU0 on some
2018                        machines although I haven't seen such issues so far
2019                        after CPU0 is offline on a few tested machines.
2020                        If the dependencies are under your control, you can
2021                        turn on cpu0_hotplug.
2022
2023        nptcg=          [IA-64] Override max number of concurrent global TLB
2024                        purges which is reported from either PAL_VM_SUMMARY or
2025                        SAL PALO.
2026
2027        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
2028                        could support.  nr_cpus=n : n >= 1 limits the kernel to
2029                        supporting 'n' processors. Later in runtime you can not
2030                        use hotplug cpu feature to put more cpu back to online.
2031                        just like you compile the kernel NR_CPUS=n
2032
2033        nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
2034
2035        numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2036                        Allowed values are enable and disable
2037
2038        numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2039                        one of ['zone', 'node', 'default'] can be specified
2040                        This can be set from sysctl after boot.
2041                        See Documentation/sysctl/vm.txt for details.
2042
2043        ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
2044                        See Documentation/debugging-via-ohci1394.txt for more
2045                        info.
2046
2047        olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2048                        Rather than timing out after 20 ms if an EC
2049                        command is not properly ACKed, override the length
2050                        of the timeout.  We have interrupts disabled while
2051                        waiting for the ACK, so if this is set too high
2052                        interrupts *may* be lost!
2053
2054        omap_mux=       [OMAP] Override bootloader pin multiplexing.
2055                        Format: <mux_mode0.mode_name=value>...
2056                        For example, to override I2C bus2:
2057                        omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2058
2059        oprofile.timer= [HW]
2060                        Use timer interrupt instead of performance counters
2061
2062        oprofile.cpu_type=      Force an oprofile cpu type
2063                        This might be useful if you have an older oprofile
2064                        userland or if you want common events.
2065                        Format: { arch_perfmon }
2066                        arch_perfmon: [X86] Force use of architectural
2067                                perfmon on Intel CPUs instead of the
2068                                CPU specific event set.
2069                        timer: [X86] Force use of architectural NMI
2070                                timer mode (see also oprofile.timer
2071                                for generic hr timer mode)
2072                                [s390] Force legacy basic mode sampling
2073                                (report cpu_type "timer")
2074
2075        oops=panic      Always panic on oopses. Default is to just kill the
2076                        process, but there is a small probability of
2077                        deadlocking the machine.
2078                        This will also cause panics on machine check exceptions.
2079                        Useful together with panic=30 to trigger a reboot.
2080
2081        OSS             [HW,OSS]
2082                        See Documentation/sound/oss/oss-parameters.txt
2083
2084        panic=          [KNL] Kernel behaviour on panic: delay <timeout>
2085                        timeout > 0: seconds before rebooting
2086                        timeout = 0: wait forever
2087                        timeout < 0: reboot immediately
2088                        Format: <timeout>
2089
2090        parkbd.port=    [HW] Parallel port number the keyboard adapter is
2091                        connected to, default is 0.
2092                        Format: <parport#>
2093        parkbd.mode=    [HW] Parallel port keyboard adapter mode of operation,
2094                        0 for XT, 1 for AT (default is AT).
2095                        Format: <mode>
2096
2097        parport=        [HW,PPT] Specify parallel ports. 0 disables.
2098                        Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2099                        Use 'auto' to force the driver to use any
2100                        IRQ/DMA settings detected (the default is to
2101                        ignore detected IRQ/DMA settings because of
2102                        possible conflicts). You can specify the base
2103                        address, IRQ, and DMA settings; IRQ and DMA
2104                        should be numbers, or 'auto' (for using detected
2105                        settings on that particular port), or 'nofifo'
2106                        (to avoid using a FIFO even if it is detected).
2107                        Parallel ports are assigned in the order they
2108                        are specified on the command line, starting
2109                        with parport0.
2110
2111        parport_init_mode=      [HW,PPT]
2112                        Configure VIA parallel port to operate in
2113                        a specific mode. This is necessary on Pegasos
2114                        computer where firmware has no options for setting
2115                        up parallel port mode and sets it to spp.
2116                        Currently this function knows 686a and 8231 chips.
2117                        Format: [spp|ps2|epp|ecp|ecpepp]
2118
2119        pause_on_oops=
2120                        Halt all CPUs after the first oops has been printed for
2121                        the specified number of seconds.  This is to be used if
2122                        your oopses keep scrolling off the screen.
2123
2124        pcbit=          [HW,ISDN]
2125
2126        pcd.            [PARIDE]
2127                        See header of drivers/block/paride/pcd.c.
2128                        See also Documentation/blockdev/paride.txt.
2129
2130        pci=option[,option...]  [PCI] various PCI subsystem options:
2131                earlydump       [X86] dump PCI config space before the kernel
2132                                changes anything
2133                off             [X86] don't probe for the PCI bus
2134                bios            [X86-32] force use of PCI BIOS, don't access
2135                                the hardware directly. Use this if your machine
2136                                has a non-standard PCI host bridge.
2137                nobios          [X86-32] disallow use of PCI BIOS, only direct
2138                                hardware access methods are allowed. Use this
2139                                if you experience crashes upon bootup and you
2140                                suspect they are caused by the BIOS.
2141                conf1           [X86] Force use of PCI Configuration
2142                                Mechanism 1.
2143                conf2           [X86] Force use of PCI Configuration
2144                                Mechanism 2.
2145                noaer           [PCIE] If the PCIEAER kernel config parameter is
2146                                enabled, this kernel boot option can be used to
2147                                disable the use of PCIE advanced error reporting.
2148                nodomains       [PCI] Disable support for multiple PCI
2149                                root domains (aka PCI segments, in ACPI-speak).
2150                nommconf        [X86] Disable use of MMCONFIG for PCI
2151                                Configuration
2152                check_enable_amd_mmconf [X86] check for and enable
2153                                properly configured MMIO access to PCI
2154                                config space on AMD family 10h CPU
2155                nomsi           [MSI] If the PCI_MSI kernel config parameter is
2156                                enabled, this kernel boot option can be used to
2157                                disable the use of MSI interrupts system-wide.
2158                noioapicquirk   [APIC] Disable all boot interrupt quirks.
2159                                Safety option to keep boot IRQs enabled. This
2160                                should never be necessary.
2161                ioapicreroute   [APIC] Enable rerouting of boot IRQs to the
2162                                primary IO-APIC for bridges that cannot disable
2163                                boot IRQs. This fixes a source of spurious IRQs
2164                                when the system masks IRQs.
2165                noioapicreroute [APIC] Disable workaround that uses the
2166                                boot IRQ equivalent of an IRQ that connects to
2167                                a chipset where boot IRQs cannot be disabled.
2168                                The opposite of ioapicreroute.
2169                biosirq         [X86-32] Use PCI BIOS calls to get the interrupt
2170                                routing table. These calls are known to be buggy
2171                                on several machines and they hang the machine
2172                                when used, but on other computers it's the only
2173                                way to get the interrupt routing table. Try
2174                                this option if the kernel is unable to allocate
2175                                IRQs or discover secondary PCI buses on your
2176                                motherboard.
2177                rom             [X86] Assign address space to expansion ROMs.
2178                                Use with caution as certain devices share
2179                                address decoders between ROMs and other
2180                                resources.
2181                norom           [X86] Do not assign address space to
2182                                expansion ROMs that do not already have
2183                                BIOS assigned address ranges.
2184                nobar           [X86] Do not assign address space to the
2185                                BARs that weren't assigned by the BIOS.
2186                irqmask=0xMMMM  [X86] Set a bit mask of IRQs allowed to be
2187                                assigned automatically to PCI devices. You can
2188                                make the kernel exclude IRQs of your ISA cards
2189                                this way.
2190                pirqaddr=0xAAAAA        [X86] Specify the physical address
2191                                of the PIRQ table (normally generated
2192                                by the BIOS) if it is outside the
2193                                F0000h-100000h range.
2194                lastbus=N       [X86] Scan all buses thru bus #N. Can be
2195                                useful if the kernel is unable to find your
2196                                secondary buses and you want to tell it
2197                                explicitly which ones they are.
2198                assign-busses   [X86] Always assign all PCI bus
2199                                numbers ourselves, overriding
2200                                whatever the firmware may have done.
2201                usepirqmask     [X86] Honor the possible IRQ mask stored
2202                                in the BIOS $PIR table. This is needed on
2203                                some systems with broken BIOSes, notably
2204                                some HP Pavilion N5400 and Omnibook XE3
2205                                notebooks. This will have no effect if ACPI
2206                                IRQ routing is enabled.
2207                noacpi          [X86] Do not use ACPI for IRQ routing
2208                                or for PCI scanning.
2209                use_crs         [X86] Use PCI host bridge window information
2210                                from ACPI.  On BIOSes from 2008 or later, this
2211                                is enabled by default.  If you need to use this,
2212                                please report a bug.
2213                nocrs           [X86] Ignore PCI host bridge windows from ACPI.
2214                                If you need to use this, please report a bug.
2215                routeirq        Do IRQ routing for all PCI devices.
2216                                This is normally done in pci_enable_device(),
2217                                so this option is a temporary workaround
2218                                for broken drivers that don't call it.
2219                skip_isa_align  [X86] do not align io start addr, so can
2220                                handle more pci cards
2221                firmware        [ARM] Do not re-enumerate the bus but instead
2222                                just use the configuration from the
2223                                bootloader. This is currently used on
2224                                IXP2000 systems where the bus has to be
2225                                configured a certain way for adjunct CPUs.
2226                noearly         [X86] Don't do any early type 1 scanning.
2227                                This might help on some broken boards which
2228                                machine check when some devices' config space
2229                                is read. But various workarounds are disabled
2230                                and some IOMMU drivers will not work.
2231                bfsort          Sort PCI devices into breadth-first order.
2232                                This sorting is done to get a device
2233                                order compatible with older (<= 2.4) kernels.
2234                nobfsort        Don't sort PCI devices into breadth-first order.
2235                cbiosize=nn[KMG]        The fixed amount of bus space which is
2236                                reserved for the CardBus bridge's IO window.
2237                                The default value is 256 bytes.
2238                cbmemsize=nn[KMG]       The fixed amount of bus space which is
2239                                reserved for the CardBus bridge's memory
2240                                window. The default value is 64 megabytes.
2241                resource_alignment=
2242                                Format:
2243                                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2244                                Specifies alignment and device to reassign
2245                                aligned memory resources.
2246                                If <order of align> is not specified,
2247                                PAGE_SIZE is used as alignment.
2248                                PCI-PCI bridge can be specified, if resource
2249                                windows need to be expanded.
2250                ecrc=           Enable/disable PCIe ECRC (transaction layer
2251                                end-to-end CRC checking).
2252                                bios: Use BIOS/firmware settings. This is the
2253                                the default.
2254                                off: Turn ECRC off
2255                                on: Turn ECRC on.
2256                realloc=        Enable/disable reallocating PCI bridge resources
2257                                if allocations done by BIOS are too small to
2258                                accommodate resources required by all child
2259                                devices.
2260                                off: Turn realloc off
2261                                on: Turn realloc on
2262                realloc         same as realloc=on
2263                noari           do not use PCIe ARI.
2264                pcie_scan_all   Scan all possible PCIe devices.  Otherwise we
2265                                only look for one device below a PCIe downstream
2266                                port.
2267
2268        pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
2269                        Management.
2270                off     Disable ASPM.
2271                force   Enable ASPM even on devices that claim not to support it.
2272                        WARNING: Forcing ASPM on may cause system lockups.
2273
2274        pcie_hp=        [PCIE] PCI Express Hotplug driver options:
2275                nomsi   Do not use MSI for PCI Express Native Hotplug (this
2276                        makes all PCIe ports use INTx for hotplug services).
2277
2278        pcie_ports=     [PCIE] PCIe ports handling:
2279                auto    Ask the BIOS whether or not to use native PCIe services
2280                        associated with PCIe ports (PME, hot-plug, AER).  Use
2281                        them only if that is allowed by the BIOS.
2282                native  Use native PCIe services associated with PCIe ports
2283                        unconditionally.
2284                compat  Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2285                        ports driver.
2286
2287        pcie_pme=       [PCIE,PM] Native PCIe PME signaling options:
2288                nomsi   Do not use MSI for native PCIe PME signaling (this makes
2289                        all PCIe root ports use INTx for all services).
2290
2291        pcmv=           [HW,PCMCIA] BadgePAD 4
2292
2293        pd.             [PARIDE]
2294                        See Documentation/blockdev/paride.txt.
2295
2296        pdcchassis=     [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2297                        boot time.
2298                        Format: { 0 | 1 }
2299                        See arch/parisc/kernel/pdc_chassis.c
2300
2301        percpu_alloc=   Select which percpu first chunk allocator to use.
2302                        Currently supported values are "embed" and "page".
2303                        Archs may support subset or none of the selections.
2304                        See comments in mm/percpu.c for details on each
2305                        allocator.  This parameter is primarily for debugging
2306                        and performance comparison.
2307
2308        pf.             [PARIDE]
2309                        See Documentation/blockdev/paride.txt.
2310
2311        pg.             [PARIDE]
2312                        See Documentation/blockdev/paride.txt.
2313
2314        pirq=           [SMP,APIC] Manual mp-table setup
2315                        See Documentation/x86/i386/IO-APIC.txt.
2316
2317        plip=           [PPT,NET] Parallel port network link
2318                        Format: { parport<nr> | timid | 0 }
2319                        See also Documentation/parport.txt.
2320
2321        pmtmr=          [X86] Manual setup of pmtmr I/O Port.
2322                        Override pmtimer IOPort with a hex value.
2323                        e.g. pmtmr=0x508
2324
2325        pnp.debug=1     [PNP]
2326                        Enable PNP debug messages (depends on the
2327                        CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
2328                        via /sys/module/pnp/parameters/debug.  We always show
2329                        current resource usage; turning this on also shows
2330                        possible settings and some assignment information.
2331
2332        pnpacpi=        [ACPI]
2333                        { off }
2334
2335        pnpbios=        [ISAPNP]
2336                        { on | off | curr | res | no-curr | no-res }
2337
2338        pnp_reserve_irq=
2339                        [ISAPNP] Exclude IRQs for the autoconfiguration
2340
2341        pnp_reserve_dma=
2342                        [ISAPNP] Exclude DMAs for the autoconfiguration
2343
2344        pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2345                        Ranges are in pairs (I/O port base and size).
2346
2347        pnp_reserve_mem=
2348                        [ISAPNP] Exclude memory regions for the
2349                        autoconfiguration.
2350                        Ranges are in pairs (memory base and size).
2351
2352        ports=          [IP_VS_FTP] IPVS ftp helper module
2353                        Default is 21.
2354                        Up to 8 (IP_VS_APP_MAX_PORTS) ports
2355                        may be specified.
2356                        Format: <port>,<port>....
2357
2358        print-fatal-signals=
2359                        [KNL] debug: print fatal signals
2360
2361                        If enabled, warn about various signal handling
2362                        related application anomalies: too many signals,
2363                        too many POSIX.1 timers, fatal signals causing a
2364                        coredump - etc.
2365
2366                        If you hit the warning due to signal overflow,
2367                        you might want to try "ulimit -i unlimited".
2368
2369                        default: off.
2370
2371        printk.always_kmsg_dump=
2372                        Trigger kmsg_dump for cases other than kernel oops or
2373                        panics
2374                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2375                        default: disabled
2376
2377        printk.time=    Show timing data prefixed to each printk message line
2378                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2379
2380        processor.max_cstate=   [HW,ACPI]
2381                        Limit processor to maximum C-state
2382                        max_cstate=9 overrides any DMI blacklist limit.
2383
2384        processor.nocst [HW,ACPI]
2385                        Ignore the _CST method to determine C-states,
2386                        instead using the legacy FADT method
2387
2388        profile=        [KNL] Enable kernel profiling via /proc/profile
2389                        Format: [schedule,]<number>
2390                        Param: "schedule" - profile schedule points.
2391                        Param: <number> - step/bucket size as a power of 2 for
2392                                statistical time based profiling.
2393                        Param: "sleep" - profile D-state sleeping (millisecs).
2394                                Requires CONFIG_SCHEDSTATS
2395                        Param: "kvm" - profile VM exits.
2396
2397        prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2398                        before loading.
2399                        See Documentation/blockdev/ramdisk.txt.
2400
2401        psmouse.proto=  [HW,MOUSE] Highest PS2 mouse protocol extension to
2402                        probe for; one of (bare|imps|exps|lifebook|any).
2403        psmouse.rate=   [HW,MOUSE] Set desired mouse report rate, in reports
2404                        per second.
2405        psmouse.resetafter=     [HW,MOUSE]
2406                        Try to reset the device after so many bad packets
2407                        (0 = never).
2408        psmouse.resolution=
2409                        [HW,MOUSE] Set desired mouse resolution, in dpi.
2410        psmouse.smartscroll=
2411                        [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2412                        0 = disabled, 1 = enabled (default).
2413
2414        pstore.backend= Specify the name of the pstore backend to use
2415
2416        pt.             [PARIDE]
2417                        See Documentation/blockdev/paride.txt.
2418
2419        pty.legacy_count=
2420                        [KNL] Number of legacy pty's. Overwrites compiled-in
2421                        default number.
2422
2423        quiet           [KNL] Disable most log messages
2424
2425        r128=           [HW,DRM]
2426
2427        raid=           [HW,RAID]
2428                        See Documentation/md.txt.
2429
2430        ramdisk_blocksize=      [RAM]
2431                        See Documentation/blockdev/ramdisk.txt.
2432
2433        ramdisk_size=   [RAM] Sizes of RAM disks in kilobytes
2434                        See Documentation/blockdev/ramdisk.txt.
2435
2436        rcu_nocbs=      [KNL,BOOT]
2437                        In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2438                        the specified list of CPUs to be no-callback CPUs.
2439                        Invocation of these CPUs' RCU callbacks will
2440                        be offloaded to "rcuoN" kthreads created for
2441                        that purpose.  This reduces OS jitter on the
2442                        offloaded CPUs, which can be useful for HPC and
2443                        real-time workloads.  It can also improve energy
2444                        efficiency for asymmetric multiprocessors.
2445
2446        rcu_nocb_poll   [KNL,BOOT]
2447                        Rather than requiring that offloaded CPUs
2448                        (specified by rcu_nocbs= above) explicitly
2449                        awaken the corresponding "rcuoN" kthreads,
2450                        make these kthreads poll for callbacks.
2451                        This improves the real-time response for the
2452                        offloaded CPUs by relieving them of the need to
2453                        wake up the corresponding kthread, but degrades
2454                        energy efficiency by requiring that the kthreads
2455                        periodically wake up to do the polling.
2456
2457        rcutree.blimit= [KNL,BOOT]
2458                        Set maximum number of finished RCU callbacks to process
2459                        in one batch.
2460
2461        rcutree.fanout_leaf=    [KNL,BOOT]
2462                        Increase the number of CPUs assigned to each
2463                        leaf rcu_node structure.  Useful for very large
2464                        systems.
2465
2466        rcutree.qhimark=        [KNL,BOOT]
2467                        Set threshold of queued
2468                        RCU callbacks over which batch limiting is disabled.
2469
2470        rcutree.qlowmark=       [KNL,BOOT]
2471                        Set threshold of queued RCU callbacks below which
2472                        batch limiting is re-enabled.
2473
2474        rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2475                        Suppress RCU CPU stall warning messages.
2476
2477        rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2478                        Set timeout for RCU CPU stall warning messages.
2479
2480        rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2481                        Set delay from grace-period initialization to
2482                        first attempt to force quiescent states.
2483                        Units are jiffies, minimum value is zero,
2484                        and maximum value is HZ.
2485
2486        rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2487                        Set delay between subsequent attempts to force
2488                        quiescent states.  Units are jiffies, minimum
2489                        value is one, and maximum value is HZ.
2490
2491        rcutorture.fqs_duration= [KNL,BOOT]
2492                        Set duration of force_quiescent_state bursts.
2493
2494        rcutorture.fqs_holdoff= [KNL,BOOT]
2495                        Set holdoff time within force_quiescent_state bursts.
2496
2497        rcutorture.fqs_stutter= [KNL,BOOT]
2498                        Set wait time between force_quiescent_state bursts.
2499
2500        rcutorture.irqreader= [KNL,BOOT]
2501                        Test RCU readers from irq handlers.
2502
2503        rcutorture.n_barrier_cbs= [KNL,BOOT]
2504                        Set callbacks/threads for rcu_barrier() testing.
2505
2506        rcutorture.nfakewriters= [KNL,BOOT]
2507                        Set number of concurrent RCU writers.  These just
2508                        stress RCU, they don't participate in the actual
2509                        test, hence the "fake".
2510
2511        rcutorture.nreaders= [KNL,BOOT]
2512                        Set number of RCU readers.
2513
2514        rcutorture.onoff_holdoff= [KNL,BOOT]
2515                        Set time (s) after boot for CPU-hotplug testing.
2516
2517        rcutorture.onoff_interval= [KNL,BOOT]
2518                        Set time (s) between CPU-hotplug operations, or
2519                        zero to disable CPU-hotplug testing.
2520
2521        rcutorture.shuffle_interval= [KNL,BOOT]
2522                        Set task-shuffle interval (s).  Shuffling tasks
2523                        allows some CPUs to go into dyntick-idle mode
2524                        during the rcutorture test.
2525
2526        rcutorture.shutdown_secs= [KNL,BOOT]
2527                        Set time (s) after boot system shutdown.  This
2528                        is useful for hands-off automated testing.
2529
2530        rcutorture.stall_cpu= [KNL,BOOT]
2531                        Duration of CPU stall (s) to test RCU CPU stall
2532                        warnings, zero to disable.
2533
2534        rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2535                        Time to wait (s) after boot before inducing stall.
2536
2537        rcutorture.stat_interval= [KNL,BOOT]
2538                        Time (s) between statistics printk()s.
2539
2540        rcutorture.stutter= [KNL,BOOT]
2541                        Time (s) to stutter testing, for example, specifying
2542                        five seconds causes the test to run for five seconds,
2543                        wait for five seconds, and so on.  This tests RCU's
2544                        ability to transition abruptly to and from idle.
2545
2546        rcutorture.test_boost= [KNL,BOOT]
2547                        Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
2548                        "Maybe" means test if the RCU implementation
2549                        under test support RCU priority boosting.
2550
2551        rcutorture.test_boost_duration= [KNL,BOOT]
2552                        Duration (s) of each individual boost test.
2553
2554        rcutorture.test_boost_interval= [KNL,BOOT]
2555                        Interval (s) between each boost test.
2556
2557        rcutorture.test_no_idle_hz= [KNL,BOOT]
2558                        Test RCU's dyntick-idle handling.  See also the
2559                        rcutorture.shuffle_interval parameter.
2560
2561        rcutorture.torture_type= [KNL,BOOT]
2562                        Specify the RCU implementation to test.
2563
2564        rcutorture.verbose= [KNL,BOOT]
2565                        Enable additional printk() statements.
2566
2567        rdinit=         [KNL]
2568                        Format: <full_path>
2569                        Run specified binary instead of /init from the ramdisk,
2570                        used for early userspace startup. See initrd.
2571
2572        reboot=         [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2573                        Format: <reboot_mode>[,<reboot_mode2>[,...]]
2574                        See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2575
2576        relax_domain_level=
2577                        [KNL, SMP] Set scheduler's default relax_domain_level.
2578                        See Documentation/cgroups/cpusets.txt.
2579
2580        reserve=        [KNL,BUGS] Force the kernel to ignore some iomem area
2581
2582        reservetop=     [X86-32]
2583                        Format: nn[KMG]
2584                        Reserves a hole at the top of the kernel virtual
2585                        address space.
2586
2587        reservelow=     [X86]
2588                        Format: nn[K]
2589                        Set the amount of memory to reserve for BIOS at
2590                        the bottom of the address space.
2591
2592        reset_devices   [KNL] Force drivers to reset the underlying device
2593                        during initialization.
2594
2595        resume=         [SWSUSP]
2596                        Specify the partition device for software suspend
2597                        Format:
2598                        {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2599
2600        resume_offset=  [SWSUSP]
2601                        Specify the offset from the beginning of the partition
2602                        given by "resume=" at which the swap header is located,
2603                        in <PAGE_SIZE> units (needed only for swap files).
2604                        See  Documentation/power/swsusp-and-swap-files.txt
2605
2606        resumedelay=    [HIBERNATION] Delay (in seconds) to pause before attempting to
2607                        read the resume files
2608
2609        resumewait      [HIBERNATION] Wait (indefinitely) for resume device to show up.
2610                        Useful for devices that are detected asynchronously
2611                        (e.g. USB and MMC devices).
2612
2613        hibernate=      [HIBERNATION]
2614                noresume        Don't check if there's a hibernation image
2615                                present during boot.
2616                nocompress      Don't compress/decompress hibernation images.
2617
2618        retain_initrd   [RAM] Keep initrd memory after extraction
2619
2620        rhash_entries=  [KNL,NET]
2621                        Set number of hash buckets for route cache
2622
2623        riscom8=        [HW,SERIAL]
2624                        Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2625
2626        ro              [KNL] Mount root device read-only on boot
2627
2628        root=           [KNL] Root filesystem
2629                        See name_to_dev_t comment in init/do_mounts.c.
2630
2631        rootdelay=      [KNL] Delay (in seconds) to pause before attempting to
2632                        mount the root filesystem
2633
2634        rootflags=      [KNL] Set root filesystem mount option string
2635
2636        rootfstype=     [KNL] Set root filesystem type
2637
2638        rootwait        [KNL] Wait (indefinitely) for root device to show up.
2639                        Useful for devices that are detected asynchronously
2640                        (e.g. USB and MMC devices).
2641
2642        rw              [KNL] Mount root device read-write on boot
2643
2644        S               [KNL] Run init in single mode
2645
2646        sa1100ir        [NET]
2647                        See drivers/net/irda/sa1100_ir.c.
2648
2649        sbni=           [NET] Granch SBNI12 leased line adapter
2650
2651        sched_debug     [KNL] Enables verbose scheduler debug messages.
2652
2653        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
2654                        xtime_lock contention on larger systems, and/or RCU lock
2655                        contention on all systems with CONFIG_MAXSMP set.
2656                        Format: { "0" | "1" }
2657                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2658                        1 -- enable.
2659                        Note: increases power consumption, thus should only be
2660                        enabled if running jitter sensitive (HPC/RT) workloads.
2661
2662        security=       [SECURITY] Choose a security module to enable at boot.
2663                        If this boot parameter is not specified, only the first
2664                        security module asking for security registration will be
2665                        loaded. An invalid security module name will be treated
2666                        as if no module has been chosen.
2667
2668        selinux=        [SELINUX] Disable or enable SELinux at boot time.
2669                        Format: { "0" | "1" }
2670                        See security/selinux/Kconfig help text.
2671                        0 -- disable.
2672                        1 -- enable.
2673                        Default value is set via kernel config option.
2674                        If enabled at boot time, /selinux/disable can be used
2675                        later to disable prior to initial policy load.
2676
2677        apparmor=       [APPARMOR] Disable or enable AppArmor at boot time
2678                        Format: { "0" | "1" }
2679                        See security/apparmor/Kconfig help text
2680                        0 -- disable.
2681                        1 -- enable.
2682                        Default value is set via kernel config option.
2683
2684        serialnumber    [BUGS=X86-32]
2685
2686        shapers=        [NET]
2687                        Maximal number of shapers.
2688
2689        show_msr=       [x86] show boot-time MSR settings
2690                        Format: { <integer> }
2691                        Show boot-time (BIOS-initialized) MSR settings.
2692                        The parameter means the number of CPUs to show,
2693                        for example 1 means boot CPU only.
2694
2695        simeth=         [IA-64]
2696        simscsi=
2697
2698        slram=          [HW,MTD]
2699
2700        slab_max_order= [MM, SLAB]
2701                        Determines the maximum allowed order for slabs.
2702                        A high setting may cause OOMs due to memory
2703                        fragmentation.  Defaults to 1 for systems with
2704                        more than 32MB of RAM, 0 otherwise.
2705
2706        slub_debug[=options[,slabs]]    [MM, SLUB]
2707                        Enabling slub_debug allows one to determine the
2708                        culprit if slab objects become corrupted. Enabling
2709                        slub_debug can create guard zones around objects and
2710                        may poison objects when not in use. Also tracks the
2711                        last alloc / free. For more information see
2712                        Documentation/vm/slub.txt.
2713
2714        slub_max_order= [MM, SLUB]
2715                        Determines the maximum allowed order for slabs.
2716                        A high setting may cause OOMs due to memory
2717                        fragmentation. For more information see
2718                        Documentation/vm/slub.txt.
2719
2720        slub_min_objects=       [MM, SLUB]
2721                        The minimum number of objects per slab. SLUB will
2722                        increase the slab order up to slub_max_order to
2723                        generate a sufficiently large slab able to contain
2724                        the number of objects indicated. The higher the number
2725                        of objects the smaller the overhead of tracking slabs
2726                        and the less frequently locks need to be acquired.
2727                        For more information see Documentation/vm/slub.txt.
2728
2729        slub_min_order= [MM, SLUB]
2730                        Determines the minimum page order for slabs. Must be
2731                        lower than slub_max_order.
2732                        For more information see Documentation/vm/slub.txt.
2733
2734        slub_nomerge    [MM, SLUB]
2735                        Disable merging of slabs with similar size. May be
2736                        necessary if there is some reason to distinguish
2737                        allocs to different slabs. Debug options disable
2738                        merging on their own.
2739                        For more information see Documentation/vm/slub.txt.
2740
2741        smart2=         [HW]
2742                        Format: <io1>[,<io2>[,...,<io8>]]
2743
2744        smsc-ircc2.nopnp        [HW] Don't use PNP to discover SMC devices
2745        smsc-ircc2.ircc_cfg=    [HW] Device configuration I/O port
2746        smsc-ircc2.ircc_sir=    [HW] SIR base I/O port
2747        smsc-ircc2.ircc_fir=    [HW] FIR base I/O port
2748        smsc-ircc2.ircc_irq=    [HW] IRQ line
2749        smsc-ircc2.ircc_dma=    [HW] DMA channel
2750        smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2751                                0: Toshiba Satellite 1800 (GP data pin select)
2752                                1: Fast pin select (default)
2753                                2: ATC IRMode
2754
2755        softlockup_panic=
2756                        [KNL] Should the soft-lockup detector generate panics.
2757                        Format: <integer>
2758
2759        sonypi.*=       [HW] Sony Programmable I/O Control Device driver
2760                        See Documentation/laptops/sonypi.txt
2761
2762        specialix=      [HW,SERIAL] Specialix multi-serial port adapter
2763                        See Documentation/serial/specialix.txt.
2764
2765        spia_io_base=   [HW,MTD]
2766        spia_fio_base=
2767        spia_pedr=
2768        spia_peddr=
2769
2770        stacktrace      [FTRACE]
2771                        Enabled the stack tracer on boot up.
2772
2773        stacktrace_filter=[function-list]
2774                        [FTRACE] Limit the functions that the stack tracer
2775                        will trace at boot up. function-list is a comma separated
2776                        list of functions. This list can be changed at run
2777                        time by the stack_trace_filter file in the debugfs
2778                        tracing directory. Note, this enables stack tracing
2779                        and the stacktrace above is not needed.
2780
2781        sti=            [PARISC,HW]
2782                        Format: <num>
2783                        Set the STI (builtin display/keyboard on the HP-PARISC
2784                        machines) console (graphic card) which should be used
2785                        as the initial boot-console.
2786                        See also comment in drivers/video/console/sticore.c.
2787
2788        sti_font=       [HW]
2789                        See comment in drivers/video/console/sticore.c.
2790
2791        stifb=          [HW]
2792                        Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2793
2794        sunrpc.min_resvport=
2795        sunrpc.max_resvport=
2796                        [NFS,SUNRPC]
2797                        SunRPC servers often require that client requests
2798                        originate from a privileged port (i.e. a port in the
2799                        range 0 < portnr < 1024).
2800                        An administrator who wishes to reserve some of these
2801                        ports for other uses may adjust the range that the
2802                        kernel's sunrpc client considers to be privileged
2803                        using these two parameters to set the minimum and
2804                        maximum port values.
2805
2806        sunrpc.pool_mode=
2807                        [NFS]
2808                        Control how the NFS server code allocates CPUs to
2809                        service thread pools.  Depending on how many NICs
2810                        you have and where their interrupts are bound, this
2811                        option will affect which CPUs will do NFS serving.
2812                        Note: this parameter cannot be changed while the
2813                        NFS server is running.
2814
2815                        auto        the server chooses an appropriate mode
2816                                    automatically using heuristics
2817                        global      a single global pool contains all CPUs
2818                        percpu      one pool for each CPU
2819                        pernode     one pool for each NUMA node (equivalent
2820                                    to global on non-NUMA machines)
2821
2822        sunrpc.tcp_slot_table_entries=
2823        sunrpc.udp_slot_table_entries=
2824                        [NFS,SUNRPC]
2825                        Sets the upper limit on the number of simultaneous
2826                        RPC calls that can be sent from the client to a
2827                        server. Increasing these values may allow you to
2828                        improve throughput, but will also increase the
2829                        amount of memory reserved for use by the client.
2830
2831        swapaccount[=0|1]
2832                        [KNL] Enable accounting of swap in memory resource
2833                        controller if no parameter or 1 is given or disable
2834                        it if 0 is given (See Documentation/cgroups/memory.txt)
2835
2836        swiotlb=        [IA-64] Number of I/O TLB slabs
2837
2838        switches=       [HW,M68k]
2839
2840        sysfs.deprecated=0|1 [KNL]
2841                        Enable/disable old style sysfs layout for old udev
2842                        on older distributions. When this option is enabled
2843                        very new udev will not work anymore. When this option
2844                        is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2845                        in older udev will not work anymore.
2846                        Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2847                        the kernel configuration.
2848
2849        sysrq_always_enabled
2850                        [KNL]
2851                        Ignore sysrq setting - this boot parameter will
2852                        neutralize any effect of /proc/sys/kernel/sysrq.
2853                        Useful for debugging.
2854
2855        tdfx=           [HW,DRM]
2856
2857        test_suspend=   [SUSPEND]
2858                        Specify "mem" (for Suspend-to-RAM) or "standby" (for
2859                        standby suspend) as the system sleep state to briefly
2860                        enter during system startup.  The system is woken from
2861                        this state using a wakeup-capable RTC alarm.
2862
2863        thash_entries=  [KNL,NET]
2864                        Set number of hash buckets for TCP connection
2865
2866        thermal.act=    [HW,ACPI]
2867                        -1: disable all active trip points in all thermal zones
2868                        <degrees C>: override all lowest active trip points
2869
2870        thermal.crt=    [HW,ACPI]
2871                        -1: disable all critical trip points in all thermal zones
2872                        <degrees C>: override all critical trip points
2873
2874        thermal.nocrt=  [HW,ACPI]
2875                        Set to disable actions on ACPI thermal zone
2876                        critical and hot trip points.
2877
2878        thermal.off=    [HW,ACPI]
2879                        1: disable ACPI thermal control
2880
2881        thermal.psv=    [HW,ACPI]
2882                        -1: disable all passive trip points
2883                        <degrees C>: override all passive trip points to this
2884                        value
2885
2886        thermal.tzp=    [HW,ACPI]
2887                        Specify global default ACPI thermal zone polling rate
2888                        <deci-seconds>: poll all this frequency
2889                        0: no polling (default)
2890
2891        threadirqs      [KNL]
2892                        Force threading of all interrupt handlers except those
2893                        marked explicitly IRQF_NO_THREAD.
2894
2895        topology=       [S390]
2896                        Format: {off | on}
2897                        Specify if the kernel should make use of the cpu
2898                        topology information if the hardware supports this.
2899                        The scheduler will make use of this information and
2900                        e.g. base its process migration decisions on it.
2901                        Default is on.
2902
2903        tp720=          [HW,PS2]
2904
2905        tpm_suspend_pcr=[HW,TPM]
2906                        Format: integer pcr id
2907                        Specify that at suspend time, the tpm driver
2908                        should extend the specified pcr with zeros,
2909                        as a workaround for some chips which fail to
2910                        flush the last written pcr on TPM_SaveState.
2911                        This will guarantee that all the other pcrs
2912                        are saved.
2913
2914        trace_buf_size=nn[KMG]
2915                        [FTRACE] will set tracing buffer size.
2916
2917        trace_event=[event-list]
2918                        [FTRACE] Set and start specified trace events in order
2919                        to facilitate early boot debugging.
2920                        See also Documentation/trace/events.txt
2921
2922        trace_options=[option-list]
2923                        [FTRACE] Enable or disable tracer options at boot.
2924                        The option-list is a comma delimited list of options
2925                        that can be enabled or disabled just as if you were
2926                        to echo the option name into
2927
2928                            /sys/kernel/debug/tracing/trace_options
2929
2930                        For example, to enable stacktrace option (to dump the
2931                        stack trace of each event), add to the command line:
2932
2933                              trace_options=stacktrace
2934
2935                        See also Documentation/trace/ftrace.txt "trace options"
2936                        section.
2937
2938        transparent_hugepage=
2939                        [KNL]
2940                        Format: [always|madvise|never]
2941                        Can be used to control the default behavior of the system
2942                        with respect to transparent hugepages.
2943                        See Documentation/vm/transhuge.txt for more details.
2944
2945        tsc=            Disable clocksource stability checks for TSC.
2946                        Format: <string>
2947                        [x86] reliable: mark tsc clocksource as reliable, this
2948                        disables clocksource verification at runtime, as well
2949                        as the stability checks done at bootup. Used to enable
2950                        high-resolution timer mode on older hardware, and in
2951                        virtualized environment.
2952                        [x86] noirqtime: Do not use TSC to do irq accounting.
2953                        Used to run time disable IRQ_TIME_ACCOUNTING on any
2954                        platforms where RDTSC is slow and this accounting
2955                        can add overhead.
2956
2957        turbografx.map[2|3]=    [HW,JOY]
2958                        TurboGraFX parallel port interface
2959                        Format:
2960                        <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2961                        See also Documentation/input/joystick-parport.txt
2962
2963        udbg-immortal   [PPC] When debugging early kernel crashes that
2964                        happen after console_init() and before a proper 
2965                        console driver takes over, this boot options might
2966                        help "seeing" what's going on.
2967
2968        uhash_entries=  [KNL,NET]
2969                        Set number of hash buckets for UDP/UDP-Lite connections
2970
2971        uhci-hcd.ignore_oc=
2972                        [USB] Ignore overcurrent events (default N).
2973                        Some badly-designed motherboards generate lots of
2974                        bogus events, for ports that aren't wired to
2975                        anything.  Set this parameter to avoid log spamming.
2976                        Note that genuine overcurrent events won't be
2977                        reported either.
2978
2979        unknown_nmi_panic
2980                        [X86] Cause panic on unknown NMI.
2981
2982        usbcore.authorized_default=
2983                        [USB] Default USB device authorization:
2984                        (default -1 = authorized except for wireless USB,
2985                        0 = not authorized, 1 = authorized)
2986
2987        usbcore.autosuspend=
2988                        [USB] The autosuspend time delay (in seconds) used
2989                        for newly-detected USB devices (default 2).  This
2990                        is the time required before an idle device will be
2991                        autosuspended.  Devices for which the delay is set
2992                        to a negative value won't be autosuspended at all.
2993
2994        usbcore.usbfs_snoop=
2995                        [USB] Set to log all usbfs traffic (default 0 = off).
2996
2997        usbcore.blinkenlights=
2998                        [USB] Set to cycle leds on hubs (default 0 = off).
2999
3000        usbcore.old_scheme_first=
3001                        [USB] Start with the old device initialization
3002                        scheme (default 0 = off).
3003
3004        usbcore.usbfs_memory_mb=
3005                        [USB] Memory limit (in MB) for buffers allocated by
3006                        usbfs (default = 16, 0 = max = 2047).
3007
3008        usbcore.use_both_schemes=
3009                        [USB] Try the other device initialization scheme
3010                        if the first one fails (default 1 = enabled).
3011
3012        usbcore.initial_descriptor_timeout=
3013                        [USB] Specifies timeout for the initial 64-byte
3014                        USB_REQ_GET_DESCRIPTOR request in milliseconds
3015                        (default 5000 = 5.0 seconds).
3016
3017        usbhid.mousepoll=
3018                        [USBHID] The interval which mice are to be polled at.
3019
3020        usb-storage.delay_use=
3021                        [UMS] The delay in seconds before a new device is
3022                        scanned for Logical Units (default 5).
3023
3024        usb-storage.quirks=
3025                        [UMS] A list of quirks entries to supplement or
3026                        override the built-in unusual_devs list.  List
3027                        entries are separated by commas.  Each entry has
3028                        the form VID:PID:Flags where VID and PID are Vendor
3029                        and Product ID values (4-digit hex numbers) and
3030                        Flags is a set of characters, each corresponding
3031                        to a common usb-storage quirk flag as follows:
3032                                a = SANE_SENSE (collect more than 18 bytes
3033                                        of sense data);
3034                                b = BAD_SENSE (don't collect more than 18
3035                                        bytes of sense data);
3036                                c = FIX_CAPACITY (decrease the reported
3037                                        device capacity by one sector);
3038                                d = NO_READ_DISC_INFO (don't use
3039                                        READ_DISC_INFO command);
3040                                e = NO_READ_CAPACITY_16 (don't use
3041                                        READ_CAPACITY_16 command);
3042                                h = CAPACITY_HEURISTICS (decrease the
3043                                        reported device capacity by one
3044                                        sector if the number is odd);
3045                                i = IGNORE_DEVICE (don't bind to this
3046                                        device);
3047                                l = NOT_LOCKABLE (don't try to lock and
3048                                        unlock ejectable media);
3049                                m = MAX_SECTORS_64 (don't transfer more
3050                                        than 64 sectors = 32 KB at a time);
3051                                n = INITIAL_READ10 (force a retry of the
3052                                        initial READ(10) command);
3053                                o = CAPACITY_OK (accept the capacity
3054                                        reported by the device);
3055                                p = WRITE_CACHE (the device cache is ON
3056                                        by default);
3057                                r = IGNORE_RESIDUE (the device reports
3058                                        bogus residue values);
3059                                s = SINGLE_LUN (the device has only one
3060                                        Logical Unit);
3061                                w = NO_WP_DETECT (don't test whether the
3062                                        medium is write-protected).
3063                        Example: quirks=0419:aaf5:rl,0421:0433:rc
3064
3065        user_debug=     [KNL,ARM]
3066                        Format: <int>
3067                        See arch/arm/Kconfig.debug help text.
3068                                 1 - undefined instruction events
3069                                 2 - system calls
3070                                 4 - invalid data aborts
3071                                 8 - SIGSEGV faults
3072                                16 - SIGBUS faults
3073                        Example: user_debug=31
3074
3075        userpte=
3076                        [X86] Flags controlling user PTE allocations.
3077
3078                                nohigh = do not allocate PTE pages in
3079                                        HIGHMEM regardless of setting
3080                                        of CONFIG_HIGHPTE.
3081
3082        vdso=           [X86,SH]
3083                        vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3084                        vdso=1: enable VDSO (default)
3085                        vdso=0: disable VDSO mapping
3086
3087        vdso32=         [X86]
3088                        vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3089                        vdso32=1: enable 32-bit VDSO (default)
3090                        vdso32=0: disable 32-bit VDSO mapping
3091
3092        vector=         [IA-64,SMP]
3093                        vector=percpu: enable percpu vector domain
3094
3095        video=          [FB] Frame buffer configuration
3096                        See Documentation/fb/modedb.txt.
3097
3098        virtio_mmio.device=
3099                        [VMMIO] Memory mapped virtio (platform) device.
3100
3101                                <size>@<baseaddr>:<irq>[:<id>]
3102                        where:
3103                                <size>     := size (can use standard suffixes
3104                                                like K, M and G)
3105                                <baseaddr> := physical base address
3106                                <irq>      := interrupt number (as passed to
3107                                                request_irq())
3108                                <id>       := (optional) platform device id
3109                        example:
3110                                virtio_mmio.device=1K@0x100b0000:48:7
3111
3112                        Can be used multiple times for multiple devices.
3113
3114        vga=            [BOOT,X86-32] Select a particular video mode
3115                        See Documentation/x86/boot.txt and
3116                        Documentation/svga.txt.
3117                        Use vga=ask for menu.
3118                        This is actually a boot loader parameter; the value is
3119                        passed to the kernel using a special protocol.
3120
3121        vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3122                        size of <nn>. This can be used to increase the
3123                        minimum size (128MB on x86). It can also be used to
3124                        decrease the size and leave more room for directly
3125                        mapped kernel RAM.
3126
3127        vmhalt=         [KNL,S390] Perform z/VM CP command after system halt.
3128                        Format: <command>
3129
3130        vmpanic=        [KNL,S390] Perform z/VM CP command after kernel panic.
3131                        Format: <command>
3132
3133        vmpoff=         [KNL,S390] Perform z/VM CP command after power off.
3134                        Format: <command>
3135
3136        vsyscall=       [X86-64]
3137                        Controls the behavior of vsyscalls (i.e. calls to
3138                        fixed addresses of 0xffffffffff600x00 from legacy
3139                        code).  Most statically-linked binaries and older
3140                        versions of glibc use these calls.  Because these
3141                        functions are at fixed addresses, they make nice
3142                        targets for exploits that can control RIP.
3143
3144                        emulate     [default] Vsyscalls turn into traps and are
3145                                    emulated reasonably safely.
3146
3147                        native      Vsyscalls are native syscall instructions.
3148                                    This is a little bit faster than trapping
3149                                    and makes a few dynamic recompilers work
3150                                    better than they would in emulation mode.
3151                                    It also makes exploits much easier to write.
3152
3153                        none        Vsyscalls don't work at all.  This makes
3154                                    them quite hard to use for exploits but
3155                                    might break your system.
3156
3157        vt.cur_default= [VT] Default cursor shape.
3158                        Format: 0xCCBBAA, where AA, BB, and CC are the same as
3159                        the parameters of the <Esc>[?A;B;Cc escape sequence;
3160                        see VGA-softcursor.txt. Default: 2 = underline.
3161
3162        vt.default_blu= [VT]
3163                        Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3164                        Change the default blue palette of the console.
3165                        This is a 16-member array composed of values
3166                        ranging from 0-255.
3167
3168        vt.default_grn= [VT]
3169                        Format: <green0>,<green1>,<green2>,...,<green15>
3170                        Change the default green palette of the console.
3171                        This is a 16-member array composed of values
3172                        ranging from 0-255.
3173
3174        vt.default_red= [VT]
3175                        Format: <red0>,<red1>,<red2>,...,<red15>
3176                        Change the default red palette of the console.
3177                        This is a 16-member array composed of values
3178                        ranging from 0-255.
3179
3180        vt.default_utf8=
3181                        [VT]
3182                        Format=<0|1>
3183                        Set system-wide default UTF-8 mode for all tty's.
3184                        Default is 1, i.e. UTF-8 mode is enabled for all
3185                        newly opened terminals.
3186
3187        vt.global_cursor_default=
3188                        [VT]
3189                        Format=<-1|0|1>
3190                        Set system-wide default for whether a cursor
3191                        is shown on new VTs. Default is -1,
3192                        i.e. cursors will be created by default unless
3193                        overridden by individual drivers. 0 will hide
3194                        cursors, 1 will display them.
3195
3196        watchdog timers [HW,WDT] For information on watchdog timers,
3197                        see Documentation/watchdog/watchdog-parameters.txt
3198                        or other driver-specific files in the
3199                        Documentation/watchdog/ directory.
3200
3201        x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
3202                        default x2apic cluster mode on platforms
3203                        supporting x2apic.
3204
3205        x86_mrst_timer= [X86-32,APBT]
3206                        Choose timer option for x86 Moorestown MID platform.
3207                        Two valid options are apbt timer only and lapic timer
3208                        plus one apbt timer for broadcast timer.
3209                        x86_mrst_timer=apbt_only | lapic_and_apbt
3210
3211        xd=             [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3212        xd_geo=         See header of drivers/block/xd.c.
3213
3214        xen_emul_unplug=                [HW,X86,XEN]
3215                        Unplug Xen emulated devices
3216                        Format: [unplug0,][unplug1]
3217                        ide-disks -- unplug primary master IDE devices
3218                        aux-ide-disks -- unplug non-primary-master IDE devices
3219                        nics -- unplug network devices
3220                        all -- unplug all emulated devices (NICs and IDE disks)
3221                        unnecessary -- unplugging emulated devices is
3222                                unnecessary even if the host did not respond to
3223                                the unplug protocol
3224                        never -- do not unplug even if version check succeeds
3225
3226        xirc2ps_cs=     [NET,PCMCIA]
3227                        Format:
3228                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3229
3230______________________________________________________________________
3231
3232TODO:
3233
3234        Add more DRM drivers.
3235
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