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