1                          Kernel Parameters
   2                          ~~~~~~~~~~~~~~~~~
   4The following is a consolidated list of the kernel parameters as
   5implemented by the __setup(), core_param() and module_param() macros
   6and sorted into English Dictionary order (defined as ignoring all
   7punctuation and sorting digits before letters in a case insensitive
   8manner), and with descriptions where known.
  10The kernel parses parameters from the kernel command line up to "--";
  11if it doesn't recognize a parameter and it doesn't contain a '.', the
  12parameter gets passed to init: parameters with '=' go into init's
  13environment, others are passed as command line arguments to init.
  14Everything after "--" is passed as an argument to init.
  16Module parameters can be specified in two ways: via the kernel command
  17line with a module name prefix, or via modprobe, e.g.:
  19        (kernel command line) usbcore.blinkenlights=1
  20        (modprobe command line) modprobe usbcore blinkenlights=1
  22Parameters for modules which are built into the kernel need to be
  23specified on the kernel command line.  modprobe looks through the
  24kernel command line (/proc/cmdline) and collects module parameters
  25when it loads a module, so the kernel command line can be used for
  26loadable modules too.
  28Hyphens (dashes) and underscores are equivalent in parameter names, so
  29        log_buf_len=1M print-fatal-signals=1
  30can also be entered as
  31        log-buf-len=1M print_fatal_signals=1
  33Double-quotes can be used to protect spaces in values, e.g.:
  34        param="spaces in here"
  36This document may not be entirely up to date and comprehensive. The command
  37"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
  38module. Loadable modules, after being loaded into the running kernel, also
  39reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
  40parameters may be changed at runtime by the command
  41"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
  43The parameters listed below are only valid if certain kernel build options were
  44enabled and if respective hardware is present. The text in square brackets at
  45the beginning of each description states the restrictions within which a
  46parameter is applicable:
  48        ACPI    ACPI support is enabled.
  49        AGP     AGP (Accelerated Graphics Port) is enabled.
  50        ALSA    ALSA sound support is enabled.
  51        APIC    APIC support is enabled.
  52        APM     Advanced Power Management support is enabled.
  53        ARM     ARM architecture is enabled.
  54        AVR32   AVR32 architecture is enabled.
  55        AX25    Appropriate AX.25 support is enabled.
  56        BLACKFIN Blackfin architecture is enabled.
  57        CLK     Common clock infrastructure is enabled.
  58        CMA     Contiguous Memory Area support is enabled.
  59        DRM     Direct Rendering Management support is enabled.
  60        DYNAMIC_DEBUG Build in debug messages and enable them at runtime
  61        EDD     BIOS Enhanced Disk Drive Services (EDD) is enabled
  62        EFI     EFI Partitioning (GPT) is enabled
  63        EIDE    EIDE/ATAPI support is enabled.
  64        EVM     Extended Verification Module
  65        FB      The frame buffer device is enabled.
  66        FTRACE  Function tracing enabled.
  67        GCOV    GCOV profiling is enabled.
  68        HW      Appropriate hardware is enabled.
  69        IA-64   IA-64 architecture is enabled.
  70        IMA     Integrity measurement architecture is enabled.
  71        IOSCHED More than one I/O scheduler is enabled.
  72        IP_PNP  IP DHCP, BOOTP, or RARP is enabled.
  73        IPV6    IPv6 support is enabled.
  74        ISAPNP  ISA PnP code is enabled.
  75        ISDN    Appropriate ISDN support is enabled.
  76        JOY     Appropriate joystick support is enabled.
  77        KGDB    Kernel debugger support is enabled.
  78        KVM     Kernel Virtual Machine support is enabled.
  79        LIBATA  Libata driver is enabled
  80        LP      Printer support is enabled.
  81        LOOP    Loopback device support is enabled.
  82        M68k    M68k architecture is enabled.
  83                        These options have more detailed description inside of
  84                        Documentation/m68k/kernel-options.txt.
  85        MDA     MDA console support is enabled.
  86        MIPS    MIPS architecture is enabled.
  87        MOUSE   Appropriate mouse support is enabled.
  88        MSI     Message Signaled Interrupts (PCI).
  89        MTD     MTD (Memory Technology Device) support is enabled.
  90        NET     Appropriate network support is enabled.
  91        NUMA    NUMA support is enabled.
  92        NFS     Appropriate NFS support is enabled.
  93        OSS     OSS sound support is enabled.
  94        PV_OPS  A paravirtualized kernel is enabled.
  95        PARIDE  The ParIDE (parallel port IDE) subsystem is enabled.
  96        PARISC  The PA-RISC architecture is enabled.
  97        PCI     PCI bus support is enabled.
  98        PCIE    PCI Express support is enabled.
  99        PCMCIA  The PCMCIA subsystem is enabled.
 100        PNP     Plug & Play support is enabled.
 101        PPC     PowerPC architecture is enabled.
 102        PPT     Parallel port support is enabled.
 103        PS2     Appropriate PS/2 support is enabled.
 104        RAM     RAM disk support is enabled.
 105        S390    S390 architecture is enabled.
 106        SCSI    Appropriate SCSI support is enabled.
 107                        A lot of drivers have their options described inside
 108                        the Documentation/scsi/ sub-directory.
 109        SECURITY Different security models are enabled.
 110        SELINUX SELinux support is enabled.
 111        APPARMOR AppArmor support is enabled.
 112        SERIAL  Serial support is enabled.
 113        SH      SuperH architecture is enabled.
 114        SMP     The kernel is an SMP kernel.
 115        SPARC   Sparc architecture is enabled.
 116        SWSUSP  Software suspend (hibernation) is enabled.
 117        SUSPEND System suspend states are enabled.
 118        TPM     TPM drivers are enabled.
 119        TS      Appropriate touchscreen support is enabled.
 120        UMS     USB Mass Storage support is enabled.
 121        USB     USB support is enabled.
 122        USBHID  USB Human Interface Device support is enabled.
 123        V4L     Video For Linux support is enabled.
 124        VMMIO   Driver for memory mapped virtio devices is enabled.
 125        VGA     The VGA console has been enabled.
 126        VT      Virtual terminal support is enabled.
 127        WDT     Watchdog support is enabled.
 128        XT      IBM PC/XT MFM hard disk support is enabled.
 129        X86-32  X86-32, aka i386 architecture is enabled.
 130        X86-64  X86-64 architecture is enabled.
 131                        More X86-64 boot options can be found in
 132                        Documentation/x86/x86_64/boot-options.txt .
 133        X86     Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
 134        XEN     Xen support is enabled
 136In addition, the following text indicates that the option:
 138        BUGS=   Relates to possible processor bugs on the said processor.
 139        KNL     Is a kernel start-up parameter.
 140        BOOT    Is a boot loader parameter.
 142Parameters denoted with BOOT are actually interpreted by the boot
 143loader, and have no meaning to the kernel directly.
 144Do not modify the syntax of boot loader parameters without extreme
 145need or coordination with <Documentation/x86/boot.txt>.
 147There are also arch-specific kernel-parameters not documented here.
 148See for example <Documentation/x86/x86_64/boot-options.txt>.
 150Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
 151a trailing = on the name of any parameter states that that parameter will
 152be entered as an environment variable, whereas its absence indicates that
 153it will appear as a kernel argument readable via /proc/cmdline by programs
 154running once the system is up.
 156The number of kernel parameters is not limited, but the length of the
 157complete command line (parameters including spaces etc.) is limited to
 158a fixed number of characters. This limit depends on the architecture
 159and is between 256 and 4096 characters. It is defined in the file
 160./include/asm/setup.h as COMMAND_LINE_SIZE.
 162Finally, the [KMG] suffix is commonly described after a number of kernel
 163parameter values. These 'K', 'M', and 'G' letters represent the _binary_
 164multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
 165bytes respectively. Such letter suffixes can also be entirely omitted.
 168        acpi=           [HW,ACPI,X86]
 169                        Advanced Configuration and Power Interface
 170                        Format: { force | off | strict | noirq | rsdt }
 171                        force -- enable ACPI if default was off
 172                        off -- disable ACPI if default was on
 173                        noirq -- do not use ACPI for IRQ routing
 174                        strict -- Be less tolerant of platforms that are not
 175                                strictly ACPI specification compliant.
 176                        rsdt -- prefer RSDT over (default) XSDT
 177                        copy_dsdt -- copy DSDT to memory
 179                        See also Documentation/power/runtime_pm.txt, pci=noacpi
 181        acpi_rsdp=      [ACPI,EFI,KEXEC]
 182                        Pass the RSDP address to the kernel, mostly used
 183                        on machines running EFI runtime service to boot the
 184                        second kernel for kdump.
 186        acpi_apic_instance=     [ACPI, IOAPIC]
 187                        Format: <int>
 188                        2: use 2nd APIC table, if available
 189                        1,0: use 1st APIC table
 190                        default: 0
 192        acpi_backlight= [HW,ACPI]
 193                        acpi_backlight=vendor
 194                        acpi_backlight=video
 195                        If set to vendor, prefer vendor specific driver
 196                        (e.g. thinkpad_acpi, sony_acpi, etc.) instead
 197                        of the ACPI video.ko driver.
 199        acpi.debug_layer=       [HW,ACPI,ACPI_DEBUG]
 200        acpi.debug_level=       [HW,ACPI,ACPI_DEBUG]
 201                        Format: <int>
 202                        CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
 203                        debug output.  Bits in debug_layer correspond to a
 204                        _COMPONENT in an ACPI source file, e.g.,
 205                            #define _COMPONENT ACPI_PCI_COMPONENT
 206                        Bits in debug_level correspond to a level in
 207                        ACPI_DEBUG_PRINT statements, e.g.,
 208                            ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
 209                        The debug_level mask defaults to "info".  See
 210                        Documentation/acpi/debug.txt for more information about
 211                        debug layers and levels.
 213                        Enable processor driver info messages:
 214                            acpi.debug_layer=0x20000000
 215                        Enable PCI/PCI interrupt routing info messages:
 216                            acpi.debug_layer=0x400000
 217                        Enable AML "Debug" output, i.e., stores to the Debug
 218                        object while interpreting AML:
 219                            acpi.debug_layer=0xffffffff acpi.debug_level=0x2
 220                        Enable all messages related to ACPI hardware:
 221                            acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
 223                        Some values produce so much output that the system is
 224                        unusable.  The "log_buf_len" parameter may be useful
 225                        if you need to capture more output.
 227        acpi_force_table_verification   [HW,ACPI]
 228                        Enable table checksum verification during early stage.
 229                        By default, this is disabled due to x86 early mapping
 230                        size limitation.
 232        acpi_irq_balance [HW,ACPI]
 233                        ACPI will balance active IRQs
 234                        default in APIC mode
 236        acpi_irq_nobalance [HW,ACPI]
 237                        ACPI will not move active IRQs (default)
 238                        default in PIC mode
 240        acpi_irq_isa=   [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
 241                        Format: <irq>,<irq>...
 243        acpi_irq_pci=   [HW,ACPI] If irq_balance, clear listed IRQs for
 244                        use by PCI
 245                        Format: <irq>,<irq>...
 247        acpi_no_auto_serialize  [HW,ACPI]
 248                        Disable auto-serialization of AML methods
 249                        AML control methods that contain the opcodes to create
 250                        named objects will be marked as "Serialized" by the
 251                        auto-serialization feature.
 252                        This feature is enabled by default.
 253                        This option allows to turn off the feature.
 255        acpi_no_static_ssdt     [HW,ACPI]
 256                        Disable installation of static SSDTs at early boot time
 257                        By default, SSDTs contained in the RSDT/XSDT will be
 258                        installed automatically and they will appear under
 259                        /sys/firmware/acpi/tables.
 260                        This option turns off this feature.
 261                        Note that specifying this option does not affect
 262                        dynamic table installation which will install SSDT
 263                        tables to /sys/firmware/acpi/tables/dynamic.
 265        acpica_no_return_repair [HW, ACPI]
 266                        Disable AML predefined validation mechanism
 267                        This mechanism can repair the evaluation result to make
 268                        the return objects more ACPI specification compliant.
 269                        This option is useful for developers to identify the
 270                        root cause of an AML interpreter issue when the issue
 271                        has something to do with the repair mechanism.
 273        acpi_os_name=   [HW,ACPI] Tell ACPI BIOS the name of the OS
 274                        Format: To spoof as Windows 98: ="Microsoft Windows"
 276        acpi_osi=       [HW,ACPI] Modify list of supported OS interface strings
 277                        acpi_osi="string1"      # add string1
 278                        acpi_osi="!string2"     # remove string2
 279                        acpi_osi=!*             # remove all strings
 280                        acpi_osi=!              # disable all built-in OS vendor
 281                                                  strings
 282                        acpi_osi=               # disable all strings
 284                        'acpi_osi=!' can be used in combination with single or
 285                        multiple 'acpi_osi="string1"' to support specific OS
 286                        vendor string(s).  Note that such command can only
 287                        affect the default state of the OS vendor strings, thus
 288                        it cannot affect the default state of the feature group
 289                        strings and the current state of the OS vendor strings,
 290                        specifying it multiple times through kernel command line
 291                        is meaningless.  This command is useful when one do not
 292                        care about the state of the feature group strings which
 293                        should be controlled by the OSPM.
 294                        Examples:
 295                          1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
 296                             to 'acpi_osi="Windows 2000" acpi_osi=!', they all
 297                             can make '_OSI("Windows 2000")' TRUE.
 299                        'acpi_osi=' cannot be used in combination with other
 300                        'acpi_osi=' command lines, the _OSI method will not
 301                        exist in the ACPI namespace.  NOTE that such command can
 302                        only affect the _OSI support state, thus specifying it
 303                        multiple times through kernel command line is also
 304                        meaningless.
 305                        Examples:
 306                          1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
 307                             FALSE.
 309                        'acpi_osi=!*' can be used in combination with single or
 310                        multiple 'acpi_osi="string1"' to support specific
 311                        string(s).  Note that such command can affect the
 312                        current state of both the OS vendor strings and the
 313                        feature group strings, thus specifying it multiple times
 314                        through kernel command line is meaningful.  But it may
 315                        still not able to affect the final state of a string if
 316                        there are quirks related to this string.  This command
 317                        is useful when one want to control the state of the
 318                        feature group strings to debug BIOS issues related to
 319                        the OSPM features.
 320                        Examples:
 321                          1. 'acpi_osi="Module Device" acpi_osi=!*' can make
 322                             '_OSI("Module Device")' FALSE.
 323                          2. 'acpi_osi=!* acpi_osi="Module Device"' can make
 324                             '_OSI("Module Device")' TRUE.
 325                          3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
 326                             equivalent to
 327                             'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
 328                             and
 329                             'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
 330                             they all will make '_OSI("Windows 2000")' TRUE.
 332        acpi_pm_good    [X86]
 333                        Override the pmtimer bug detection: force the kernel
 334                        to assume that this machine's pmtimer latches its value
 335                        and always returns good values.
 337        acpi_sci=       [HW,ACPI] ACPI System Control Interrupt trigger mode
 338                        Format: { level | edge | high | low }
 340        acpi_skip_timer_override [HW,ACPI]
 341                        Recognize and ignore IRQ0/pin2 Interrupt Override.
 342                        For broken nForce2 BIOS resulting in XT-PIC timer.
 344        acpi_sleep=     [HW,ACPI] Sleep options
 345                        Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
 346                                  old_ordering, nonvs, sci_force_enable }
 347                        See Documentation/power/video.txt for information on
 348                        s3_bios and s3_mode.
 349                        s3_beep is for debugging; it makes the PC's speaker beep
 350                        as soon as the kernel's real-mode entry point is called.
 351                        s4_nohwsig prevents ACPI hardware signature from being
 352                        used during resume from hibernation.
 353                        old_ordering causes the ACPI 1.0 ordering of the _PTS
 354                        control method, with respect to putting devices into
 355                        low power states, to be enforced (the ACPI 2.0 ordering
 356                        of _PTS is used by default).
 357                        nonvs prevents the kernel from saving/restoring the
 358                        ACPI NVS memory during suspend/hibernation and resume.
 359                        sci_force_enable causes the kernel to set SCI_EN directly
 360                        on resume from S1/S3 (which is against the ACPI spec,
 361                        but some broken systems don't work without it).
 363        acpi_use_timer_override [HW,ACPI]
 364                        Use timer override. For some broken Nvidia NF5 boards
 365                        that require a timer override, but don't have HPET
 367        acpi_enforce_resources= [ACPI]
 368                        { strict | lax | no }
 369                        Check for resource conflicts between native drivers
 370                        and ACPI OperationRegions (SystemIO and SystemMemory
 371                        only). IO ports and memory declared in ACPI might be
 372                        used by the ACPI subsystem in arbitrary AML code and
 373                        can interfere with legacy drivers.
 374                        strict (default): access to resources claimed by ACPI
 375                        is denied; legacy drivers trying to access reserved
 376                        resources will fail to bind to device using them.
 377                        lax: access to resources claimed by ACPI is allowed;
 378                        legacy drivers trying to access reserved resources
 379                        will bind successfully but a warning message is logged.
 380                        no: ACPI OperationRegions are not marked as reserved,
 381                        no further checks are performed.
 383        acpi_no_memhotplug [ACPI] Disable memory hotplug.  Useful for kdump
 384                           kernels.
 386        add_efi_memmap  [EFI; X86] Include EFI memory map in
 387                        kernel's map of available physical RAM.
 389        agp=            [AGP]
 390                        { off | try_unsupported }
 391                        off: disable AGP support
 392                        try_unsupported: try to drive unsupported chipsets
 393                                (may crash computer or cause data corruption)
 395        ALSA            [HW,ALSA]
 396                        See Documentation/sound/alsa/alsa-parameters.txt
 398        alignment=      [KNL,ARM]
 399                        Allow the default userspace alignment fault handler
 400                        behaviour to be specified.  Bit 0 enables warnings,
 401                        bit 1 enables fixups, and bit 2 sends a segfault.
 403        align_va_addr=  [X86-64]
 404                        Align virtual addresses by clearing slice [14:12] when
 405                        allocating a VMA at process creation time. This option
 406                        gives you up to 3% performance improvement on AMD F15h
 407                        machines (where it is enabled by default) for a
 408                        CPU-intensive style benchmark, and it can vary highly in
 409                        a microbenchmark depending on workload and compiler.
 411                        32: only for 32-bit processes
 412                        64: only for 64-bit processes
 413                        on: enable for both 32- and 64-bit processes
 414                        off: disable for both 32- and 64-bit processes
 416        alloc_snapshot  [FTRACE]
 417                        Allocate the ftrace snapshot buffer on boot up when the
 418                        main buffer is allocated. This is handy if debugging
 419                        and you need to use tracing_snapshot() on boot up, and
 420                        do not want to use tracing_snapshot_alloc() as it needs
 421                        to be done where GFP_KERNEL allocations are allowed.
 423        amd_iommu=      [HW,X86-64]
 424                        Pass parameters to the AMD IOMMU driver in the system.
 425                        Possible values are:
 426                        fullflush - enable flushing of IO/TLB entries when
 427                                    they are unmapped. Otherwise they are
 428                                    flushed before they will be reused, which
 429                                    is a lot of faster
 430                        off       - do not initialize any AMD IOMMU found in
 431                                    the system
 432                        force_isolation - Force device isolation for all
 433                                          devices. The IOMMU driver is not
 434                                          allowed anymore to lift isolation
 435                                          requirements as needed. This option
 436                                          does not override iommu=pt
 438        amd_iommu_dump= [HW,X86-64]
 439                        Enable AMD IOMMU driver option to dump the ACPI table
 440                        for AMD IOMMU. With this option enabled, AMD IOMMU
 441                        driver will print ACPI tables for AMD IOMMU during
 442                        IOMMU initialization.
 444     [HW,JOY] Amiga joystick support
 445                        Map of devices attached to JOY0DAT and JOY1DAT
 446                        Format: <a>,<b>
 447                        See also Documentation/input/joystick.txt
 449     [HW,JOY] Analog joystick and gamepad support
 450                        Specifies type or capabilities of an analog joystick
 451                        connected to one of 16 gameports
 452                        Format: <type1>,<type2>,..<type16>
 454        apc=            [HW,SPARC]
 455                        Power management functions (SPARCstation-4/5 + deriv.)
 456                        Format: noidle
 457                        Disable APC CPU standby support. SPARCstation-Fox does
 458                        not play well with APC CPU idle - disable it if you have
 459                        APC and your system crashes randomly.
 461        apic=           [APIC,X86-32] Advanced Programmable Interrupt Controller
 462                        Change the output verbosity whilst booting
 463                        Format: { quiet (default) | verbose | debug }
 464                        Change the amount of debugging information output
 465                        when initialising the APIC and IO-APIC components.
 467        autoconf=       [IPV6]
 468                        See Documentation/networking/ipv6.txt.
 470        show_lapic=     [APIC,X86] Advanced Programmable Interrupt Controller
 471                        Limit apic dumping. The parameter defines the maximal
 472                        number of local apics being dumped. Also it is possible
 473                        to set it to "all" by meaning -- no limit here.
 474                        Format: { 1 (default) | 2 | ... | all }.
 475                        The parameter valid if only apic=debug or
 476                        apic=verbose is specified.
 477                        Example: apic=debug show_lapic=all
 479        apm=            [APM] Advanced Power Management
 480                        See header of arch/x86/kernel/apm_32.c.
 482        arcrimi=        [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
 483                        Format: <io>,<irq>,<nodeID>
 485        ataflop=        [HW,M68k]
 487        atarimouse=     [HW,MOUSE] Atari Mouse
 489        atkbd.extra=    [HW] Enable extra LEDs and keys on IBM RapidAccess,
 490                        EzKey and similar keyboards
 492        atkbd.reset=    [HW] Reset keyboard during initialization
 494        atkbd.set=      [HW] Select keyboard code set
 495                        Format: <int> (2 = AT (default), 3 = PS/2)
 497        atkbd.scroll=   [HW] Enable scroll wheel on MS Office and similar
 498                        keyboards
 500        atkbd.softraw=  [HW] Choose between synthetic and real raw mode
 501                        Format: <bool> (0 = real, 1 = synthetic (default))
 503        atkbd.softrepeat= [HW]
 504                        Use software keyboard repeat
 506        audit=          [KNL] Enable the audit sub-system
 507                        Format: { "0" | "1" } (0 = disabled, 1 = enabled)
 508                        0 - kernel audit is disabled and can not be enabled
 509                            until the next reboot
 510                        unset - kernel audit is initialized but disabled and
 511                            will be fully enabled by the userspace auditd.
 512                        1 - kernel audit is initialized and partially enabled,
 513                            storing at most audit_backlog_limit messages in
 514                            RAM until it is fully enabled by the userspace
 515                            auditd.
 516                        Default: unset
 518        audit_backlog_limit= [KNL] Set the audit queue size limit.
 519                        Format: <int> (must be >=0)
 520                        Default: 64
 522        baycom_epp=     [HW,AX25]
 523                        Format: <io>,<mode>
 525        baycom_par=     [HW,AX25] BayCom Parallel Port AX.25 Modem
 526                        Format: <io>,<mode>
 527                        See header of drivers/net/hamradio/baycom_par.c.
 529        baycom_ser_fdx= [HW,AX25]
 530                        BayCom Serial Port AX.25 Modem (Full Duplex Mode)
 531                        Format: <io>,<irq>,<mode>[,<baud>]
 532                        See header of drivers/net/hamradio/baycom_ser_fdx.c.
 534        baycom_ser_hdx= [HW,AX25]
 535                        BayCom Serial Port AX.25 Modem (Half Duplex Mode)
 536                        Format: <io>,<irq>,<mode>
 537                        See header of drivers/net/hamradio/baycom_ser_hdx.c.
 539        blkdevparts=    Manual partition parsing of block device(s) for
 540                        embedded devices based on command line input.
 541                        See Documentation/block/cmdline-partition.txt
 543        boot_delay=     Milliseconds to delay each printk during boot.
 544                        Values larger than 10 seconds (10000) are changed to
 545                        no delay (0).
 546                        Format: integer
 548        bootmem_debug   [KNL] Enable bootmem allocator debug messages.
 550        bttv.card=      [HW,V4L] bttv (bt848 + bt878 based grabber cards)
 551     Most important insmod options are available as
 552                        kernel args too.
 553        bttv.pll=       See Documentation/video4linux/bttv/Insmod-options
 554        bttv.tuner=
 556        bulk_remove=off [PPC]  This parameter disables the use of the pSeries
 557                        firmware feature for flushing multiple hpte entries
 558                        at a time.
 560        c101=           [NET] Moxa C101 synchronous serial card
 562        cachesize=      [BUGS=X86-32] Override level 2 CPU cache size detection.
 563                        Sometimes CPU hardware bugs make them report the cache
 564                        size incorrectly. The kernel will attempt work arounds
 565                        to fix known problems, but for some CPUs it is not
 566                        possible to determine what the correct size should be.
 567                        This option provides an override for these situations.
 569        ca_keys=        [KEYS] This parameter identifies a specific key(s) on
 570                        the system trusted keyring to be used for certificate
 571                        trust validation.
 572                        format: { id:<keyid> | builtin }
 574        cca=            [MIPS] Override the kernel pages' cache coherency
 575                        algorithm.  Accepted values range from 0 to 7
 576                        inclusive. See arch/mips/include/asm/pgtable-bits.h
 577                        for platform specific values (SB1, Loongson3 and
 578                        others).
 580        ccw_timeout_log [S390]
 581                        See Documentation/s390/CommonIO for details.
 583        cgroup_disable= [KNL] Disable a particular controller
 584                        Format: {name of the controller(s) to disable}
 585                        The effects of cgroup_disable=foo are:
 586                        - foo isn't auto-mounted if you mount all cgroups in
 587                          a single hierarchy
 588                        - foo isn't visible as an individually mountable
 589                          subsystem
 590                        {Currently only "memory" controller deal with this and
 591                        cut the overhead, others just disable the usage. So
 592                        only cgroup_disable=memory is actually worthy}
 594        checkreqprot    [SELINUX] Set initial checkreqprot flag value.
 595                        Format: { "0" | "1" }
 596                        See security/selinux/Kconfig help text.
 597                        0 -- check protection applied by kernel (includes
 598                                any implied execute protection).
 599                        1 -- check protection requested by application.
 600                        Default value is set via a kernel config option.
 601                        Value can be changed at runtime via
 602                                /selinux/checkreqprot.
 604        cio_ignore=     [S390]
 605                        See Documentation/s390/CommonIO for details.
 606        clk_ignore_unused
 607                        [CLK]
 608                        Prevents the clock framework from automatically gating
 609                        clocks that have not been explicitly enabled by a Linux
 610                        device driver but are enabled in hardware at reset or
 611                        by the bootloader/firmware. Note that this does not
 612                        force such clocks to be always-on nor does it reserve
 613                        those clocks in any way. This parameter is useful for
 614                        debug and development, but should not be needed on a
 615                        platform with proper driver support.  For more
 616                        information, see Documentation/clk.txt.
 618        clock=          [BUGS=X86-32, HW] gettimeofday clocksource override.
 619                        [Deprecated]
 620                        Forces specified clocksource (if available) to be used
 621                        when calculating gettimeofday(). If specified
 622                        clocksource is not available, it defaults to PIT.
 623                        Format: { pit | tsc | cyclone | pmtmr }
 625        clocksource=    Override the default clocksource
 626                        Format: <string>
 627                        Override the default clocksource and use the clocksource
 628                        with the name specified.
 629                        Some clocksource names to choose from, depending on
 630                        the platform:
 631                        [all] jiffies (this is the base, fallback clocksource)
 632                        [ACPI] acpi_pm
 633                        [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
 634                                pxa_timer,timer3,32k_counter,timer0_1
 635                        [AVR32] avr32
 636                        [X86-32] pit,hpet,tsc;
 637                                scx200_hrt on Geode; cyclone on IBM x440
 638                        [MIPS] MIPS
 639                        [PARISC] cr16
 640                        [S390] tod
 641                        [SH] SuperH
 642                        [SPARC64] tick
 643                        [X86-64] hpet,tsc
 645        clearcpuid=BITNUM [X86]
 646                        Disable CPUID feature X for the kernel. See
 647                        arch/x86/include/asm/cpufeature.h for the valid bit
 648                        numbers. Note the Linux specific bits are not necessarily
 649                        stable over kernel options, but the vendor specific
 650                        ones should be.
 651                        Also note that user programs calling CPUID directly
 652                        or using the feature without checking anything
 653                        will still see it. This just prevents it from
 654                        being used by the kernel or shown in /proc/cpuinfo.
 655                        Also note the kernel might malfunction if you disable
 656                        some critical bits.
 658        cma=nn[MG]@[start[MG][-end[MG]]]
 659                        [ARM,X86,KNL]
 660                        Sets the size of kernel global memory area for
 661                        contiguous memory allocations and optionally the
 662                        placement constraint by the physical address range of
 663                        memory allocations. A value of 0 disables CMA
 664                        altogether. For more information, see
 665                        include/linux/dma-contiguous.h
 667        cmo_free_hint=  [PPC] Format: { yes | no }
 668                        Specify whether pages are marked as being inactive
 669                        when they are freed.  This is used in CMO environments
 670                        to determine OS memory pressure for page stealing by
 671                        a hypervisor.
 672                        Default: yes
 674        coherent_pool=nn[KMG]   [ARM,KNL]
 675                        Sets the size of memory pool for coherent, atomic dma
 676                        allocations, by default set to 256K.
 678        code_bytes      [X86] How many bytes of object code to print
 679                        in an oops report.
 680                        Range: 0 - 8192
 681                        Default: 64
 683        com20020=       [HW,NET] ARCnet - COM20020 chipset
 684                        Format:
 685                        <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
 687        com90io=        [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
 688                        Format: <io>[,<irq>]
 690        com90xx=        [HW,NET]
 691                        ARCnet - COM90xx chipset (memory-mapped buffers)
 692                        Format: <io>[,<irq>[,<memstart>]]
 694        condev=         [HW,S390] console device
 695        conmode=
 697        console=        [KNL] Output console device and options.
 699                tty<n>  Use the virtual console device <n>.
 701                ttyS<n>[,options]
 702                ttyUSB0[,options]
 703                        Use the specified serial port.  The options are of
 704                        the form "bbbbpnf", where "bbbb" is the baud rate,
 705                        "p" is parity ("n", "o", or "e"), "n" is number of
 706                        bits, and "f" is flow control ("r" for RTS or
 707                        omit it).  Default is "9600n8".
 709                        See Documentation/serial-console.txt for more
 710                        information.  See
 711                        Documentation/networking/netconsole.txt for an
 712                        alternative.
 714                uart[8250],io,<addr>[,options]
 715                uart[8250],mmio,<addr>[,options]
 716                        Start an early, polled-mode console on the 8250/16550
 717                        UART at the specified I/O port or MMIO address,
 718                        switching to the matching ttyS device later.  The
 719                        options are the same as for ttyS, above.
 720                hvc<n>  Use the hypervisor console device <n>. This is for
 721                        both Xen and PowerPC hypervisors.
 723                If the device connected to the port is not a TTY but a braille
 724                device, prepend "brl," before the device type, for instance
 725                        console=brl,ttyS0
 726                For now, only VisioBraille is supported.
 728        consoleblank=   [KNL] The console blank (screen saver) timeout in
 729                        seconds. Defaults to 10*60 = 10mins. A value of 0
 730                        disables the blank timer.
 732        coredump_filter=
 733                        [KNL] Change the default value for
 734                        /proc/<pid>/coredump_filter.
 735                        See also Documentation/filesystems/proc.txt.
 737   [CPU_IDLE]
 738                        disable the cpuidle sub-system
 740        cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
 741                        Format:
 742                        <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
 744        crashkernel=size[KMG][@offset[KMG]]
 745                        [KNL] Using kexec, Linux can switch to a 'crash kernel'
 746                        upon panic. This parameter reserves the physical
 747                        memory region [offset, offset + size] for that kernel
 748                        image. If '@offset' is omitted, then a suitable offset
 749                        is selected automatically. Check
 750                        Documentation/kdump/kdump.txt for further details.
 752        crashkernel=range1:size1[,range2:size2,...][@offset]
 753                        [KNL] Same as above, but depends on the memory
 754                        in the running system. The syntax of range is
 755                        start-[end] where start and end are both
 756                        a memory unit (amount[KMG]). See also
 757                        Documentation/kdump/kdump.txt for an example.
 759        crashkernel=size[KMG],high
 760                        [KNL, x86_64] range could be above 4G. Allow kernel
 761                        to allocate physical memory region from top, so could
 762                        be above 4G if system have more than 4G ram installed.
 763                        Otherwise memory region will be allocated below 4G, if
 764                        available.
 765                        It will be ignored if crashkernel=X is specified.
 766        crashkernel=size[KMG],low
 767                        [KNL, x86_64] range under 4G. When crashkernel=X,high
 768                        is passed, kernel could allocate physical memory region
 769                        above 4G, that cause second kernel crash on system
 770                        that require some amount of low memory, e.g. swiotlb
 771                        requires at least 64M+32K low memory.  Kernel would
 772                        try to allocate 72M below 4G automatically.
 773                        This one let user to specify own low range under 4G
 774                        for second kernel instead.
 775                        0: to disable low allocation.
 776                        It will be ignored when crashkernel=X,high is not used
 777                        or memory reserved is below 4G.
 779        cs89x0_dma=     [HW,NET]
 780                        Format: <dma>
 782        cs89x0_media=   [HW,NET]
 783                        Format: { rj45 | aui | bnc }
 785        dasd=           [HW,NET]
 786                        See header of drivers/s390/block/dasd_devmap.c.
 788[2|3]=   [HW,JOY] Multisystem joystick support via parallel port
 789                        (one device per port)
 790                        Format: <port#>,<type>
 791                        See also Documentation/input/joystick-parport.txt
 793        ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
 794                        time. See Documentation/dynamic-debug-howto.txt for
 795                        details.  Deprecated, see dyndbg.
 797        debug           [KNL] Enable kernel debugging (events log level).
 799        debug_locks_verbose=
 800                        [KNL] verbose self-tests
 801                        Format=<0|1>
 802                        Print debugging info while doing the locking API
 803                        self-tests.
 804                        We default to 0 (no extra messages), setting it to
 805                        1 will print _a lot_ more information - normally
 806                        only useful to kernel developers.
 808        debug_objects   [KNL] Enable object debugging
 810        no_debug_objects
 811                        [KNL] Disable object debugging
 813        debug_guardpage_minorder=
 814                        [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
 815                        parameter allows control of the order of pages that will
 816                        be intentionally kept free (and hence protected) by the
 817                        buddy allocator. Bigger value increase the probability
 818                        of catching random memory corruption, but reduce the
 819                        amount of memory for normal system use. The maximum
 820                        possible value is MAX_ORDER/2.  Setting this parameter
 821                        to 1 or 2 should be enough to identify most random
 822                        memory corruption problems caused by bugs in kernel or
 823                        driver code when a CPU writes to (or reads from) a
 824                        random memory location. Note that there exists a class
 825                        of memory corruptions problems caused by buggy H/W or
 826                        F/W or by drivers badly programing DMA (basically when
 827                        memory is written at bus level and the CPU MMU is
 828                        bypassed) which are not detectable by
 829                        CONFIG_DEBUG_PAGEALLOC, hence this option will not help
 830                        tracking down these problems.
 832        debugpat        [X86] Enable PAT debugging
 834        decnet.addr=    [HW,NET]
 835                        Format: <area>[,<node>]
 836                        See also Documentation/networking/decnet.txt.
 838        default_hugepagesz=
 839                        [same as hugepagesz=] The size of the default
 840                        HugeTLB page size. This is the size represented by
 841                        the legacy /proc/ hugepages APIs, used for SHM, and
 842                        default size when mounting hugetlbfs filesystems.
 843                        Defaults to the default architecture's huge page size
 844                        if not specified.
 846        dhash_entries=  [KNL]
 847                        Set number of hash buckets for dentry cache.
 849        disable=        [IPV6]
 850                        See Documentation/networking/ipv6.txt.
 852        disable_cpu_apicid= [X86,APIC,SMP]
 853                        Format: <int>
 854                        The number of initial APIC ID for the
 855                        corresponding CPU to be disabled at boot,
 856                        mostly used for the kdump 2nd kernel to
 857                        disable BSP to wake up multiple CPUs without
 858                        causing system reset or hang due to sending
 859                        INIT from AP to BSP.
 861        disable_ddw     [PPC/PSERIES]
 862                        Disable Dynamic DMA Window support. Use this if
 863                        to workaround buggy firmware.
 865        disable_ipv6=   [IPV6]
 866                        See Documentation/networking/ipv6.txt.
 868        disable_mtrr_cleanup [X86]
 869                        The kernel tries to adjust MTRR layout from continuous
 870                        to discrete, to make X server driver able to add WB
 871                        entry later. This parameter disables that.
 873        disable_mtrr_trim [X86, Intel and AMD only]
 874                        By default the kernel will trim any uncacheable
 875                        memory out of your available memory pool based on
 876                        MTRR settings.  This parameter disables that behavior,
 877                        possibly causing your machine to run very slowly.
 879        disable_timer_pin_1 [X86]
 880                        Disable PIN 1 of APIC timer
 881                        Can be useful to work around chipset bugs.
 883        dma_debug=off   If the kernel is compiled with DMA_API_DEBUG support,
 884                        this option disables the debugging code at boot.
 886        dma_debug_entries=<number>
 887                        This option allows to tune the number of preallocated
 888                        entries for DMA-API debugging code. One entry is
 889                        required per DMA-API allocation. Use this if the
 890                        DMA-API debugging code disables itself because the
 891                        architectural default is too low.
 893        dma_debug_driver=<driver_name>
 894                        With this option the DMA-API debugging driver
 895                        filter feature can be enabled at boot time. Just
 896                        pass the driver to filter for as the parameter.
 897                        The filter can be disabled or changed to another
 898                        driver later using sysfs.
 900        drm_kms_helper.edid_firmware=[<connector>:]<file>
 901                        Broken monitors, graphic adapters and KVMs may
 902                        send no or incorrect EDID data sets. This parameter
 903                        allows to specify an EDID data set in the
 904                        /lib/firmware directory that is used instead.
 905                        Generic built-in EDID data sets are used, if one of
 906                        edid/1024x768.bin, edid/1280x1024.bin,
 907                        edid/1680x1050.bin, or edid/1920x1080.bin is given
 908                        and no file with the same name exists. Details and
 909                        instructions how to build your own EDID data are
 910                        available in Documentation/EDID/HOWTO.txt. An EDID
 911                        data set will only be used for a particular connector,
 912                        if its name and a colon are prepended to the EDID
 913                        name.
 915        dscc4.setup=    [NET]
 917        dyndbg[="val"]          [KNL,DYNAMIC_DEBUG]
 918        module.dyndbg[="val"]
 919                        Enable debug messages at boot time.  See
 920                        Documentation/dynamic-debug-howto.txt for details.
 922        early_ioremap_debug [KNL]
 923                        Enable debug messages in early_ioremap support. This
 924                        is useful for tracking down temporary early mappings
 925                        which are not unmapped.
 927        earlycon=       [KNL] Output early console device and options.
 929                cdns,<addr>
 930                        Start an early, polled-mode console on a cadence serial
 931                        port at the specified address. The cadence serial port
 932                        must already be setup and configured. Options are not
 933                        yet supported.
 935                uart[8250],io,<addr>[,options]
 936                uart[8250],mmio,<addr>[,options]
 937                uart[8250],mmio32,<addr>[,options]
 938                        Start an early, polled-mode console on the 8250/16550
 939                        UART at the specified I/O port or MMIO address.
 940                        MMIO inter-register address stride is either 8-bit
 941                        (mmio) or 32-bit (mmio32).
 942                        The options are the same as for ttyS, above.
 944                pl011,<addr>
 945                        Start an early, polled-mode console on a pl011 serial
 946                        port at the specified address. The pl011 serial port
 947                        must already be setup and configured. Options are not
 948                        yet supported.
 950                msm_serial,<addr>
 951                        Start an early, polled-mode console on an msm serial
 952                        port at the specified address. The serial port
 953                        must already be setup and configured. Options are not
 954                        yet supported.
 956                msm_serial_dm,<addr>
 957                        Start an early, polled-mode console on an msm serial
 958                        dm port at the specified address. The serial port
 959                        must already be setup and configured. Options are not
 960                        yet supported.
 962                smh     Use ARM semihosting calls for early console.
 964        earlyprintk=    [X86,SH,BLACKFIN,ARM,M68k]
 965                        earlyprintk=vga
 966                        earlyprintk=efi
 967                        earlyprintk=xen
 968                        earlyprintk=serial[,ttySn[,baudrate]]
 969                        earlyprintk=serial[,0x...[,baudrate]]
 970                        earlyprintk=ttySn[,baudrate]
 971                        earlyprintk=dbgp[debugController#]
 973                        earlyprintk is useful when the kernel crashes before
 974                        the normal console is initialized. It is not enabled by
 975                        default because it has some cosmetic problems.
 977                        Append ",keep" to not disable it when the real console
 978                        takes over.
 980                        Only one of vga, efi, serial, or usb debug port can
 981                        be used at a time.
 983                        Currently only ttyS0 and ttyS1 may be specified by
 984                        name.  Other I/O ports may be explicitly specified
 985                        on some architectures (x86 and arm at least) by
 986                        replacing ttySn with an I/O port address, like this:
 987                                earlyprintk=serial,0x1008,115200
 988                        You can find the port for a given device in
 989                        /proc/tty/driver/serial:
 990                                2: uart:ST16650V2 port:00001008 irq:18 ...
 992                        Interaction with the standard serial driver is not
 993                        very good.
 995                        The VGA and EFI output is eventually overwritten by
 996                        the real console.
 998                        The xen output can only be used by Xen PV guests.
1000        edac_report=    [HW,EDAC] Control how to report EDAC event
1001                        Format: {"on" | "off" | "force"}
1002                        on: enable EDAC to report H/W event. May be overridden
1003                        by other higher priority error reporting module.
1004                        off: disable H/W event reporting through EDAC.
1005                        force: enforce the use of EDAC to report H/W event.
1006                        default: on.
1008        ekgdboc=        [X86,KGDB] Allow early kernel console debugging
1009                        ekgdboc=kbd
1011                        This is designed to be used in conjunction with
1012                        the boot argument: earlyprintk=vga
1014        edd=            [EDD]
1015                        Format: {"off" | "on" | "skip[mbr]"}
1017        efi=            [EFI]
1018                        Format: { "old_map", "nochunk", "noruntime" }
1019                        old_map [X86-64]: switch to the old ioremap-based EFI
1020                        runtime services mapping. 32-bit still uses this one by
1021                        default.
1022                        nochunk: disable reading files in "chunks" in the EFI
1023                        boot stub, as chunking can cause problems with some
1024                        firmware implementations.
1025                        noruntime : disable EFI runtime services support
1027        efi_no_storage_paranoia [EFI; X86]
1028                        Using this parameter you can use more than 50% of
1029                        your efi variable storage. Use this parameter only if
1030                        you are really sure that your UEFI does sane gc and
1031                        fulfills the spec otherwise your board may brick.
1033        eisa_irq_edge=  [PARISC,HW]
1034                        See header of drivers/parisc/eisa.c.
1036        elanfreq=       [X86-32]
1037                        See comment before function elanfreq_setup() in
1038                        arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1040        elevator=       [IOSCHED]
1041                        Format: {"cfq" | "deadline" | "noop"}
1042                        See Documentation/block/cfq-iosched.txt and
1043                        Documentation/block/deadline-iosched.txt for details.
1045        elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1046                        Specifies physical address of start of kernel core
1047                        image elf header and optionally the size. Generally
1048                        kexec loader will pass this option to capture kernel.
1049                        See Documentation/kdump/kdump.txt for details.
1051        enable_mtrr_cleanup [X86]
1052                        The kernel tries to adjust MTRR layout from continuous
1053                        to discrete, to make X server driver able to add WB
1054                        entry later. This parameter enables that.
1056        enable_timer_pin_1 [X86]
1057                        Enable PIN 1 of APIC timer
1058                        Can be useful to work around chipset bugs
1059                        (in particular on some ATI chipsets).
1060                        The kernel tries to set a reasonable default.
1062        enforcing       [SELINUX] Set initial enforcing status.
1063                        Format: {"0" | "1"}
1064                        See security/selinux/Kconfig help text.
1065                        0 -- permissive (log only, no denials).
1066                        1 -- enforcing (deny and log).
1067                        Default value is 0.
1068                        Value can be changed at runtime via /selinux/enforce.
1070        erst_disable    [ACPI]
1071                        Disable Error Record Serialization Table (ERST)
1072                        support.
1074        ether=          [HW,NET] Ethernet cards parameters
1075                        This option is obsoleted by the "netdev=" option, which
1076                        has equivalent usage. See its documentation for details.
1078        evm=            [EVM]
1079                        Format: { "fix" }
1080                        Permit 'security.evm' to be updated regardless of
1081                        current integrity status.
1083        failslab=
1084        fail_page_alloc=
1085        fail_make_request=[KNL]
1086                        General fault injection mechanism.
1087                        Format: <interval>,<probability>,<space>,<times>
1088                        See also Documentation/fault-injection/.
1090        floppy=         [HW]
1091                        See Documentation/blockdev/floppy.txt.
1093        force_pal_cache_flush
1094                        [IA-64] Avoid check_sal_cache_flush which may hang on
1095                        buggy SAL_CACHE_FLUSH implementations. Using this
1096                        parameter will force ia64_sal_cache_flush to call
1097                        ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1099        forcepae [X86-32]
1100                        Forcefully enable Physical Address Extension (PAE).
1101                        Many Pentium M systems disable PAE but may have a
1102                        functionally usable PAE implementation.
1103                        Warning: use of this parameter will taint the kernel
1104                        and may cause unknown problems.
1106        ftrace=[tracer]
1107                        [FTRACE] will set and start the specified tracer
1108                        as early as possible in order to facilitate early
1109                        boot debugging.
1111        ftrace_dump_on_oops[=orig_cpu]
1112                        [FTRACE] will dump the trace buffers on oops.
1113                        If no parameter is passed, ftrace will dump
1114                        buffers of all CPUs, but if you pass orig_cpu, it will
1115                        dump only the buffer of the CPU that triggered the
1116                        oops.
1118        ftrace_filter=[function-list]
1119                        [FTRACE] Limit the functions traced by the function
1120                        tracer at boot up. function-list is a comma separated
1121                        list of functions. This list can be changed at run
1122                        time by the set_ftrace_filter file in the debugfs
1123                        tracing directory.
1125        ftrace_notrace=[function-list]
1126                        [FTRACE] Do not trace the functions specified in
1127                        function-list. This list can be changed at run time
1128                        by the set_ftrace_notrace file in the debugfs
1129                        tracing directory.
1131        ftrace_graph_filter=[function-list]
1132                        [FTRACE] Limit the top level callers functions traced
1133                        by the function graph tracer at boot up.
1134                        function-list is a comma separated list of functions
1135                        that can be changed at run time by the
1136                        set_graph_function file in the debugfs tracing directory.
1138        ftrace_graph_notrace=[function-list]
1139                        [FTRACE] Do not trace from the functions specified in
1140                        function-list.  This list is a comma separated list of
1141                        functions that can be changed at run time by the
1142                        set_graph_notrace file in the debugfs tracing directory.
1145                        [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1146                        support via parallel port (up to 5 devices per port)
1147                        Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1148                        See also Documentation/input/joystick-parport.txt
1150        gamma=          [HW,DRM]
1152        gart_fix_e820=  [X86_64] disable the fix e820 for K8 GART
1153                        Format: off | on
1154                        default: on
1156        gcov_persist=   [GCOV] When non-zero (default), profiling data for
1157                        kernel modules is saved and remains accessible via
1158                        debugfs, even when the module is unloaded/reloaded.
1159                        When zero, profiling data is discarded and associated
1160                        debugfs files are removed at module unload time.
1162        gpt             [EFI] Forces disk with valid GPT signature but
1163                        invalid Protective MBR to be treated as GPT. If the
1164                        primary GPT is corrupted, it enables the backup/alternate
1165                        GPT to be used instead.
1167        grcan.enable0=  [HW] Configuration of physical interface 0. Determines
1168                        the "Enable 0" bit of the configuration register.
1169                        Format: 0 | 1
1170                        Default: 0
1171        grcan.enable1=  [HW] Configuration of physical interface 1. Determines
1172                        the "Enable 0" bit of the configuration register.
1173                        Format: 0 | 1
1174                        Default: 0
1175   [HW] Select which physical interface to use.
1176                        Format: 0 | 1
1177                        Default: 0
1178        grcan.txsize=   [HW] Sets the size of the tx buffer.
1179                        Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1180                        Default: 1024
1181        grcan.rxsize=   [HW] Sets the size of the rx buffer.
1182                        Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1183                        Default: 1024
1185        hashdist=       [KNL,NUMA] Large hashes allocated during boot
1186                        are distributed across NUMA nodes.  Defaults on
1187                        for 64-bit NUMA, off otherwise.
1188                        Format: 0 | 1 (for off | on)
1190        hcl=            [IA-64] SGI's Hardware Graph compatibility layer
1192        hd=             [EIDE] (E)IDE hard drive subsystem geometry
1193                        Format: <cyl>,<head>,<sect>
1195        hest_disable    [ACPI]
1196                        Disable Hardware Error Source Table (HEST) support;
1197                        corresponding firmware-first mode error processing
1198                        logic will be disabled.
1200        highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1201                        size of <nn>. This works even on boxes that have no
1202                        highmem otherwise. This also works to reduce highmem
1203                        size on bigger boxes.
1205        highres=        [KNL] Enable/disable high resolution timer mode.
1206                        Valid parameters: "on", "off"
1207                        Default: "on"
1209        hisax=          [HW,ISDN]
1210                        See Documentation/isdn/README.HiSax.
1212        hlt             [BUGS=ARM,SH]
1214        hpet=           [X86-32,HPET] option to control HPET usage
1215                        Format: { enable (default) | disable | force |
1216                                verbose }
1217                        disable: disable HPET and use PIT instead
1218                        force: allow force enabled of undocumented chips (ICH4,
1219                                VIA, nVidia)
1220                        verbose: show contents of HPET registers during setup
1222        hpet_mmap=      [X86, HPET_MMAP] Allow userspace to mmap HPET
1223                        registers.  Default set by CONFIG_HPET_MMAP_DEFAULT.
1225        hugepages=      [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1226        hugepagesz=     [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1227                        On x86-64 and powerpc, this option can be specified
1228                        multiple times interleaved with hugepages= to reserve
1229                        huge pages of different sizes. Valid pages sizes on
1230                        x86-64 are 2M (when the CPU supports "pse") and 1G
1231                        (when the CPU supports the "pdpe1gb" cpuinfo flag)
1232                        Note that 1GB pages can only be allocated at boot time
1233                        using hugepages= and not freed afterwards.
1235        hvc_iucv=       [S390] Number of z/VM IUCV hypervisor console (HVC)
1236                               terminal devices. Valid values: 0..8
1237        hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1238                               If specified, z/VM IUCV HVC accepts connections
1239                               from listed z/VM user IDs only.
1241        hwthread_map=   [METAG] Comma-separated list of Linux cpu id to
1242                                hardware thread id mappings.
1243                                Format: <cpu>:<hwthread>
1245        keep_bootcon    [KNL]
1246                        Do not unregister boot console at start. This is only
1247                        useful for debugging when something happens in the window
1248                        between unregistering the boot console and initializing
1249                        the real console.
1251        i2c_bus=        [HW] Override the default board specific I2C bus speed
1252                             or register an additional I2C bus that is not
1253                             registered from board initialization code.
1254                             Format:
1255                             <bus_id>,<clkrate>
1257        i8042.debug     [HW] Toggle i8042 debug mode
1258    [HW] Put keyboard port into non-translated mode
1259        i8042.dumbkbd   [HW] Pretend that controller can only read data from
1260                             keyboard and cannot control its state
1261                             (Don't attempt to blink the leds)
1262        i8042.noaux     [HW] Don't check for auxiliary (== mouse) port
1263        i8042.nokbd     [HW] Don't check/create keyboard port
1264        i8042.noloop    [HW] Disable the AUX Loopback command while probing
1265                             for the AUX port
1266        i8042.nomux     [HW] Don't check presence of an active multiplexing
1267                             controller
1268        i8042.nopnp     [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1269                             controllers
1270        i8042.notimeout [HW] Ignore timeout condition signalled by controller
1271        i8042.reset     [HW] Reset the controller during init and cleanup
1272        i8042.unlock    [HW] Unlock (ignore) the keylock
1273        i8042.kbdreset  [HW] Reset device connected to KBD port
1275        i810=           [HW,DRM]
1277        i8k.ignore_dmi  [HW] Continue probing hardware even if DMI data
1278                        indicates that the driver is running on unsupported
1279                        hardware.
1280        i8k.force       [HW] Activate i8k driver even if SMM BIOS signature
1281                        does not match list of supported models.
1282        i8k.power_status
1283                        [HW] Report power status in /proc/i8k
1284                        (disabled by default)
1285        i8k.restricted  [HW] Allow controlling fans only if SYS_ADMIN
1286                        capability is set.
1288        i915.invert_brightness=
1289                        [DRM] Invert the sense of the variable that is used to
1290                        set the brightness of the panel backlight. Normally a
1291                        brightness value of 0 indicates backlight switched off,
1292                        and the maximum of the brightness value sets the backlight
1293                        to maximum brightness. If this parameter is set to 0
1294                        (default) and the machine requires it, or this parameter
1295                        is set to 1, a brightness value of 0 sets the backlight
1296                        to maximum brightness, and the maximum of the brightness
1297                        value switches the backlight off.
1298                        -1 -- never invert brightness
1299                         0 -- machine default
1300                         1 -- force brightness inversion
1302        icn=            [HW,ISDN]
1303                        Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1305        ide-core.nodma= [HW] (E)IDE subsystem
1306                        Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1307                        .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1308                        .cdrom .chs .ignore_cable are additional options
1309                        See Documentation/ide/ide.txt.
1311        ide-generic.probe-mask= [HW] (E)IDE subsystem
1312                        Format: <int>
1313                        Probe mask for legacy ISA IDE ports.  Depending on
1314                        platform up to 6 ports are supported, enabled by
1315                        setting corresponding bits in the mask to 1.  The
1316                        default value is 0x0, which has a special meaning.
1317                        On systems that have PCI, it triggers scanning the
1318                        PCI bus for the first and the second port, which
1319                        are then probed.  On systems without PCI the value
1320                        of 0x0 enables probing the two first ports as if it
1321                        was 0x3.
1323        ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1324                        Claim all unknown PCI IDE storage controllers.
1326        idle=           [X86]
1327                        Format: idle=poll, idle=halt, idle=nomwait
1328                        Poll forces a polling idle loop that can slightly
1329                        improve the performance of waking up a idle CPU, but
1330                        will use a lot of power and make the system run hot.
1331                        Not recommended.
1332                        idle=halt: Halt is forced to be used for CPU idle.
1333                        In such case C2/C3 won't be used again.
1334                        idle=nomwait: Disable mwait for CPU C-states
1336        ignore_loglevel [KNL]
1337                        Ignore loglevel setting - this will print /all/
1338                        kernel messages to the console. Useful for debugging.
1339                        We also add it as printk module parameter, so users
1340                        could change it dynamically, usually by
1341                        /sys/module/printk/parameters/ignore_loglevel.
1343        ihash_entries=  [KNL]
1344                        Set number of hash buckets for inode cache.
1346        ima_appraise=   [IMA] appraise integrity measurements
1347                        Format: { "off" | "enforce" | "fix" | "log" }
1348                        default: "enforce"
1350        ima_appraise_tcb [IMA]
1351                        The builtin appraise policy appraises all files
1352                        owned by uid=0.
1354        ima_hash=       [IMA]
1355                        Format: { md5 | sha1 | rmd160 | sha256 | sha384
1356                                   | sha512 | ... }
1357                        default: "sha1"
1359                        The list of supported hash algorithms is defined
1360                        in crypto/hash_info.h.
1362        ima_tcb         [IMA]
1363                        Load a policy which meets the needs of the Trusted
1364                        Computing Base.  This means IMA will measure all
1365                        programs exec'd, files mmap'd for exec, and all files
1366                        opened for read by uid=0.
1368        ima_template=   [IMA]
1369                        Select one of defined IMA measurements template formats.
1370                        Formats: { "ima" | "ima-ng" }
1371                        Default: "ima-ng"
1373        ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1374                        Format: <min_file_size>
1375                        Set the minimal file size for using asynchronous hash.
1376                        If left unspecified, ahash usage is disabled.
1378                        ahash performance varies for different data sizes on
1379                        different crypto accelerators. This option can be used
1380                        to achieve the best performance for a particular HW.
1382        ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1383                        Format: <bufsize>
1384                        Set hashing buffer size. Default: 4k.
1386                        ahash performance varies for different chunk sizes on
1387                        different crypto accelerators. This option can be used
1388                        to achieve best performance for particular HW.
1390        init=           [KNL]
1391                        Format: <full_path>
1392                        Run specified binary instead of /sbin/init as init
1393                        process.
1395        initcall_debug  [KNL] Trace initcalls as they are executed.  Useful
1396                        for working out where the kernel is dying during
1397                        startup.
1399        initcall_blacklist=  [KNL] Do not execute a comma-separated list of
1400                        initcall functions.  Useful for debugging built-in
1401                        modules and initcalls.
1403        initrd=         [BOOT] Specify the location of the initial ramdisk
1405        inport.irq=     [HW] Inport (ATI XL and Microsoft) busmouse driver
1406                        Format: <irq>
1408        int_pln_enable  [x86] Enable power limit notification interrupt
1410        integrity_audit=[IMA]
1411                        Format: { "0" | "1" }
1412                        0 -- basic integrity auditing messages. (Default)
1413                        1 -- additional integrity auditing messages.
1415        intel_iommu=    [DMAR] Intel IOMMU driver (DMAR) option
1416                on
1417                        Enable intel iommu driver.
1418                off
1419                        Disable intel iommu driver.
1420                igfx_off [Default Off]
1421                        By default, gfx is mapped as normal device. If a gfx
1422                        device has a dedicated DMAR unit, the DMAR unit is
1423                        bypassed by not enabling DMAR with this option. In
1424                        this case, gfx device will use physical address for
1425                        DMA.
1426                forcedac [x86_64]
1427                        With this option iommu will not optimize to look
1428                        for io virtual address below 32-bit forcing dual
1429                        address cycle on pci bus for cards supporting greater
1430                        than 32-bit addressing. The default is to look
1431                        for translation below 32-bit and if not available
1432                        then look in the higher range.
1433                strict [Default Off]
1434                        With this option on every unmap_single operation will
1435                        result in a hardware IOTLB flush operation as opposed
1436                        to batching them for performance.
1437                sp_off [Default Off]
1438                        By default, super page will be supported if Intel IOMMU
1439                        has the capability. With this option, super page will
1440                        not be supported.
1442        intel_idle.max_cstate=  [KNL,HW,ACPI,X86]
1443                        0       disables intel_idle and fall back on acpi_idle.
1444                        1 to 6  specify maximum depth of C-state.
1446        intel_pstate=  [X86]
1447                       disable
1448                         Do not enable intel_pstate as the default
1449                         scaling driver for the supported processors
1451        intremap=       [X86-64, Intel-IOMMU]
1452                        on      enable Interrupt Remapping (default)
1453                        off     disable Interrupt Remapping
1454                        nosid   disable Source ID checking
1455                        no_x2apic_optout
1456                                BIOS x2APIC opt-out request will be ignored
1458        iomem=          Disable strict checking of access to MMIO memory
1459                strict  regions from userspace.
1460                relaxed
1462        iommu=          [x86]
1463                off
1464                force
1465                noforce
1466                biomerge
1467                panic
1468                nopanic
1469                merge
1470                nomerge
1471                forcesac
1472                soft
1473                pt              [x86, IA-64]
1476        io7=            [HW] IO7 for Marvel based alpha systems
1477                        See comment before marvel_specify_io7 in
1478                        arch/alpha/kernel/core_marvel.c.
1480        io_delay=       [X86] I/O delay method
1481                0x80
1482                        Standard port 0x80 based delay
1483                0xed
1484                        Alternate port 0xed based delay (needed on some systems)
1485                udelay
1486                        Simple two microseconds delay
1487                none
1488                        No delay
1490        ip=             [IP_PNP]
1491                        See Documentation/filesystems/nfs/nfsroot.txt.
1493        irqfixup        [HW]
1494                        When an interrupt is not handled search all handlers
1495                        for it. Intended to get systems with badly broken
1496                        firmware running.
1498        irqpoll         [HW]
1499                        When an interrupt is not handled search all handlers
1500                        for it. Also check all handlers each timer
1501                        interrupt. Intended to get systems with badly broken
1502                        firmware running.
1504        isapnp=         [ISAPNP]
1505                        Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1507        isolcpus=       [KNL,SMP] Isolate CPUs from the general scheduler.
1508                        Format:
1509                        <cpu number>,...,<cpu number>
1510                        or
1511                        <cpu number>-<cpu number>
1512                        (must be a positive range in ascending order)
1513                        or a mixture
1514                        <cpu number>,...,<cpu number>-<cpu number>
1516                        This option can be used to specify one or more CPUs
1517                        to isolate from the general SMP balancing and scheduling
1518                        algorithms. You can move a process onto or off an
1519                        "isolated" CPU via the CPU affinity syscalls or cpuset.
1520                        <cpu number> begins at 0 and the maximum value is
1521                        "number of CPUs in system - 1".
1523                        This option is the preferred way to isolate CPUs. The
1524                        alternative -- manually setting the CPU mask of all
1525                        tasks in the system -- can cause problems and
1526                        suboptimal load balancer performance.
1528        iucv=           [HW,NET]
1530        ivrs_ioapic     [HW,X86_64]
1531                        Provide an override to the IOAPIC-ID<->DEVICE-ID
1532                        mapping provided in the IVRS ACPI table. For
1533                        example, to map IOAPIC-ID decimal 10 to
1534                        PCI device 00:14.0 write the parameter as:
1535                                ivrs_ioapic[10]=00:14.0
1537        ivrs_hpet       [HW,X86_64]
1538                        Provide an override to the HPET-ID<->DEVICE-ID
1539                        mapping provided in the IVRS ACPI table. For
1540                        example, to map HPET-ID decimal 0 to
1541                        PCI device 00:14.0 write the parameter as:
1542                                ivrs_hpet[0]=00:14.0
1544        js=             [HW,JOY] Analog joystick
1545                        See Documentation/input/joystick.txt.
1547        kaslr/nokaslr   [X86]
1548                        Enable/disable kernel and module base offset ASLR
1549                        (Address Space Layout Randomization) if built into
1550                        the kernel. When CONFIG_HIBERNATION is selected,
1551                        kASLR is disabled by default. When kASLR is enabled,
1552                        hibernation will be disabled.
1554        keepinitrd      [HW,ARM]
1556        kernelcore=nn[KMG]      [KNL,X86,IA-64,PPC] This parameter
1557                        specifies the amount of memory usable by the kernel
1558                        for non-movable allocations.  The requested amount is
1559                        spread evenly throughout all nodes in the system. The
1560                        remaining memory in each node is used for Movable
1561                        pages. In the event, a node is too small to have both
1562                        kernelcore and Movable pages, kernelcore pages will
1563                        take priority and other nodes will have a larger number
1564                        of Movable pages.  The Movable zone is used for the
1565                        allocation of pages that may be reclaimed or moved
1566                        by the page migration subsystem.  This means that
1567                        HugeTLB pages may not be allocated from this zone.
1568                        Note that allocations like PTEs-from-HighMem still
1569                        use the HighMem zone if it exists, and the Normal
1570                        zone if it does not.
1572        kgdbdbgp=       [KGDB,HW] kgdb over EHCI usb debug port.
1573                        Format: <Controller#>[,poll interval]
1574                        The controller # is the number of the ehci usb debug
1575                        port as it is probed via PCI.  The poll interval is
1576                        optional and is the number seconds in between
1577                        each poll cycle to the debug port in case you need
1578                        the functionality for interrupting the kernel with
1579                        gdb or control-c on the dbgp connection.  When
1580                        not using this parameter you use sysrq-g to break into
1581                        the kernel debugger.
1583        kgdboc=         [KGDB,HW] kgdb over consoles.
1584                        Requires a tty driver that supports console polling,
1585                        or a supported polling keyboard driver (non-usb).
1586                         Serial only format: <serial_device>[,baud]
1587                         keyboard only format: kbd
1588                         keyboard and serial format: kbd,<serial_device>[,baud]
1589                        Optional Kernel mode setting:
1590                         kms, kbd format: kms,kbd
1591                         kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1593        kgdbwait        [KGDB] Stop kernel execution and enter the
1594                        kernel debugger at the earliest opportunity.
1596        kmac=           [MIPS] korina ethernet MAC address.
1597                        Configure the RouterBoard 532 series on-chip
1598                        Ethernet adapter MAC address.
1600        kmemleak=       [KNL] Boot-time kmemleak enable/disable
1601                        Valid arguments: on, off
1602                        Default: on
1603                        Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1604                        the default is off.
1606        kmemcheck=      [X86] Boot-time kmemcheck enable/disable/one-shot mode
1607                        Valid arguments: 0, 1, 2
1608                        kmemcheck=0 (disabled)
1609                        kmemcheck=1 (enabled)
1610                        kmemcheck=2 (one-shot mode)
1611                        Default: 2 (one-shot mode)
1613        kstack=N        [X86] Print N words from the kernel stack
1614                        in oops dumps.
1616        kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1617                        Default is 0 (don't ignore, but inject #GP)
1619        kvm.mmu_audit=  [KVM] This is a R/W parameter which allows audit
1620                        KVM MMU at runtime.
1621                        Default is 0 (off)
1623        kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1624                        Default is 1 (enabled)
1626        kvm-amd.npt=    [KVM,AMD] Disable nested paging (virtualized MMU)
1627                        for all guests.
1628                        Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1630        kvm-intel.ept=  [KVM,Intel] Disable extended page tables
1631                        (virtualized MMU) support on capable Intel chips.
1632                        Default is 1 (enabled)
1634        kvm-intel.emulate_invalid_guest_state=
1635                        [KVM,Intel] Enable emulation of invalid guest states
1636                        Default is 0 (disabled)
1638        kvm-intel.flexpriority=
1639                        [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1640                        Default is 1 (enabled)
1642        kvm-intel.nested=
1643                        [KVM,Intel] Enable VMX nesting (nVMX).
1644                        Default is 0 (disabled)
1646        kvm-intel.unrestricted_guest=
1647                        [KVM,Intel] Disable unrestricted guest feature
1648                        (virtualized real and unpaged mode) on capable
1649                        Intel chips. Default is 1 (enabled)
1651        kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1652                        feature (tagged TLBs) on capable Intel chips.
1653                        Default is 1 (enabled)
1655        l2cr=           [PPC]
1657        l3cr=           [PPC]
1659        lapic           [X86-32,APIC] Enable the local APIC even if BIOS
1660                        disabled it.
1662        lapic=          [x86,APIC] "notscdeadline" Do not use TSC deadline
1663                        value for LAPIC timer one-shot implementation. Default
1664                        back to the programmable timer unit in the LAPIC.
1666        lapic_timer_c2_ok       [X86,APIC] trust the local apic timer
1667                        in C2 power state.
1669        libata.dma=     [LIBATA] DMA control
1670                        libata.dma=0      Disable all PATA and SATA DMA
1671                        libata.dma=1      PATA and SATA Disk DMA only
1672                        libata.dma=2      ATAPI (CDROM) DMA only
1673                        libata.dma=4      Compact Flash DMA only
1674                        Combinations also work, so libata.dma=3 enables DMA
1675                        for disks and CDROMs, but not CFs.
1677        libata.ignore_hpa=      [LIBATA] Ignore HPA limit
1678                        libata.ignore_hpa=0       keep BIOS limits (default)
1679                        libata.ignore_hpa=1       ignore limits, using full disk
1681        libata.noacpi   [LIBATA] Disables use of ACPI in libata suspend/resume
1682                        when set.
1683                        Format: <int>
1685        libata.force=   [LIBATA] Force configurations.  The format is comma
1686                        separated list of "[ID:]VAL" where ID is
1687                        PORT[.DEVICE].  PORT and DEVICE are decimal numbers
1688                        matching port, link or device.  Basically, it matches
1689                        the ATA ID string printed on console by libata.  If
1690                        the whole ID part is omitted, the last PORT and DEVICE
1691                        values are used.  If ID hasn't been specified yet, the
1692                        configuration applies to all ports, links and devices.
1694                        If only DEVICE is omitted, the parameter applies to
1695                        the port and all links and devices behind it.  DEVICE
1696                        number of 0 either selects the first device or the
1697                        first fan-out link behind PMP device.  It does not
1698                        select the host link.  DEVICE number of 15 selects the
1699                        host link and device attached to it.
1701                        The VAL specifies the configuration to force.  As long
1702                        as there's no ambiguity shortcut notation is allowed.
1703                        For example, both 1.5 and 1.5G would work for 1.5Gbps.
1704                        The following configurations can be forced.
1706                        * Cable type: 40c, 80c, short40c, unk, ign or sata.
1707                          Any ID with matching PORT is used.
1709                        * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1711                        * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1712                          udma[/][16,25,33,44,66,100,133] notation is also
1713                          allowed.
1715                        * [no]ncq: Turn on or off NCQ.
1717                        * nohrst, nosrst, norst: suppress hard, soft
1718                          and both resets.
1720                        * rstonce: only attempt one reset during
1721                          hot-unplug link recovery
1723                        * dump_id: dump IDENTIFY data.
1725                        * atapi_dmadir: Enable ATAPI DMADIR bridge support
1727                        * disable: Disable this device.
1729                        If there are multiple matching configurations changing
1730                        the same attribute, the last one is used.
1732        memblock=debug  [KNL] Enable memblock debug messages.
1734        load_ramdisk=   [RAM] List of ramdisks to load from floppy
1735                        See Documentation/blockdev/ramdisk.txt.
1737        lockd.nlm_grace_period=P  [NFS] Assign grace period.
1738                        Format: <integer>
1740        lockd.nlm_tcpport=N     [NFS] Assign TCP port.
1741                        Format: <integer>
1743        lockd.nlm_timeout=T     [NFS] Assign timeout value.
1744                        Format: <integer>
1746        lockd.nlm_udpport=M     [NFS] Assign UDP port.
1747                        Format: <integer>
1749        locktorture.nreaders_stress= [KNL]
1750                        Set the number of locking read-acquisition kthreads.
1751                        Defaults to being automatically set based on the
1752                        number of online CPUs.
1754        locktorture.nwriters_stress= [KNL]
1755                        Set the number of locking write-acquisition kthreads.
1757        locktorture.onoff_holdoff= [KNL]
1758                        Set time (s) after boot for CPU-hotplug testing.
1760        locktorture.onoff_interval= [KNL]
1761                        Set time (s) between CPU-hotplug operations, or
1762                        zero to disable CPU-hotplug testing.
1764        locktorture.shuffle_interval= [KNL]
1765                        Set task-shuffle interval (jiffies).  Shuffling
1766                        tasks allows some CPUs to go into dyntick-idle
1767                        mode during the locktorture test.
1769        locktorture.shutdown_secs= [KNL]
1770                        Set time (s) after boot system shutdown.  This
1771                        is useful for hands-off automated testing.
1773        locktorture.stat_interval= [KNL]
1774                        Time (s) between statistics printk()s.
1776        locktorture.stutter= [KNL]
1777                        Time (s) to stutter testing, for example,
1778                        specifying five seconds causes the test to run for
1779                        five seconds, wait for five seconds, and so on.
1780                        This tests the locking primitive's ability to
1781                        transition abruptly to and from idle.
1783        locktorture.torture_runnable= [BOOT]
1784                        Start locktorture running at boot time.
1786        locktorture.torture_type= [KNL]
1787                        Specify the locking implementation to test.
1789        locktorture.verbose= [KNL]
1790                        Enable additional printk() statements.
1792        logibm.irq=     [HW,MOUSE] Logitech Bus Mouse Driver
1793                        Format: <irq>
1795        loglevel=       All Kernel Messages with a loglevel smaller than the
1796                        console loglevel will be printed to the console. It can
1797                        also be changed with klogd or other programs. The
1798                        loglevels are defined as follows:
1800                        0 (KERN_EMERG)          system is unusable
1801                        1 (KERN_ALERT)          action must be taken immediately
1802                        2 (KERN_CRIT)           critical conditions
1803                        3 (KERN_ERR)            error conditions
1804                        4 (KERN_WARNING)        warning conditions
1805                        5 (KERN_NOTICE)         normal but significant condition
1806                        6 (KERN_INFO)           informational
1807                        7 (KERN_DEBUG)          debug-level messages
1809        log_buf_len=n[KMG]      Sets the size of the printk ring buffer,
1810                        in bytes.  n must be a power of two and greater
1811                        than the minimal size. The minimal size is defined
1812                        by LOG_BUF_SHIFT kernel config parameter. There is
1813                        also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1814                        that allows to increase the default size depending on
1815                        the number of CPUs. See init/Kconfig for more details.
1817        logo.nologo     [FB] Disables display of the built-in Linux logo.
1818                        This may be used to provide more screen space for
1819                        kernel log messages and is useful when debugging
1820                        kernel boot problems.
1822        lp=0            [LP]    Specify parallel ports to use, e.g,
1823        lp=port[,port...]       lp=none,parport0 (lp0 not configured, lp1 uses
1824        lp=reset                first parallel port). 'lp=0' disables the
1825        lp=auto                 printer driver. 'lp=reset' (which can be
1826                                specified in addition to the ports) causes
1827                                attached printers to be reset. Using
1828                                lp=port1,port2,... specifies the parallel ports
1829                                to associate lp devices with, starting with
1830                                lp0. A port specification may be 'none' to skip
1831                                that lp device, or a parport name such as
1832                                'parport0'. Specifying 'lp=auto' instead of a
1833                                port specification list means that device IDs
1834                                from each port should be examined, to see if
1835                                an IEEE 1284-compliant printer is attached; if
1836                                so, the driver will manage that printer.
1837                                See also header of drivers/char/lp.c.
1839        lpj=n           [KNL]
1840                        Sets loops_per_jiffy to given constant, thus avoiding
1841                        time-consuming boot-time autodetection (up to 250 ms per
1842                        CPU). 0 enables autodetection (default). To determine
1843                        the correct value for your kernel, boot with normal
1844                        autodetection and see what value is printed. Note that
1845                        on SMP systems the preset will be applied to all CPUs,
1846                        which is likely to cause problems if your CPUs need
1847                        significantly divergent settings. An incorrect value
1848                        will cause delays in the kernel to be wrong, leading to
1849                        unpredictable I/O errors and other breakage. Although
1850                        unlikely, in the extreme case this might damage your
1851                        hardware.
1853        ltpc=           [NET]
1854                        Format: <io>,<irq>,<dma>
1856        machvec=        [IA-64] Force the use of a particular machine-vector
1857                        (machvec) in a generic kernel.
1858                        Example: machvec=hpzx1_swiotlb
1860        machtype=       [Loongson] Share the same kernel image file between different
1861                         yeeloong laptop.
1862                        Example: machtype=lemote-yeeloong-2f-7inch
1864        max_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory greater
1865                        than or equal to this physical address is ignored.
1867        maxcpus=        [SMP] Maximum number of processors that an SMP kernel
1868                        should make use of.  maxcpus=n : n >= 0 limits the
1869                        kernel to using 'n' processors.  n=0 is a special case,
1870                        it is equivalent to "nosmp", which also disables
1871                        the IO APIC.
1873        max_loop=       [LOOP] The number of loop block devices that get
1874        (loop.max_loop) unconditionally pre-created at init time. The default
1875                        number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1876                        of statically allocating a predefined number, loop
1877                        devices can be requested on-demand with the
1878                        /dev/loop-control interface.
1880        mce             [X86-32] Machine Check Exception
1882        mce=option      [X86-64] See Documentation/x86/x86_64/boot-options.txt
1884        md=             [HW] RAID subsystems devices and level
1885                        See Documentation/md.txt.
1887        mdacon=         [MDA]
1888                        Format: <first>,<last>
1889                        Specifies range of consoles to be captured by the MDA.
1891        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
1892                        Amount of memory to be used when the kernel is not able
1893                        to see the whole system memory or for test.
1894                        [X86] Work as limiting max address. Use together
1895                        with memmap= to avoid physical address space collisions.
1896                        Without memmap= PCI devices could be placed at addresses
1897                        belonging to unused RAM.
1899        mem=nopentium   [BUGS=X86-32] Disable usage of 4MB pages for kernel
1900                        memory.
1902        memchunk=nn[KMG]
1903                        [KNL,SH] Allow user to override the default size for
1904                        per-device physically contiguous DMA buffers.
1906        memmap=exactmap [KNL,X86] Enable setting of an exact
1907                        E820 memory map, as specified by the user.
1908                        Such memmap=exactmap lines can be constructed based on
1909                        BIOS output or other requirements. See the memmap=nn@ss
1910                        option description.
1912        memmap=nn[KMG]@ss[KMG]
1913                        [KNL] Force usage of a specific region of memory.
1914                        Region of memory to be used is from ss to ss+nn.
1916        memmap=nn[KMG]#ss[KMG]
1917                        [KNL,ACPI] Mark specific memory as ACPI data.
1918                        Region of memory to be marked is from ss to ss+nn.
1920        memmap=nn[KMG]$ss[KMG]
1921                        [KNL,ACPI] Mark specific memory as reserved.
1922                        Region of memory to be reserved is from ss to ss+nn.
1923                        Example: Exclude memory from 0x18690000-0x1869ffff
1924                                 memmap=64K$0x18690000
1925                                 or
1926                                 memmap=0x10000$0x18690000
1928        memory_corruption_check=0/1 [X86]
1929                        Some BIOSes seem to corrupt the first 64k of
1930                        memory when doing things like suspend/resume.
1931                        Setting this option will scan the memory
1932                        looking for corruption.  Enabling this will
1933                        both detect corruption and prevent the kernel
1934                        from using the memory being corrupted.
1935                        However, its intended as a diagnostic tool; if
1936                        repeatable BIOS-originated corruption always
1937                        affects the same memory, you can use memmap=
1938                        to prevent the kernel from using that memory.
1940        memory_corruption_check_size=size [X86]
1941                        By default it checks for corruption in the low
1942                        64k, making this memory unavailable for normal
1943                        use.  Use this parameter to scan for
1944                        corruption in more or less memory.
1946        memory_corruption_check_period=seconds [X86]
1947                        By default it checks for corruption every 60
1948                        seconds.  Use this parameter to check at some
1949                        other rate.  0 disables periodic checking.
1951        memtest=        [KNL,X86] Enable memtest
1952                        Format: <integer>
1953                        default : 0 <disable>
1954                        Specifies the number of memtest passes to be
1955                        performed. Each pass selects another test
1956                        pattern from a given set of patterns. Memtest
1957                        fills the memory with this pattern, validates
1958                        memory contents and reserves bad memory
1959                        regions that are detected.
1961        meye.*=         [HW] Set MotionEye Camera parameters
1962                        See Documentation/video4linux/meye.txt.
1964        mfgpt_irq=      [IA-32] Specify the IRQ to use for the
1965                        Multi-Function General Purpose Timers on AMD Geode
1966                        platforms.
1968        mfgptfix        [X86-32] Fix MFGPT timers on AMD Geode platforms when
1969                        the BIOS has incorrectly applied a workaround. TinyBIOS
1970                        version 0.98 is known to be affected, 0.99 fixes the
1971                        problem by letting the user disable the workaround.
1973        mga=            [HW,DRM]
1975        min_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory below this
1976                        physical address is ignored.
1978        mini2440=       [ARM,HW,KNL]
1979                        Format:[0..2][b][c][t]
1980                        Default: "0tb"
1981                        MINI2440 configuration specification:
1982                        0 - The attached screen is the 3.5" TFT
1983                        1 - The attached screen is the 7" TFT
1984                        2 - The VGA Shield is attached (1024x768)
1985                        Leaving out the screen size parameter will not load
1986                        the TFT driver, and the framebuffer will be left
1987                        unconfigured.
1988                        b - Enable backlight. The TFT backlight pin will be
1989                        linked to the kernel VESA blanking code and a GPIO
1990                        LED. This parameter is not necessary when using the
1991                        VGA shield.
1992                        c - Enable the s3c camera interface.
1993                        t - Reserved for enabling touchscreen support. The
1994                        touchscreen support is not enabled in the mainstream
1995                        kernel as of 2.6.30, a preliminary port can be found
1996                        in the "bleeding edge" mini2440 support kernel at
1999        mminit_loglevel=
2000                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2001                        parameter allows control of the logging verbosity for
2002                        the additional memory initialisation checks. A value
2003                        of 0 disables mminit logging and a level of 4 will
2004                        log everything. Information is printed at KERN_DEBUG
2005                        so loglevel=8 may also need to be specified.
2007        module.sig_enforce
2008                        [KNL] When CONFIG_MODULE_SIG is set, this means that
2009                        modules without (valid) signatures will fail to load.
2010                        Note that if CONFIG_MODULE_SIG_FORCE is set, that
2011                        is always true, so this option does nothing.
2013        mousedev.tap_time=
2014                        [MOUSE] Maximum time between finger touching and
2015                        leaving touchpad surface for touch to be considered
2016                        a tap and be reported as a left button click (for
2017                        touchpads working in absolute mode only).
2018                        Format: <msecs>
2019        mousedev.xres=  [MOUSE] Horizontal screen resolution, used for devices
2020                        reporting absolute coordinates, such as tablets
2021        mousedev.yres=  [MOUSE] Vertical screen resolution, used for devices
2022                        reporting absolute coordinates, such as tablets
2024        movablecore=nn[KMG]     [KNL,X86,IA-64,PPC] This parameter
2025                        is similar to kernelcore except it specifies the
2026                        amount of memory used for migratable allocations.
2027                        If both kernelcore and movablecore is specified,
2028                        then kernelcore will be at *least* the specified
2029                        value but may be more. If movablecore on its own
2030                        is specified, the administrator must be careful
2031                        that the amount of memory usable for all allocations
2032                        is not too small.
2034        movable_node    [KNL,X86] Boot-time switch to enable the effects
2035                        of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2037        MTD_Partition=  [MTD]
2038                        Format: <name>,<region-number>,<size>,<offset>
2040        MTD_Region=     [MTD] Format:
2041                        <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2043        mtdparts=       [MTD]
2044                        See drivers/mtd/cmdlinepart.c.
2046        multitce=off    [PPC]  This parameter disables the use of the pSeries
2047                        firmware feature for updating multiple TCE entries
2048                        at a time.
2050        onenand.bdry=   [HW,MTD] Flex-OneNAND Boundary Configuration
2052                        Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2054                        boundary - index of last SLC block on Flex-OneNAND.
2055                                   The remaining blocks are configured as MLC blocks.
2056                        lock     - Configure if Flex-OneNAND boundary should be locked.
2057                                   Once locked, the boundary cannot be changed.
2058                                   1 indicates lock status, 0 indicates unlock status.
2060        mtdset=         [ARM]
2061                        ARM/S3C2412 JIVE boot control
2063                        See arch/arm/mach-s3c2412/mach-jive.c
2065        mtouchusb.raw_coordinates=
2066                        [HW] Make the MicroTouch USB driver use raw coordinates
2067                        ('y', default) or cooked coordinates ('n')
2069        mtrr_chunk_size=nn[KMG] [X86]
2070                        used for mtrr cleanup. It is largest continuous chunk
2071                        that could hold holes aka. UC entries.
2073        mtrr_gran_size=nn[KMG] [X86]
2074                        Used for mtrr cleanup. It is granularity of mtrr block.
2075                        Default is 1.
2076                        Large value could prevent small alignment from
2077                        using up MTRRs.
2079        mtrr_spare_reg_nr=n [X86]
2080                        Format: <integer>
2081                        Range: 0,7 : spare reg number
2082                        Default : 1
2083                        Used for mtrr cleanup. It is spare mtrr entries number.
2084                        Set to 2 or more if your graphical card needs more.
2086        n2=             [NET] SDL Inc. RISCom/N2 synchronous serial card
2088        netdev=         [NET] Network devices parameters
2089                        Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2090                        Note that mem_start is often overloaded to mean
2091                        something different and driver-specific.
2092                        This usage is only documented in each driver source
2093                        file if at all.
2095        nf_conntrack.acct=
2096                        [NETFILTER] Enable connection tracking flow accounting
2097                        0 to disable accounting
2098                        1 to enable accounting
2099                        Default value is 0.
2101        nfsaddrs=       [NFS] Deprecated.  Use ip= instead.
2102                        See Documentation/filesystems/nfs/nfsroot.txt.
2104        nfsroot=        [NFS] nfs root filesystem for disk-less boxes.
2105                        See Documentation/filesystems/nfs/nfsroot.txt.
2107        nfsrootdebug    [NFS] enable nfsroot debugging messages.
2108                        See Documentation/filesystems/nfs/nfsroot.txt.
2110        nfs.callback_tcpport=
2111                        [NFS] set the TCP port on which the NFSv4 callback
2112                        channel should listen.
2114        nfs.cache_getent=
2115                        [NFS] sets the pathname to the program which is used
2116                        to update the NFS client cache entries.
2118        nfs.cache_getent_timeout=
2119                        [NFS] sets the timeout after which an attempt to
2120                        update a cache entry is deemed to have failed.
2122        nfs.idmap_cache_timeout=
2123                        [NFS] set the maximum lifetime for idmapper cache
2124                        entries.
2126        nfs.enable_ino64=
2127                        [NFS] enable 64-bit inode numbers.
2128                        If zero, the NFS client will fake up a 32-bit inode
2129                        number for the readdir() and stat() syscalls instead
2130                        of returning the full 64-bit number.
2131                        The default is to return 64-bit inode numbers.
2133        nfs.max_session_slots=
2134                        [NFSv4.1] Sets the maximum number of session slots
2135                        the client will attempt to negotiate with the server.
2136                        This limits the number of simultaneous RPC requests
2137                        that the client can send to the NFSv4.1 server.
2138                        Note that there is little point in setting this
2139                        value higher than the max_tcp_slot_table_limit.
2141        nfs.nfs4_disable_idmapping=
2142                        [NFSv4] When set to the default of '1', this option
2143                        ensures that both the RPC level authentication
2144                        scheme and the NFS level operations agree to use
2145                        numeric uids/gids if the mount is using the
2146                        'sec=sys' security flavour. In effect it is
2147                        disabling idmapping, which can make migration from
2148                        legacy NFSv2/v3 systems to NFSv4 easier.
2149                        Servers that do not support this mode of operation
2150                        will be autodetected by the client, and it will fall
2151                        back to using the idmapper.
2152                        To turn off this behaviour, set the value to '0'.
2153        nfs.nfs4_unique_id=
2154                        [NFS4] Specify an additional fixed unique ident-
2155                        ification string that NFSv4 clients can insert into
2156                        their nfs_client_id4 string.  This is typically a
2157                        UUID that is generated at system install time.
2159        nfs.send_implementation_id =
2160                        [NFSv4.1] Send client implementation identification
2161                        information in exchange_id requests.
2162                        If zero, no implementation identification information
2163                        will be sent.
2164                        The default is to send the implementation identification
2165                        information.
2167        nfs.recover_lost_locks =
2168                        [NFSv4] Attempt to recover locks that were lost due
2169                        to a lease timeout on the server. Please note that
2170                        doing this risks data corruption, since there are
2171                        no guarantees that the file will remain unchanged
2172                        after the locks are lost.
2173                        If you want to enable the kernel legacy behaviour of
2174                        attempting to recover these locks, then set this
2175                        parameter to '1'.
2176                        The default parameter value of '0' causes the kernel
2177                        not to attempt recovery of lost locks.
2179        nfsd.nfs4_disable_idmapping=
2180                        [NFSv4] When set to the default of '1', the NFSv4
2181                        server will return only numeric uids and gids to
2182                        clients using auth_sys, and will accept numeric uids
2183                        and gids from such clients.  This is intended to ease
2184                        migration from NFSv2/v3.
2186        objlayoutdriver.osd_login_prog=
2187                        [NFS] [OBJLAYOUT] sets the pathname to the program which
2188                        is used to automatically discover and login into new
2189                        osd-targets. Please see:
2190                        Documentation/filesystems/pnfs.txt for more explanations
2192        nmi_debug=      [KNL,AVR32,SH] Specify one or more actions to take
2193                        when a NMI is triggered.
2194                        Format: [state][,regs][,debounce][,die]
2196        nmi_watchdog=   [KNL,BUGS=X86] Debugging features for SMP kernels
2197                        Format: [panic,][nopanic,][num]
2198                        Valid num: 0
2199                        0 - turn nmi_watchdog off
2200                        When panic is specified, panic when an NMI watchdog
2201                        timeout occurs (or 'nopanic' to override the opposite
2202                        default).
2203                        This is useful when you use a panic=... timeout and
2204                        need the box quickly up again.
2206        netpoll.carrier_timeout=
2207                        [NET] Specifies amount of time (in seconds) that
2208                        netpoll should wait for a carrier. By default netpoll
2209                        waits 4 seconds.
2211        no387           [BUGS=X86-32] Tells the kernel to use the 387 maths
2212                        emulation library even if a 387 maths coprocessor
2213                        is present.
2215        no_console_suspend
2216                        [HW] Never suspend the console
2217                        Disable suspending of consoles during suspend and
2218                        hibernate operations.  Once disabled, debugging
2219                        messages can reach various consoles while the rest
2220                        of the system is being put to sleep (ie, while
2221                        debugging driver suspend/resume hooks).  This may
2222                        not work reliably with all consoles, but is known
2223                        to work with serial and VGA consoles.
2224                        To facilitate more flexible debugging, we also add
2225                        console_suspend, a printk module parameter to control
2226                        it. Users could use console_suspend (usually
2227                        /sys/module/printk/parameters/console_suspend) to
2228                        turn on/off it dynamically.
2230        noaliencache    [MM, NUMA, SLAB] Disables the allocation of alien
2231                        caches in the slab allocator.  Saves per-node memory,
2232                        but will impact performance.
2234        noalign         [KNL,ARM]
2236        noapic          [SMP,APIC] Tells the kernel to not make use of any
2237                        IOAPICs that may be present in the system.
2239        noautogroup     Disable scheduler automatic task group creation.
2241        nobats          [PPC] Do not use BATs for mapping kernel lowmem
2242                        on "Classic" PPC cores.
2244        nocache         [ARM]
2246        noclflush       [BUGS=X86] Don't use the CLFLUSH instruction
2248        nodelayacct     [KNL] Disable per-task delay accounting
2250        nodisconnect    [HW,SCSI,M68K] Disables SCSI disconnects.
2252        nodsp           [SH] Disable hardware DSP at boot time.
2254        noefi           Disable EFI runtime services support.
2256        noexec          [IA-64]
2258        noexec          [X86]
2259                        On X86-32 available only on PAE configured kernels.
2260                        noexec=on: enable non-executable mappings (default)
2261                        noexec=off: disable non-executable mappings
2263        nosmap          [X86]
2264                        Disable SMAP (Supervisor Mode Access Prevention)
2265                        even if it is supported by processor.
2267        nosmep          [X86]
2268                        Disable SMEP (Supervisor Mode Execution Prevention)
2269                        even if it is supported by processor.
2271        noexec32        [X86-64]
2272                        This affects only 32-bit executables.
2273                        noexec32=on: enable non-executable mappings (default)
2274                                read doesn't imply executable mappings
2275                        noexec32=off: disable non-executable mappings
2276                                read implies executable mappings
2278        nofpu           [SH] Disable hardware FPU at boot time.
2280        nofxsr          [BUGS=X86-32] Disables x86 floating point extended
2281                        register save and restore. The kernel will only save
2282                        legacy floating-point registers on task switch.
2284        noxsave         [BUGS=X86] Disables x86 extended register state save
2285                        and restore using xsave. The kernel will fallback to
2286                        enabling legacy floating-point and sse state.
2288        noxsaveopt      [X86] Disables xsaveopt used in saving x86 extended
2289                        register states. The kernel will fall back to use
2290                        xsave to save the states. By using this parameter,
2291                        performance of saving the states is degraded because
2292                        xsave doesn't support modified optimization while
2293                        xsaveopt supports it on xsaveopt enabled systems.
2295        noxsaves        [X86] Disables xsaves and xrstors used in saving and
2296                        restoring x86 extended register state in compacted
2297                        form of xsave area. The kernel will fall back to use
2298                        xsaveopt and xrstor to save and restore the states
2299                        in standard form of xsave area. By using this
2300                        parameter, xsave area per process might occupy more
2301                        memory on xsaves enabled systems.
2303        eagerfpu=       [X86]
2304                        on      enable eager fpu restore
2305                        off     disable eager fpu restore
2306                        auto    selects the default scheme, which automatically
2307                                enables eagerfpu restore for xsaveopt.
2309        nohlt           [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2310                        wfi(ARM) instruction doesn't work correctly and not to
2311                        use it. This is also useful when using JTAG debugger.
2313        no_file_caps    Tells the kernel not to honor file capabilities.  The
2314                        only way then for a file to be executed with privilege
2315                        is to be setuid root or executed by root.
2317        nohalt          [IA-64] Tells the kernel not to use the power saving
2318                        function PAL_HALT_LIGHT when idle. This increases
2319                        power-consumption. On the positive side, it reduces
2320                        interrupt wake-up latency, which may improve performance
2321                        in certain environments such as networked servers or
2322                        real-time systems.
2324        nohibernate     [HIBERNATION] Disable hibernation and resume.
2326        nohz=           [KNL] Boottime enable/disable dynamic ticks
2327                        Valid arguments: on, off
2328                        Default: on
2330        nohz_full=      [KNL,BOOT]
2331                        In kernels built with CONFIG_NO_HZ_FULL=y, set
2332                        the specified list of CPUs whose tick will be stopped
2333                        whenever possible. The boot CPU will be forced outside
2334                        the range to maintain the timekeeping.
2335                        The CPUs in this range must also be included in the
2336                        rcu_nocbs= set.
2338        noiotrap        [SH] Disables trapped I/O port accesses.
2340        noirqdebug      [X86-32] Disables the code which attempts to detect and
2341                        disable unhandled interrupt sources.
2343        no_timer_check  [X86,APIC] Disables the code which tests for
2344                        broken timer IRQ sources.
2346        noisapnp        [ISAPNP] Disables ISA PnP code.
2348        noinitrd        [RAM] Tells the kernel not to load any configured
2349                        initial RAM disk.
2351        nointremap      [X86-64, Intel-IOMMU] Do not enable interrupt
2352                        remapping.
2353                        [Deprecated - use intremap=off]
2355        nointroute      [IA-64]
2357        nojitter        [IA-64] Disables jitter checking for ITC timers.
2359        no-kvmclock     [X86,KVM] Disable paravirtualized KVM clock driver
2361        no-kvmapf       [X86,KVM] Disable paravirtualized asynchronous page
2362                        fault handling.
2364        no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
2365                        steal time is computed, but won't influence scheduler
2366                        behaviour
2368        nolapic         [X86-32,APIC] Do not enable or use the local APIC.
2370        nolapic_timer   [X86-32,APIC] Do not use the local APIC timer.
2372        noltlbs         [PPC] Do not use large page/tlb entries for kernel
2373                        lowmem mapping on PPC40x.
2375        nomca           [IA-64] Disable machine check abort handling
2377        nomce           [X86-32] Machine Check Exception
2379        nomfgpt         [X86-32] Disable Multi-Function General Purpose
2380                        Timer usage (for AMD Geode machines).
2382        nonmi_ipi       [X86] Disable using NMI IPIs during panic/reboot to
2383                        shutdown the other cpus.  Instead use the REBOOT_VECTOR
2384                        irq.
2386        nomodule        Disable module load
2388        nopat           [X86] Disable PAT (page attribute table extension of
2389                        pagetables) support.
2391        norandmaps      Don't use address space randomization.  Equivalent to
2392                        echo 0 > /proc/sys/kernel/randomize_va_space
2394        noreplace-paravirt      [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2396        noreplace-smp   [X86-32,SMP] Don't replace SMP instructions
2397                        with UP alternatives
2399        nordrand        [X86] Disable kernel use of the RDRAND and
2400                        RDSEED instructions even if they are supported
2401                        by the processor.  RDRAND and RDSEED are still
2402                        available to user space applications.
2404        noresume        [SWSUSP] Disables resume and restores original swap
2405                        space.
2407        no-scroll       [VGA] Disables scrollback.
2408                        This is required for the Braillex ib80-piezo Braille
2409                        reader made by F.H. Papenmeier (Germany).
2411        nosbagart       [IA-64]
2413        nosep           [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2415        nosmp           [SMP] Tells an SMP kernel to act as a UP kernel,
2416                        and disable the IO APIC.  legacy for "maxcpus=0".
2418        nosoftlockup    [KNL] Disable the soft-lockup detector.
2420        nosync          [HW,M68K] Disables sync negotiation for all devices.
2422        notsc           [BUGS=X86-32] Disable Time Stamp Counter
2424        nousb           [USB] Disable the USB subsystem
2426        nowatchdog      [KNL] Disable the lockup detector (NMI watchdog).
2428        nowb            [ARM]
2430        nox2apic        [X86-64,APIC] Do not enable x2APIC mode.
2432        cpu0_hotplug    [X86] Turn on CPU0 hotplug feature when
2433                        CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2434                        Some features depend on CPU0. Known dependencies are:
2435                        1. Resume from suspend/hibernate depends on CPU0.
2436                        Suspend/hibernate will fail if CPU0 is offline and you
2437                        need to online CPU0 before suspend/hibernate.
2438                        2. PIC interrupts also depend on CPU0. CPU0 can't be
2439                        removed if a PIC interrupt is detected.
2440                        It's said poweroff/reboot may depend on CPU0 on some
2441                        machines although I haven't seen such issues so far
2442                        after CPU0 is offline on a few tested machines.
2443                        If the dependencies are under your control, you can
2444                        turn on cpu0_hotplug.
2446        nptcg=          [IA-64] Override max number of concurrent global TLB
2447                        purges which is reported from either PAL_VM_SUMMARY or
2448                        SAL PALO.
2450        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
2451                        could support.  nr_cpus=n : n >= 1 limits the kernel to
2452                        supporting 'n' processors. Later in runtime you can not
2453                        use hotplug cpu feature to put more cpu back to online.
2454                        just like you compile the kernel NR_CPUS=n
2456        nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
2458        numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2459                        Allowed values are enable and disable
2461        numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2462                        one of ['zone', 'node', 'default'] can be specified
2463                        This can be set from sysctl after boot.
2464                        See Documentation/sysctl/vm.txt for details.
2466        ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
2467                        See Documentation/debugging-via-ohci1394.txt for more
2468                        info.
2470        olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2471                        Rather than timing out after 20 ms if an EC
2472                        command is not properly ACKed, override the length
2473                        of the timeout.  We have interrupts disabled while
2474                        waiting for the ACK, so if this is set too high
2475                        interrupts *may* be lost!
2477        omap_mux=       [OMAP] Override bootloader pin multiplexing.
2478                        Format: <mux_mode0.mode_name=value>...
2479                        For example, to override I2C bus2:
2480                        omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2482        oprofile.timer= [HW]
2483                        Use timer interrupt instead of performance counters
2485        oprofile.cpu_type=      Force an oprofile cpu type
2486                        This might be useful if you have an older oprofile
2487                        userland or if you want common events.
2488                        Format: { arch_perfmon }
2489                        arch_perfmon: [X86] Force use of architectural
2490                                perfmon on Intel CPUs instead of the
2491                                CPU specific event set.
2492                        timer: [X86] Force use of architectural NMI
2493                                timer mode (see also oprofile.timer
2494                                for generic hr timer mode)
2495                                [s390] Force legacy basic mode sampling
2496                                (report cpu_type "timer")
2498        oops=panic      Always panic on oopses. Default is to just kill the
2499                        process, but there is a small probability of
2500                        deadlocking the machine.
2501                        This will also cause panics on machine check exceptions.
2502                        Useful together with panic=30 to trigger a reboot.
2504        OSS             [HW,OSS]
2505                        See Documentation/sound/oss/oss-parameters.txt
2507        panic=          [KNL] Kernel behaviour on panic: delay <timeout>
2508                        timeout > 0: seconds before rebooting
2509                        timeout = 0: wait forever
2510                        timeout < 0: reboot immediately
2511                        Format: <timeout>
2513        crash_kexec_post_notifiers
2514                        Run kdump after running panic-notifiers and dumping
2515                        kmsg. This only for the users who doubt kdump always
2516                        succeeds in any situation.
2517                        Note that this also increases risks of kdump failure,
2518                        because some panic notifiers can make the crashed
2519                        kernel more unstable.
2521        parkbd.port=    [HW] Parallel port number the keyboard adapter is
2522                        connected to, default is 0.
2523                        Format: <parport#>
2524        parkbd.mode=    [HW] Parallel port keyboard adapter mode of operation,
2525                        0 for XT, 1 for AT (default is AT).
2526                        Format: <mode>
2528        parport=        [HW,PPT] Specify parallel ports. 0 disables.
2529                        Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2530                        Use 'auto' to force the driver to use any
2531                        IRQ/DMA settings detected (the default is to
2532                        ignore detected IRQ/DMA settings because of
2533                        possible conflicts). You can specify the base
2534                        address, IRQ, and DMA settings; IRQ and DMA
2535                        should be numbers, or 'auto' (for using detected
2536                        settings on that particular port), or 'nofifo'
2537                        (to avoid using a FIFO even if it is detected).
2538                        Parallel ports are assigned in the order they
2539                        are specified on the command line, starting
2540                        with parport0.
2542        parport_init_mode=      [HW,PPT]
2543                        Configure VIA parallel port to operate in
2544                        a specific mode. This is necessary on Pegasos
2545                        computer where firmware has no options for setting
2546                        up parallel port mode and sets it to spp.
2547                        Currently this function knows 686a and 8231 chips.
2548                        Format: [spp|ps2|epp|ecp|ecpepp]
2550        pause_on_oops=
2551                        Halt all CPUs after the first oops has been printed for
2552                        the specified number of seconds.  This is to be used if
2553                        your oopses keep scrolling off the screen.
2555        pcbit=          [HW,ISDN]
2557        pcd.            [PARIDE]
2558                        See header of drivers/block/paride/pcd.c.
2559                        See also Documentation/blockdev/paride.txt.
2561        pci=option[,option...]  [PCI] various PCI subsystem options:
2562                earlydump       [X86] dump PCI config space before the kernel
2563                                changes anything
2564                off             [X86] don't probe for the PCI bus
2565                bios            [X86-32] force use of PCI BIOS, don't access
2566                                the hardware directly. Use this if your machine
2567                                has a non-standard PCI host bridge.
2568                nobios          [X86-32] disallow use of PCI BIOS, only direct
2569                                hardware access methods are allowed. Use this
2570                                if you experience crashes upon bootup and you
2571                                suspect they are caused by the BIOS.
2572                conf1           [X86] Force use of PCI Configuration
2573                                Mechanism 1.
2574                conf2           [X86] Force use of PCI Configuration
2575                                Mechanism 2.
2576                noaer           [PCIE] If the PCIEAER kernel config parameter is
2577                                enabled, this kernel boot option can be used to
2578                                disable the use of PCIE advanced error reporting.
2579                nodomains       [PCI] Disable support for multiple PCI
2580                                root domains (aka PCI segments, in ACPI-speak).
2581                nommconf        [X86] Disable use of MMCONFIG for PCI
2582                                Configuration
2583                check_enable_amd_mmconf [X86] check for and enable
2584                                properly configured MMIO access to PCI
2585                                config space on AMD family 10h CPU
2586                nomsi           [MSI] If the PCI_MSI kernel config parameter is
2587                                enabled, this kernel boot option can be used to
2588                                disable the use of MSI interrupts system-wide.
2589                noioapicquirk   [APIC] Disable all boot interrupt quirks.
2590                                Safety option to keep boot IRQs enabled. This
2591                                should never be necessary.
2592                ioapicreroute   [APIC] Enable rerouting of boot IRQs to the
2593                                primary IO-APIC for bridges that cannot disable
2594                                boot IRQs. This fixes a source of spurious IRQs
2595                                when the system masks IRQs.
2596                noioapicreroute [APIC] Disable workaround that uses the
2597                                boot IRQ equivalent of an IRQ that connects to
2598                                a chipset where boot IRQs cannot be disabled.
2599                                The opposite of ioapicreroute.
2600                biosirq         [X86-32] Use PCI BIOS calls to get the interrupt
2601                                routing table. These calls are known to be buggy
2602                                on several machines and they hang the machine
2603                                when used, but on other computers it's the only
2604                                way to get the interrupt routing table. Try
2605                                this option if the kernel is unable to allocate
2606                                IRQs or discover secondary PCI buses on your
2607                                motherboard.
2608                rom             [X86] Assign address space to expansion ROMs.
2609                                Use with caution as certain devices share
2610                                address decoders between ROMs and other
2611                                resources.
2612                norom           [X86] Do not assign address space to
2613                                expansion ROMs that do not already have
2614                                BIOS assigned address ranges.
2615                nobar           [X86] Do not assign address space to the
2616                                BARs that weren't assigned by the BIOS.
2617                irqmask=0xMMMM  [X86] Set a bit mask of IRQs allowed to be
2618                                assigned automatically to PCI devices. You can
2619                                make the kernel exclude IRQs of your ISA cards
2620                                this way.
2621                pirqaddr=0xAAAAA        [X86] Specify the physical address
2622                                of the PIRQ table (normally generated
2623                                by the BIOS) if it is outside the
2624                                F0000h-100000h range.
2625                lastbus=N       [X86] Scan all buses thru bus #N. Can be
2626                                useful if the kernel is unable to find your
2627                                secondary buses and you want to tell it
2628                                explicitly which ones they are.
2629                assign-busses   [X86] Always assign all PCI bus
2630                                numbers ourselves, overriding
2631                                whatever the firmware may have done.
2632                usepirqmask     [X86] Honor the possible IRQ mask stored
2633                                in the BIOS $PIR table. This is needed on
2634                                some systems with broken BIOSes, notably
2635                                some HP Pavilion N5400 and Omnibook XE3
2636                                notebooks. This will have no effect if ACPI
2637                                IRQ routing is enabled.
2638                noacpi          [X86] Do not use ACPI for IRQ routing
2639                                or for PCI scanning.
2640                use_crs         [X86] Use PCI host bridge window information
2641                                from ACPI.  On BIOSes from 2008 or later, this
2642                                is enabled by default.  If you need to use this,
2643                                please report a bug.
2644                nocrs           [X86] Ignore PCI host bridge windows from ACPI.
2645                                If you need to use this, please report a bug.
2646                routeirq        Do IRQ routing for all PCI devices.
2647                                This is normally done in pci_enable_device(),
2648                                so this option is a temporary workaround
2649                                for broken drivers that don't call it.
2650                skip_isa_align  [X86] do not align io start addr, so can
2651                                handle more pci cards
2652                firmware        [ARM] Do not re-enumerate the bus but instead
2653                                just use the configuration from the
2654                                bootloader. This is currently used on
2655                                IXP2000 systems where the bus has to be
2656                                configured a certain way for adjunct CPUs.
2657                noearly         [X86] Don't do any early type 1 scanning.
2658                                This might help on some broken boards which
2659                                machine check when some devices' config space
2660                                is read. But various workarounds are disabled
2661                                and some IOMMU drivers will not work.
2662                bfsort          Sort PCI devices into breadth-first order.
2663                                This sorting is done to get a device
2664                                order compatible with older (<= 2.4) kernels.
2665                nobfsort        Don't sort PCI devices into breadth-first order.
2666                pcie_bus_tune_off       Disable PCIe MPS (Max Payload Size)
2667                                tuning and use the BIOS-configured MPS defaults.
2668                pcie_bus_safe   Set every device's MPS to the largest value
2669                                supported by all devices below the root complex.
2670                pcie_bus_perf   Set device MPS to the largest allowable MPS
2671                                based on its parent bus. Also set MRRS (Max
2672                                Read Request Size) to the largest supported
2673                                value (no larger than the MPS that the device
2674                                or bus can support) for best performance.
2675                pcie_bus_peer2peer      Set every device's MPS to 128B, which
2676                                every device is guaranteed to support. This
2677                                configuration allows peer-to-peer DMA between
2678                                any pair of devices, possibly at the cost of
2679                                reduced performance.  This also guarantees
2680                                that hot-added devices will work.
2681                cbiosize=nn[KMG]        The fixed amount of bus space which is
2682                                reserved for the CardBus bridge's IO window.
2683                                The default value is 256 bytes.
2684                cbmemsize=nn[KMG]       The fixed amount of bus space which is
2685                                reserved for the CardBus bridge's memory
2686                                window. The default value is 64 megabytes.
2687                resource_alignment=
2688                                Format:
2689                                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2690                                Specifies alignment and device to reassign
2691                                aligned memory resources.
2692                                If <order of align> is not specified,
2693                                PAGE_SIZE is used as alignment.
2694                                PCI-PCI bridge can be specified, if resource
2695                                windows need to be expanded.
2696                ecrc=           Enable/disable PCIe ECRC (transaction layer
2697                                end-to-end CRC checking).
2698                                bios: Use BIOS/firmware settings. This is the
2699                                the default.
2700                                off: Turn ECRC off
2701                                on: Turn ECRC on.
2702                hpiosize=nn[KMG]        The fixed amount of bus space which is
2703                                reserved for hotplug bridge's IO window.
2704                                Default size is 256 bytes.
2705                hpmemsize=nn[KMG]       The fixed amount of bus space which is
2706                                reserved for hotplug bridge's memory window.
2707                                Default size is 2 megabytes.
2708                realloc=        Enable/disable reallocating PCI bridge resources
2709                                if allocations done by BIOS are too small to
2710                                accommodate resources required by all child
2711                                devices.
2712                                off: Turn realloc off
2713                                on: Turn realloc on
2714                realloc         same as realloc=on
2715                noari           do not use PCIe ARI.
2716                pcie_scan_all   Scan all possible PCIe devices.  Otherwise we
2717                                only look for one device below a PCIe downstream
2718                                port.
2720        pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
2721                        Management.
2722                off     Disable ASPM.
2723                force   Enable ASPM even on devices that claim not to support it.
2724                        WARNING: Forcing ASPM on may cause system lockups.
2726        pcie_hp=        [PCIE] PCI Express Hotplug driver options:
2727                nomsi   Do not use MSI for PCI Express Native Hotplug (this
2728                        makes all PCIe ports use INTx for hotplug services).
2730        pcie_ports=     [PCIE] PCIe ports handling:
2731                auto    Ask the BIOS whether or not to use native PCIe services
2732                        associated with PCIe ports (PME, hot-plug, AER).  Use
2733                        them only if that is allowed by the BIOS.
2734                native  Use native PCIe services associated with PCIe ports
2735                        unconditionally.
2736                compat  Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2737                        ports driver.
2739        pcie_pme=       [PCIE,PM] Native PCIe PME signaling options:
2740                nomsi   Do not use MSI for native PCIe PME signaling (this makes
2741                        all PCIe root ports use INTx for all services).
2743        pcmv=           [HW,PCMCIA] BadgePAD 4
2745        pd_ignore_unused
2746                        [PM]
2747                        Keep all power-domains already enabled by bootloader on,
2748                        even if no driver has claimed them. This is useful
2749                        for debug and development, but should not be
2750                        needed on a platform with proper driver support.
2752        pd.             [PARIDE]
2753                        See Documentation/blockdev/paride.txt.
2755        pdcchassis=     [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2756                        boot time.
2757                        Format: { 0 | 1 }
2758                        See arch/parisc/kernel/pdc_chassis.c
2760        percpu_alloc=   Select which percpu first chunk allocator to use.
2761                        Currently supported values are "embed" and "page".
2762                        Archs may support subset or none of the selections.
2763                        See comments in mm/percpu.c for details on each
2764                        allocator.  This parameter is primarily for debugging
2765                        and performance comparison.
2767        pf.             [PARIDE]
2768                        See Documentation/blockdev/paride.txt.
2770        pg.             [PARIDE]
2771                        See Documentation/blockdev/paride.txt.
2773        pirq=           [SMP,APIC] Manual mp-table setup
2774                        See Documentation/x86/i386/IO-APIC.txt.
2776        plip=           [PPT,NET] Parallel port network link
2777                        Format: { parport<nr> | timid | 0 }
2778                        See also Documentation/parport.txt.
2780        pmtmr=          [X86] Manual setup of pmtmr I/O Port.
2781                        Override pmtimer IOPort with a hex value.
2782                        e.g. pmtmr=0x508
2784        pnp.debug=1     [PNP]
2785                        Enable PNP debug messages (depends on the
2786                        CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
2787                        via /sys/module/pnp/parameters/debug.  We always show
2788                        current resource usage; turning this on also shows
2789                        possible settings and some assignment information.
2791        pnpacpi=        [ACPI]
2792                        { off }
2794        pnpbios=        [ISAPNP]
2795                        { on | off | curr | res | no-curr | no-res }
2797        pnp_reserve_irq=
2798                        [ISAPNP] Exclude IRQs for the autoconfiguration
2800        pnp_reserve_dma=
2801                        [ISAPNP] Exclude DMAs for the autoconfiguration
2803        pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2804                        Ranges are in pairs (I/O port base and size).
2806        pnp_reserve_mem=
2807                        [ISAPNP] Exclude memory regions for the
2808                        autoconfiguration.
2809                        Ranges are in pairs (memory base and size).
2811        ports=          [IP_VS_FTP] IPVS ftp helper module
2812                        Default is 21.
2813                        Up to 8 (IP_VS_APP_MAX_PORTS) ports
2814                        may be specified.
2815                        Format: <port>,<port>....
2817        print-fatal-signals=
2818                        [KNL] debug: print fatal signals
2820                        If enabled, warn about various signal handling
2821                        related application anomalies: too many signals,
2822                        too many POSIX.1 timers, fatal signals causing a
2823                        coredump - etc.
2825                        If you hit the warning due to signal overflow,
2826                        you might want to try "ulimit -i unlimited".
2828                        default: off.
2830        printk.always_kmsg_dump=
2831                        Trigger kmsg_dump for cases other than kernel oops or
2832                        panics
2833                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2834                        default: disabled
2836        printk.time=    Show timing data prefixed to each printk message line
2837                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2839        processor.max_cstate=   [HW,ACPI]
2840                        Limit processor to maximum C-state
2841                        max_cstate=9 overrides any DMI blacklist limit.
2843        processor.nocst [HW,ACPI]
2844                        Ignore the _CST method to determine C-states,
2845                        instead using the legacy FADT method
2847        profile=        [KNL] Enable kernel profiling via /proc/profile
2848                        Format: [schedule,]<number>
2849                        Param: "schedule" - profile schedule points.
2850                        Param: <number> - step/bucket size as a power of 2 for
2851                                statistical time based profiling.
2852                        Param: "sleep" - profile D-state sleeping (millisecs).
2853                                Requires CONFIG_SCHEDSTATS
2854                        Param: "kvm" - profile VM exits.
2856        prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2857                        before loading.
2858                        See Documentation/blockdev/ramdisk.txt.
2860        psmouse.proto=  [HW,MOUSE] Highest PS2 mouse protocol extension to
2861                        probe for; one of (bare|imps|exps|lifebook|any).
2862        psmouse.rate=   [HW,MOUSE] Set desired mouse report rate, in reports
2863                        per second.
2864        psmouse.resetafter=     [HW,MOUSE]
2865                        Try to reset the device after so many bad packets
2866                        (0 = never).
2867        psmouse.resolution=
2868                        [HW,MOUSE] Set desired mouse resolution, in dpi.
2869        psmouse.smartscroll=
2870                        [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2871                        0 = disabled, 1 = enabled (default).
2873        pstore.backend= Specify the name of the pstore backend to use
2875        pt.             [PARIDE]
2876                        See Documentation/blockdev/paride.txt.
2878        pty.legacy_count=
2879                        [KNL] Number of legacy pty's. Overwrites compiled-in
2880                        default number.
2882        quiet           [KNL] Disable most log messages
2884        r128=           [HW,DRM]
2886        raid=           [HW,RAID]
2887                        See Documentation/md.txt.
2889        ramdisk_blocksize=      [RAM]
2890                        See Documentation/blockdev/ramdisk.txt.
2892        ramdisk_size=   [RAM] Sizes of RAM disks in kilobytes
2893                        See Documentation/blockdev/ramdisk.txt.
2895        rcu_nocbs=      [KNL]
2896                        In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2897                        the specified list of CPUs to be no-callback CPUs.
2898                        Invocation of these CPUs' RCU callbacks will
2899                        be offloaded to "rcuox/N" kthreads created for
2900                        that purpose, where "x" is "b" for RCU-bh, "p"
2901                        for RCU-preempt, and "s" for RCU-sched, and "N"
2902                        is the CPU number.  This reduces OS jitter on the
2903                        offloaded CPUs, which can be useful for HPC and
2904                        real-time workloads.  It can also improve energy
2905                        efficiency for asymmetric multiprocessors.
2907        rcu_nocb_poll   [KNL]
2908                        Rather than requiring that offloaded CPUs
2909                        (specified by rcu_nocbs= above) explicitly
2910                        awaken the corresponding "rcuoN" kthreads,
2911                        make these kthreads poll for callbacks.
2912                        This improves the real-time response for the
2913                        offloaded CPUs by relieving them of the need to
2914                        wake up the corresponding kthread, but degrades
2915                        energy efficiency by requiring that the kthreads
2916                        periodically wake up to do the polling.
2918        rcutree.blimit= [KNL]
2919                        Set maximum number of finished RCU callbacks to
2920                        process in one batch.
2922        rcutree.rcu_fanout_leaf= [KNL]
2923                        Increase the number of CPUs assigned to each
2924                        leaf rcu_node structure.  Useful for very large
2925                        systems.
2927        rcutree.jiffies_till_sched_qs= [KNL]
2928                        Set required age in jiffies for a
2929                        given grace period before RCU starts
2930                        soliciting quiescent-state help from
2931                        rcu_note_context_switch().
2933        rcutree.jiffies_till_first_fqs= [KNL]
2934                        Set delay from grace-period initialization to
2935                        first attempt to force quiescent states.
2936                        Units are jiffies, minimum value is zero,
2937                        and maximum value is HZ.
2939        rcutree.jiffies_till_next_fqs= [KNL]
2940                        Set delay between subsequent attempts to force
2941                        quiescent states.  Units are jiffies, minimum
2942                        value is one, and maximum value is HZ.
2944        rcutree.rcu_nocb_leader_stride= [KNL]
2945                        Set the number of NOCB kthread groups, which
2946                        defaults to the square root of the number of
2947                        CPUs.  Larger numbers reduces the wakeup overhead
2948                        on the per-CPU grace-period kthreads, but increases
2949                        that same overhead on each group's leader.
2951        rcutree.qhimark= [KNL]
2952                        Set threshold of queued RCU callbacks beyond which
2953                        batch limiting is disabled.
2955        rcutree.qlowmark= [KNL]
2956                        Set threshold of queued RCU callbacks below which
2957                        batch limiting is re-enabled.
2959        rcutree.rcu_idle_gp_delay= [KNL]
2960                        Set wakeup interval for idle CPUs that have
2961                        RCU callbacks (RCU_FAST_NO_HZ=y).
2963        rcutree.rcu_idle_lazy_gp_delay= [KNL]
2964                        Set wakeup interval for idle CPUs that have
2965                        only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2966                        Lazy RCU callbacks are those which RCU can
2967                        prove do nothing more than free memory.
2969        rcutorture.cbflood_inter_holdoff= [KNL]
2970                        Set holdoff time (jiffies) between successive
2971                        callback-flood tests.
2973        rcutorture.cbflood_intra_holdoff= [KNL]
2974                        Set holdoff time (jiffies) between successive
2975                        bursts of callbacks within a given callback-flood
2976                        test.
2978        rcutorture.cbflood_n_burst= [KNL]
2979                        Set the number of bursts making up a given
2980                        callback-flood test.  Set this to zero to
2981                        disable callback-flood testing.
2983        rcutorture.cbflood_n_per_burst= [KNL]
2984                        Set the number of callbacks to be registered
2985                        in a given burst of a callback-flood test.
2987        rcutorture.fqs_duration= [KNL]
2988                        Set duration of force_quiescent_state bursts.
2990        rcutorture.fqs_holdoff= [KNL]
2991                        Set holdoff time within force_quiescent_state bursts.
2993        rcutorture.fqs_stutter= [KNL]
2994                        Set wait time between force_quiescent_state bursts.
2996        rcutorture.gp_exp= [KNL]
2997                        Use expedited update-side primitives.
2999        rcutorture.gp_normal= [KNL]
3000                        Use normal (non-expedited) update-side primitives.
3001                        If both gp_exp and gp_normal are set, do both.
3002                        If neither gp_exp nor gp_normal are set, still
3003                        do both.
3005        rcutorture.n_barrier_cbs= [KNL]
3006                        Set callbacks/threads for rcu_barrier() testing.
3008        rcutorture.nfakewriters= [KNL]
3009                        Set number of concurrent RCU writers.  These just
3010                        stress RCU, they don't participate in the actual
3011                        test, hence the "fake".
3013        rcutorture.nreaders= [KNL]
3014                        Set number of RCU readers.
3016        rcutorture.object_debug= [KNL]
3017                        Enable debug-object double-call_rcu() testing.
3019        rcutorture.onoff_holdoff= [KNL]
3020                        Set time (s) after boot for CPU-hotplug testing.
3022        rcutorture.onoff_interval= [KNL]
3023                        Set time (s) between CPU-hotplug operations, or
3024                        zero to disable CPU-hotplug testing.
3026        rcutorture.torture_runnable= [BOOT]
3027                        Start rcutorture running at boot time.
3029        rcutorture.shuffle_interval= [KNL]
3030                        Set task-shuffle interval (s).  Shuffling tasks
3031                        allows some CPUs to go into dyntick-idle mode
3032                        during the rcutorture test.
3034        rcutorture.shutdown_secs= [KNL]
3035                        Set time (s) after boot system shutdown.  This
3036                        is useful for hands-off automated testing.
3038        rcutorture.stall_cpu= [KNL]
3039                        Duration of CPU stall (s) to test RCU CPU stall
3040                        warnings, zero to disable.
3042        rcutorture.stall_cpu_holdoff= [KNL]
3043                        Time to wait (s) after boot before inducing stall.
3045        rcutorture.stat_interval= [KNL]
3046                        Time (s) between statistics printk()s.
3048        rcutorture.stutter= [KNL]
3049                        Time (s) to stutter testing, for example, specifying
3050                        five seconds causes the test to run for five seconds,
3051                        wait for five seconds, and so on.  This tests RCU's
3052                        ability to transition abruptly to and from idle.
3054        rcutorture.test_boost= [KNL]
3055                        Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
3056                        "Maybe" means test if the RCU implementation
3057                        under test support RCU priority boosting.
3059        rcutorture.test_boost_duration= [KNL]
3060                        Duration (s) of each individual boost test.
3062        rcutorture.test_boost_interval= [KNL]
3063                        Interval (s) between each boost test.
3065        rcutorture.test_no_idle_hz= [KNL]
3066                        Test RCU's dyntick-idle handling.  See also the
3067                        rcutorture.shuffle_interval parameter.
3069        rcutorture.torture_type= [KNL]
3070                        Specify the RCU implementation to test.
3072        rcutorture.verbose= [KNL]
3073                        Enable additional printk() statements.
3075        rcupdate.rcu_expedited= [KNL]
3076                        Use expedited grace-period primitives, for
3077                        example, synchronize_rcu_expedited() instead
3078                        of synchronize_rcu().  This reduces latency,
3079                        but can increase CPU utilization, degrade
3080                        real-time latency, and degrade energy efficiency.
3082        rcupdate.rcu_cpu_stall_suppress= [KNL]
3083                        Suppress RCU CPU stall warning messages.
3085        rcupdate.rcu_cpu_stall_timeout= [KNL]
3086                        Set timeout for RCU CPU stall warning messages.
3088        rcupdate.rcu_task_stall_timeout= [KNL]
3089                        Set timeout in jiffies for RCU task stall warning
3090                        messages.  Disable with a value less than or equal
3091                        to zero.
3093        rdinit=         [KNL]
3094                        Format: <full_path>
3095                        Run specified binary instead of /init from the ramdisk,
3096                        used for early userspace startup. See initrd.
3098        reboot=         [KNL]
3099                        Format (x86 or x86_64):
3100                                [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3101                                [[,]s[mp]#### \
3102                                [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3103                                [[,]f[orce]
3104                        Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3105                              reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3106                              reboot_force is either force or not specified,
3107                              reboot_cpu is s[mp]#### with #### being the processor
3108                                        to be used for rebooting.
3110        relax_domain_level=
3111                        [KNL, SMP] Set scheduler's default relax_domain_level.
3112                        See Documentation/cgroups/cpusets.txt.
3114        relative_sleep_states=
3115                        [SUSPEND] Use sleep state labeling where the deepest
3116                        state available other than hibernation is always "mem".
3117                        Format: { "0" | "1" }
3118                        0 -- Traditional sleep state labels.
3119                        1 -- Relative sleep state labels.
3121        reserve=        [KNL,BUGS] Force the kernel to ignore some iomem area
3123        reservetop=     [X86-32]
3124                        Format: nn[KMG]
3125                        Reserves a hole at the top of the kernel virtual
3126                        address space.
3128        reservelow=     [X86]
3129                        Format: nn[K]
3130                        Set the amount of memory to reserve for BIOS at
3131                        the bottom of the address space.
3133        reset_devices   [KNL] Force drivers to reset the underlying device
3134                        during initialization.
3136        resume=         [SWSUSP]
3137                        Specify the partition device for software suspend
3138                        Format:
3139                        {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3141        resume_offset=  [SWSUSP]
3142                        Specify the offset from the beginning of the partition
3143                        given by "resume=" at which the swap header is located,
3144                        in <PAGE_SIZE> units (needed only for swap files).
3145                        See  Documentation/power/swsusp-and-swap-files.txt
3147        resumedelay=    [HIBERNATION] Delay (in seconds) to pause before attempting to
3148                        read the resume files
3150        resumewait      [HIBERNATION] Wait (indefinitely) for resume device to show up.
3151                        Useful for devices that are detected asynchronously
3152                        (e.g. USB and MMC devices).
3154        hibernate=      [HIBERNATION]
3155                noresume        Don't check if there's a hibernation image
3156                                present during boot.
3157                nocompress      Don't compress/decompress hibernation images.
3158                no              Disable hibernation and resume.
3160        retain_initrd   [RAM] Keep initrd memory after extraction
3162        rhash_entries=  [KNL,NET]
3163                        Set number of hash buckets for route cache
3165        ro              [KNL] Mount root device read-only on boot
3167        root=           [KNL] Root filesystem
3168                        See name_to_dev_t comment in init/do_mounts.c.
3170        rootdelay=      [KNL] Delay (in seconds) to pause before attempting to
3171                        mount the root filesystem
3173        rootflags=      [KNL] Set root filesystem mount option string
3175        rootfstype=     [KNL] Set root filesystem type
3177        rootwait        [KNL] Wait (indefinitely) for root device to show up.
3178                        Useful for devices that are detected asynchronously
3179                        (e.g. USB and MMC devices).
3181        rproc_mem=nn[KMG][@address]
3182                        [KNL,ARM,CMA] Remoteproc physical memory block.
3183                        Memory area to be used by remote processor image,
3184                        managed by CMA.
3186        rw              [KNL] Mount root device read-write on boot
3188        S               [KNL] Run init in single mode
3190        s390_iommu=     [HW,S390]
3191                        Set s390 IOTLB flushing mode
3192                strict
3193                        With strict flushing every unmap operation will result in
3194                        an IOTLB flush. Default is lazy flushing before reuse,
3195                        which is faster.
3197        sa1100ir        [NET]
3198                        See drivers/net/irda/sa1100_ir.c.
3200        sbni=           [NET] Granch SBNI12 leased line adapter
3202        sched_debug     [KNL] Enables verbose scheduler debug messages.
3204        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
3205                        xtime_lock contention on larger systems, and/or RCU lock
3206                        contention on all systems with CONFIG_MAXSMP set.
3207                        Format: { "0" | "1" }
3208                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3209                        1 -- enable.
3210                        Note: increases power consumption, thus should only be
3211                        enabled if running jitter sensitive (HPC/RT) workloads.
3213        security=       [SECURITY] Choose a security module to enable at boot.
3214                        If this boot parameter is not specified, only the first
3215                        security module asking for security registration will be
3216                        loaded. An invalid security module name will be treated
3217                        as if no module has been chosen.
3219        selinux=        [SELINUX] Disable or enable SELinux at boot time.
3220                        Format: { "0" | "1" }
3221                        See security/selinux/Kconfig help text.
3222                        0 -- disable.
3223                        1 -- enable.
3224                        Default value is set via kernel config option.
3225                        If enabled at boot time, /selinux/disable can be used
3226                        later to disable prior to initial policy load.
3228        apparmor=       [APPARMOR] Disable or enable AppArmor at boot time
3229                        Format: { "0" | "1" }
3230                        See security/apparmor/Kconfig help text
3231                        0 -- disable.
3232                        1 -- enable.
3233                        Default value is set via kernel config option.
3235        serialnumber    [BUGS=X86-32]
3237        shapers=        [NET]
3238                        Maximal number of shapers.
3240        show_msr=       [x86] show boot-time MSR settings
3241                        Format: { <integer> }
3242                        Show boot-time (BIOS-initialized) MSR settings.
3243                        The parameter means the number of CPUs to show,
3244                        for example 1 means boot CPU only.
3246        simeth=         [IA-64]
3247        simscsi=
3249        slram=          [HW,MTD]
3251        slab_nomerge    [MM]
3252                        Disable merging of slabs with similar size. May be
3253                        necessary if there is some reason to distinguish
3254                        allocs to different slabs. Debug options disable
3255                        merging on their own.
3256                        For more information see Documentation/vm/slub.txt.
3258        slab_max_order= [MM, SLAB]
3259                        Determines the maximum allowed order for slabs.
3260                        A high setting may cause OOMs due to memory
3261                        fragmentation.  Defaults to 1 for systems with
3262                        more than 32MB of RAM, 0 otherwise.
3264        slub_debug[=options[,slabs]]    [MM, SLUB]
3265                        Enabling slub_debug allows one to determine the
3266                        culprit if slab objects become corrupted. Enabling
3267                        slub_debug can create guard zones around objects and
3268                        may poison objects when not in use. Also tracks the
3269                        last alloc / free. For more information see
3270                        Documentation/vm/slub.txt.
3272        slub_max_order= [MM, SLUB]
3273                        Determines the maximum allowed order for slabs.
3274                        A high setting may cause OOMs due to memory
3275                        fragmentation. For more information see
3276                        Documentation/vm/slub.txt.
3278        slub_min_objects=       [MM, SLUB]
3279                        The minimum number of objects per slab. SLUB will
3280                        increase the slab order up to slub_max_order to
3281                        generate a sufficiently large slab able to contain
3282                        the number of objects indicated. The higher the number
3283                        of objects the smaller the overhead of tracking slabs
3284                        and the less frequently locks need to be acquired.
3285                        For more information see Documentation/vm/slub.txt.
3287        slub_min_order= [MM, SLUB]
3288                        Determines the minimum page order for slabs. Must be
3289                        lower than slub_max_order.
3290                        For more information see Documentation/vm/slub.txt.
3292        slub_nomerge    [MM, SLUB]
3293                        Same with slab_nomerge. This is supported for legacy.
3294                        See slab_nomerge for more information.
3296        smart2=         [HW]
3297                        Format: <io1>[,<io2>[,...,<io8>]]
3299        smsc-ircc2.nopnp        [HW] Don't use PNP to discover SMC devices
3300        smsc-ircc2.ircc_cfg=    [HW] Device configuration I/O port
3301        smsc-ircc2.ircc_sir=    [HW] SIR base I/O port
3302        smsc-ircc2.ircc_fir=    [HW] FIR base I/O port
3303        smsc-ircc2.ircc_irq=    [HW] IRQ line
3304        smsc-ircc2.ircc_dma=    [HW] DMA channel
3305        smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3306                                0: Toshiba Satellite 1800 (GP data pin select)
3307                                1: Fast pin select (default)
3308                                2: ATC IRMode
3310        softlockup_panic=
3311                        [KNL] Should the soft-lockup detector generate panics.
3312                        Format: <integer>
3314        softlockup_all_cpu_backtrace=
3315                        [KNL] Should the soft-lockup detector generate
3316                        backtraces on all cpus.
3317                        Format: <integer>
3319        sonypi.*=       [HW] Sony Programmable I/O Control Device driver
3320                        See Documentation/laptops/sonypi.txt
3322        spia_io_base=   [HW,MTD]
3323        spia_fio_base=
3324        spia_pedr=
3325        spia_peddr=
3327        stacktrace      [FTRACE]
3328                        Enabled the stack tracer on boot up.
3330        stacktrace_filter=[function-list]
3331                        [FTRACE] Limit the functions that the stack tracer
3332                        will trace at boot up. function-list is a comma separated
3333                        list of functions. This list can be changed at run
3334                        time by the stack_trace_filter file in the debugfs
3335                        tracing directory. Note, this enables stack tracing
3336                        and the stacktrace above is not needed.
3338        sti=            [PARISC,HW]
3339                        Format: <num>
3340                        Set the STI (builtin display/keyboard on the HP-PARISC
3341                        machines) console (graphic card) which should be used
3342                        as the initial boot-console.
3343                        See also comment in drivers/video/console/sticore.c.
3345        sti_font=       [HW]
3346                        See comment in drivers/video/console/sticore.c.
3348        stifb=          [HW]
3349                        Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3351        sunrpc.min_resvport=
3352        sunrpc.max_resvport=
3353                        [NFS,SUNRPC]
3354                        SunRPC servers often require that client requests
3355                        originate from a privileged port (i.e. a port in the
3356                        range 0 < portnr < 1024).
3357                        An administrator who wishes to reserve some of these
3358                        ports for other uses may adjust the range that the
3359                        kernel's sunrpc client considers to be privileged
3360                        using these two parameters to set the minimum and
3361                        maximum port values.
3363        sunrpc.pool_mode=
3364                        [NFS]
3365                        Control how the NFS server code allocates CPUs to
3366                        service thread pools.  Depending on how many NICs
3367                        you have and where their interrupts are bound, this
3368                        option will affect which CPUs will do NFS serving.
3369                        Note: this parameter cannot be changed while the
3370                        NFS server is running.
3372                        auto        the server chooses an appropriate mode
3373                                    automatically using heuristics
3374                        global      a single global pool contains all CPUs
3375                        percpu      one pool for each CPU
3376                        pernode     one pool for each NUMA node (equivalent
3377                                    to global on non-NUMA machines)
3379        sunrpc.tcp_slot_table_entries=
3380        sunrpc.udp_slot_table_entries=
3381                        [NFS,SUNRPC]
3382                        Sets the upper limit on the number of simultaneous
3383                        RPC calls that can be sent from the client to a
3384                        server. Increasing these values may allow you to
3385                        improve throughput, but will also increase the
3386                        amount of memory reserved for use by the client.
3388        swapaccount=[0|1]
3389                        [KNL] Enable accounting of swap in memory resource
3390                        controller if no parameter or 1 is given or disable
3391                        it if 0 is given (See Documentation/cgroups/memory.txt)
3393        swiotlb=        [ARM,IA-64,PPC,MIPS,X86]
3394                        Format: { <int> | force }
3395                        <int> -- Number of I/O TLB slabs
3396                        force -- force using of bounce buffers even if they
3397                                 wouldn't be automatically used by the kernel
3399        switches=       [HW,M68k]
3401        sysfs.deprecated=0|1 [KNL]
3402                        Enable/disable old style sysfs layout for old udev
3403                        on older distributions. When this option is enabled
3404                        very new udev will not work anymore. When this option
3405                        is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3406                        in older udev will not work anymore.
3407                        Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3408                        the kernel configuration.
3410        sysrq_always_enabled
3411                        [KNL]
3412                        Ignore sysrq setting - this boot parameter will
3413                        neutralize any effect of /proc/sys/kernel/sysrq.
3414                        Useful for debugging.
3416        tdfx=           [HW,DRM]
3418        test_suspend=   [SUSPEND][,N]
3419                        Specify "mem" (for Suspend-to-RAM) or "standby" (for
3420                        standby suspend) or "freeze" (for suspend type freeze)
3421                        as the system sleep state during system startup with
3422                        the optional capability to repeat N number of times.
3423                        The system is woken from this state using a
3424                        wakeup-capable RTC alarm.
3426        thash_entries=  [KNL,NET]
3427                        Set number of hash buckets for TCP connection
3429        thermal.act=    [HW,ACPI]
3430                        -1: disable all active trip points in all thermal zones
3431                        <degrees C>: override all lowest active trip points
3433        thermal.crt=    [HW,ACPI]
3434                        -1: disable all critical trip points in all thermal zones
3435                        <degrees C>: override all critical trip points
3437        thermal.nocrt=  [HW,ACPI]
3438                        Set to disable actions on ACPI thermal zone
3439                        critical and hot trip points.
3441    [HW,ACPI]
3442                        1: disable ACPI thermal control
3444        thermal.psv=    [HW,ACPI]
3445                        -1: disable all passive trip points
3446                        <degrees C>: override all passive trip points to this
3447                        value
3449        thermal.tzp=    [HW,ACPI]
3450                        Specify global default ACPI thermal zone polling rate
3451                        <deci-seconds>: poll all this frequency
3452                        0: no polling (default)
3454        threadirqs      [KNL]
3455                        Force threading of all interrupt handlers except those
3456                        marked explicitly IRQF_NO_THREAD.
3458        tmem            [KNL,XEN]
3459                        Enable the Transcendent memory driver if built-in.
3461        tmem.cleancache=0|1 [KNL, XEN]
3462                        Default is on (1). Disable the usage of the cleancache
3463                        API to send anonymous pages to the hypervisor.
3465        tmem.frontswap=0|1 [KNL, XEN]
3466                        Default is on (1). Disable the usage of the frontswap
3467                        API to send swap pages to the hypervisor. If disabled
3468                        the selfballooning and selfshrinking are force disabled.
3470        tmem.selfballooning=0|1 [KNL, XEN]
3471                        Default is on (1). Disable the driving of swap pages
3472                        to the hypervisor.
3474        tmem.selfshrinking=0|1 [KNL, XEN]
3475                        Default is on (1). Partial swapoff that immediately
3476                        transfers pages from Xen hypervisor back to the
3477                        kernel based on different criteria.
3479        topology=       [S390]
3480                        Format: {off | on}
3481                        Specify if the kernel should make use of the cpu
3482                        topology information if the hardware supports this.
3483                        The scheduler will make use of this information and
3484                        e.g. base its process migration decisions on it.
3485                        Default is on.
3487        topology_updates= [KNL, PPC, NUMA]
3488                        Format: {off}
3489                        Specify if the kernel should ignore (off)
3490                        topology updates sent by the hypervisor to this
3491                        LPAR.
3493        tp720=          [HW,PS2]
3495        tpm_suspend_pcr=[HW,TPM]
3496                        Format: integer pcr id
3497                        Specify that at suspend time, the tpm driver
3498                        should extend the specified pcr with zeros,
3499                        as a workaround for some chips which fail to
3500                        flush the last written pcr on TPM_SaveState.
3501                        This will guarantee that all the other pcrs
3502                        are saved.
3504        trace_buf_size=nn[KMG]
3505                        [FTRACE] will set tracing buffer size.
3507        trace_event=[event-list]
3508                        [FTRACE] Set and start specified trace events in order
3509                        to facilitate early boot debugging.
3510                        See also Documentation/trace/events.txt
3512        trace_options=[option-list]
3513                        [FTRACE] Enable or disable tracer options at boot.
3514                        The option-list is a comma delimited list of options
3515                        that can be enabled or disabled just as if you were
3516                        to echo the option name into
3518                            /sys/kernel/debug/tracing/trace_options
3520                        For example, to enable stacktrace option (to dump the
3521                        stack trace of each event), add to the command line:
3523                              trace_options=stacktrace
3525                        See also Documentation/trace/ftrace.txt "trace options"
3526                        section.
3528        traceoff_on_warning
3529                        [FTRACE] enable this option to disable tracing when a
3530                        warning is hit. This turns off "tracing_on". Tracing can
3531                        be enabled again by echoing '1' into the "tracing_on"
3532                        file located in /sys/kernel/debug/tracing/
3534                        This option is useful, as it disables the trace before
3535                        the WARNING dump is called, which prevents the trace to
3536                        be filled with content caused by the warning output.
3538                        This option can also be set at run time via the sysctl
3539                        option:  kernel/traceoff_on_warning
3541        transparent_hugepage=
3542                        [KNL]
3543                        Format: [always|madvise|never]
3544                        Can be used to control the default behavior of the system
3545                        with respect to transparent hugepages.
3546                        See Documentation/vm/transhuge.txt for more details.
3548        tsc=            Disable clocksource stability checks for TSC.
3549                        Format: <string>
3550                        [x86] reliable: mark tsc clocksource as reliable, this
3551                        disables clocksource verification at runtime, as well
3552                        as the stability checks done at bootup. Used to enable
3553                        high-resolution timer mode on older hardware, and in
3554                        virtualized environment.
3555                        [x86] noirqtime: Do not use TSC to do irq accounting.
3556                        Used to run time disable IRQ_TIME_ACCOUNTING on any
3557                        platforms where RDTSC is slow and this accounting
3558                        can add overhead.
3560[2|3]=    [HW,JOY]
3561                        TurboGraFX parallel port interface
3562                        Format:
3563                        <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3564                        See also Documentation/input/joystick-parport.txt
3566        udbg-immortal   [PPC] When debugging early kernel crashes that
3567                        happen after console_init() and before a proper 
3568                        console driver takes over, this boot options might
3569                        help "seeing" what's going on.
3571        uhash_entries=  [KNL,NET]
3572                        Set number of hash buckets for UDP/UDP-Lite connections
3574        uhci-hcd.ignore_oc=
3575                        [USB] Ignore overcurrent events (default N).
3576                        Some badly-designed motherboards generate lots of
3577                        bogus events, for ports that aren't wired to
3578                        anything.  Set this parameter to avoid log spamming.
3579                        Note that genuine overcurrent events won't be
3580                        reported either.
3582        unknown_nmi_panic
3583                        [X86] Cause panic on unknown NMI.
3585        usbcore.authorized_default=
3586                        [USB] Default USB device authorization:
3587                        (default -1 = authorized except for wireless USB,
3588                        0 = not authorized, 1 = authorized)
3590        usbcore.autosuspend=
3591                        [USB] The autosuspend time delay (in seconds) used
3592                        for newly-detected USB devices (default 2).  This
3593                        is the time required before an idle device will be
3594                        autosuspended.  Devices for which the delay is set
3595                        to a negative value won't be autosuspended at all.
3597        usbcore.usbfs_snoop=
3598                        [USB] Set to log all usbfs traffic (default 0 = off).
3600        usbcore.blinkenlights=
3601                        [USB] Set to cycle leds on hubs (default 0 = off).
3603        usbcore.old_scheme_first=
3604                        [USB] Start with the old device initialization
3605                        scheme (default 0 = off).
3607        usbcore.usbfs_memory_mb=
3608                        [USB] Memory limit (in MB) for buffers allocated by
3609                        usbfs (default = 16, 0 = max = 2047).
3611        usbcore.use_both_schemes=
3612                        [USB] Try the other device initialization scheme
3613                        if the first one fails (default 1 = enabled).
3615        usbcore.initial_descriptor_timeout=
3616                        [USB] Specifies timeout for the initial 64-byte
3617                        USB_REQ_GET_DESCRIPTOR request in milliseconds
3618                        (default 5000 = 5.0 seconds).
3620        usbhid.mousepoll=
3621                        [USBHID] The interval which mice are to be polled at.
3623        usb-storage.delay_use=
3624                        [UMS] The delay in seconds before a new device is
3625                        scanned for Logical Units (default 1).
3627        usb-storage.quirks=
3628                        [UMS] A list of quirks entries to supplement or
3629                        override the built-in unusual_devs list.  List
3630                        entries are separated by commas.  Each entry has
3631                        the form VID:PID:Flags where VID and PID are Vendor
3632                        and Product ID values (4-digit hex numbers) and
3633                        Flags is a set of characters, each corresponding
3634                        to a common usb-storage quirk flag as follows:
3635                                a = SANE_SENSE (collect more than 18 bytes
3636                                        of sense data);
3637                                b = BAD_SENSE (don't collect more than 18
3638                                        bytes of sense data);
3639                                c = FIX_CAPACITY (decrease the reported
3640                                        device capacity by one sector);
3641                                d = NO_READ_DISC_INFO (don't use
3642                                        READ_DISC_INFO command);
3643                                e = NO_READ_CAPACITY_16 (don't use
3644                                        READ_CAPACITY_16 command);
3645                                f = NO_REPORT_OPCODES (don't use report opcodes
3646                                        command, uas only);
3647                                g = MAX_SECTORS_240 (don't transfer more than
3648                                        240 sectors at a time, uas only);
3649                                h = CAPACITY_HEURISTICS (decrease the
3650                                        reported device capacity by one
3651                                        sector if the number is odd);
3652                                i = IGNORE_DEVICE (don't bind to this
3653                                        device);
3654                                l = NOT_LOCKABLE (don't try to lock and
3655                                        unlock ejectable media);
3656                                m = MAX_SECTORS_64 (don't transfer more
3657                                        than 64 sectors = 32 KB at a time);
3658                                n = INITIAL_READ10 (force a retry of the
3659                                        initial READ(10) command);
3660                                o = CAPACITY_OK (accept the capacity
3661                                        reported by the device);
3662                                p = WRITE_CACHE (the device cache is ON
3663                                        by default);
3664                                r = IGNORE_RESIDUE (the device reports
3665                                        bogus residue values);
3666                                s = SINGLE_LUN (the device has only one
3667                                        Logical Unit);
3668                                t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3669                                        commands, uas only);
3670                                u = IGNORE_UAS (don't bind to the uas driver);
3671                                w = NO_WP_DETECT (don't test whether the
3672                                        medium is write-protected).
3673                        Example: quirks=0419:aaf5:rl,0421:0433:rc
3675        user_debug=     [KNL,ARM]
3676                        Format: <int>
3677                        See arch/arm/Kconfig.debug help text.
3678                                 1 - undefined instruction events
3679                                 2 - system calls
3680                                 4 - invalid data aborts
3681                                 8 - SIGSEGV faults
3682                                16 - SIGBUS faults
3683                        Example: user_debug=31
3685        userpte=
3686                        [X86] Flags controlling user PTE allocations.
3688                                nohigh = do not allocate PTE pages in
3689                                        HIGHMEM regardless of setting
3690                                        of CONFIG_HIGHPTE.
3692        vdso=           [X86,SH]
3693                        On X86_32, this is an alias for vdso32=.  Otherwise:
3695                        vdso=1: enable VDSO (the default)
3696                        vdso=0: disable VDSO mapping
3698        vdso32=         [X86] Control the 32-bit vDSO
3699                        vdso32=1: enable 32-bit VDSO
3700                        vdso32=0 or vdso32=2: disable 32-bit VDSO
3702                        See the help text for CONFIG_COMPAT_VDSO for more
3703                        details.  If CONFIG_COMPAT_VDSO is set, the default is
3704                        vdso32=0; otherwise, the default is vdso32=1.
3706                        For compatibility with older kernels, vdso32=2 is an
3707                        alias for vdso32=0.
3709                        Try vdso32=0 if you encounter an error that says:
3710                        dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
3712        vector=         [IA-64,SMP]
3713                        vector=percpu: enable percpu vector domain
3715        video=          [FB] Frame buffer configuration
3716                        See Documentation/fb/modedb.txt.
3718        video.brightness_switch_enabled= [0,1]
3719                        If set to 1, on receiving an ACPI notify event
3720                        generated by hotkey, video driver will adjust brightness
3721                        level and then send out the event to user space through
3722                        the allocated input device; If set to 0, video driver
3723                        will only send out the event without touching backlight
3724                        brightness level.
3725                        default: 1
3727        virtio_mmio.device=
3728                        [VMMIO] Memory mapped virtio (platform) device.
3730                                <size>@<baseaddr>:<irq>[:<id>]
3731                        where:
3732                                <size>     := size (can use standard suffixes
3733                                                like K, M and G)
3734                                <baseaddr> := physical base address
3735                                <irq>      := interrupt number (as passed to
3736                                                request_irq())
3737                                <id>       := (optional) platform device id
3738                        example:
3739                                virtio_mmio.device=1K@0x100b0000:48:7
3741                        Can be used multiple times for multiple devices.
3743        vga=            [BOOT,X86-32] Select a particular video mode
3744                        See Documentation/x86/boot.txt and
3745                        Documentation/svga.txt.
3746                        Use vga=ask for menu.
3747                        This is actually a boot loader parameter; the value is
3748                        passed to the kernel using a special protocol.
3750        vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3751                        size of <nn>. This can be used to increase the
3752                        minimum size (128MB on x86). It can also be used to
3753                        decrease the size and leave more room for directly
3754                        mapped kernel RAM.
3756        vmhalt=         [KNL,S390] Perform z/VM CP command after system halt.
3757                        Format: <command>
3759        vmpanic=        [KNL,S390] Perform z/VM CP command after kernel panic.
3760                        Format: <command>
3762        vmpoff=         [KNL,S390] Perform z/VM CP command after power off.
3763                        Format: <command>
3765        vsyscall=       [X86-64]
3766                        Controls the behavior of vsyscalls (i.e. calls to
3767                        fixed addresses of 0xffffffffff600x00 from legacy
3768                        code).  Most statically-linked binaries and older
3769                        versions of glibc use these calls.  Because these
3770                        functions are at fixed addresses, they make nice
3771                        targets for exploits that can control RIP.
3773                        emulate     [default] Vsyscalls turn into traps and are
3774                                    emulated reasonably safely.
3776                        native      Vsyscalls are native syscall instructions.
3777                                    This is a little bit faster than trapping
3778                                    and makes a few dynamic recompilers work
3779                                    better than they would in emulation mode.
3780                                    It also makes exploits much easier to write.
3782                        none        Vsyscalls don't work at all.  This makes
3783                                    them quite hard to use for exploits but
3784                                    might break your system.
3786        vt.color=       [VT] Default text color.
3787                        Format: 0xYX, X = foreground, Y = background.
3788                        Default: 0x07 = light gray on black.
3790        vt.cur_default= [VT] Default cursor shape.
3791                        Format: 0xCCBBAA, where AA, BB, and CC are the same as
3792                        the parameters of the <Esc>[?A;B;Cc escape sequence;
3793                        see VGA-softcursor.txt. Default: 2 = underline.
3795        vt.default_blu= [VT]
3796                        Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3797                        Change the default blue palette of the console.
3798                        This is a 16-member array composed of values
3799                        ranging from 0-255.
3801        vt.default_grn= [VT]
3802                        Format: <green0>,<green1>,<green2>,...,<green15>
3803                        Change the default green palette of the console.
3804                        This is a 16-member array composed of values
3805                        ranging from 0-255.
3807        vt.default_red= [VT]
3808                        Format: <red0>,<red1>,<red2>,...,<red15>
3809                        Change the default red palette of the console.
3810                        This is a 16-member array composed of values
3811                        ranging from 0-255.
3813        vt.default_utf8=
3814                        [VT]
3815                        Format=<0|1>
3816                        Set system-wide default UTF-8 mode for all tty's.
3817                        Default is 1, i.e. UTF-8 mode is enabled for all
3818                        newly opened terminals.
3820        vt.global_cursor_default=
3821                        [VT]
3822                        Format=<-1|0|1>
3823                        Set system-wide default for whether a cursor
3824                        is shown on new VTs. Default is -1,
3825                        i.e. cursors will be created by default unless
3826                        overridden by individual drivers. 0 will hide
3827                        cursors, 1 will display them.
3829        vt.italic=      [VT] Default color for italic text; 0-15.
3830                        Default: 2 = green.
3832        vt.underline=   [VT] Default color for underlined text; 0-15.
3833                        Default: 3 = cyan.
3835        watchdog timers [HW,WDT] For information on watchdog timers,
3836                        see Documentation/watchdog/watchdog-parameters.txt
3837                        or other driver-specific files in the
3838                        Documentation/watchdog/ directory.
3840        workqueue.disable_numa
3841                        By default, all work items queued to unbound
3842                        workqueues are affine to the NUMA nodes they're
3843                        issued on, which results in better behavior in
3844                        general.  If NUMA affinity needs to be disabled for
3845                        whatever reason, this option can be used.  Note
3846                        that this also can be controlled per-workqueue for
3847                        workqueues visible under /sys/bus/workqueue/.
3849        workqueue.power_efficient
3850                        Per-cpu workqueues are generally preferred because
3851                        they show better performance thanks to cache
3852                        locality; unfortunately, per-cpu workqueues tend to
3853                        be more power hungry than unbound workqueues.
3855                        Enabling this makes the per-cpu workqueues which
3856                        were observed to contribute significantly to power
3857                        consumption unbound, leading to measurably lower
3858                        power usage at the cost of small performance
3859                        overhead.
3861                        The default value of this parameter is determined by
3862                        the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3864        x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
3865                        default x2apic cluster mode on platforms
3866                        supporting x2apic.
3868        x86_intel_mid_timer= [X86-32,APBT]
3869                        Choose timer option for x86 Intel MID platform.
3870                        Two valid options are apbt timer only and lapic timer
3871                        plus one apbt timer for broadcast timer.
3872                        x86_intel_mid_timer=apbt_only | lapic_and_apbt
3874        xen_emul_unplug=                [HW,X86,XEN]
3875                        Unplug Xen emulated devices
3876                        Format: [unplug0,][unplug1]
3877                        ide-disks -- unplug primary master IDE devices
3878                        aux-ide-disks -- unplug non-primary-master IDE devices
3879                        nics -- unplug network devices
3880                        all -- unplug all emulated devices (NICs and IDE disks)
3881                        unnecessary -- unplugging emulated devices is
3882                                unnecessary even if the host did not respond to
3883                                the unplug protocol
3884                        never -- do not unplug even if version check succeeds
3886        xen_nopvspin    [X86,XEN]
3887                        Disables the ticketlock slowpath using Xen PV
3888                        optimizations.
3890        xen_nopv        [X86]
3891                        Disables the PV optimizations forcing the HVM guest to
3892                        run as generic HVM guest with no PV drivers.
3894        xirc2ps_cs=     [NET,PCMCIA]
3895                        Format:
3896                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3902        Add more DRM drivers.
3903 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.