linux/Documentation/kernel-parameters.txt
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   1                          Kernel Parameters
   2                          ~~~~~~~~~~~~~~~~~
   3
   4The following is a consolidated list of the kernel parameters as implemented
   5(mostly) by the __setup() macro and sorted into English Dictionary order
   6(defined as ignoring all punctuation and sorting digits before letters in a
   7case insensitive manner), and with descriptions where known.
   8
   9Module parameters for loadable modules are specified only as the
  10parameter name with optional '=' and value as appropriate, such as:
  11
  12        modprobe usbcore blinkenlights=1
  13
  14Module parameters for modules that are built into the kernel image
  15are specified on the kernel command line with the module name plus
  16'.' plus parameter name, with '=' and value if appropriate, such as:
  17
  18        usbcore.blinkenlights=1
  19
  20Hyphens (dashes) and underscores are equivalent in parameter names, so
  21        log_buf_len=1M print-fatal-signals=1
  22can also be entered as
  23        log-buf-len=1M print_fatal_signals=1
  24
  25
  26This document may not be entirely up to date and comprehensive. The command
  27"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
  28module. Loadable modules, after being loaded into the running kernel, also
  29reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
  30parameters may be changed at runtime by the command
  31"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
  32
  33The parameters listed below are only valid if certain kernel build options were
  34enabled and if respective hardware is present. The text in square brackets at
  35the beginning of each description states the restrictions within which a
  36parameter is applicable:
  37
  38        ACPI    ACPI support is enabled.
  39        AGP     AGP (Accelerated Graphics Port) is enabled.
  40        ALSA    ALSA sound support is enabled.
  41        APIC    APIC support is enabled.
  42        APM     Advanced Power Management support is enabled.
  43        ARM     ARM architecture is enabled.
  44        AVR32   AVR32 architecture is enabled.
  45        AX25    Appropriate AX.25 support is enabled.
  46        BLACKFIN Blackfin architecture is enabled.
  47        CLK     Common clock infrastructure is enabled.
  48        CMA     Contiguous Memory Area support is enabled.
  49        DRM     Direct Rendering Management support is enabled.
  50        DYNAMIC_DEBUG Build in debug messages and enable them at runtime
  51        EDD     BIOS Enhanced Disk Drive Services (EDD) is enabled
  52        EFI     EFI Partitioning (GPT) is enabled
  53        EIDE    EIDE/ATAPI support is enabled.
  54        EVM     Extended Verification Module
  55        FB      The frame buffer device is enabled.
  56        FTRACE  Function tracing enabled.
  57        GCOV    GCOV profiling is enabled.
  58        HW      Appropriate hardware is enabled.
  59        IA-64   IA-64 architecture is enabled.
  60        IMA     Integrity measurement architecture is enabled.
  61        IOSCHED More than one I/O scheduler is enabled.
  62        IP_PNP  IP DHCP, BOOTP, or RARP is enabled.
  63        IPV6    IPv6 support is enabled.
  64        ISAPNP  ISA PnP code is enabled.
  65        ISDN    Appropriate ISDN support is enabled.
  66        JOY     Appropriate joystick support is enabled.
  67        KGDB    Kernel debugger support is enabled.
  68        KVM     Kernel Virtual Machine support is enabled.
  69        LIBATA  Libata driver is enabled
  70        LP      Printer support is enabled.
  71        LOOP    Loopback device support is enabled.
  72        M68k    M68k architecture is enabled.
  73                        These options have more detailed description inside of
  74                        Documentation/m68k/kernel-options.txt.
  75        MDA     MDA console support is enabled.
  76        MIPS    MIPS architecture is enabled.
  77        MOUSE   Appropriate mouse support is enabled.
  78        MSI     Message Signaled Interrupts (PCI).
  79        MTD     MTD (Memory Technology Device) support is enabled.
  80        NET     Appropriate network support is enabled.
  81        NUMA    NUMA support is enabled.
  82        NFS     Appropriate NFS support is enabled.
  83        OSS     OSS sound support is enabled.
  84        PV_OPS  A paravirtualized kernel is enabled.
  85        PARIDE  The ParIDE (parallel port IDE) subsystem is enabled.
  86        PARISC  The PA-RISC architecture is enabled.
  87        PCI     PCI bus support is enabled.
  88        PCIE    PCI Express support is enabled.
  89        PCMCIA  The PCMCIA subsystem is enabled.
  90        PNP     Plug & Play support is enabled.
  91        PPC     PowerPC architecture is enabled.
  92        PPT     Parallel port support is enabled.
  93        PS2     Appropriate PS/2 support is enabled.
  94        RAM     RAM disk support is enabled.
  95        S390    S390 architecture is enabled.
  96        SCSI    Appropriate SCSI support is enabled.
  97                        A lot of drivers have their options described inside
  98                        the Documentation/scsi/ sub-directory.
  99        SECURITY Different security models are enabled.
 100        SELINUX SELinux support is enabled.
 101        APPARMOR AppArmor support is enabled.
 102        SERIAL  Serial support is enabled.
 103        SH      SuperH architecture is enabled.
 104        SMP     The kernel is an SMP kernel.
 105        SPARC   Sparc architecture is enabled.
 106        SWSUSP  Software suspend (hibernation) is enabled.
 107        SUSPEND System suspend states are enabled.
 108        TPM     TPM drivers are enabled.
 109        TS      Appropriate touchscreen support is enabled.
 110        UMS     USB Mass Storage support is enabled.
 111        USB     USB support is enabled.
 112        USBHID  USB Human Interface Device support is enabled.
 113        V4L     Video For Linux support is enabled.
 114        VMMIO   Driver for memory mapped virtio devices is enabled.
 115        VGA     The VGA console has been enabled.
 116        VT      Virtual terminal support is enabled.
 117        WDT     Watchdog support is enabled.
 118        XT      IBM PC/XT MFM hard disk support is enabled.
 119        X86-32  X86-32, aka i386 architecture is enabled.
 120        X86-64  X86-64 architecture is enabled.
 121                        More X86-64 boot options can be found in
 122                        Documentation/x86/x86_64/boot-options.txt .
 123        X86     Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
 124        XEN     Xen support is enabled
 125
 126In addition, the following text indicates that the option:
 127
 128        BUGS=   Relates to possible processor bugs on the said processor.
 129        KNL     Is a kernel start-up parameter.
 130        BOOT    Is a boot loader parameter.
 131
 132Parameters denoted with BOOT are actually interpreted by the boot
 133loader, and have no meaning to the kernel directly.
 134Do not modify the syntax of boot loader parameters without extreme
 135need or coordination with <Documentation/x86/boot.txt>.
 136
 137There are also arch-specific kernel-parameters not documented here.
 138See for example <Documentation/x86/x86_64/boot-options.txt>.
 139
 140Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
 141a trailing = on the name of any parameter states that that parameter will
 142be entered as an environment variable, whereas its absence indicates that
 143it will appear as a kernel argument readable via /proc/cmdline by programs
 144running once the system is up.
 145
 146The number of kernel parameters is not limited, but the length of the
 147complete command line (parameters including spaces etc.) is limited to
 148a fixed number of characters. This limit depends on the architecture
 149and is between 256 and 4096 characters. It is defined in the file
 150./include/asm/setup.h as COMMAND_LINE_SIZE.
 151
 152Finally, the [KMG] suffix is commonly described after a number of kernel
 153parameter values. These 'K', 'M', and 'G' letters represent the _binary_
 154multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
 155bytes respectively. Such letter suffixes can also be entirely omitted.
 156
 157
 158        acpi=           [HW,ACPI,X86]
 159                        Advanced Configuration and Power Interface
 160                        Format: { force | off | strict | noirq | rsdt }
 161                        force -- enable ACPI if default was off
 162                        off -- disable ACPI if default was on
 163                        noirq -- do not use ACPI for IRQ routing
 164                        strict -- Be less tolerant of platforms that are not
 165                                strictly ACPI specification compliant.
 166                        rsdt -- prefer RSDT over (default) XSDT
 167                        copy_dsdt -- copy DSDT to memory
 168
 169                        See also Documentation/power/runtime_pm.txt, pci=noacpi
 170
 171        acpi_rsdp=      [ACPI,EFI,KEXEC]
 172                        Pass the RSDP address to the kernel, mostly used
 173                        on machines running EFI runtime service to boot the
 174                        second kernel for kdump.
 175
 176        acpi_apic_instance=     [ACPI, IOAPIC]
 177                        Format: <int>
 178                        2: use 2nd APIC table, if available
 179                        1,0: use 1st APIC table
 180                        default: 0
 181
 182        acpi_backlight= [HW,ACPI]
 183                        acpi_backlight=vendor
 184                        acpi_backlight=video
 185                        If set to vendor, prefer vendor specific driver
 186                        (e.g. thinkpad_acpi, sony_acpi, etc.) instead
 187                        of the ACPI video.ko driver.
 188
 189        acpi.debug_layer=       [HW,ACPI,ACPI_DEBUG]
 190        acpi.debug_level=       [HW,ACPI,ACPI_DEBUG]
 191                        Format: <int>
 192                        CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
 193                        debug output.  Bits in debug_layer correspond to a
 194                        _COMPONENT in an ACPI source file, e.g.,
 195                            #define _COMPONENT ACPI_PCI_COMPONENT
 196                        Bits in debug_level correspond to a level in
 197                        ACPI_DEBUG_PRINT statements, e.g.,
 198                            ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
 199                        The debug_level mask defaults to "info".  See
 200                        Documentation/acpi/debug.txt for more information about
 201                        debug layers and levels.
 202
 203                        Enable processor driver info messages:
 204                            acpi.debug_layer=0x20000000
 205                        Enable PCI/PCI interrupt routing info messages:
 206                            acpi.debug_layer=0x400000
 207                        Enable AML "Debug" output, i.e., stores to the Debug
 208                        object while interpreting AML:
 209                            acpi.debug_layer=0xffffffff acpi.debug_level=0x2
 210                        Enable all messages related to ACPI hardware:
 211                            acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
 212
 213                        Some values produce so much output that the system is
 214                        unusable.  The "log_buf_len" parameter may be useful
 215                        if you need to capture more output.
 216
 217        acpi_irq_balance [HW,ACPI]
 218                        ACPI will balance active IRQs
 219                        default in APIC mode
 220
 221        acpi_irq_nobalance [HW,ACPI]
 222                        ACPI will not move active IRQs (default)
 223                        default in PIC mode
 224
 225        acpi_irq_isa=   [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
 226                        Format: <irq>,<irq>...
 227
 228        acpi_irq_pci=   [HW,ACPI] If irq_balance, clear listed IRQs for
 229                        use by PCI
 230                        Format: <irq>,<irq>...
 231
 232        acpi_no_auto_ssdt       [HW,ACPI] Disable automatic loading of SSDT
 233
 234        acpi_os_name=   [HW,ACPI] Tell ACPI BIOS the name of the OS
 235                        Format: To spoof as Windows 98: ="Microsoft Windows"
 236
 237        acpi_osi=       [HW,ACPI] Modify list of supported OS interface strings
 238                        acpi_osi="string1"      # add string1 -- only one string
 239                        acpi_osi="!string2"     # remove built-in string2
 240                        acpi_osi=               # disable all strings
 241
 242        acpi_pm_good    [X86]
 243                        Override the pmtimer bug detection: force the kernel
 244                        to assume that this machine's pmtimer latches its value
 245                        and always returns good values.
 246
 247        acpi_sci=       [HW,ACPI] ACPI System Control Interrupt trigger mode
 248                        Format: { level | edge | high | low }
 249
 250        acpi_serialize  [HW,ACPI] force serialization of AML methods
 251
 252        acpi_skip_timer_override [HW,ACPI]
 253                        Recognize and ignore IRQ0/pin2 Interrupt Override.
 254                        For broken nForce2 BIOS resulting in XT-PIC timer.
 255
 256        acpi_sleep=     [HW,ACPI] Sleep options
 257                        Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
 258                                  old_ordering, nonvs, sci_force_enable }
 259                        See Documentation/power/video.txt for information on
 260                        s3_bios and s3_mode.
 261                        s3_beep is for debugging; it makes the PC's speaker beep
 262                        as soon as the kernel's real-mode entry point is called.
 263                        s4_nohwsig prevents ACPI hardware signature from being
 264                        used during resume from hibernation.
 265                        old_ordering causes the ACPI 1.0 ordering of the _PTS
 266                        control method, with respect to putting devices into
 267                        low power states, to be enforced (the ACPI 2.0 ordering
 268                        of _PTS is used by default).
 269                        nonvs prevents the kernel from saving/restoring the
 270                        ACPI NVS memory during suspend/hibernation and resume.
 271                        sci_force_enable causes the kernel to set SCI_EN directly
 272                        on resume from S1/S3 (which is against the ACPI spec,
 273                        but some broken systems don't work without it).
 274
 275        acpi_use_timer_override [HW,ACPI]
 276                        Use timer override. For some broken Nvidia NF5 boards
 277                        that require a timer override, but don't have HPET
 278
 279        acpi_enforce_resources= [ACPI]
 280                        { strict | lax | no }
 281                        Check for resource conflicts between native drivers
 282                        and ACPI OperationRegions (SystemIO and SystemMemory
 283                        only). IO ports and memory declared in ACPI might be
 284                        used by the ACPI subsystem in arbitrary AML code and
 285                        can interfere with legacy drivers.
 286                        strict (default): access to resources claimed by ACPI
 287                        is denied; legacy drivers trying to access reserved
 288                        resources will fail to bind to device using them.
 289                        lax: access to resources claimed by ACPI is allowed;
 290                        legacy drivers trying to access reserved resources
 291                        will bind successfully but a warning message is logged.
 292                        no: ACPI OperationRegions are not marked as reserved,
 293                        no further checks are performed.
 294
 295        add_efi_memmap  [EFI; X86] Include EFI memory map in
 296                        kernel's map of available physical RAM.
 297
 298        agp=            [AGP]
 299                        { off | try_unsupported }
 300                        off: disable AGP support
 301                        try_unsupported: try to drive unsupported chipsets
 302                                (may crash computer or cause data corruption)
 303
 304        ALSA            [HW,ALSA]
 305                        See Documentation/sound/alsa/alsa-parameters.txt
 306
 307        alignment=      [KNL,ARM]
 308                        Allow the default userspace alignment fault handler
 309                        behaviour to be specified.  Bit 0 enables warnings,
 310                        bit 1 enables fixups, and bit 2 sends a segfault.
 311
 312        align_va_addr=  [X86-64]
 313                        Align virtual addresses by clearing slice [14:12] when
 314                        allocating a VMA at process creation time. This option
 315                        gives you up to 3% performance improvement on AMD F15h
 316                        machines (where it is enabled by default) for a
 317                        CPU-intensive style benchmark, and it can vary highly in
 318                        a microbenchmark depending on workload and compiler.
 319
 320                        32: only for 32-bit processes
 321                        64: only for 64-bit processes
 322                        on: enable for both 32- and 64-bit processes
 323                        off: disable for both 32- and 64-bit processes
 324
 325        alloc_snapshot  [FTRACE]
 326                        Allocate the ftrace snapshot buffer on boot up when the
 327                        main buffer is allocated. This is handy if debugging
 328                        and you need to use tracing_snapshot() on boot up, and
 329                        do not want to use tracing_snapshot_alloc() as it needs
 330                        to be done where GFP_KERNEL allocations are allowed.
 331
 332        amd_iommu=      [HW,X86-64]
 333                        Pass parameters to the AMD IOMMU driver in the system.
 334                        Possible values are:
 335                        fullflush - enable flushing of IO/TLB entries when
 336                                    they are unmapped. Otherwise they are
 337                                    flushed before they will be reused, which
 338                                    is a lot of faster
 339                        off       - do not initialize any AMD IOMMU found in
 340                                    the system
 341                        force_isolation - Force device isolation for all
 342                                          devices. The IOMMU driver is not
 343                                          allowed anymore to lift isolation
 344                                          requirements as needed. This option
 345                                          does not override iommu=pt
 346
 347        amd_iommu_dump= [HW,X86-64]
 348                        Enable AMD IOMMU driver option to dump the ACPI table
 349                        for AMD IOMMU. With this option enabled, AMD IOMMU
 350                        driver will print ACPI tables for AMD IOMMU during
 351                        IOMMU initialization.
 352
 353        amijoy.map=     [HW,JOY] Amiga joystick support
 354                        Map of devices attached to JOY0DAT and JOY1DAT
 355                        Format: <a>,<b>
 356                        See also Documentation/input/joystick.txt
 357
 358        analog.map=     [HW,JOY] Analog joystick and gamepad support
 359                        Specifies type or capabilities of an analog joystick
 360                        connected to one of 16 gameports
 361                        Format: <type1>,<type2>,..<type16>
 362
 363        apc=            [HW,SPARC]
 364                        Power management functions (SPARCstation-4/5 + deriv.)
 365                        Format: noidle
 366                        Disable APC CPU standby support. SPARCstation-Fox does
 367                        not play well with APC CPU idle - disable it if you have
 368                        APC and your system crashes randomly.
 369
 370        apic=           [APIC,X86-32] Advanced Programmable Interrupt Controller
 371                        Change the output verbosity whilst booting
 372                        Format: { quiet (default) | verbose | debug }
 373                        Change the amount of debugging information output
 374                        when initialising the APIC and IO-APIC components.
 375
 376        autoconf=       [IPV6]
 377                        See Documentation/networking/ipv6.txt.
 378
 379        show_lapic=     [APIC,X86] Advanced Programmable Interrupt Controller
 380                        Limit apic dumping. The parameter defines the maximal
 381                        number of local apics being dumped. Also it is possible
 382                        to set it to "all" by meaning -- no limit here.
 383                        Format: { 1 (default) | 2 | ... | all }.
 384                        The parameter valid if only apic=debug or
 385                        apic=verbose is specified.
 386                        Example: apic=debug show_lapic=all
 387
 388        apm=            [APM] Advanced Power Management
 389                        See header of arch/x86/kernel/apm_32.c.
 390
 391        arcrimi=        [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
 392                        Format: <io>,<irq>,<nodeID>
 393
 394        ataflop=        [HW,M68k]
 395
 396        atarimouse=     [HW,MOUSE] Atari Mouse
 397
 398        atkbd.extra=    [HW] Enable extra LEDs and keys on IBM RapidAccess,
 399                        EzKey and similar keyboards
 400
 401        atkbd.reset=    [HW] Reset keyboard during initialization
 402
 403        atkbd.set=      [HW] Select keyboard code set
 404                        Format: <int> (2 = AT (default), 3 = PS/2)
 405
 406        atkbd.scroll=   [HW] Enable scroll wheel on MS Office and similar
 407                        keyboards
 408
 409        atkbd.softraw=  [HW] Choose between synthetic and real raw mode
 410                        Format: <bool> (0 = real, 1 = synthetic (default))
 411
 412        atkbd.softrepeat= [HW]
 413                        Use software keyboard repeat
 414
 415        baycom_epp=     [HW,AX25]
 416                        Format: <io>,<mode>
 417
 418        baycom_par=     [HW,AX25] BayCom Parallel Port AX.25 Modem
 419                        Format: <io>,<mode>
 420                        See header of drivers/net/hamradio/baycom_par.c.
 421
 422        baycom_ser_fdx= [HW,AX25]
 423                        BayCom Serial Port AX.25 Modem (Full Duplex Mode)
 424                        Format: <io>,<irq>,<mode>[,<baud>]
 425                        See header of drivers/net/hamradio/baycom_ser_fdx.c.
 426
 427        baycom_ser_hdx= [HW,AX25]
 428                        BayCom Serial Port AX.25 Modem (Half Duplex Mode)
 429                        Format: <io>,<irq>,<mode>
 430                        See header of drivers/net/hamradio/baycom_ser_hdx.c.
 431
 432        boot_delay=     Milliseconds to delay each printk during boot.
 433                        Values larger than 10 seconds (10000) are changed to
 434                        no delay (0).
 435                        Format: integer
 436
 437        bootmem_debug   [KNL] Enable bootmem allocator debug messages.
 438
 439        bttv.card=      [HW,V4L] bttv (bt848 + bt878 based grabber cards)
 440        bttv.radio=     Most important insmod options are available as
 441                        kernel args too.
 442        bttv.pll=       See Documentation/video4linux/bttv/Insmod-options
 443        bttv.tuner=
 444
 445        bulk_remove=off [PPC]  This parameter disables the use of the pSeries
 446                        firmware feature for flushing multiple hpte entries
 447                        at a time.
 448
 449        c101=           [NET] Moxa C101 synchronous serial card
 450
 451        cachesize=      [BUGS=X86-32] Override level 2 CPU cache size detection.
 452                        Sometimes CPU hardware bugs make them report the cache
 453                        size incorrectly. The kernel will attempt work arounds
 454                        to fix known problems, but for some CPUs it is not
 455                        possible to determine what the correct size should be.
 456                        This option provides an override for these situations.
 457
 458        ccw_timeout_log [S390]
 459                        See Documentation/s390/CommonIO for details.
 460
 461        cgroup_disable= [KNL] Disable a particular controller
 462                        Format: {name of the controller(s) to disable}
 463                                {Currently supported controllers - "memory"}
 464
 465        checkreqprot    [SELINUX] Set initial checkreqprot flag value.
 466                        Format: { "0" | "1" }
 467                        See security/selinux/Kconfig help text.
 468                        0 -- check protection applied by kernel (includes
 469                                any implied execute protection).
 470                        1 -- check protection requested by application.
 471                        Default value is set via a kernel config option.
 472                        Value can be changed at runtime via
 473                                /selinux/checkreqprot.
 474
 475        cio_ignore=     [S390]
 476                        See Documentation/s390/CommonIO for details.
 477        clk_ignore_unused
 478                        [CLK]
 479                        Keep all clocks already enabled by bootloader on,
 480                        even if no driver has claimed them. This is useful
 481                        for debug and development, but should not be
 482                        needed on a platform with proper driver support.
 483                        For more information, see Documentation/clk.txt.
 484
 485        clock=          [BUGS=X86-32, HW] gettimeofday clocksource override.
 486                        [Deprecated]
 487                        Forces specified clocksource (if available) to be used
 488                        when calculating gettimeofday(). If specified
 489                        clocksource is not available, it defaults to PIT.
 490                        Format: { pit | tsc | cyclone | pmtmr }
 491
 492        clocksource=    Override the default clocksource
 493                        Format: <string>
 494                        Override the default clocksource and use the clocksource
 495                        with the name specified.
 496                        Some clocksource names to choose from, depending on
 497                        the platform:
 498                        [all] jiffies (this is the base, fallback clocksource)
 499                        [ACPI] acpi_pm
 500                        [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
 501                                pxa_timer,timer3,32k_counter,timer0_1
 502                        [AVR32] avr32
 503                        [X86-32] pit,hpet,tsc;
 504                                scx200_hrt on Geode; cyclone on IBM x440
 505                        [MIPS] MIPS
 506                        [PARISC] cr16
 507                        [S390] tod
 508                        [SH] SuperH
 509                        [SPARC64] tick
 510                        [X86-64] hpet,tsc
 511
 512        clearcpuid=BITNUM [X86]
 513                        Disable CPUID feature X for the kernel. See
 514                        arch/x86/include/asm/cpufeature.h for the valid bit
 515                        numbers. Note the Linux specific bits are not necessarily
 516                        stable over kernel options, but the vendor specific
 517                        ones should be.
 518                        Also note that user programs calling CPUID directly
 519                        or using the feature without checking anything
 520                        will still see it. This just prevents it from
 521                        being used by the kernel or shown in /proc/cpuinfo.
 522                        Also note the kernel might malfunction if you disable
 523                        some critical bits.
 524
 525        cma=nn[MG]      [ARM,KNL]
 526                        Sets the size of kernel global memory area for contiguous
 527                        memory allocations. For more information, see
 528                        include/linux/dma-contiguous.h
 529
 530        cmo_free_hint=  [PPC] Format: { yes | no }
 531                        Specify whether pages are marked as being inactive
 532                        when they are freed.  This is used in CMO environments
 533                        to determine OS memory pressure for page stealing by
 534                        a hypervisor.
 535                        Default: yes
 536
 537        coherent_pool=nn[KMG]   [ARM,KNL]
 538                        Sets the size of memory pool for coherent, atomic dma
 539                        allocations, by default set to 256K.
 540
 541        code_bytes      [X86] How many bytes of object code to print
 542                        in an oops report.
 543                        Range: 0 - 8192
 544                        Default: 64
 545
 546        com20020=       [HW,NET] ARCnet - COM20020 chipset
 547                        Format:
 548                        <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
 549
 550        com90io=        [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
 551                        Format: <io>[,<irq>]
 552
 553        com90xx=        [HW,NET]
 554                        ARCnet - COM90xx chipset (memory-mapped buffers)
 555                        Format: <io>[,<irq>[,<memstart>]]
 556
 557        condev=         [HW,S390] console device
 558        conmode=
 559
 560        console=        [KNL] Output console device and options.
 561
 562                tty<n>  Use the virtual console device <n>.
 563
 564                ttyS<n>[,options]
 565                ttyUSB0[,options]
 566                        Use the specified serial port.  The options are of
 567                        the form "bbbbpnf", where "bbbb" is the baud rate,
 568                        "p" is parity ("n", "o", or "e"), "n" is number of
 569                        bits, and "f" is flow control ("r" for RTS or
 570                        omit it).  Default is "9600n8".
 571
 572                        See Documentation/serial-console.txt for more
 573                        information.  See
 574                        Documentation/networking/netconsole.txt for an
 575                        alternative.
 576
 577                uart[8250],io,<addr>[,options]
 578                uart[8250],mmio,<addr>[,options]
 579                        Start an early, polled-mode console on the 8250/16550
 580                        UART at the specified I/O port or MMIO address,
 581                        switching to the matching ttyS device later.  The
 582                        options are the same as for ttyS, above.
 583                hvc<n>  Use the hypervisor console device <n>. This is for
 584                        both Xen and PowerPC hypervisors.
 585
 586                If the device connected to the port is not a TTY but a braille
 587                device, prepend "brl," before the device type, for instance
 588                        console=brl,ttyS0
 589                For now, only VisioBraille is supported.
 590
 591        consoleblank=   [KNL] The console blank (screen saver) timeout in
 592                        seconds. Defaults to 10*60 = 10mins. A value of 0
 593                        disables the blank timer.
 594
 595        coredump_filter=
 596                        [KNL] Change the default value for
 597                        /proc/<pid>/coredump_filter.
 598                        See also Documentation/filesystems/proc.txt.
 599
 600        cpuidle.off=1   [CPU_IDLE]
 601                        disable the cpuidle sub-system
 602
 603        cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
 604                        Format:
 605                        <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
 606
 607        crashkernel=size[KMG][@offset[KMG]]
 608                        [KNL] Using kexec, Linux can switch to a 'crash kernel'
 609                        upon panic. This parameter reserves the physical
 610                        memory region [offset, offset + size] for that kernel
 611                        image. If '@offset' is omitted, then a suitable offset
 612                        is selected automatically. Check
 613                        Documentation/kdump/kdump.txt for further details.
 614
 615        crashkernel=range1:size1[,range2:size2,...][@offset]
 616                        [KNL] Same as above, but depends on the memory
 617                        in the running system. The syntax of range is
 618                        start-[end] where start and end are both
 619                        a memory unit (amount[KMG]). See also
 620                        Documentation/kdump/kdump.txt for an example.
 621
 622        crashkernel=size[KMG],high
 623                        [KNL, x86_64] range could be above 4G. Allow kernel
 624                        to allocate physical memory region from top, so could
 625                        be above 4G if system have more than 4G ram installed.
 626                        Otherwise memory region will be allocated below 4G, if
 627                        available.
 628                        It will be ignored if crashkernel=X is specified.
 629        crashkernel=size[KMG],low
 630                        [KNL, x86_64] range under 4G. When crashkernel=X,high
 631                        is passed, kernel could allocate physical memory region
 632                        above 4G, that cause second kernel crash on system
 633                        that require some amount of low memory, e.g. swiotlb
 634                        requires at least 64M+32K low memory.  Kernel would
 635                        try to allocate 72M below 4G automatically.
 636                        This one let user to specify own low range under 4G
 637                        for second kernel instead.
 638                        0: to disable low allocation.
 639                        It will be ignored when crashkernel=X,high is not used
 640                        or memory reserved is below 4G.
 641
 642        cs89x0_dma=     [HW,NET]
 643                        Format: <dma>
 644
 645        cs89x0_media=   [HW,NET]
 646                        Format: { rj45 | aui | bnc }
 647
 648        dasd=           [HW,NET]
 649                        See header of drivers/s390/block/dasd_devmap.c.
 650
 651        db9.dev[2|3]=   [HW,JOY] Multisystem joystick support via parallel port
 652                        (one device per port)
 653                        Format: <port#>,<type>
 654                        See also Documentation/input/joystick-parport.txt
 655
 656        ddebug_query=   [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
 657                        time. See Documentation/dynamic-debug-howto.txt for
 658                        details.  Deprecated, see dyndbg.
 659
 660        debug           [KNL] Enable kernel debugging (events log level).
 661
 662        debug_locks_verbose=
 663                        [KNL] verbose self-tests
 664                        Format=<0|1>
 665                        Print debugging info while doing the locking API
 666                        self-tests.
 667                        We default to 0 (no extra messages), setting it to
 668                        1 will print _a lot_ more information - normally
 669                        only useful to kernel developers.
 670
 671        debug_objects   [KNL] Enable object debugging
 672
 673        no_debug_objects
 674                        [KNL] Disable object debugging
 675
 676        debug_guardpage_minorder=
 677                        [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
 678                        parameter allows control of the order of pages that will
 679                        be intentionally kept free (and hence protected) by the
 680                        buddy allocator. Bigger value increase the probability
 681                        of catching random memory corruption, but reduce the
 682                        amount of memory for normal system use. The maximum
 683                        possible value is MAX_ORDER/2.  Setting this parameter
 684                        to 1 or 2 should be enough to identify most random
 685                        memory corruption problems caused by bugs in kernel or
 686                        driver code when a CPU writes to (or reads from) a
 687                        random memory location. Note that there exists a class
 688                        of memory corruptions problems caused by buggy H/W or
 689                        F/W or by drivers badly programing DMA (basically when
 690                        memory is written at bus level and the CPU MMU is
 691                        bypassed) which are not detectable by
 692                        CONFIG_DEBUG_PAGEALLOC, hence this option will not help
 693                        tracking down these problems.
 694
 695        debugpat        [X86] Enable PAT debugging
 696
 697        decnet.addr=    [HW,NET]
 698                        Format: <area>[,<node>]
 699                        See also Documentation/networking/decnet.txt.
 700
 701        default_hugepagesz=
 702                        [same as hugepagesz=] The size of the default
 703                        HugeTLB page size. This is the size represented by
 704                        the legacy /proc/ hugepages APIs, used for SHM, and
 705                        default size when mounting hugetlbfs filesystems.
 706                        Defaults to the default architecture's huge page size
 707                        if not specified.
 708
 709        dhash_entries=  [KNL]
 710                        Set number of hash buckets for dentry cache.
 711
 712        digi=           [HW,SERIAL]
 713                        IO parameters + enable/disable command.
 714
 715        digiepca=       [HW,SERIAL]
 716                        See drivers/char/README.epca and
 717                        Documentation/serial/digiepca.txt.
 718
 719        disable=        [IPV6]
 720                        See Documentation/networking/ipv6.txt.
 721
 722        disable_ddw     [PPC/PSERIES]
 723                        Disable Dynamic DMA Window support. Use this if
 724                        to workaround buggy firmware.
 725
 726        disable_ipv6=   [IPV6]
 727                        See Documentation/networking/ipv6.txt.
 728
 729        disable_mtrr_cleanup [X86]
 730                        The kernel tries to adjust MTRR layout from continuous
 731                        to discrete, to make X server driver able to add WB
 732                        entry later. This parameter disables that.
 733
 734        disable_mtrr_trim [X86, Intel and AMD only]
 735                        By default the kernel will trim any uncacheable
 736                        memory out of your available memory pool based on
 737                        MTRR settings.  This parameter disables that behavior,
 738                        possibly causing your machine to run very slowly.
 739
 740        disable_timer_pin_1 [X86]
 741                        Disable PIN 1 of APIC timer
 742                        Can be useful to work around chipset bugs.
 743
 744        dma_debug=off   If the kernel is compiled with DMA_API_DEBUG support,
 745                        this option disables the debugging code at boot.
 746
 747        dma_debug_entries=<number>
 748                        This option allows to tune the number of preallocated
 749                        entries for DMA-API debugging code. One entry is
 750                        required per DMA-API allocation. Use this if the
 751                        DMA-API debugging code disables itself because the
 752                        architectural default is too low.
 753
 754        dma_debug_driver=<driver_name>
 755                        With this option the DMA-API debugging driver
 756                        filter feature can be enabled at boot time. Just
 757                        pass the driver to filter for as the parameter.
 758                        The filter can be disabled or changed to another
 759                        driver later using sysfs.
 760
 761        drm_kms_helper.edid_firmware=[<connector>:]<file>
 762                        Broken monitors, graphic adapters and KVMs may
 763                        send no or incorrect EDID data sets. This parameter
 764                        allows to specify an EDID data set in the
 765                        /lib/firmware directory that is used instead.
 766                        Generic built-in EDID data sets are used, if one of
 767                        edid/1024x768.bin, edid/1280x1024.bin,
 768                        edid/1680x1050.bin, or edid/1920x1080.bin is given
 769                        and no file with the same name exists. Details and
 770                        instructions how to build your own EDID data are
 771                        available in Documentation/EDID/HOWTO.txt. An EDID
 772                        data set will only be used for a particular connector,
 773                        if its name and a colon are prepended to the EDID
 774                        name.
 775
 776        dscc4.setup=    [NET]
 777
 778        dyndbg[="val"]          [KNL,DYNAMIC_DEBUG]
 779        module.dyndbg[="val"]
 780                        Enable debug messages at boot time.  See
 781                        Documentation/dynamic-debug-howto.txt for details.
 782
 783        earlycon=       [KNL] Output early console device and options.
 784                uart[8250],io,<addr>[,options]
 785                uart[8250],mmio,<addr>[,options]
 786                uart[8250],mmio32,<addr>[,options]
 787                        Start an early, polled-mode console on the 8250/16550
 788                        UART at the specified I/O port or MMIO address.
 789                        MMIO inter-register address stride is either 8-bit
 790                        (mmio) or 32-bit (mmio32).
 791                        The options are the same as for ttyS, above.
 792
 793        earlyprintk=    [X86,SH,BLACKFIN,ARM]
 794                        earlyprintk=vga
 795                        earlyprintk=xen
 796                        earlyprintk=serial[,ttySn[,baudrate]]
 797                        earlyprintk=serial[,0x...[,baudrate]]
 798                        earlyprintk=ttySn[,baudrate]
 799                        earlyprintk=dbgp[debugController#]
 800
 801                        earlyprintk is useful when the kernel crashes before
 802                        the normal console is initialized. It is not enabled by
 803                        default because it has some cosmetic problems.
 804
 805                        Append ",keep" to not disable it when the real console
 806                        takes over.
 807
 808                        Only vga or serial or usb debug port at a time.
 809
 810                        Currently only ttyS0 and ttyS1 may be specified by
 811                        name.  Other I/O ports may be explicitly specified
 812                        on some architectures (x86 and arm at least) by
 813                        replacing ttySn with an I/O port address, like this:
 814                                earlyprintk=serial,0x1008,115200
 815                        You can find the port for a given device in
 816                        /proc/tty/driver/serial:
 817                                2: uart:ST16650V2 port:00001008 irq:18 ...
 818
 819                        Interaction with the standard serial driver is not
 820                        very good.
 821
 822                        The VGA output is eventually overwritten by the real
 823                        console.
 824
 825                        The xen output can only be used by Xen PV guests.
 826
 827        ekgdboc=        [X86,KGDB] Allow early kernel console debugging
 828                        ekgdboc=kbd
 829
 830                        This is designed to be used in conjunction with
 831                        the boot argument: earlyprintk=vga
 832
 833        edd=            [EDD]
 834                        Format: {"off" | "on" | "skip[mbr]"}
 835
 836        efi_no_storage_paranoia [EFI; X86]
 837                        Using this parameter you can use more than 50% of
 838                        your efi variable storage. Use this parameter only if
 839                        you are really sure that your UEFI does sane gc and
 840                        fulfills the spec otherwise your board may brick.
 841
 842        eisa_irq_edge=  [PARISC,HW]
 843                        See header of drivers/parisc/eisa.c.
 844
 845        elanfreq=       [X86-32]
 846                        See comment before function elanfreq_setup() in
 847                        arch/x86/kernel/cpu/cpufreq/elanfreq.c.
 848
 849        elevator=       [IOSCHED]
 850                        Format: {"cfq" | "deadline" | "noop"}
 851                        See Documentation/block/cfq-iosched.txt and
 852                        Documentation/block/deadline-iosched.txt for details.
 853
 854        elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
 855                        Specifies physical address of start of kernel core
 856                        image elf header and optionally the size. Generally
 857                        kexec loader will pass this option to capture kernel.
 858                        See Documentation/kdump/kdump.txt for details.
 859
 860        enable_mtrr_cleanup [X86]
 861                        The kernel tries to adjust MTRR layout from continuous
 862                        to discrete, to make X server driver able to add WB
 863                        entry later. This parameter enables that.
 864
 865        enable_timer_pin_1 [X86]
 866                        Enable PIN 1 of APIC timer
 867                        Can be useful to work around chipset bugs
 868                        (in particular on some ATI chipsets).
 869                        The kernel tries to set a reasonable default.
 870
 871        enforcing       [SELINUX] Set initial enforcing status.
 872                        Format: {"0" | "1"}
 873                        See security/selinux/Kconfig help text.
 874                        0 -- permissive (log only, no denials).
 875                        1 -- enforcing (deny and log).
 876                        Default value is 0.
 877                        Value can be changed at runtime via /selinux/enforce.
 878
 879        erst_disable    [ACPI]
 880                        Disable Error Record Serialization Table (ERST)
 881                        support.
 882
 883        ether=          [HW,NET] Ethernet cards parameters
 884                        This option is obsoleted by the "netdev=" option, which
 885                        has equivalent usage. See its documentation for details.
 886
 887        evm=            [EVM]
 888                        Format: { "fix" }
 889                        Permit 'security.evm' to be updated regardless of
 890                        current integrity status.
 891
 892        failslab=
 893        fail_page_alloc=
 894        fail_make_request=[KNL]
 895                        General fault injection mechanism.
 896                        Format: <interval>,<probability>,<space>,<times>
 897                        See also Documentation/fault-injection/.
 898
 899        floppy=         [HW]
 900                        See Documentation/blockdev/floppy.txt.
 901
 902        force_pal_cache_flush
 903                        [IA-64] Avoid check_sal_cache_flush which may hang on
 904                        buggy SAL_CACHE_FLUSH implementations. Using this
 905                        parameter will force ia64_sal_cache_flush to call
 906                        ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
 907
 908        ftrace=[tracer]
 909                        [FTRACE] will set and start the specified tracer
 910                        as early as possible in order to facilitate early
 911                        boot debugging.
 912
 913        ftrace_dump_on_oops[=orig_cpu]
 914                        [FTRACE] will dump the trace buffers on oops.
 915                        If no parameter is passed, ftrace will dump
 916                        buffers of all CPUs, but if you pass orig_cpu, it will
 917                        dump only the buffer of the CPU that triggered the
 918                        oops.
 919
 920        ftrace_filter=[function-list]
 921                        [FTRACE] Limit the functions traced by the function
 922                        tracer at boot up. function-list is a comma separated
 923                        list of functions. This list can be changed at run
 924                        time by the set_ftrace_filter file in the debugfs
 925                        tracing directory.
 926
 927        ftrace_notrace=[function-list]
 928                        [FTRACE] Do not trace the functions specified in
 929                        function-list. This list can be changed at run time
 930                        by the set_ftrace_notrace file in the debugfs
 931                        tracing directory.
 932
 933        ftrace_graph_filter=[function-list]
 934                        [FTRACE] Limit the top level callers functions traced
 935                        by the function graph tracer at boot up.
 936                        function-list is a comma separated list of functions
 937                        that can be changed at run time by the
 938                        set_graph_function file in the debugfs tracing directory.
 939
 940        gamecon.map[2|3]=
 941                        [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
 942                        support via parallel port (up to 5 devices per port)
 943                        Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
 944                        See also Documentation/input/joystick-parport.txt
 945
 946        gamma=          [HW,DRM]
 947
 948        gart_fix_e820=  [X86_64] disable the fix e820 for K8 GART
 949                        Format: off | on
 950                        default: on
 951
 952        gcov_persist=   [GCOV] When non-zero (default), profiling data for
 953                        kernel modules is saved and remains accessible via
 954                        debugfs, even when the module is unloaded/reloaded.
 955                        When zero, profiling data is discarded and associated
 956                        debugfs files are removed at module unload time.
 957
 958        gpt             [EFI] Forces disk with valid GPT signature but
 959                        invalid Protective MBR to be treated as GPT.
 960
 961        grcan.enable0=  [HW] Configuration of physical interface 0. Determines
 962                        the "Enable 0" bit of the configuration register.
 963                        Format: 0 | 1
 964                        Default: 0
 965        grcan.enable1=  [HW] Configuration of physical interface 1. Determines
 966                        the "Enable 0" bit of the configuration register.
 967                        Format: 0 | 1
 968                        Default: 0
 969        grcan.select=   [HW] Select which physical interface to use.
 970                        Format: 0 | 1
 971                        Default: 0
 972        grcan.txsize=   [HW] Sets the size of the tx buffer.
 973                        Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
 974                        Default: 1024
 975        grcan.rxsize=   [HW] Sets the size of the rx buffer.
 976                        Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
 977                        Default: 1024
 978
 979        hashdist=       [KNL,NUMA] Large hashes allocated during boot
 980                        are distributed across NUMA nodes.  Defaults on
 981                        for 64-bit NUMA, off otherwise.
 982                        Format: 0 | 1 (for off | on)
 983
 984        hcl=            [IA-64] SGI's Hardware Graph compatibility layer
 985
 986        hd=             [EIDE] (E)IDE hard drive subsystem geometry
 987                        Format: <cyl>,<head>,<sect>
 988
 989        hest_disable    [ACPI]
 990                        Disable Hardware Error Source Table (HEST) support;
 991                        corresponding firmware-first mode error processing
 992                        logic will be disabled.
 993
 994        highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
 995                        size of <nn>. This works even on boxes that have no
 996                        highmem otherwise. This also works to reduce highmem
 997                        size on bigger boxes.
 998
 999        highres=        [KNL] Enable/disable high resolution timer mode.
1000                        Valid parameters: "on", "off"
1001                        Default: "on"
1002
1003        hisax=          [HW,ISDN]
1004                        See Documentation/isdn/README.HiSax.
1005
1006        hlt             [BUGS=ARM,SH]
1007
1008        hpet=           [X86-32,HPET] option to control HPET usage
1009                        Format: { enable (default) | disable | force |
1010                                verbose }
1011                        disable: disable HPET and use PIT instead
1012                        force: allow force enabled of undocumented chips (ICH4,
1013                                VIA, nVidia)
1014                        verbose: show contents of HPET registers during setup
1015
1016        hugepages=      [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1017        hugepagesz=     [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1018                        On x86-64 and powerpc, this option can be specified
1019                        multiple times interleaved with hugepages= to reserve
1020                        huge pages of different sizes. Valid pages sizes on
1021                        x86-64 are 2M (when the CPU supports "pse") and 1G
1022                        (when the CPU supports the "pdpe1gb" cpuinfo flag)
1023                        Note that 1GB pages can only be allocated at boot time
1024                        using hugepages= and not freed afterwards.
1025
1026        hvc_iucv=       [S390] Number of z/VM IUCV hypervisor console (HVC)
1027                               terminal devices. Valid values: 0..8
1028        hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1029                               If specified, z/VM IUCV HVC accepts connections
1030                               from listed z/VM user IDs only.
1031
1032        hwthread_map=   [METAG] Comma-separated list of Linux cpu id to
1033                                hardware thread id mappings.
1034                                Format: <cpu>:<hwthread>
1035
1036        keep_bootcon    [KNL]
1037                        Do not unregister boot console at start. This is only
1038                        useful for debugging when something happens in the window
1039                        between unregistering the boot console and initializing
1040                        the real console.
1041
1042        i2c_bus=        [HW] Override the default board specific I2C bus speed
1043                             or register an additional I2C bus that is not
1044                             registered from board initialization code.
1045                             Format:
1046                             <bus_id>,<clkrate>
1047
1048        i8042.debug     [HW] Toggle i8042 debug mode
1049        i8042.direct    [HW] Put keyboard port into non-translated mode
1050        i8042.dumbkbd   [HW] Pretend that controller can only read data from
1051                             keyboard and cannot control its state
1052                             (Don't attempt to blink the leds)
1053        i8042.noaux     [HW] Don't check for auxiliary (== mouse) port
1054        i8042.nokbd     [HW] Don't check/create keyboard port
1055        i8042.noloop    [HW] Disable the AUX Loopback command while probing
1056                             for the AUX port
1057        i8042.nomux     [HW] Don't check presence of an active multiplexing
1058                             controller
1059        i8042.nopnp     [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1060                             controllers
1061        i8042.notimeout [HW] Ignore timeout condition signalled by controller
1062        i8042.reset     [HW] Reset the controller during init and cleanup
1063        i8042.unlock    [HW] Unlock (ignore) the keylock
1064
1065        i810=           [HW,DRM]
1066
1067        i8k.ignore_dmi  [HW] Continue probing hardware even if DMI data
1068                        indicates that the driver is running on unsupported
1069                        hardware.
1070        i8k.force       [HW] Activate i8k driver even if SMM BIOS signature
1071                        does not match list of supported models.
1072        i8k.power_status
1073                        [HW] Report power status in /proc/i8k
1074                        (disabled by default)
1075        i8k.restricted  [HW] Allow controlling fans only if SYS_ADMIN
1076                        capability is set.
1077
1078        i915.invert_brightness=
1079                        [DRM] Invert the sense of the variable that is used to
1080                        set the brightness of the panel backlight. Normally a
1081                        brightness value of 0 indicates backlight switched off,
1082                        and the maximum of the brightness value sets the backlight
1083                        to maximum brightness. If this parameter is set to 0
1084                        (default) and the machine requires it, or this parameter
1085                        is set to 1, a brightness value of 0 sets the backlight
1086                        to maximum brightness, and the maximum of the brightness
1087                        value switches the backlight off.
1088                        -1 -- never invert brightness
1089                         0 -- machine default
1090                         1 -- force brightness inversion
1091
1092        icn=            [HW,ISDN]
1093                        Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1094
1095        ide-core.nodma= [HW] (E)IDE subsystem
1096                        Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1097                        .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1098                        .cdrom .chs .ignore_cable are additional options
1099                        See Documentation/ide/ide.txt.
1100
1101        ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1102                        Claim all unknown PCI IDE storage controllers.
1103
1104        idle=           [X86]
1105                        Format: idle=poll, idle=halt, idle=nomwait
1106                        Poll forces a polling idle loop that can slightly
1107                        improve the performance of waking up a idle CPU, but
1108                        will use a lot of power and make the system run hot.
1109                        Not recommended.
1110                        idle=halt: Halt is forced to be used for CPU idle.
1111                        In such case C2/C3 won't be used again.
1112                        idle=nomwait: Disable mwait for CPU C-states
1113
1114        ignore_loglevel [KNL]
1115                        Ignore loglevel setting - this will print /all/
1116                        kernel messages to the console. Useful for debugging.
1117                        We also add it as printk module parameter, so users
1118                        could change it dynamically, usually by
1119                        /sys/module/printk/parameters/ignore_loglevel.
1120
1121        ihash_entries=  [KNL]
1122                        Set number of hash buckets for inode cache.
1123
1124        ima_appraise=   [IMA] appraise integrity measurements
1125                        Format: { "off" | "enforce" | "fix" }
1126                        default: "enforce"
1127
1128        ima_appraise_tcb [IMA]
1129                        The builtin appraise policy appraises all files
1130                        owned by uid=0.
1131
1132        ima_audit=      [IMA]
1133                        Format: { "0" | "1" }
1134                        0 -- integrity auditing messages. (Default)
1135                        1 -- enable informational integrity auditing messages.
1136
1137        ima_hash=       [IMA]
1138                        Format: { "sha1" | "md5" }
1139                        default: "sha1"
1140
1141        ima_tcb         [IMA]
1142                        Load a policy which meets the needs of the Trusted
1143                        Computing Base.  This means IMA will measure all
1144                        programs exec'd, files mmap'd for exec, and all files
1145                        opened for read by uid=0.
1146
1147        init=           [KNL]
1148                        Format: <full_path>
1149                        Run specified binary instead of /sbin/init as init
1150                        process.
1151
1152        initcall_debug  [KNL] Trace initcalls as they are executed.  Useful
1153                        for working out where the kernel is dying during
1154                        startup.
1155
1156        initrd=         [BOOT] Specify the location of the initial ramdisk
1157
1158        inport.irq=     [HW] Inport (ATI XL and Microsoft) busmouse driver
1159                        Format: <irq>
1160
1161        intel_iommu=    [DMAR] Intel IOMMU driver (DMAR) option
1162                on
1163                        Enable intel iommu driver.
1164                off
1165                        Disable intel iommu driver.
1166                igfx_off [Default Off]
1167                        By default, gfx is mapped as normal device. If a gfx
1168                        device has a dedicated DMAR unit, the DMAR unit is
1169                        bypassed by not enabling DMAR with this option. In
1170                        this case, gfx device will use physical address for
1171                        DMA.
1172                forcedac [x86_64]
1173                        With this option iommu will not optimize to look
1174                        for io virtual address below 32-bit forcing dual
1175                        address cycle on pci bus for cards supporting greater
1176                        than 32-bit addressing. The default is to look
1177                        for translation below 32-bit and if not available
1178                        then look in the higher range.
1179                strict [Default Off]
1180                        With this option on every unmap_single operation will
1181                        result in a hardware IOTLB flush operation as opposed
1182                        to batching them for performance.
1183                sp_off [Default Off]
1184                        By default, super page will be supported if Intel IOMMU
1185                        has the capability. With this option, super page will
1186                        not be supported.
1187
1188        intel_idle.max_cstate=  [KNL,HW,ACPI,X86]
1189                        0       disables intel_idle and fall back on acpi_idle.
1190                        1 to 6  specify maximum depth of C-state.
1191
1192        intel_pstate=  [X86]
1193                       disable
1194                         Do not enable intel_pstate as the default
1195                         scaling driver for the supported processors
1196
1197        intremap=       [X86-64, Intel-IOMMU]
1198                        on      enable Interrupt Remapping (default)
1199                        off     disable Interrupt Remapping
1200                        nosid   disable Source ID checking
1201                        no_x2apic_optout
1202                                BIOS x2APIC opt-out request will be ignored
1203
1204        iomem=          Disable strict checking of access to MMIO memory
1205                strict  regions from userspace.
1206                relaxed
1207
1208        iommu=          [x86]
1209                off
1210                force
1211                noforce
1212                biomerge
1213                panic
1214                nopanic
1215                merge
1216                nomerge
1217                forcesac
1218                soft
1219                pt              [x86, IA-64]
1220
1221
1222        io7=            [HW] IO7 for Marvel based alpha systems
1223                        See comment before marvel_specify_io7 in
1224                        arch/alpha/kernel/core_marvel.c.
1225
1226        io_delay=       [X86] I/O delay method
1227                0x80
1228                        Standard port 0x80 based delay
1229                0xed
1230                        Alternate port 0xed based delay (needed on some systems)
1231                udelay
1232                        Simple two microseconds delay
1233                none
1234                        No delay
1235
1236        ip=             [IP_PNP]
1237                        See Documentation/filesystems/nfs/nfsroot.txt.
1238
1239        ip2=            [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1240                        See comment before ip2_setup() in
1241                        drivers/char/ip2/ip2base.c.
1242
1243        irqfixup        [HW]
1244                        When an interrupt is not handled search all handlers
1245                        for it. Intended to get systems with badly broken
1246                        firmware running.
1247
1248        irqpoll         [HW]
1249                        When an interrupt is not handled search all handlers
1250                        for it. Also check all handlers each timer
1251                        interrupt. Intended to get systems with badly broken
1252                        firmware running.
1253
1254        isapnp=         [ISAPNP]
1255                        Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1256
1257        isolcpus=       [KNL,SMP] Isolate CPUs from the general scheduler.
1258                        Format:
1259                        <cpu number>,...,<cpu number>
1260                        or
1261                        <cpu number>-<cpu number>
1262                        (must be a positive range in ascending order)
1263                        or a mixture
1264                        <cpu number>,...,<cpu number>-<cpu number>
1265
1266                        This option can be used to specify one or more CPUs
1267                        to isolate from the general SMP balancing and scheduling
1268                        algorithms. You can move a process onto or off an
1269                        "isolated" CPU via the CPU affinity syscalls or cpuset.
1270                        <cpu number> begins at 0 and the maximum value is
1271                        "number of CPUs in system - 1".
1272
1273                        This option is the preferred way to isolate CPUs. The
1274                        alternative -- manually setting the CPU mask of all
1275                        tasks in the system -- can cause problems and
1276                        suboptimal load balancer performance.
1277
1278        iucv=           [HW,NET]
1279
1280        ivrs_ioapic     [HW,X86_64]
1281                        Provide an override to the IOAPIC-ID<->DEVICE-ID
1282                        mapping provided in the IVRS ACPI table. For
1283                        example, to map IOAPIC-ID decimal 10 to
1284                        PCI device 00:14.0 write the parameter as:
1285                                ivrs_ioapic[10]=00:14.0
1286
1287        ivrs_hpet       [HW,X86_64]
1288                        Provide an override to the HPET-ID<->DEVICE-ID
1289                        mapping provided in the IVRS ACPI table. For
1290                        example, to map HPET-ID decimal 0 to
1291                        PCI device 00:14.0 write the parameter as:
1292                                ivrs_hpet[0]=00:14.0
1293
1294        js=             [HW,JOY] Analog joystick
1295                        See Documentation/input/joystick.txt.
1296
1297        keepinitrd      [HW,ARM]
1298
1299        kernelcore=nn[KMG]      [KNL,X86,IA-64,PPC] This parameter
1300                        specifies the amount of memory usable by the kernel
1301                        for non-movable allocations.  The requested amount is
1302                        spread evenly throughout all nodes in the system. The
1303                        remaining memory in each node is used for Movable
1304                        pages. In the event, a node is too small to have both
1305                        kernelcore and Movable pages, kernelcore pages will
1306                        take priority and other nodes will have a larger number
1307                        of kernelcore pages.  The Movable zone is used for the
1308                        allocation of pages that may be reclaimed or moved
1309                        by the page migration subsystem.  This means that
1310                        HugeTLB pages may not be allocated from this zone.
1311                        Note that allocations like PTEs-from-HighMem still
1312                        use the HighMem zone if it exists, and the Normal
1313                        zone if it does not.
1314
1315        kgdbdbgp=       [KGDB,HW] kgdb over EHCI usb debug port.
1316                        Format: <Controller#>[,poll interval]
1317                        The controller # is the number of the ehci usb debug
1318                        port as it is probed via PCI.  The poll interval is
1319                        optional and is the number seconds in between
1320                        each poll cycle to the debug port in case you need
1321                        the functionality for interrupting the kernel with
1322                        gdb or control-c on the dbgp connection.  When
1323                        not using this parameter you use sysrq-g to break into
1324                        the kernel debugger.
1325
1326        kgdboc=         [KGDB,HW] kgdb over consoles.
1327                        Requires a tty driver that supports console polling,
1328                        or a supported polling keyboard driver (non-usb).
1329                         Serial only format: <serial_device>[,baud]
1330                         keyboard only format: kbd
1331                         keyboard and serial format: kbd,<serial_device>[,baud]
1332                        Optional Kernel mode setting:
1333                         kms, kbd format: kms,kbd
1334                         kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1335
1336        kgdbwait        [KGDB] Stop kernel execution and enter the
1337                        kernel debugger at the earliest opportunity.
1338
1339        kmac=           [MIPS] korina ethernet MAC address.
1340                        Configure the RouterBoard 532 series on-chip
1341                        Ethernet adapter MAC address.
1342
1343        kmemleak=       [KNL] Boot-time kmemleak enable/disable
1344                        Valid arguments: on, off
1345                        Default: on
1346
1347        kstack=N        [X86] Print N words from the kernel stack
1348                        in oops dumps.
1349
1350        kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1351                        Default is 0 (don't ignore, but inject #GP)
1352
1353        kvm.mmu_audit=  [KVM] This is a R/W parameter which allows audit
1354                        KVM MMU at runtime.
1355                        Default is 0 (off)
1356
1357        kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1358                        Default is 1 (enabled)
1359
1360        kvm-amd.npt=    [KVM,AMD] Disable nested paging (virtualized MMU)
1361                        for all guests.
1362                        Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1363
1364        kvm-intel.ept=  [KVM,Intel] Disable extended page tables
1365                        (virtualized MMU) support on capable Intel chips.
1366                        Default is 1 (enabled)
1367
1368        kvm-intel.emulate_invalid_guest_state=
1369                        [KVM,Intel] Enable emulation of invalid guest states
1370                        Default is 0 (disabled)
1371
1372        kvm-intel.flexpriority=
1373                        [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1374                        Default is 1 (enabled)
1375
1376        kvm-intel.nested=
1377                        [KVM,Intel] Enable VMX nesting (nVMX).
1378                        Default is 0 (disabled)
1379
1380        kvm-intel.unrestricted_guest=
1381                        [KVM,Intel] Disable unrestricted guest feature
1382                        (virtualized real and unpaged mode) on capable
1383                        Intel chips. Default is 1 (enabled)
1384
1385        kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1386                        feature (tagged TLBs) on capable Intel chips.
1387                        Default is 1 (enabled)
1388
1389        l2cr=           [PPC]
1390
1391        l3cr=           [PPC]
1392
1393        lapic           [X86-32,APIC] Enable the local APIC even if BIOS
1394                        disabled it.
1395
1396        lapic=          [x86,APIC] "notscdeadline" Do not use TSC deadline
1397                        value for LAPIC timer one-shot implementation. Default
1398                        back to the programmable timer unit in the LAPIC.
1399
1400        lapic_timer_c2_ok       [X86,APIC] trust the local apic timer
1401                        in C2 power state.
1402
1403        libata.dma=     [LIBATA] DMA control
1404                        libata.dma=0      Disable all PATA and SATA DMA
1405                        libata.dma=1      PATA and SATA Disk DMA only
1406                        libata.dma=2      ATAPI (CDROM) DMA only
1407                        libata.dma=4      Compact Flash DMA only
1408                        Combinations also work, so libata.dma=3 enables DMA
1409                        for disks and CDROMs, but not CFs.
1410
1411        libata.ignore_hpa=      [LIBATA] Ignore HPA limit
1412                        libata.ignore_hpa=0       keep BIOS limits (default)
1413                        libata.ignore_hpa=1       ignore limits, using full disk
1414
1415        libata.noacpi   [LIBATA] Disables use of ACPI in libata suspend/resume
1416                        when set.
1417                        Format: <int>
1418
1419        libata.force=   [LIBATA] Force configurations.  The format is comma
1420                        separated list of "[ID:]VAL" where ID is
1421                        PORT[.DEVICE].  PORT and DEVICE are decimal numbers
1422                        matching port, link or device.  Basically, it matches
1423                        the ATA ID string printed on console by libata.  If
1424                        the whole ID part is omitted, the last PORT and DEVICE
1425                        values are used.  If ID hasn't been specified yet, the
1426                        configuration applies to all ports, links and devices.
1427
1428                        If only DEVICE is omitted, the parameter applies to
1429                        the port and all links and devices behind it.  DEVICE
1430                        number of 0 either selects the first device or the
1431                        first fan-out link behind PMP device.  It does not
1432                        select the host link.  DEVICE number of 15 selects the
1433                        host link and device attached to it.
1434
1435                        The VAL specifies the configuration to force.  As long
1436                        as there's no ambiguity shortcut notation is allowed.
1437                        For example, both 1.5 and 1.5G would work for 1.5Gbps.
1438                        The following configurations can be forced.
1439
1440                        * Cable type: 40c, 80c, short40c, unk, ign or sata.
1441                          Any ID with matching PORT is used.
1442
1443                        * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1444
1445                        * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1446                          udma[/][16,25,33,44,66,100,133] notation is also
1447                          allowed.
1448
1449                        * [no]ncq: Turn on or off NCQ.
1450
1451                        * nohrst, nosrst, norst: suppress hard, soft
1452                          and both resets.
1453
1454                        * rstonce: only attempt one reset during
1455                          hot-unplug link recovery
1456
1457                        * dump_id: dump IDENTIFY data.
1458
1459                        If there are multiple matching configurations changing
1460                        the same attribute, the last one is used.
1461
1462        memblock=debug  [KNL] Enable memblock debug messages.
1463
1464        load_ramdisk=   [RAM] List of ramdisks to load from floppy
1465                        See Documentation/blockdev/ramdisk.txt.
1466
1467        lockd.nlm_grace_period=P  [NFS] Assign grace period.
1468                        Format: <integer>
1469
1470        lockd.nlm_tcpport=N     [NFS] Assign TCP port.
1471                        Format: <integer>
1472
1473        lockd.nlm_timeout=T     [NFS] Assign timeout value.
1474                        Format: <integer>
1475
1476        lockd.nlm_udpport=M     [NFS] Assign UDP port.
1477                        Format: <integer>
1478
1479        logibm.irq=     [HW,MOUSE] Logitech Bus Mouse Driver
1480                        Format: <irq>
1481
1482        loglevel=       All Kernel Messages with a loglevel smaller than the
1483                        console loglevel will be printed to the console. It can
1484                        also be changed with klogd or other programs. The
1485                        loglevels are defined as follows:
1486
1487                        0 (KERN_EMERG)          system is unusable
1488                        1 (KERN_ALERT)          action must be taken immediately
1489                        2 (KERN_CRIT)           critical conditions
1490                        3 (KERN_ERR)            error conditions
1491                        4 (KERN_WARNING)        warning conditions
1492                        5 (KERN_NOTICE)         normal but significant condition
1493                        6 (KERN_INFO)           informational
1494                        7 (KERN_DEBUG)          debug-level messages
1495
1496        log_buf_len=n[KMG]      Sets the size of the printk ring buffer,
1497                        in bytes.  n must be a power of two.  The default
1498                        size is set in the kernel config file.
1499
1500        logo.nologo     [FB] Disables display of the built-in Linux logo.
1501                        This may be used to provide more screen space for
1502                        kernel log messages and is useful when debugging
1503                        kernel boot problems.
1504
1505        lp=0            [LP]    Specify parallel ports to use, e.g,
1506        lp=port[,port...]       lp=none,parport0 (lp0 not configured, lp1 uses
1507        lp=reset                first parallel port). 'lp=0' disables the
1508        lp=auto                 printer driver. 'lp=reset' (which can be
1509                                specified in addition to the ports) causes
1510                                attached printers to be reset. Using
1511                                lp=port1,port2,... specifies the parallel ports
1512                                to associate lp devices with, starting with
1513                                lp0. A port specification may be 'none' to skip
1514                                that lp device, or a parport name such as
1515                                'parport0'. Specifying 'lp=auto' instead of a
1516                                port specification list means that device IDs
1517                                from each port should be examined, to see if
1518                                an IEEE 1284-compliant printer is attached; if
1519                                so, the driver will manage that printer.
1520                                See also header of drivers/char/lp.c.
1521
1522        lpj=n           [KNL]
1523                        Sets loops_per_jiffy to given constant, thus avoiding
1524                        time-consuming boot-time autodetection (up to 250 ms per
1525                        CPU). 0 enables autodetection (default). To determine
1526                        the correct value for your kernel, boot with normal
1527                        autodetection and see what value is printed. Note that
1528                        on SMP systems the preset will be applied to all CPUs,
1529                        which is likely to cause problems if your CPUs need
1530                        significantly divergent settings. An incorrect value
1531                        will cause delays in the kernel to be wrong, leading to
1532                        unpredictable I/O errors and other breakage. Although
1533                        unlikely, in the extreme case this might damage your
1534                        hardware.
1535
1536        ltpc=           [NET]
1537                        Format: <io>,<irq>,<dma>
1538
1539        machvec=        [IA-64] Force the use of a particular machine-vector
1540                        (machvec) in a generic kernel.
1541                        Example: machvec=hpzx1_swiotlb
1542
1543        machtype=       [Loongson] Share the same kernel image file between different
1544                         yeeloong laptop.
1545                        Example: machtype=lemote-yeeloong-2f-7inch
1546
1547        max_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory greater
1548                        than or equal to this physical address is ignored.
1549
1550        maxcpus=        [SMP] Maximum number of processors that an SMP kernel
1551                        should make use of.  maxcpus=n : n >= 0 limits the
1552                        kernel to using 'n' processors.  n=0 is a special case,
1553                        it is equivalent to "nosmp", which also disables
1554                        the IO APIC.
1555
1556        max_loop=       [LOOP] The number of loop block devices that get
1557        (loop.max_loop) unconditionally pre-created at init time. The default
1558                        number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1559                        of statically allocating a predefined number, loop
1560                        devices can be requested on-demand with the
1561                        /dev/loop-control interface.
1562
1563        mce             [X86-32] Machine Check Exception
1564
1565        mce=option      [X86-64] See Documentation/x86/x86_64/boot-options.txt
1566
1567        md=             [HW] RAID subsystems devices and level
1568                        See Documentation/md.txt.
1569
1570        mdacon=         [MDA]
1571                        Format: <first>,<last>
1572                        Specifies range of consoles to be captured by the MDA.
1573
1574        mem=nn[KMG]     [KNL,BOOT] Force usage of a specific amount of memory
1575                        Amount of memory to be used when the kernel is not able
1576                        to see the whole system memory or for test.
1577                        [X86] Work as limiting max address. Use together
1578                        with memmap= to avoid physical address space collisions.
1579                        Without memmap= PCI devices could be placed at addresses
1580                        belonging to unused RAM.
1581
1582        mem=nopentium   [BUGS=X86-32] Disable usage of 4MB pages for kernel
1583                        memory.
1584
1585        memchunk=nn[KMG]
1586                        [KNL,SH] Allow user to override the default size for
1587                        per-device physically contiguous DMA buffers.
1588
1589        memmap=exactmap [KNL,X86] Enable setting of an exact
1590                        E820 memory map, as specified by the user.
1591                        Such memmap=exactmap lines can be constructed based on
1592                        BIOS output or other requirements. See the memmap=nn@ss
1593                        option description.
1594
1595        memmap=nn[KMG]@ss[KMG]
1596                        [KNL] Force usage of a specific region of memory
1597                        Region of memory to be used, from ss to ss+nn.
1598
1599        memmap=nn[KMG]#ss[KMG]
1600                        [KNL,ACPI] Mark specific memory as ACPI data.
1601                        Region of memory to be used, from ss to ss+nn.
1602
1603        memmap=nn[KMG]$ss[KMG]
1604                        [KNL,ACPI] Mark specific memory as reserved.
1605                        Region of memory to be used, from ss to ss+nn.
1606                        Example: Exclude memory from 0x18690000-0x1869ffff
1607                                 memmap=64K$0x18690000
1608                                 or
1609                                 memmap=0x10000$0x18690000
1610
1611        memory_corruption_check=0/1 [X86]
1612                        Some BIOSes seem to corrupt the first 64k of
1613                        memory when doing things like suspend/resume.
1614                        Setting this option will scan the memory
1615                        looking for corruption.  Enabling this will
1616                        both detect corruption and prevent the kernel
1617                        from using the memory being corrupted.
1618                        However, its intended as a diagnostic tool; if
1619                        repeatable BIOS-originated corruption always
1620                        affects the same memory, you can use memmap=
1621                        to prevent the kernel from using that memory.
1622
1623        memory_corruption_check_size=size [X86]
1624                        By default it checks for corruption in the low
1625                        64k, making this memory unavailable for normal
1626                        use.  Use this parameter to scan for
1627                        corruption in more or less memory.
1628
1629        memory_corruption_check_period=seconds [X86]
1630                        By default it checks for corruption every 60
1631                        seconds.  Use this parameter to check at some
1632                        other rate.  0 disables periodic checking.
1633
1634        memtest=        [KNL,X86] Enable memtest
1635                        Format: <integer>
1636                        default : 0 <disable>
1637                        Specifies the number of memtest passes to be
1638                        performed. Each pass selects another test
1639                        pattern from a given set of patterns. Memtest
1640                        fills the memory with this pattern, validates
1641                        memory contents and reserves bad memory
1642                        regions that are detected.
1643
1644        meye.*=         [HW] Set MotionEye Camera parameters
1645                        See Documentation/video4linux/meye.txt.
1646
1647        mfgpt_irq=      [IA-32] Specify the IRQ to use for the
1648                        Multi-Function General Purpose Timers on AMD Geode
1649                        platforms.
1650
1651        mfgptfix        [X86-32] Fix MFGPT timers on AMD Geode platforms when
1652                        the BIOS has incorrectly applied a workaround. TinyBIOS
1653                        version 0.98 is known to be affected, 0.99 fixes the
1654                        problem by letting the user disable the workaround.
1655
1656        mga=            [HW,DRM]
1657
1658        min_addr=nn[KMG]        [KNL,BOOT,ia64] All physical memory below this
1659                        physical address is ignored.
1660
1661        mini2440=       [ARM,HW,KNL]
1662                        Format:[0..2][b][c][t]
1663                        Default: "0tb"
1664                        MINI2440 configuration specification:
1665                        0 - The attached screen is the 3.5" TFT
1666                        1 - The attached screen is the 7" TFT
1667                        2 - The VGA Shield is attached (1024x768)
1668                        Leaving out the screen size parameter will not load
1669                        the TFT driver, and the framebuffer will be left
1670                        unconfigured.
1671                        b - Enable backlight. The TFT backlight pin will be
1672                        linked to the kernel VESA blanking code and a GPIO
1673                        LED. This parameter is not necessary when using the
1674                        VGA shield.
1675                        c - Enable the s3c camera interface.
1676                        t - Reserved for enabling touchscreen support. The
1677                        touchscreen support is not enabled in the mainstream
1678                        kernel as of 2.6.30, a preliminary port can be found
1679                        in the "bleeding edge" mini2440 support kernel at
1680                        http://repo.or.cz/w/linux-2.6/mini2440.git
1681
1682        mminit_loglevel=
1683                        [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1684                        parameter allows control of the logging verbosity for
1685                        the additional memory initialisation checks. A value
1686                        of 0 disables mminit logging and a level of 4 will
1687                        log everything. Information is printed at KERN_DEBUG
1688                        so loglevel=8 may also need to be specified.
1689
1690        module.sig_enforce
1691                        [KNL] When CONFIG_MODULE_SIG is set, this means that
1692                        modules without (valid) signatures will fail to load.
1693                        Note that if CONFIG_MODULE_SIG_FORCE is set, that
1694                        is always true, so this option does nothing.
1695
1696        mousedev.tap_time=
1697                        [MOUSE] Maximum time between finger touching and
1698                        leaving touchpad surface for touch to be considered
1699                        a tap and be reported as a left button click (for
1700                        touchpads working in absolute mode only).
1701                        Format: <msecs>
1702        mousedev.xres=  [MOUSE] Horizontal screen resolution, used for devices
1703                        reporting absolute coordinates, such as tablets
1704        mousedev.yres=  [MOUSE] Vertical screen resolution, used for devices
1705                        reporting absolute coordinates, such as tablets
1706
1707        movablecore=nn[KMG]     [KNL,X86,IA-64,PPC] This parameter
1708                        is similar to kernelcore except it specifies the
1709                        amount of memory used for migratable allocations.
1710                        If both kernelcore and movablecore is specified,
1711                        then kernelcore will be at *least* the specified
1712                        value but may be more. If movablecore on its own
1713                        is specified, the administrator must be careful
1714                        that the amount of memory usable for all allocations
1715                        is not too small.
1716
1717        MTD_Partition=  [MTD]
1718                        Format: <name>,<region-number>,<size>,<offset>
1719
1720        MTD_Region=     [MTD] Format:
1721                        <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1722
1723        mtdparts=       [MTD]
1724                        See drivers/mtd/cmdlinepart.c.
1725
1726        multitce=off    [PPC]  This parameter disables the use of the pSeries
1727                        firmware feature for updating multiple TCE entries
1728                        at a time.
1729
1730        onenand.bdry=   [HW,MTD] Flex-OneNAND Boundary Configuration
1731
1732                        Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1733
1734                        boundary - index of last SLC block on Flex-OneNAND.
1735                                   The remaining blocks are configured as MLC blocks.
1736                        lock     - Configure if Flex-OneNAND boundary should be locked.
1737                                   Once locked, the boundary cannot be changed.
1738                                   1 indicates lock status, 0 indicates unlock status.
1739
1740        mtdset=         [ARM]
1741                        ARM/S3C2412 JIVE boot control
1742
1743                        See arch/arm/mach-s3c2412/mach-jive.c
1744
1745        mtouchusb.raw_coordinates=
1746                        [HW] Make the MicroTouch USB driver use raw coordinates
1747                        ('y', default) or cooked coordinates ('n')
1748
1749        mtrr_chunk_size=nn[KMG] [X86]
1750                        used for mtrr cleanup. It is largest continuous chunk
1751                        that could hold holes aka. UC entries.
1752
1753        mtrr_gran_size=nn[KMG] [X86]
1754                        Used for mtrr cleanup. It is granularity of mtrr block.
1755                        Default is 1.
1756                        Large value could prevent small alignment from
1757                        using up MTRRs.
1758
1759        mtrr_spare_reg_nr=n [X86]
1760                        Format: <integer>
1761                        Range: 0,7 : spare reg number
1762                        Default : 1
1763                        Used for mtrr cleanup. It is spare mtrr entries number.
1764                        Set to 2 or more if your graphical card needs more.
1765
1766        n2=             [NET] SDL Inc. RISCom/N2 synchronous serial card
1767
1768        netdev=         [NET] Network devices parameters
1769                        Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1770                        Note that mem_start is often overloaded to mean
1771                        something different and driver-specific.
1772                        This usage is only documented in each driver source
1773                        file if at all.
1774
1775        nf_conntrack.acct=
1776                        [NETFILTER] Enable connection tracking flow accounting
1777                        0 to disable accounting
1778                        1 to enable accounting
1779                        Default value is 0.
1780
1781        nfsaddrs=       [NFS] Deprecated.  Use ip= instead.
1782                        See Documentation/filesystems/nfs/nfsroot.txt.
1783
1784        nfsroot=        [NFS] nfs root filesystem for disk-less boxes.
1785                        See Documentation/filesystems/nfs/nfsroot.txt.
1786
1787        nfsrootdebug    [NFS] enable nfsroot debugging messages.
1788                        See Documentation/filesystems/nfs/nfsroot.txt.
1789
1790        nfs.callback_tcpport=
1791                        [NFS] set the TCP port on which the NFSv4 callback
1792                        channel should listen.
1793
1794        nfs.cache_getent=
1795                        [NFS] sets the pathname to the program which is used
1796                        to update the NFS client cache entries.
1797
1798        nfs.cache_getent_timeout=
1799                        [NFS] sets the timeout after which an attempt to
1800                        update a cache entry is deemed to have failed.
1801
1802        nfs.idmap_cache_timeout=
1803                        [NFS] set the maximum lifetime for idmapper cache
1804                        entries.
1805
1806        nfs.enable_ino64=
1807                        [NFS] enable 64-bit inode numbers.
1808                        If zero, the NFS client will fake up a 32-bit inode
1809                        number for the readdir() and stat() syscalls instead
1810                        of returning the full 64-bit number.
1811                        The default is to return 64-bit inode numbers.
1812
1813        nfs.max_session_slots=
1814                        [NFSv4.1] Sets the maximum number of session slots
1815                        the client will attempt to negotiate with the server.
1816                        This limits the number of simultaneous RPC requests
1817                        that the client can send to the NFSv4.1 server.
1818                        Note that there is little point in setting this
1819                        value higher than the max_tcp_slot_table_limit.
1820
1821        nfs.nfs4_disable_idmapping=
1822                        [NFSv4] When set to the default of '1', this option
1823                        ensures that both the RPC level authentication
1824                        scheme and the NFS level operations agree to use
1825                        numeric uids/gids if the mount is using the
1826                        'sec=sys' security flavour. In effect it is
1827                        disabling idmapping, which can make migration from
1828                        legacy NFSv2/v3 systems to NFSv4 easier.
1829                        Servers that do not support this mode of operation
1830                        will be autodetected by the client, and it will fall
1831                        back to using the idmapper.
1832                        To turn off this behaviour, set the value to '0'.
1833        nfs.nfs4_unique_id=
1834                        [NFS4] Specify an additional fixed unique ident-
1835                        ification string that NFSv4 clients can insert into
1836                        their nfs_client_id4 string.  This is typically a
1837                        UUID that is generated at system install time.
1838
1839        nfs.send_implementation_id =
1840                        [NFSv4.1] Send client implementation identification
1841                        information in exchange_id requests.
1842                        If zero, no implementation identification information
1843                        will be sent.
1844                        The default is to send the implementation identification
1845                        information.
1846
1847        nfsd.nfs4_disable_idmapping=
1848                        [NFSv4] When set to the default of '1', the NFSv4
1849                        server will return only numeric uids and gids to
1850                        clients using auth_sys, and will accept numeric uids
1851                        and gids from such clients.  This is intended to ease
1852                        migration from NFSv2/v3.
1853
1854        objlayoutdriver.osd_login_prog=
1855                        [NFS] [OBJLAYOUT] sets the pathname to the program which
1856                        is used to automatically discover and login into new
1857                        osd-targets. Please see:
1858                        Documentation/filesystems/pnfs.txt for more explanations
1859
1860        nmi_debug=      [KNL,AVR32,SH] Specify one or more actions to take
1861                        when a NMI is triggered.
1862                        Format: [state][,regs][,debounce][,die]
1863
1864        nmi_watchdog=   [KNL,BUGS=X86] Debugging features for SMP kernels
1865                        Format: [panic,][nopanic,][num]
1866                        Valid num: 0
1867                        0 - turn nmi_watchdog off
1868                        When panic is specified, panic when an NMI watchdog
1869                        timeout occurs (or 'nopanic' to override the opposite
1870                        default).
1871                        This is useful when you use a panic=... timeout and
1872                        need the box quickly up again.
1873
1874        netpoll.carrier_timeout=
1875                        [NET] Specifies amount of time (in seconds) that
1876                        netpoll should wait for a carrier. By default netpoll
1877                        waits 4 seconds.
1878
1879        no387           [BUGS=X86-32] Tells the kernel to use the 387 maths
1880                        emulation library even if a 387 maths coprocessor
1881                        is present.
1882
1883        no_console_suspend
1884                        [HW] Never suspend the console
1885                        Disable suspending of consoles during suspend and
1886                        hibernate operations.  Once disabled, debugging
1887                        messages can reach various consoles while the rest
1888                        of the system is being put to sleep (ie, while
1889                        debugging driver suspend/resume hooks).  This may
1890                        not work reliably with all consoles, but is known
1891                        to work with serial and VGA consoles.
1892                        To facilitate more flexible debugging, we also add
1893                        console_suspend, a printk module parameter to control
1894                        it. Users could use console_suspend (usually
1895                        /sys/module/printk/parameters/console_suspend) to
1896                        turn on/off it dynamically.
1897
1898        noaliencache    [MM, NUMA, SLAB] Disables the allocation of alien
1899                        caches in the slab allocator.  Saves per-node memory,
1900                        but will impact performance.
1901
1902        noalign         [KNL,ARM]
1903
1904        noapic          [SMP,APIC] Tells the kernel to not make use of any
1905                        IOAPICs that may be present in the system.
1906
1907        noautogroup     Disable scheduler automatic task group creation.
1908
1909        nobats          [PPC] Do not use BATs for mapping kernel lowmem
1910                        on "Classic" PPC cores.
1911
1912        nocache         [ARM]
1913
1914        noclflush       [BUGS=X86] Don't use the CLFLUSH instruction
1915
1916        nodelayacct     [KNL] Disable per-task delay accounting
1917
1918        nodisconnect    [HW,SCSI,M68K] Disables SCSI disconnects.
1919
1920        nodsp           [SH] Disable hardware DSP at boot time.
1921
1922        noefi           [X86] Disable EFI runtime services support.
1923
1924        noexec          [IA-64]
1925
1926        noexec          [X86]
1927                        On X86-32 available only on PAE configured kernels.
1928                        noexec=on: enable non-executable mappings (default)
1929                        noexec=off: disable non-executable mappings
1930
1931        nosmap          [X86]
1932                        Disable SMAP (Supervisor Mode Access Prevention)
1933                        even if it is supported by processor.
1934
1935        nosmep          [X86]
1936                        Disable SMEP (Supervisor Mode Execution Prevention)
1937                        even if it is supported by processor.
1938
1939        noexec32        [X86-64]
1940                        This affects only 32-bit executables.
1941                        noexec32=on: enable non-executable mappings (default)
1942                                read doesn't imply executable mappings
1943                        noexec32=off: disable non-executable mappings
1944                                read implies executable mappings
1945
1946        nofpu           [SH] Disable hardware FPU at boot time.
1947
1948        nofxsr          [BUGS=X86-32] Disables x86 floating point extended
1949                        register save and restore. The kernel will only save
1950                        legacy floating-point registers on task switch.
1951
1952        noxsave         [BUGS=X86] Disables x86 extended register state save
1953                        and restore using xsave. The kernel will fallback to
1954                        enabling legacy floating-point and sse state.
1955
1956        eagerfpu=       [X86]
1957                        on      enable eager fpu restore
1958                        off     disable eager fpu restore
1959                        auto    selects the default scheme, which automatically
1960                                enables eagerfpu restore for xsaveopt.
1961
1962        nohlt           [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1963                        wfi(ARM) instruction doesn't work correctly and not to
1964                        use it. This is also useful when using JTAG debugger.
1965
1966        no_file_caps    Tells the kernel not to honor file capabilities.  The
1967                        only way then for a file to be executed with privilege
1968                        is to be setuid root or executed by root.
1969
1970        nohalt          [IA-64] Tells the kernel not to use the power saving
1971                        function PAL_HALT_LIGHT when idle. This increases
1972                        power-consumption. On the positive side, it reduces
1973                        interrupt wake-up latency, which may improve performance
1974                        in certain environments such as networked servers or
1975                        real-time systems.
1976
1977        nohz=           [KNL] Boottime enable/disable dynamic ticks
1978                        Valid arguments: on, off
1979                        Default: on
1980
1981        nohz_full=      [KNL,BOOT]
1982                        In kernels built with CONFIG_NO_HZ_FULL=y, set
1983                        the specified list of CPUs whose tick will be stopped
1984                        whenever possible. The boot CPU will be forced outside
1985                        the range to maintain the timekeeping.
1986                        The CPUs in this range must also be included in the
1987                        rcu_nocbs= set.
1988
1989        noiotrap        [SH] Disables trapped I/O port accesses.
1990
1991        noirqdebug      [X86-32] Disables the code which attempts to detect and
1992                        disable unhandled interrupt sources.
1993
1994        no_timer_check  [X86,APIC] Disables the code which tests for
1995                        broken timer IRQ sources.
1996
1997        noisapnp        [ISAPNP] Disables ISA PnP code.
1998
1999        noinitrd        [RAM] Tells the kernel not to load any configured
2000                        initial RAM disk.
2001
2002        nointremap      [X86-64, Intel-IOMMU] Do not enable interrupt
2003                        remapping.
2004                        [Deprecated - use intremap=off]
2005
2006        nointroute      [IA-64]
2007
2008        nojitter        [IA-64] Disables jitter checking for ITC timers.
2009
2010        no-kvmclock     [X86,KVM] Disable paravirtualized KVM clock driver
2011
2012        no-kvmapf       [X86,KVM] Disable paravirtualized asynchronous page
2013                        fault handling.
2014
2015        no-steal-acc    [X86,KVM] Disable paravirtualized steal time accounting.
2016                        steal time is computed, but won't influence scheduler
2017                        behaviour
2018
2019        nolapic         [X86-32,APIC] Do not enable or use the local APIC.
2020
2021        nolapic_timer   [X86-32,APIC] Do not use the local APIC timer.
2022
2023        noltlbs         [PPC] Do not use large page/tlb entries for kernel
2024                        lowmem mapping on PPC40x.
2025
2026        nomca           [IA-64] Disable machine check abort handling
2027
2028        nomce           [X86-32] Machine Check Exception
2029
2030        nomfgpt         [X86-32] Disable Multi-Function General Purpose
2031                        Timer usage (for AMD Geode machines).
2032
2033        nonmi_ipi       [X86] Disable using NMI IPIs during panic/reboot to
2034                        shutdown the other cpus.  Instead use the REBOOT_VECTOR
2035                        irq.
2036
2037        nomodule        Disable module load
2038
2039        nopat           [X86] Disable PAT (page attribute table extension of
2040                        pagetables) support.
2041
2042        norandmaps      Don't use address space randomization.  Equivalent to
2043                        echo 0 > /proc/sys/kernel/randomize_va_space
2044
2045        noreplace-paravirt      [X86,IA-64,PV_OPS] Don't patch paravirt_ops
2046
2047        noreplace-smp   [X86-32,SMP] Don't replace SMP instructions
2048                        with UP alternatives
2049
2050        nordrand        [X86] Disable the direct use of the RDRAND
2051                        instruction even if it is supported by the
2052                        processor.  RDRAND is still available to user
2053                        space applications.
2054
2055        noresume        [SWSUSP] Disables resume and restores original swap
2056                        space.
2057
2058        no-scroll       [VGA] Disables scrollback.
2059                        This is required for the Braillex ib80-piezo Braille
2060                        reader made by F.H. Papenmeier (Germany).
2061
2062        nosbagart       [IA-64]
2063
2064        nosep           [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2065
2066        nosmp           [SMP] Tells an SMP kernel to act as a UP kernel,
2067                        and disable the IO APIC.  legacy for "maxcpus=0".
2068
2069        nosoftlockup    [KNL] Disable the soft-lockup detector.
2070
2071        nosync          [HW,M68K] Disables sync negotiation for all devices.
2072
2073        notsc           [BUGS=X86-32] Disable Time Stamp Counter
2074
2075        nousb           [USB] Disable the USB subsystem
2076
2077        nowatchdog      [KNL] Disable the lockup detector (NMI watchdog).
2078
2079        nowb            [ARM]
2080
2081        nox2apic        [X86-64,APIC] Do not enable x2APIC mode.
2082
2083        cpu0_hotplug    [X86] Turn on CPU0 hotplug feature when
2084                        CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2085                        Some features depend on CPU0. Known dependencies are:
2086                        1. Resume from suspend/hibernate depends on CPU0.
2087                        Suspend/hibernate will fail if CPU0 is offline and you
2088                        need to online CPU0 before suspend/hibernate.
2089                        2. PIC interrupts also depend on CPU0. CPU0 can't be
2090                        removed if a PIC interrupt is detected.
2091                        It's said poweroff/reboot may depend on CPU0 on some
2092                        machines although I haven't seen such issues so far
2093                        after CPU0 is offline on a few tested machines.
2094                        If the dependencies are under your control, you can
2095                        turn on cpu0_hotplug.
2096
2097        nptcg=          [IA-64] Override max number of concurrent global TLB
2098                        purges which is reported from either PAL_VM_SUMMARY or
2099                        SAL PALO.
2100
2101        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
2102                        could support.  nr_cpus=n : n >= 1 limits the kernel to
2103                        supporting 'n' processors. Later in runtime you can not
2104                        use hotplug cpu feature to put more cpu back to online.
2105                        just like you compile the kernel NR_CPUS=n
2106
2107        nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
2108
2109        numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2110                        Allowed values are enable and disable
2111
2112        numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2113                        one of ['zone', 'node', 'default'] can be specified
2114                        This can be set from sysctl after boot.
2115                        See Documentation/sysctl/vm.txt for details.
2116
2117        ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
2118                        See Documentation/debugging-via-ohci1394.txt for more
2119                        info.
2120
2121        olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2122                        Rather than timing out after 20 ms if an EC
2123                        command is not properly ACKed, override the length
2124                        of the timeout.  We have interrupts disabled while
2125                        waiting for the ACK, so if this is set too high
2126                        interrupts *may* be lost!
2127
2128        omap_mux=       [OMAP] Override bootloader pin multiplexing.
2129                        Format: <mux_mode0.mode_name=value>...
2130                        For example, to override I2C bus2:
2131                        omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2132
2133        oprofile.timer= [HW]
2134                        Use timer interrupt instead of performance counters
2135
2136        oprofile.cpu_type=      Force an oprofile cpu type
2137                        This might be useful if you have an older oprofile
2138                        userland or if you want common events.
2139                        Format: { arch_perfmon }
2140                        arch_perfmon: [X86] Force use of architectural
2141                                perfmon on Intel CPUs instead of the
2142                                CPU specific event set.
2143                        timer: [X86] Force use of architectural NMI
2144                                timer mode (see also oprofile.timer
2145                                for generic hr timer mode)
2146                                [s390] Force legacy basic mode sampling
2147                                (report cpu_type "timer")
2148
2149        oops=panic      Always panic on oopses. Default is to just kill the
2150                        process, but there is a small probability of
2151                        deadlocking the machine.
2152                        This will also cause panics on machine check exceptions.
2153                        Useful together with panic=30 to trigger a reboot.
2154
2155        OSS             [HW,OSS]
2156                        See Documentation/sound/oss/oss-parameters.txt
2157
2158        panic=          [KNL] Kernel behaviour on panic: delay <timeout>
2159                        timeout > 0: seconds before rebooting
2160                        timeout = 0: wait forever
2161                        timeout < 0: reboot immediately
2162                        Format: <timeout>
2163
2164        parkbd.port=    [HW] Parallel port number the keyboard adapter is
2165                        connected to, default is 0.
2166                        Format: <parport#>
2167        parkbd.mode=    [HW] Parallel port keyboard adapter mode of operation,
2168                        0 for XT, 1 for AT (default is AT).
2169                        Format: <mode>
2170
2171        parport=        [HW,PPT] Specify parallel ports. 0 disables.
2172                        Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2173                        Use 'auto' to force the driver to use any
2174                        IRQ/DMA settings detected (the default is to
2175                        ignore detected IRQ/DMA settings because of
2176                        possible conflicts). You can specify the base
2177                        address, IRQ, and DMA settings; IRQ and DMA
2178                        should be numbers, or 'auto' (for using detected
2179                        settings on that particular port), or 'nofifo'
2180                        (to avoid using a FIFO even if it is detected).
2181                        Parallel ports are assigned in the order they
2182                        are specified on the command line, starting
2183                        with parport0.
2184
2185        parport_init_mode=      [HW,PPT]
2186                        Configure VIA parallel port to operate in
2187                        a specific mode. This is necessary on Pegasos
2188                        computer where firmware has no options for setting
2189                        up parallel port mode and sets it to spp.
2190                        Currently this function knows 686a and 8231 chips.
2191                        Format: [spp|ps2|epp|ecp|ecpepp]
2192
2193        pause_on_oops=
2194                        Halt all CPUs after the first oops has been printed for
2195                        the specified number of seconds.  This is to be used if
2196                        your oopses keep scrolling off the screen.
2197
2198        pcbit=          [HW,ISDN]
2199
2200        pcd.            [PARIDE]
2201                        See header of drivers/block/paride/pcd.c.
2202                        See also Documentation/blockdev/paride.txt.
2203
2204        pci=option[,option...]  [PCI] various PCI subsystem options:
2205                earlydump       [X86] dump PCI config space before the kernel
2206                                changes anything
2207                off             [X86] don't probe for the PCI bus
2208                bios            [X86-32] force use of PCI BIOS, don't access
2209                                the hardware directly. Use this if your machine
2210                                has a non-standard PCI host bridge.
2211                nobios          [X86-32] disallow use of PCI BIOS, only direct
2212                                hardware access methods are allowed. Use this
2213                                if you experience crashes upon bootup and you
2214                                suspect they are caused by the BIOS.
2215                conf1           [X86] Force use of PCI Configuration
2216                                Mechanism 1.
2217                conf2           [X86] Force use of PCI Configuration
2218                                Mechanism 2.
2219                noaer           [PCIE] If the PCIEAER kernel config parameter is
2220                                enabled, this kernel boot option can be used to
2221                                disable the use of PCIE advanced error reporting.
2222                nodomains       [PCI] Disable support for multiple PCI
2223                                root domains (aka PCI segments, in ACPI-speak).
2224                nommconf        [X86] Disable use of MMCONFIG for PCI
2225                                Configuration
2226                check_enable_amd_mmconf [X86] check for and enable
2227                                properly configured MMIO access to PCI
2228                                config space on AMD family 10h CPU
2229                nomsi           [MSI] If the PCI_MSI kernel config parameter is
2230                                enabled, this kernel boot option can be used to
2231                                disable the use of MSI interrupts system-wide.
2232                noioapicquirk   [APIC] Disable all boot interrupt quirks.
2233                                Safety option to keep boot IRQs enabled. This
2234                                should never be necessary.
2235                ioapicreroute   [APIC] Enable rerouting of boot IRQs to the
2236                                primary IO-APIC for bridges that cannot disable
2237                                boot IRQs. This fixes a source of spurious IRQs
2238                                when the system masks IRQs.
2239                noioapicreroute [APIC] Disable workaround that uses the
2240                                boot IRQ equivalent of an IRQ that connects to
2241                                a chipset where boot IRQs cannot be disabled.
2242                                The opposite of ioapicreroute.
2243                biosirq         [X86-32] Use PCI BIOS calls to get the interrupt
2244                                routing table. These calls are known to be buggy
2245                                on several machines and they hang the machine
2246                                when used, but on other computers it's the only
2247                                way to get the interrupt routing table. Try
2248                                this option if the kernel is unable to allocate
2249                                IRQs or discover secondary PCI buses on your
2250                                motherboard.
2251                rom             [X86] Assign address space to expansion ROMs.
2252                                Use with caution as certain devices share
2253                                address decoders between ROMs and other
2254                                resources.
2255                norom           [X86] Do not assign address space to
2256                                expansion ROMs that do not already have
2257                                BIOS assigned address ranges.
2258                nobar           [X86] Do not assign address space to the
2259                                BARs that weren't assigned by the BIOS.
2260                irqmask=0xMMMM  [X86] Set a bit mask of IRQs allowed to be
2261                                assigned automatically to PCI devices. You can
2262                                make the kernel exclude IRQs of your ISA cards
2263                                this way.
2264                pirqaddr=0xAAAAA        [X86] Specify the physical address
2265                                of the PIRQ table (normally generated
2266                                by the BIOS) if it is outside the
2267                                F0000h-100000h range.
2268                lastbus=N       [X86] Scan all buses thru bus #N. Can be
2269                                useful if the kernel is unable to find your
2270                                secondary buses and you want to tell it
2271                                explicitly which ones they are.
2272                assign-busses   [X86] Always assign all PCI bus
2273                                numbers ourselves, overriding
2274                                whatever the firmware may have done.
2275                usepirqmask     [X86] Honor the possible IRQ mask stored
2276                                in the BIOS $PIR table. This is needed on
2277                                some systems with broken BIOSes, notably
2278                                some HP Pavilion N5400 and Omnibook XE3
2279                                notebooks. This will have no effect if ACPI
2280                                IRQ routing is enabled.
2281                noacpi          [X86] Do not use ACPI for IRQ routing
2282                                or for PCI scanning.
2283                use_crs         [X86] Use PCI host bridge window information
2284                                from ACPI.  On BIOSes from 2008 or later, this
2285                                is enabled by default.  If you need to use this,
2286                                please report a bug.
2287                nocrs           [X86] Ignore PCI host bridge windows from ACPI.
2288                                If you need to use this, please report a bug.
2289                routeirq        Do IRQ routing for all PCI devices.
2290                                This is normally done in pci_enable_device(),
2291                                so this option is a temporary workaround
2292                                for broken drivers that don't call it.
2293                skip_isa_align  [X86] do not align io start addr, so can
2294                                handle more pci cards
2295                firmware        [ARM] Do not re-enumerate the bus but instead
2296                                just use the configuration from the
2297                                bootloader. This is currently used on
2298                                IXP2000 systems where the bus has to be
2299                                configured a certain way for adjunct CPUs.
2300                noearly         [X86] Don't do any early type 1 scanning.
2301                                This might help on some broken boards which
2302                                machine check when some devices' config space
2303                                is read. But various workarounds are disabled
2304                                and some IOMMU drivers will not work.
2305                bfsort          Sort PCI devices into breadth-first order.
2306                                This sorting is done to get a device
2307                                order compatible with older (<= 2.4) kernels.
2308                nobfsort        Don't sort PCI devices into breadth-first order.
2309                pcie_bus_tune_off       Disable PCIe MPS (Max Payload Size)
2310                                tuning and use the BIOS-configured MPS defaults.
2311                pcie_bus_safe   Set every device's MPS to the largest value
2312                                supported by all devices below the root complex.
2313                pcie_bus_perf   Set device MPS to the largest allowable MPS
2314                                based on its parent bus. Also set MRRS (Max
2315                                Read Request Size) to the largest supported
2316                                value (no larger than the MPS that the device
2317                                or bus can support) for best performance.
2318                pcie_bus_peer2peer      Set every device's MPS to 128B, which
2319                                every device is guaranteed to support. This
2320                                configuration allows peer-to-peer DMA between
2321                                any pair of devices, possibly at the cost of
2322                                reduced performance.  This also guarantees
2323                                that hot-added devices will work.
2324                cbiosize=nn[KMG]        The fixed amount of bus space which is
2325                                reserved for the CardBus bridge's IO window.
2326                                The default value is 256 bytes.
2327                cbmemsize=nn[KMG]       The fixed amount of bus space which is
2328                                reserved for the CardBus bridge's memory
2329                                window. The default value is 64 megabytes.
2330                resource_alignment=
2331                                Format:
2332                                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2333                                Specifies alignment and device to reassign
2334                                aligned memory resources.
2335                                If <order of align> is not specified,
2336                                PAGE_SIZE is used as alignment.
2337                                PCI-PCI bridge can be specified, if resource
2338                                windows need to be expanded.
2339                ecrc=           Enable/disable PCIe ECRC (transaction layer
2340                                end-to-end CRC checking).
2341                                bios: Use BIOS/firmware settings. This is the
2342                                the default.
2343                                off: Turn ECRC off
2344                                on: Turn ECRC on.
2345                hpiosize=nn[KMG]        The fixed amount of bus space which is
2346                                reserved for hotplug bridge's IO window.
2347                                Default size is 256 bytes.
2348                hpmemsize=nn[KMG]       The fixed amount of bus space which is
2349                                reserved for hotplug bridge's memory window.
2350                                Default size is 2 megabytes.
2351                realloc=        Enable/disable reallocating PCI bridge resources
2352                                if allocations done by BIOS are too small to
2353                                accommodate resources required by all child
2354                                devices.
2355                                off: Turn realloc off
2356                                on: Turn realloc on
2357                realloc         same as realloc=on
2358                noari           do not use PCIe ARI.
2359                pcie_scan_all   Scan all possible PCIe devices.  Otherwise we
2360                                only look for one device below a PCIe downstream
2361                                port.
2362
2363        pcie_aspm=      [PCIE] Forcibly enable or disable PCIe Active State Power
2364                        Management.
2365                off     Disable ASPM.
2366                force   Enable ASPM even on devices that claim not to support it.
2367                        WARNING: Forcing ASPM on may cause system lockups.
2368
2369        pcie_hp=        [PCIE] PCI Express Hotplug driver options:
2370                nomsi   Do not use MSI for PCI Express Native Hotplug (this
2371                        makes all PCIe ports use INTx for hotplug services).
2372
2373        pcie_ports=     [PCIE] PCIe ports handling:
2374                auto    Ask the BIOS whether or not to use native PCIe services
2375                        associated with PCIe ports (PME, hot-plug, AER).  Use
2376                        them only if that is allowed by the BIOS.
2377                native  Use native PCIe services associated with PCIe ports
2378                        unconditionally.
2379                compat  Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2380                        ports driver.
2381
2382        pcie_pme=       [PCIE,PM] Native PCIe PME signaling options:
2383                nomsi   Do not use MSI for native PCIe PME signaling (this makes
2384                        all PCIe root ports use INTx for all services).
2385
2386        pcmv=           [HW,PCMCIA] BadgePAD 4
2387
2388        pd.             [PARIDE]
2389                        See Documentation/blockdev/paride.txt.
2390
2391        pdcchassis=     [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2392                        boot time.
2393                        Format: { 0 | 1 }
2394                        See arch/parisc/kernel/pdc_chassis.c
2395
2396        percpu_alloc=   Select which percpu first chunk allocator to use.
2397                        Currently supported values are "embed" and "page".
2398                        Archs may support subset or none of the selections.
2399                        See comments in mm/percpu.c for details on each
2400                        allocator.  This parameter is primarily for debugging
2401                        and performance comparison.
2402
2403        pf.             [PARIDE]
2404                        See Documentation/blockdev/paride.txt.
2405
2406        pg.             [PARIDE]
2407                        See Documentation/blockdev/paride.txt.
2408
2409        pirq=           [SMP,APIC] Manual mp-table setup
2410                        See Documentation/x86/i386/IO-APIC.txt.
2411
2412        plip=           [PPT,NET] Parallel port network link
2413                        Format: { parport<nr> | timid | 0 }
2414                        See also Documentation/parport.txt.
2415
2416        pmtmr=          [X86] Manual setup of pmtmr I/O Port.
2417                        Override pmtimer IOPort with a hex value.
2418                        e.g. pmtmr=0x508
2419
2420        pnp.debug=1     [PNP]
2421                        Enable PNP debug messages (depends on the
2422                        CONFIG_PNP_DEBUG_MESSAGES option).  Change at run-time
2423                        via /sys/module/pnp/parameters/debug.  We always show
2424                        current resource usage; turning this on also shows
2425                        possible settings and some assignment information.
2426
2427        pnpacpi=        [ACPI]
2428                        { off }
2429
2430        pnpbios=        [ISAPNP]
2431                        { on | off | curr | res | no-curr | no-res }
2432
2433        pnp_reserve_irq=
2434                        [ISAPNP] Exclude IRQs for the autoconfiguration
2435
2436        pnp_reserve_dma=
2437                        [ISAPNP] Exclude DMAs for the autoconfiguration
2438
2439        pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2440                        Ranges are in pairs (I/O port base and size).
2441
2442        pnp_reserve_mem=
2443                        [ISAPNP] Exclude memory regions for the
2444                        autoconfiguration.
2445                        Ranges are in pairs (memory base and size).
2446
2447        ports=          [IP_VS_FTP] IPVS ftp helper module
2448                        Default is 21.
2449                        Up to 8 (IP_VS_APP_MAX_PORTS) ports
2450                        may be specified.
2451                        Format: <port>,<port>....
2452
2453        print-fatal-signals=
2454                        [KNL] debug: print fatal signals
2455
2456                        If enabled, warn about various signal handling
2457                        related application anomalies: too many signals,
2458                        too many POSIX.1 timers, fatal signals causing a
2459                        coredump - etc.
2460
2461                        If you hit the warning due to signal overflow,
2462                        you might want to try "ulimit -i unlimited".
2463
2464                        default: off.
2465
2466        printk.always_kmsg_dump=
2467                        Trigger kmsg_dump for cases other than kernel oops or
2468                        panics
2469                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2470                        default: disabled
2471
2472        printk.time=    Show timing data prefixed to each printk message line
2473                        Format: <bool>  (1/Y/y=enable, 0/N/n=disable)
2474
2475        processor.max_cstate=   [HW,ACPI]
2476                        Limit processor to maximum C-state
2477                        max_cstate=9 overrides any DMI blacklist limit.
2478
2479        processor.nocst [HW,ACPI]
2480                        Ignore the _CST method to determine C-states,
2481                        instead using the legacy FADT method
2482
2483        profile=        [KNL] Enable kernel profiling via /proc/profile
2484                        Format: [schedule,]<number>
2485                        Param: "schedule" - profile schedule points.
2486                        Param: <number> - step/bucket size as a power of 2 for
2487                                statistical time based profiling.
2488                        Param: "sleep" - profile D-state sleeping (millisecs).
2489                                Requires CONFIG_SCHEDSTATS
2490                        Param: "kvm" - profile VM exits.
2491
2492        prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2493                        before loading.
2494                        See Documentation/blockdev/ramdisk.txt.
2495
2496        psmouse.proto=  [HW,MOUSE] Highest PS2 mouse protocol extension to
2497                        probe for; one of (bare|imps|exps|lifebook|any).
2498        psmouse.rate=   [HW,MOUSE] Set desired mouse report rate, in reports
2499                        per second.
2500        psmouse.resetafter=     [HW,MOUSE]
2501                        Try to reset the device after so many bad packets
2502                        (0 = never).
2503        psmouse.resolution=
2504                        [HW,MOUSE] Set desired mouse resolution, in dpi.
2505        psmouse.smartscroll=
2506                        [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2507                        0 = disabled, 1 = enabled (default).
2508
2509        pstore.backend= Specify the name of the pstore backend to use
2510
2511        pt.             [PARIDE]
2512                        See Documentation/blockdev/paride.txt.
2513
2514        pty.legacy_count=
2515                        [KNL] Number of legacy pty's. Overwrites compiled-in
2516                        default number.
2517
2518        quiet           [KNL] Disable most log messages
2519
2520        r128=           [HW,DRM]
2521
2522        raid=           [HW,RAID]
2523                        See Documentation/md.txt.
2524
2525        ramdisk_blocksize=      [RAM]
2526                        See Documentation/blockdev/ramdisk.txt.
2527
2528        ramdisk_size=   [RAM] Sizes of RAM disks in kilobytes
2529                        See Documentation/blockdev/ramdisk.txt.
2530
2531        rcu_nocbs=      [KNL,BOOT]
2532                        In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2533                        the specified list of CPUs to be no-callback CPUs.
2534                        Invocation of these CPUs' RCU callbacks will
2535                        be offloaded to "rcuox/N" kthreads created for
2536                        that purpose, where "x" is "b" for RCU-bh, "p"
2537                        for RCU-preempt, and "s" for RCU-sched, and "N"
2538                        is the CPU number.  This reduces OS jitter on the
2539                        offloaded CPUs, which can be useful for HPC and
2540
2541                        real-time workloads.  It can also improve energy
2542                        efficiency for asymmetric multiprocessors.
2543
2544        rcu_nocb_poll   [KNL,BOOT]
2545                        Rather than requiring that offloaded CPUs
2546                        (specified by rcu_nocbs= above) explicitly
2547                        awaken the corresponding "rcuoN" kthreads,
2548                        make these kthreads poll for callbacks.
2549                        This improves the real-time response for the
2550                        offloaded CPUs by relieving them of the need to
2551                        wake up the corresponding kthread, but degrades
2552                        energy efficiency by requiring that the kthreads
2553                        periodically wake up to do the polling.
2554
2555        rcutree.blimit= [KNL,BOOT]
2556                        Set maximum number of finished RCU callbacks to process
2557                        in one batch.
2558
2559        rcutree.fanout_leaf=    [KNL,BOOT]
2560                        Increase the number of CPUs assigned to each
2561                        leaf rcu_node structure.  Useful for very large
2562                        systems.
2563
2564        rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2565                        Set delay from grace-period initialization to
2566                        first attempt to force quiescent states.
2567                        Units are jiffies, minimum value is zero,
2568                        and maximum value is HZ.
2569
2570        rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2571                        Set delay between subsequent attempts to force
2572                        quiescent states.  Units are jiffies, minimum
2573                        value is one, and maximum value is HZ.
2574
2575        rcutree.qhimark=        [KNL,BOOT]
2576                        Set threshold of queued
2577                        RCU callbacks over which batch limiting is disabled.
2578
2579        rcutree.qlowmark=       [KNL,BOOT]
2580                        Set threshold of queued RCU callbacks below which
2581                        batch limiting is re-enabled.
2582
2583        rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2584                        Suppress RCU CPU stall warning messages.
2585
2586        rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2587                        Set timeout for RCU CPU stall warning messages.
2588
2589        rcutree.rcu_idle_gp_delay=      [KNL,BOOT]
2590                        Set wakeup interval for idle CPUs that have
2591                        RCU callbacks (RCU_FAST_NO_HZ=y).
2592
2593        rcutree.rcu_idle_lazy_gp_delay= [KNL,BOOT]
2594                        Set wakeup interval for idle CPUs that have
2595                        only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2596                        Lazy RCU callbacks are those which RCU can
2597                        prove do nothing more than free memory.
2598
2599        rcutorture.fqs_duration= [KNL,BOOT]
2600                        Set duration of force_quiescent_state bursts.
2601
2602        rcutorture.fqs_holdoff= [KNL,BOOT]
2603                        Set holdoff time within force_quiescent_state bursts.
2604
2605        rcutorture.fqs_stutter= [KNL,BOOT]
2606                        Set wait time between force_quiescent_state bursts.
2607
2608        rcutorture.irqreader= [KNL,BOOT]
2609                        Test RCU readers from irq handlers.
2610
2611        rcutorture.n_barrier_cbs= [KNL,BOOT]
2612                        Set callbacks/threads for rcu_barrier() testing.
2613
2614        rcutorture.nfakewriters= [KNL,BOOT]
2615                        Set number of concurrent RCU writers.  These just
2616                        stress RCU, they don't participate in the actual
2617                        test, hence the "fake".
2618
2619        rcutorture.nreaders= [KNL,BOOT]
2620                        Set number of RCU readers.
2621
2622        rcutorture.onoff_holdoff= [KNL,BOOT]
2623                        Set time (s) after boot for CPU-hotplug testing.
2624
2625        rcutorture.onoff_interval= [KNL,BOOT]
2626                        Set time (s) between CPU-hotplug operations, or
2627                        zero to disable CPU-hotplug testing.
2628
2629        rcutorture.shuffle_interval= [KNL,BOOT]
2630                        Set task-shuffle interval (s).  Shuffling tasks
2631                        allows some CPUs to go into dyntick-idle mode
2632                        during the rcutorture test.
2633
2634        rcutorture.shutdown_secs= [KNL,BOOT]
2635                        Set time (s) after boot system shutdown.  This
2636                        is useful for hands-off automated testing.
2637
2638        rcutorture.stall_cpu= [KNL,BOOT]
2639                        Duration of CPU stall (s) to test RCU CPU stall
2640                        warnings, zero to disable.
2641
2642        rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2643                        Time to wait (s) after boot before inducing stall.
2644
2645        rcutorture.stat_interval= [KNL,BOOT]
2646                        Time (s) between statistics printk()s.
2647
2648        rcutorture.stutter= [KNL,BOOT]
2649                        Time (s) to stutter testing, for example, specifying
2650                        five seconds causes the test to run for five seconds,
2651                        wait for five seconds, and so on.  This tests RCU's
2652                        ability to transition abruptly to and from idle.
2653
2654        rcutorture.test_boost= [KNL,BOOT]
2655                        Test RCU priority boosting?  0=no, 1=maybe, 2=yes.
2656                        "Maybe" means test if the RCU implementation
2657                        under test support RCU priority boosting.
2658
2659        rcutorture.test_boost_duration= [KNL,BOOT]
2660                        Duration (s) of each individual boost test.
2661
2662        rcutorture.test_boost_interval= [KNL,BOOT]
2663                        Interval (s) between each boost test.
2664
2665        rcutorture.test_no_idle_hz= [KNL,BOOT]
2666                        Test RCU's dyntick-idle handling.  See also the
2667                        rcutorture.shuffle_interval parameter.
2668
2669        rcutorture.torture_type= [KNL,BOOT]
2670                        Specify the RCU implementation to test.
2671
2672        rcutorture.verbose= [KNL,BOOT]
2673                        Enable additional printk() statements.
2674
2675        rdinit=         [KNL]
2676                        Format: <full_path>
2677                        Run specified binary instead of /init from the ramdisk,
2678                        used for early userspace startup. See initrd.
2679
2680        reboot=         [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2681                        Format: <reboot_mode>[,<reboot_mode2>[,...]]
2682                        See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2683
2684        relax_domain_level=
2685                        [KNL, SMP] Set scheduler's default relax_domain_level.
2686                        See Documentation/cgroups/cpusets.txt.
2687
2688        reserve=        [KNL,BUGS] Force the kernel to ignore some iomem area
2689
2690        reservetop=     [X86-32]
2691                        Format: nn[KMG]
2692                        Reserves a hole at the top of the kernel virtual
2693                        address space.
2694
2695        reservelow=     [X86]
2696                        Format: nn[K]
2697                        Set the amount of memory to reserve for BIOS at
2698                        the bottom of the address space.
2699
2700        reset_devices   [KNL] Force drivers to reset the underlying device
2701                        during initialization.
2702
2703        resume=         [SWSUSP]
2704                        Specify the partition device for software suspend
2705                        Format:
2706                        {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2707
2708        resume_offset=  [SWSUSP]
2709                        Specify the offset from the beginning of the partition
2710                        given by "resume=" at which the swap header is located,
2711                        in <PAGE_SIZE> units (needed only for swap files).
2712                        See  Documentation/power/swsusp-and-swap-files.txt
2713
2714        resumedelay=    [HIBERNATION] Delay (in seconds) to pause before attempting to
2715                        read the resume files
2716
2717        resumewait      [HIBERNATION] Wait (indefinitely) for resume device to show up.
2718                        Useful for devices that are detected asynchronously
2719                        (e.g. USB and MMC devices).
2720
2721        hibernate=      [HIBERNATION]
2722                noresume        Don't check if there's a hibernation image
2723                                present during boot.
2724                nocompress      Don't compress/decompress hibernation images.
2725
2726        retain_initrd   [RAM] Keep initrd memory after extraction
2727
2728        rhash_entries=  [KNL,NET]
2729                        Set number of hash buckets for route cache
2730
2731        riscom8=        [HW,SERIAL]
2732                        Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2733
2734        ro              [KNL] Mount root device read-only on boot
2735
2736        root=           [KNL] Root filesystem
2737                        See name_to_dev_t comment in init/do_mounts.c.
2738
2739        rootdelay=      [KNL] Delay (in seconds) to pause before attempting to
2740                        mount the root filesystem
2741
2742        rootflags=      [KNL] Set root filesystem mount option string
2743
2744        rootfstype=     [KNL] Set root filesystem type
2745
2746        rootwait        [KNL] Wait (indefinitely) for root device to show up.
2747                        Useful for devices that are detected asynchronously
2748                        (e.g. USB and MMC devices).
2749
2750        rproc_mem=nn[KMG][@address]
2751                        [KNL,ARM,CMA] Remoteproc physical memory block.
2752                        Memory area to be used by remote processor image,
2753                        managed by CMA.
2754
2755        rw              [KNL] Mount root device read-write on boot
2756
2757        S               [KNL] Run init in single mode
2758
2759        sa1100ir        [NET]
2760                        See drivers/net/irda/sa1100_ir.c.
2761
2762        sbni=           [NET] Granch SBNI12 leased line adapter
2763
2764        sched_debug     [KNL] Enables verbose scheduler debug messages.
2765
2766        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
2767                        xtime_lock contention on larger systems, and/or RCU lock
2768                        contention on all systems with CONFIG_MAXSMP set.
2769                        Format: { "0" | "1" }
2770                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2771                        1 -- enable.
2772                        Note: increases power consumption, thus should only be
2773                        enabled if running jitter sensitive (HPC/RT) workloads.
2774
2775        security=       [SECURITY] Choose a security module to enable at boot.
2776                        If this boot parameter is not specified, only the first
2777                        security module asking for security registration will be
2778                        loaded. An invalid security module name will be treated
2779                        as if no module has been chosen.
2780
2781        selinux=        [SELINUX] Disable or enable SELinux at boot time.
2782                        Format: { "0" | "1" }
2783                        See security/selinux/Kconfig help text.
2784                        0 -- disable.
2785                        1 -- enable.
2786                        Default value is set via kernel config option.
2787                        If enabled at boot time, /selinux/disable can be used
2788                        later to disable prior to initial policy load.
2789
2790        apparmor=       [APPARMOR] Disable or enable AppArmor at boot time
2791                        Format: { "0" | "1" }
2792                        See security/apparmor/Kconfig help text
2793                        0 -- disable.
2794                        1 -- enable.
2795                        Default value is set via kernel config option.
2796
2797        serialnumber    [BUGS=X86-32]
2798
2799        shapers=        [NET]
2800                        Maximal number of shapers.
2801
2802        show_msr=       [x86] show boot-time MSR settings
2803                        Format: { <integer> }
2804                        Show boot-time (BIOS-initialized) MSR settings.
2805                        The parameter means the number of CPUs to show,
2806                        for example 1 means boot CPU only.
2807
2808        simeth=         [IA-64]
2809        simscsi=
2810
2811        slram=          [HW,MTD]
2812
2813        slab_max_order= [MM, SLAB]
2814                        Determines the maximum allowed order for slabs.
2815                        A high setting may cause OOMs due to memory
2816                        fragmentation.  Defaults to 1 for systems with
2817                        more than 32MB of RAM, 0 otherwise.
2818
2819        slub_debug[=options[,slabs]]    [MM, SLUB]
2820                        Enabling slub_debug allows one to determine the
2821                        culprit if slab objects become corrupted. Enabling
2822                        slub_debug can create guard zones around objects and
2823                        may poison objects when not in use. Also tracks the
2824                        last alloc / free. For more information see
2825                        Documentation/vm/slub.txt.
2826
2827        slub_max_order= [MM, SLUB]
2828                        Determines the maximum allowed order for slabs.
2829                        A high setting may cause OOMs due to memory
2830                        fragmentation. For more information see
2831                        Documentation/vm/slub.txt.
2832
2833        slub_min_objects=       [MM, SLUB]
2834                        The minimum number of objects per slab. SLUB will
2835                        increase the slab order up to slub_max_order to
2836                        generate a sufficiently large slab able to contain
2837                        the number of objects indicated. The higher the number
2838                        of objects the smaller the overhead of tracking slabs
2839                        and the less frequently locks need to be acquired.
2840                        For more information see Documentation/vm/slub.txt.
2841
2842        slub_min_order= [MM, SLUB]
2843                        Determines the minimum page order for slabs. Must be
2844                        lower than slub_max_order.
2845                        For more information see Documentation/vm/slub.txt.
2846
2847        slub_nomerge    [MM, SLUB]
2848                        Disable merging of slabs with similar size. May be
2849                        necessary if there is some reason to distinguish
2850                        allocs to different slabs. Debug options disable
2851                        merging on their own.
2852                        For more information see Documentation/vm/slub.txt.
2853
2854        smart2=         [HW]
2855                        Format: <io1>[,<io2>[,...,<io8>]]
2856
2857        smsc-ircc2.nopnp        [HW] Don't use PNP to discover SMC devices
2858        smsc-ircc2.ircc_cfg=    [HW] Device configuration I/O port
2859        smsc-ircc2.ircc_sir=    [HW] SIR base I/O port
2860        smsc-ircc2.ircc_fir=    [HW] FIR base I/O port
2861        smsc-ircc2.ircc_irq=    [HW] IRQ line
2862        smsc-ircc2.ircc_dma=    [HW] DMA channel
2863        smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2864                                0: Toshiba Satellite 1800 (GP data pin select)
2865                                1: Fast pin select (default)
2866                                2: ATC IRMode
2867
2868        softlockup_panic=
2869                        [KNL] Should the soft-lockup detector generate panics.
2870                        Format: <integer>
2871
2872        sonypi.*=       [HW] Sony Programmable I/O Control Device driver
2873                        See Documentation/laptops/sonypi.txt
2874
2875        specialix=      [HW,SERIAL] Specialix multi-serial port adapter
2876                        See Documentation/serial/specialix.txt.
2877
2878        spia_io_base=   [HW,MTD]
2879        spia_fio_base=
2880        spia_pedr=
2881        spia_peddr=
2882
2883        stacktrace      [FTRACE]
2884                        Enabled the stack tracer on boot up.
2885
2886        stacktrace_filter=[function-list]
2887                        [FTRACE] Limit the functions that the stack tracer
2888                        will trace at boot up. function-list is a comma separated
2889                        list of functions. This list can be changed at run
2890                        time by the stack_trace_filter file in the debugfs
2891                        tracing directory. Note, this enables stack tracing
2892                        and the stacktrace above is not needed.
2893
2894        sti=            [PARISC,HW]
2895                        Format: <num>
2896                        Set the STI (builtin display/keyboard on the HP-PARISC
2897                        machines) console (graphic card) which should be used
2898                        as the initial boot-console.
2899                        See also comment in drivers/video/console/sticore.c.
2900
2901        sti_font=       [HW]
2902                        See comment in drivers/video/console/sticore.c.
2903
2904        stifb=          [HW]
2905                        Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2906
2907        sunrpc.min_resvport=
2908        sunrpc.max_resvport=
2909                        [NFS,SUNRPC]
2910                        SunRPC servers often require that client requests
2911                        originate from a privileged port (i.e. a port in the
2912                        range 0 < portnr < 1024).
2913                        An administrator who wishes to reserve some of these
2914                        ports for other uses may adjust the range that the
2915                        kernel's sunrpc client considers to be privileged
2916                        using these two parameters to set the minimum and
2917                        maximum port values.
2918
2919        sunrpc.pool_mode=
2920                        [NFS]
2921                        Control how the NFS server code allocates CPUs to
2922                        service thread pools.  Depending on how many NICs
2923                        you have and where their interrupts are bound, this
2924                        option will affect which CPUs will do NFS serving.
2925                        Note: this parameter cannot be changed while the
2926                        NFS server is running.
2927
2928                        auto        the server chooses an appropriate mode
2929                                    automatically using heuristics
2930                        global      a single global pool contains all CPUs
2931                        percpu      one pool for each CPU
2932                        pernode     one pool for each NUMA node (equivalent
2933                                    to global on non-NUMA machines)
2934
2935        sunrpc.tcp_slot_table_entries=
2936        sunrpc.udp_slot_table_entries=
2937                        [NFS,SUNRPC]
2938                        Sets the upper limit on the number of simultaneous
2939                        RPC calls that can be sent from the client to a
2940                        server. Increasing these values may allow you to
2941                        improve throughput, but will also increase the
2942                        amount of memory reserved for use by the client.
2943
2944        swapaccount[=0|1]
2945                        [KNL] Enable accounting of swap in memory resource
2946                        controller if no parameter or 1 is given or disable
2947                        it if 0 is given (See Documentation/cgroups/memory.txt)
2948
2949        swiotlb=        [IA-64] Number of I/O TLB slabs
2950
2951        switches=       [HW,M68k]
2952
2953        sysfs.deprecated=0|1 [KNL]
2954                        Enable/disable old style sysfs layout for old udev
2955                        on older distributions. When this option is enabled
2956                        very new udev will not work anymore. When this option
2957                        is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2958                        in older udev will not work anymore.
2959                        Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2960                        the kernel configuration.
2961
2962        sysrq_always_enabled
2963                        [KNL]
2964                        Ignore sysrq setting - this boot parameter will
2965                        neutralize any effect of /proc/sys/kernel/sysrq.
2966                        Useful for debugging.
2967
2968        tdfx=           [HW,DRM]
2969
2970        test_suspend=   [SUSPEND]
2971                        Specify "mem" (for Suspend-to-RAM) or "standby" (for
2972                        standby suspend) as the system sleep state to briefly
2973                        enter during system startup.  The system is woken from
2974                        this state using a wakeup-capable RTC alarm.
2975
2976        thash_entries=  [KNL,NET]
2977                        Set number of hash buckets for TCP connection
2978
2979        thermal.act=    [HW,ACPI]
2980                        -1: disable all active trip points in all thermal zones
2981                        <degrees C>: override all lowest active trip points
2982
2983        thermal.crt=    [HW,ACPI]
2984                        -1: disable all critical trip points in all thermal zones
2985                        <degrees C>: override all critical trip points
2986
2987        thermal.nocrt=  [HW,ACPI]
2988                        Set to disable actions on ACPI thermal zone
2989                        critical and hot trip points.
2990
2991        thermal.off=    [HW,ACPI]
2992                        1: disable ACPI thermal control
2993
2994        thermal.psv=    [HW,ACPI]
2995                        -1: disable all passive trip points
2996                        <degrees C>: override all passive trip points to this
2997                        value
2998
2999        thermal.tzp=    [HW,ACPI]
3000                        Specify global default ACPI thermal zone polling rate
3001                        <deci-seconds>: poll all this frequency
3002                        0: no polling (default)
3003
3004        threadirqs      [KNL]
3005                        Force threading of all interrupt handlers except those
3006                        marked explicitly IRQF_NO_THREAD.
3007
3008        tmem            [KNL,XEN]
3009                        Enable the Transcendent memory driver if built-in.
3010
3011        tmem.cleancache=0|1 [KNL, XEN]
3012                        Default is on (1). Disable the usage of the cleancache
3013                        API to send anonymous pages to the hypervisor.
3014
3015        tmem.frontswap=0|1 [KNL, XEN]
3016                        Default is on (1). Disable the usage of the frontswap
3017                        API to send swap pages to the hypervisor. If disabled
3018                        the selfballooning and selfshrinking are force disabled.
3019
3020        tmem.selfballooning=0|1 [KNL, XEN]
3021                        Default is on (1). Disable the driving of swap pages
3022                        to the hypervisor.
3023
3024        tmem.selfshrinking=0|1 [KNL, XEN]
3025                        Default is on (1). Partial swapoff that immediately
3026                        transfers pages from Xen hypervisor back to the
3027                        kernel based on different criteria.
3028
3029        topology=       [S390]
3030                        Format: {off | on}
3031                        Specify if the kernel should make use of the cpu
3032                        topology information if the hardware supports this.
3033                        The scheduler will make use of this information and
3034                        e.g. base its process migration decisions on it.
3035                        Default is on.
3036
3037        tp720=          [HW,PS2]
3038
3039        tpm_suspend_pcr=[HW,TPM]
3040                        Format: integer pcr id
3041                        Specify that at suspend time, the tpm driver
3042                        should extend the specified pcr with zeros,
3043                        as a workaround for some chips which fail to
3044                        flush the last written pcr on TPM_SaveState.
3045                        This will guarantee that all the other pcrs
3046                        are saved.
3047
3048        trace_buf_size=nn[KMG]
3049                        [FTRACE] will set tracing buffer size.
3050
3051        trace_event=[event-list]
3052                        [FTRACE] Set and start specified trace events in order
3053                        to facilitate early boot debugging.
3054                        See also Documentation/trace/events.txt
3055
3056        trace_options=[option-list]
3057                        [FTRACE] Enable or disable tracer options at boot.
3058                        The option-list is a comma delimited list of options
3059                        that can be enabled or disabled just as if you were
3060                        to echo the option name into
3061
3062                            /sys/kernel/debug/tracing/trace_options
3063
3064                        For example, to enable stacktrace option (to dump the
3065                        stack trace of each event), add to the command line:
3066
3067                              trace_options=stacktrace
3068
3069                        See also Documentation/trace/ftrace.txt "trace options"
3070                        section.
3071
3072        transparent_hugepage=
3073                        [KNL]
3074                        Format: [always|madvise|never]
3075                        Can be used to control the default behavior of the system
3076                        with respect to transparent hugepages.
3077                        See Documentation/vm/transhuge.txt for more details.
3078
3079        tsc=            Disable clocksource stability checks for TSC.
3080                        Format: <string>
3081                        [x86] reliable: mark tsc clocksource as reliable, this
3082                        disables clocksource verification at runtime, as well
3083                        as the stability checks done at bootup. Used to enable
3084                        high-resolution timer mode on older hardware, and in
3085                        virtualized environment.
3086                        [x86] noirqtime: Do not use TSC to do irq accounting.
3087                        Used to run time disable IRQ_TIME_ACCOUNTING on any
3088                        platforms where RDTSC is slow and this accounting
3089                        can add overhead.
3090
3091        turbografx.map[2|3]=    [HW,JOY]
3092                        TurboGraFX parallel port interface
3093                        Format:
3094                        <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3095                        See also Documentation/input/joystick-parport.txt
3096
3097        udbg-immortal   [PPC] When debugging early kernel crashes that
3098                        happen after console_init() and before a proper 
3099                        console driver takes over, this boot options might
3100                        help "seeing" what's going on.
3101
3102        uhash_entries=  [KNL,NET]
3103                        Set number of hash buckets for UDP/UDP-Lite connections
3104
3105        uhci-hcd.ignore_oc=
3106                        [USB] Ignore overcurrent events (default N).
3107                        Some badly-designed motherboards generate lots of
3108                        bogus events, for ports that aren't wired to
3109                        anything.  Set this parameter to avoid log spamming.
3110                        Note that genuine overcurrent events won't be
3111                        reported either.
3112
3113        unknown_nmi_panic
3114                        [X86] Cause panic on unknown NMI.
3115
3116        usbcore.authorized_default=
3117                        [USB] Default USB device authorization:
3118                        (default -1 = authorized except for wireless USB,
3119                        0 = not authorized, 1 = authorized)
3120
3121        usbcore.autosuspend=
3122                        [USB] The autosuspend time delay (in seconds) used
3123                        for newly-detected USB devices (default 2).  This
3124                        is the time required before an idle device will be
3125                        autosuspended.  Devices for which the delay is set
3126                        to a negative value won't be autosuspended at all.
3127
3128        usbcore.usbfs_snoop=
3129                        [USB] Set to log all usbfs traffic (default 0 = off).
3130
3131        usbcore.blinkenlights=
3132                        [USB] Set to cycle leds on hubs (default 0 = off).
3133
3134        usbcore.old_scheme_first=
3135                        [USB] Start with the old device initialization
3136                        scheme (default 0 = off).
3137
3138        usbcore.usbfs_memory_mb=
3139                        [USB] Memory limit (in MB) for buffers allocated by
3140                        usbfs (default = 16, 0 = max = 2047).
3141
3142        usbcore.use_both_schemes=
3143                        [USB] Try the other device initialization scheme
3144                        if the first one fails (default 1 = enabled).
3145
3146        usbcore.initial_descriptor_timeout=
3147                        [USB] Specifies timeout for the initial 64-byte
3148                        USB_REQ_GET_DESCRIPTOR request in milliseconds
3149                        (default 5000 = 5.0 seconds).
3150
3151        usbhid.mousepoll=
3152                        [USBHID] The interval which mice are to be polled at.
3153
3154        usb-storage.delay_use=
3155                        [UMS] The delay in seconds before a new device is
3156                        scanned for Logical Units (default 5).
3157
3158        usb-storage.quirks=
3159                        [UMS] A list of quirks entries to supplement or
3160                        override the built-in unusual_devs list.  List
3161                        entries are separated by commas.  Each entry has
3162                        the form VID:PID:Flags where VID and PID are Vendor
3163                        and Product ID values (4-digit hex numbers) and
3164                        Flags is a set of characters, each corresponding
3165                        to a common usb-storage quirk flag as follows:
3166                                a = SANE_SENSE (collect more than 18 bytes
3167                                        of sense data);
3168                                b = BAD_SENSE (don't collect more than 18
3169                                        bytes of sense data);
3170                                c = FIX_CAPACITY (decrease the reported
3171                                        device capacity by one sector);
3172                                d = NO_READ_DISC_INFO (don't use
3173                                        READ_DISC_INFO command);
3174                                e = NO_READ_CAPACITY_16 (don't use
3175                                        READ_CAPACITY_16 command);
3176                                h = CAPACITY_HEURISTICS (decrease the
3177                                        reported device capacity by one
3178                                        sector if the number is odd);
3179                                i = IGNORE_DEVICE (don't bind to this
3180                                        device);
3181                                l = NOT_LOCKABLE (don't try to lock and
3182                                        unlock ejectable media);
3183                                m = MAX_SECTORS_64 (don't transfer more
3184                                        than 64 sectors = 32 KB at a time);
3185                                n = INITIAL_READ10 (force a retry of the
3186                                        initial READ(10) command);
3187                                o = CAPACITY_OK (accept the capacity
3188                                        reported by the device);
3189                                p = WRITE_CACHE (the device cache is ON
3190                                        by default);
3191                                r = IGNORE_RESIDUE (the device reports
3192                                        bogus residue values);
3193                                s = SINGLE_LUN (the device has only one
3194                                        Logical Unit);
3195                                w = NO_WP_DETECT (don't test whether the
3196                                        medium is write-protected).
3197                        Example: quirks=0419:aaf5:rl,0421:0433:rc
3198
3199        user_debug=     [KNL,ARM]
3200                        Format: <int>
3201                        See arch/arm/Kconfig.debug help text.
3202                                 1 - undefined instruction events
3203                                 2 - system calls
3204                                 4 - invalid data aborts
3205                                 8 - SIGSEGV faults
3206                                16 - SIGBUS faults
3207                        Example: user_debug=31
3208
3209        userpte=
3210                        [X86] Flags controlling user PTE allocations.
3211
3212                                nohigh = do not allocate PTE pages in
3213                                        HIGHMEM regardless of setting
3214                                        of CONFIG_HIGHPTE.
3215
3216        vdso=           [X86,SH]
3217                        vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3218                        vdso=1: enable VDSO (default)
3219                        vdso=0: disable VDSO mapping
3220
3221        vdso32=         [X86]
3222                        vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3223                        vdso32=1: enable 32-bit VDSO (default)
3224                        vdso32=0: disable 32-bit VDSO mapping
3225
3226        vector=         [IA-64,SMP]
3227                        vector=percpu: enable percpu vector domain
3228
3229        video=          [FB] Frame buffer configuration
3230                        See Documentation/fb/modedb.txt.
3231
3232        virtio_mmio.device=
3233                        [VMMIO] Memory mapped virtio (platform) device.
3234
3235                                <size>@<baseaddr>:<irq>[:<id>]
3236                        where:
3237                                <size>     := size (can use standard suffixes
3238                                                like K, M and G)
3239                                <baseaddr> := physical base address
3240                                <irq>      := interrupt number (as passed to
3241                                                request_irq())
3242                                <id>       := (optional) platform device id
3243                        example:
3244                                virtio_mmio.device=1K@0x100b0000:48:7
3245
3246                        Can be used multiple times for multiple devices.
3247
3248        vga=            [BOOT,X86-32] Select a particular video mode
3249                        See Documentation/x86/boot.txt and
3250                        Documentation/svga.txt.
3251                        Use vga=ask for menu.
3252                        This is actually a boot loader parameter; the value is
3253                        passed to the kernel using a special protocol.
3254
3255        vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3256                        size of <nn>. This can be used to increase the
3257                        minimum size (128MB on x86). It can also be used to
3258                        decrease the size and leave more room for directly
3259                        mapped kernel RAM.
3260
3261        vmhalt=         [KNL,S390] Perform z/VM CP command after system halt.
3262                        Format: <command>
3263
3264        vmpanic=        [KNL,S390] Perform z/VM CP command after kernel panic.
3265                        Format: <command>
3266
3267        vmpoff=         [KNL,S390] Perform z/VM CP command after power off.
3268                        Format: <command>
3269
3270        vsyscall=       [X86-64]
3271                        Controls the behavior of vsyscalls (i.e. calls to
3272                        fixed addresses of 0xffffffffff600x00 from legacy
3273                        code).  Most statically-linked binaries and older
3274                        versions of glibc use these calls.  Because these
3275                        functions are at fixed addresses, they make nice
3276                        targets for exploits that can control RIP.
3277
3278                        emulate     [default] Vsyscalls turn into traps and are
3279                                    emulated reasonably safely.
3280
3281                        native      Vsyscalls are native syscall instructions.
3282                                    This is a little bit faster than trapping
3283                                    and makes a few dynamic recompilers work
3284                                    better than they would in emulation mode.
3285                                    It also makes exploits much easier to write.
3286
3287                        none        Vsyscalls don't work at all.  This makes
3288                                    them quite hard to use for exploits but
3289                                    might break your system.
3290
3291        vt.cur_default= [VT] Default cursor shape.
3292                        Format: 0xCCBBAA, where AA, BB, and CC are the same as
3293                        the parameters of the <Esc>[?A;B;Cc escape sequence;
3294                        see VGA-softcursor.txt. Default: 2 = underline.
3295
3296        vt.default_blu= [VT]
3297                        Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3298                        Change the default blue palette of the console.
3299                        This is a 16-member array composed of values
3300                        ranging from 0-255.
3301
3302        vt.default_grn= [VT]
3303                        Format: <green0>,<green1>,<green2>,...,<green15>
3304                        Change the default green palette of the console.
3305                        This is a 16-member array composed of values
3306                        ranging from 0-255.
3307
3308        vt.default_red= [VT]
3309                        Format: <red0>,<red1>,<red2>,...,<red15>
3310                        Change the default red palette of the console.
3311                        This is a 16-member array composed of values
3312                        ranging from 0-255.
3313
3314        vt.default_utf8=
3315                        [VT]
3316                        Format=<0|1>
3317                        Set system-wide default UTF-8 mode for all tty's.
3318                        Default is 1, i.e. UTF-8 mode is enabled for all
3319                        newly opened terminals.
3320
3321        vt.global_cursor_default=
3322                        [VT]
3323                        Format=<-1|0|1>
3324                        Set system-wide default for whether a cursor
3325                        is shown on new VTs. Default is -1,
3326                        i.e. cursors will be created by default unless
3327                        overridden by individual drivers. 0 will hide
3328                        cursors, 1 will display them.
3329
3330        watchdog timers [HW,WDT] For information on watchdog timers,
3331                        see Documentation/watchdog/watchdog-parameters.txt
3332                        or other driver-specific files in the
3333                        Documentation/watchdog/ directory.
3334
3335        workqueue.disable_numa
3336                        By default, all work items queued to unbound
3337                        workqueues are affine to the NUMA nodes they're
3338                        issued on, which results in better behavior in
3339                        general.  If NUMA affinity needs to be disabled for
3340                        whatever reason, this option can be used.  Note
3341                        that this also can be controlled per-workqueue for
3342                        workqueues visible under /sys/bus/workqueue/.
3343
3344        x2apic_phys     [X86-64,APIC] Use x2apic physical mode instead of
3345                        default x2apic cluster mode on platforms
3346                        supporting x2apic.
3347
3348        x86_mrst_timer= [X86-32,APBT]
3349                        Choose timer option for x86 Moorestown MID platform.
3350                        Two valid options are apbt timer only and lapic timer
3351                        plus one apbt timer for broadcast timer.
3352                        x86_mrst_timer=apbt_only | lapic_and_apbt
3353
3354        xen_emul_unplug=                [HW,X86,XEN]
3355                        Unplug Xen emulated devices
3356                        Format: [unplug0,][unplug1]
3357                        ide-disks -- unplug primary master IDE devices
3358                        aux-ide-disks -- unplug non-primary-master IDE devices
3359                        nics -- unplug network devices
3360                        all -- unplug all emulated devices (NICs and IDE disks)
3361                        unnecessary -- unplugging emulated devices is
3362                                unnecessary even if the host did not respond to
3363                                the unplug protocol
3364                        never -- do not unplug even if version check succeeds
3365
3366        xirc2ps_cs=     [NET,PCMCIA]
3367                        Format:
3368                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3369
3370______________________________________________________________________
3371
3372TODO:
3373
3374        Add more DRM drivers.
3375
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