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<pre code_snippet_id="269587" snippet_file_name="blog_20140401_2_5699080" name="code" class="plain">                          Kernel Parameters

                          ~~~~~~~~~~~~~~~~~

 

The following is a consolidated list of the kernel parameters as implemented

(mostly) by the __setup() macro and sorted into English Dictionary order

(defined as ignoring all punctuation and sorting digits before letters in a

case insensitive manner), and with descriptions where known.

 

Module parameters for loadable modules are specified only as the

parameter name with optional '=' and value as appropriate, such as:

 

    modprobe usbcore blinkenlights=1

 

Module parameters for modules that are built into the kernel image

are specified on the kernel command line with the module name plus

'.' plus parameter name, with '=' and value if appropriate, such as:

 

    usbcore.blinkenlights=1

 

Hyphens (dashes) and underscores are equivalent in parameter names, so

    log_buf_len=1M print-fatal-signals=1

can also be entered as

    log-buf-len=1M print_fatal_signals=1

 

 

This document may not be entirely up to date and comprehensive. The command

"modinfo -p ${modulename}" shows a current list of all parameters of a loadable

module. Loadable modules, after being loaded into the running kernel, also

reveal their parameters in /sys/module/${modulename}/parameters/. Some of these

parameters may be changed at runtime by the command

"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".

 

The parameters listed below are only valid if certain kernel build options were

enabled and if respective hardware is present. The text in square brackets at

the beginning of each description states the restrictions within which a

parameter is applicable:

 

    ACPI    ACPI support is enabled.

    AGP AGP (Accelerated Graphics Port) is enabled.

    ALSA    ALSA sound support is enabled.

    APIC    APIC support is enabled.

    APM Advanced Power Management support is enabled.

    AVR32   AVR32 architecture is enabled.

    AX25    Appropriate AX.25 support is enabled.

    BLACKFIN Blackfin architecture is enabled.

    DRM Direct Rendering Management support is enabled.

    EDD BIOS Enhanced Disk Drive Services (EDD) is enabled

    EFI EFI Partitioning (GPT) is enabled

    EIDE    EIDE/ATAPI support is enabled.

    FB  The frame buffer device is enabled.

    GCOV    GCOV profiling is enabled.

    HW  Appropriate hardware is enabled.

    IA-64   IA-64 architecture is enabled.

    IMA     Integrity measurement architecture is enabled.

    IOSCHED More than one I/O scheduler is enabled.

    IP_PNP  IP DHCP, BOOTP, or RARP is enabled.

    ISAPNP  ISA PnP code is enabled.

    ISDN    Appropriate ISDN support is enabled.

    JOY Appropriate joystick support is enabled.

    KVM Kernel Virtual Machine support is enabled.

    LIBATA  Libata driver is enabled

    LP  Printer support is enabled.

    LOOP    Loopback device support is enabled.

    M68k    M68k architecture is enabled.

            These options have more detailed description inside of

            Documentation/m68k/kernel-options.txt.

    MCA MCA bus support is enabled.

    MDA MDA console support is enabled.

    MOUSE   Appropriate mouse support is enabled.

    MSI Message Signaled Interrupts (PCI).

    MTD MTD (Memory Technology Device) support is enabled.

    NET Appropriate network support is enabled.

    NUMA    NUMA support is enabled.

    GENERIC_TIME The generic timeofday code is enabled.

    NFS Appropriate NFS support is enabled.

    OSS OSS sound support is enabled.

    PV_OPS  A paravirtualized kernel is enabled.

    PARIDE  The ParIDE (parallel port IDE) subsystem is enabled.

    PARISC  The PA-RISC architecture is enabled.

    PCI PCI bus support is enabled.

    PCIE    PCI Express support is enabled.

    PCMCIA  The PCMCIA subsystem is enabled.

    PNP Plug & Play support is enabled.

    PPC PowerPC architecture is enabled.

    PPT Parallel port support is enabled.

    PS2 Appropriate PS/2 support is enabled.

    RAM RAM disk support is enabled.

    ROOTPLUG The example Root Plug LSM is enabled.

    S390    S390 architecture is enabled.

    SCSI    Appropriate SCSI support is enabled.

            A lot of drivers has their options described inside of

            Documentation/scsi/.

    SECURITY Different security models are enabled.

    SELINUX SELinux support is enabled.

    SERIAL  Serial support is enabled.

    SH  SuperH architecture is enabled.

    SMP The kernel is an SMP kernel.

    SPARC   Sparc architecture is enabled.

    SWSUSP  Software suspend (hibernation) is enabled.

    SUSPEND System suspend states are enabled.

    FTRACE  Function tracing enabled.

    TS  Appropriate touchscreen support is enabled.

    UMS USB Mass Storage support is enabled.

    USB USB support is enabled.

    USBHID  USB Human Interface Device support is enabled.

    V4L Video For Linux support is enabled.

    VGA The VGA console has been enabled.

    VT  Virtual terminal support is enabled.

    WDT Watchdog support is enabled.

    XT  IBM PC/XT MFM hard disk support is enabled.

    X86-32  X86-32, aka i386 architecture is enabled.

    X86-64  X86-64 architecture is enabled.

            More X86-64 boot options can be found in

            Documentation/x86/x86_64/boot-options.txt .

    X86 Either 32bit or 64bit x86 (same as X86-32+X86-64)

 

In addition, the following text indicates that the option:

 

    BUGS=   Relates to possible processor bugs on the said processor.

    KNL Is a kernel start-up parameter.

    BOOT    Is a boot loader parameter.

 

Parameters denoted with BOOT are actually interpreted by the boot

loader, and have no meaning to the kernel directly.

Do not modify the syntax of boot loader parameters without extreme

need or coordination with <Documentation/x86/boot.txt>.

 

There are also arch-specific kernel-parameters not documented here.

See for example <Documentation/x86/x86_64/boot-options.txt>.

 

Note that ALL kernel parameters listed below are CASE SENSITIVE, and that

a trailing = on the name of any parameter states that that parameter will

be entered as an environment variable, whereas its absence indicates that

it will appear as a kernel argument readable via /proc/cmdline by programs

running once the system is up.

 

The number of kernel parameters is not limited, but the length of the

complete command line (parameters including spaces etc.) is limited to

a fixed number of characters. This limit depends on the architecture

and is between 256 and 4096 characters. It is defined in the file

./include/asm/setup.h as COMMAND_LINE_SIZE.

 

 

    acpi=       [HW,ACPI,X86]

            Advanced Configuration and Power Interface

            Format: { force | off | ht | strict | noirq | rsdt }

            force -- enable ACPI if default was off

            off -- disable ACPI if default was on

            noirq -- do not use ACPI for IRQ routing

            ht -- run only enough ACPI to enable Hyper Threading

            strict -- Be less tolerant of platforms that are not

                strictly ACPI specification compliant.

            rsdt -- prefer RSDT over (default) XSDT

 

            See also Documentation/power/pm.txt, pci=noacpi

 

    acpi_apic_instance= [ACPI, IOAPIC]

            Format: <int>

            2: use 2nd APIC table, if available

            1,0: use 1st APIC table

            default: 0

 

    acpi_backlight= [HW,ACPI]

            acpi_backlight=vendor

            acpi_backlight=video

            If set to vendor, prefer vendor specific driver

            (e.g. thinkpad_acpi, sony_acpi, etc.) instead

            of the ACPI video.ko driver.

 

    acpi.debug_layer=   [HW,ACPI,ACPI_DEBUG]

    acpi.debug_level=   [HW,ACPI,ACPI_DEBUG]

            Format: <int>

            CONFIG_ACPI_DEBUG must be enabled to produce any ACPI

            debug output.  Bits in debug_layer correspond to a

            _COMPONENT in an ACPI source file, e.g.,

                #define _COMPONENT ACPI_PCI_COMPONENT

            Bits in debug_level correspond to a level in

            ACPI_DEBUG_PRINT statements, e.g.,

                ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...

            The debug_level mask defaults to "info".  See

            Documentation/acpi/debug.txt for more information about

            debug layers and levels.

 

            Enable processor driver info messages:

                acpi.debug_layer=0x20000000

            Enable PCI/PCI interrupt routing info messages:

                acpi.debug_layer=0x400000

            Enable AML "Debug" output, i.e., stores to the Debug

            object while interpreting AML:

                acpi.debug_layer=0xffffffff acpi.debug_level=0x2

            Enable all messages related to ACPI hardware:

                acpi.debug_layer=0x2 acpi.debug_level=0xffffffff

 

            Some values produce so much output that the system is

            unusable.  The "log_buf_len" parameter may be useful

            if you need to capture more output.

 

    acpi_display_output=    [HW,ACPI]

            acpi_display_output=vendor

            acpi_display_output=video

            See above.

 

    acpi_irq_balance [HW,ACPI]

            ACPI will balance active IRQs

            default in APIC mode

 

    acpi_irq_nobalance [HW,ACPI]

            ACPI will not move active IRQs (default)

            default in PIC mode

 

    acpi_irq_isa=   [HW,ACPI] If irq_balance, mark listed IRQs used by ISA

            Format: <irq>,<irq>...

 

    acpi_irq_pci=   [HW,ACPI] If irq_balance, clear listed IRQs for

            use by PCI

            Format: <irq>,<irq>...

 

    acpi_no_auto_ssdt   [HW,ACPI] Disable automatic loading of SSDT

 

    acpi_os_name=   [HW,ACPI] Tell ACPI BIOS the name of the OS

            Format: To spoof as Windows 98: ="Microsoft Windows"

 

    acpi_osi=   [HW,ACPI] Modify list of supported OS interface strings

            acpi_osi="string1"  # add string1 -- only one string

            acpi_osi="!string2" # remove built-in string2

            acpi_osi=       # disable all strings

 

    acpi_pm_good    [X86]

            Override the pmtimer bug detection: force the kernel

            to assume that this machine's pmtimer latches its value

            and always returns good values.

 

    acpi_sci=   [HW,ACPI] ACPI System Control Interrupt trigger mode

            Format: { level | edge | high | low }

 

    acpi_serialize  [HW,ACPI] force serialization of AML methods

 

    acpi_skip_timer_override [HW,ACPI]

            Recognize and ignore IRQ0/pin2 Interrupt Override.

            For broken nForce2 BIOS resulting in XT-PIC timer.

 

    acpi_sleep= [HW,ACPI] Sleep options

            Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,

                  old_ordering, s4_nonvs }

            See Documentation/power/video.txt for information on

            s3_bios and s3_mode.

            s3_beep is for debugging; it makes the PC's speaker beep

            as soon as the kernel's real-mode entry point is called.

            s4_nohwsig prevents ACPI hardware signature from being

            used during resume from hibernation.

            old_ordering causes the ACPI 1.0 ordering of the _PTS

            control method, with respect to putting devices into

            low power states, to be enforced (the ACPI 2.0 ordering

            of _PTS is used by default).

            s4_nonvs prevents the kernel from saving/restoring the

            ACPI NVS memory during hibernation.

 

    acpi_use_timer_override [HW,ACPI]

            Use timer override. For some broken Nvidia NF5 boards

            that require a timer override, but don't have HPET

 

    acpi_enforce_resources= [ACPI]

            { strict | lax | no }

            Check for resource conflicts between native drivers

            and ACPI OperationRegions (SystemIO and SystemMemory

            only). IO ports and memory declared in ACPI might be

            used by the ACPI subsystem in arbitrary AML code and

            can interfere with legacy drivers.

            strict (default): access to resources claimed by ACPI

            is denied; legacy drivers trying to access reserved

            resources will fail to bind to device using them.

            lax: access to resources claimed by ACPI is allowed;

            legacy drivers trying to access reserved resources

            will bind successfully but a warning message is logged.

            no: ACPI OperationRegions are not marked as reserved,

            no further checks are performed.

 

    ad1848=     [HW,OSS]

            Format: <io>,<irq>,<dma>,<dma2>,<type>

 

    add_efi_memmap  [EFI; X86] Include EFI memory map in

            kernel's map of available physical RAM.

 

    advansys=   [HW,SCSI]

            See header of drivers/scsi/advansys.c.

 

    advwdt=     [HW,WDT] Advantech WDT

            Format: <iostart>,<iostop>

 

    aedsp16=    [HW,OSS] Audio Excel DSP 16

            Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq>

            See also header of sound/oss/aedsp16.c.

 

    agp=        [AGP]

            { off | try_unsupported }

            off: disable AGP support

            try_unsupported: try to drive unsupported chipsets

                (may crash computer or cause data corruption)

 

    aha152x=    [HW,SCSI]

            See Documentation/scsi/aha152x.txt.

 

    aha1542=    [HW,SCSI]

            Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]]

 

    aic7xxx=    [HW,SCSI]

            See Documentation/scsi/aic7xxx.txt.

 

    aic79xx=    [HW,SCSI]

            See Documentation/scsi/aic79xx.txt.

 

    amd_iommu=  [HW,X86-84]

            Pass parameters to the AMD IOMMU driver in the system.

            Possible values are:

            isolate - enable device isolation (each device, as far

                      as possible, will get its own protection

                      domain) [default]

            share - put every device behind one IOMMU into the

                same protection domain

            fullflush - enable flushing of IO/TLB entries when

                    they are unmapped. Otherwise they are

                    flushed before they will be reused, which

                    is a lot of faster

 

    amijoy.map= [HW,JOY] Amiga joystick support

            Map of devices attached to JOY0DAT and JOY1DAT

            Format: <a>,<b>

            See also Documentation/kernel/input/joystick.txt

 

    analog.map= [HW,JOY] Analog joystick and gamepad support

            Specifies type or capabilities of an analog joystick

            connected to one of 16 gameports

            Format: <type1>,<type2>,..<type16>

 

    apc=        [HW,SPARC]

            Power management functions (SPARCstation-4/5 + deriv.)

            Format: noidle

            Disable APC CPU standby support. SPARCstation-Fox does

            not play well with APC CPU idle - disable it if you have

            APC and your system crashes randomly.

 

    apic=       [APIC,X86-32] Advanced Programmable Interrupt Controller

            Change the output verbosity whilst booting

            Format: { quiet (default) | verbose | debug }

            Change the amount of debugging information output

            when initialising the APIC and IO-APIC components.

 

    apm=        [APM] Advanced Power Management

            See header of arch/x86/kernel/apm_32.c.

 

    arcrimi=    [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards

            Format: <io>,<irq>,<nodeID>

 

    ataflop=    [HW,M68k]

 

    atarimouse= [HW,MOUSE] Atari Mouse

 

    atascsi=    [HW,SCSI] Atari SCSI

 

    atkbd.extra=    [HW] Enable extra LEDs and keys on IBM RapidAccess,

            EzKey and similar keyboards

 

    atkbd.reset=    [HW] Reset keyboard during initialization

 

    atkbd.set=  [HW] Select keyboard code set

            Format: <int> (2 = AT (default), 3 = PS/2)

 

    atkbd.scroll=   [HW] Enable scroll wheel on MS Office and similar

            keyboards

 

    atkbd.softraw=  [HW] Choose between synthetic and real raw mode

            Format: <bool> (0 = real, 1 = synthetic (default))

 

    atkbd.softrepeat= [HW]

            Use software keyboard repeat

 

    autotest    [IA64]

 

    baycom_epp= [HW,AX25]

            Format: <io>,<mode>

 

    baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem

            Format: <io>,<mode>

            See header of drivers/net/hamradio/baycom_par.c.

 

    baycom_ser_fdx= [HW,AX25]

            BayCom Serial Port AX.25 Modem (Full Duplex Mode)

            Format: <io>,<irq>,<mode>[,<baud>]

            See header of drivers/net/hamradio/baycom_ser_fdx.c.

 

    baycom_ser_hdx= [HW,AX25]

            BayCom Serial Port AX.25 Modem (Half Duplex Mode)

            Format: <io>,<irq>,<mode>

            See header of drivers/net/hamradio/baycom_ser_hdx.c.

 

    boot_delay= Milliseconds to delay each printk during boot.

            Values larger than 10 seconds (10000) are changed to

            no delay (0).

            Format: integer

 

    bootmem_debug   [KNL] Enable bootmem allocator debug messages.

 

    bttv.card=  [HW,V4L] bttv (bt848 + bt878 based grabber cards)

    bttv.radio= Most important insmod options are available as

            kernel args too.

    bttv.pll=   See Documentation/video4linux/bttv/Insmod-options

    bttv.tuner= and Documentation/video4linux/bttv/CARDLIST

 

    BusLogic=   [HW,SCSI]

            See drivers/scsi/BusLogic.c, comment before function

            BusLogic_ParseDriverOptions().

 

    c101=       [NET] Moxa C101 synchronous serial card

 

    cachesize=  [BUGS=X86-32] Override level 2 CPU cache size detection.

            Sometimes CPU hardware bugs make them report the cache

            size incorrectly. The kernel will attempt work arounds

            to fix known problems, but for some CPUs it is not

            possible to determine what the correct size should be.

            This option provides an override for these situations.

 

    capability.disable=

            [SECURITY] Disable capabilities.  This would normally

            be used only if an alternative security model is to be

            configured.  Potentially dangerous and should only be

            used if you are entirely sure of the consequences.

 

    ccw_timeout_log [S390]

            See Documentation/s390/CommonIO for details.

 

    cgroup_disable= [KNL] Disable a particular controller

            Format: {name of the controller(s) to disable}

                {Currently supported controllers - "memory"}

 

    checkreqprot    [SELINUX] Set initial checkreqprot flag value.

            Format: { "0" | "1" }

            See security/selinux/Kconfig help text.

            0 -- check protection applied by kernel (includes

                any implied execute protection).

            1 -- check protection requested by application.

            Default value is set via a kernel config option.

            Value can be changed at runtime via

                /selinux/checkreqprot.

 

    cio_ignore= [S390]

            See Documentation/s390/CommonIO for details.

 

    clock=      [BUGS=X86-32, HW] gettimeofday clocksource override.

            [Deprecated]

            Forces specified clocksource (if available) to be used

            when calculating gettimeofday(). If specified

            clocksource is not available, it defaults to PIT.

            Format: { pit | tsc | cyclone | pmtmr }

 

    clocksource=    [GENERIC_TIME] Override the default clocksource

            Format: <string>

            Override the default clocksource and use the clocksource

            with the name specified.

            Some clocksource names to choose from, depending on

            the platform:

            [all] jiffies (this is the base, fallback clocksource)

            [ACPI] acpi_pm

            [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,

                pxa_timer,timer3,32k_counter,timer0_1

            [AVR32] avr32

            [X86-32] pit,hpet,tsc,vmi-timer;

                scx200_hrt on Geode; cyclone on IBM x440

            [MIPS] MIPS

            [PARISC] cr16

            [S390] tod

            [SH] SuperH

            [SPARC64] tick

            [X86-64] hpet,tsc

 

 

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