Root/Documentation/kernel-parameters.txt

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    AVR32 AVR32 architecture is enabled.
44    AX25 Appropriate AX.25 support is enabled.
45    BLACKFIN Blackfin architecture is enabled.
46    EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
47    EFI EFI Partitioning (GPT) is enabled
48    EIDE EIDE/ATAPI support is enabled.
49    DRM Direct Rendering Management support is enabled.
50    DYNAMIC_DEBUG Build in debug messages and enable them at runtime
51    FB The frame buffer device is enabled.
52    GCOV GCOV profiling is enabled.
53    HW Appropriate hardware is enabled.
54    IA-64 IA-64 architecture is enabled.
55    IMA Integrity measurement architecture is enabled.
56    IOSCHED More than one I/O scheduler is enabled.
57    IP_PNP IP DHCP, BOOTP, or RARP is enabled.
58    IPV6 IPv6 support is enabled.
59    ISAPNP ISA PnP code is enabled.
60    ISDN Appropriate ISDN support is enabled.
61    JOY Appropriate joystick support is enabled.
62    KGDB Kernel debugger support is enabled.
63    KVM Kernel Virtual Machine support is enabled.
64    LIBATA Libata driver is enabled
65    LP Printer support is enabled.
66    LOOP Loopback device support is enabled.
67    M68k M68k architecture is enabled.
68            These options have more detailed description inside of
69            Documentation/m68k/kernel-options.txt.
70    MCA MCA bus support is enabled.
71    MDA MDA console support is enabled.
72    MOUSE Appropriate mouse support is enabled.
73    MSI Message Signaled Interrupts (PCI).
74    MTD MTD (Memory Technology Device) support is enabled.
75    NET Appropriate network support is enabled.
76    NUMA NUMA support is enabled.
77    NFS Appropriate NFS support is enabled.
78    OSS OSS sound support is enabled.
79    PV_OPS A paravirtualized kernel is enabled.
80    PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
81    PARISC The PA-RISC architecture is enabled.
82    PCI PCI bus support is enabled.
83    PCIE PCI Express support is enabled.
84    PCMCIA The PCMCIA subsystem is enabled.
85    PNP Plug & Play support is enabled.
86    PPC PowerPC architecture is enabled.
87    PPT Parallel port support is enabled.
88    PS2 Appropriate PS/2 support is enabled.
89    RAM RAM disk support is enabled.
90    S390 S390 architecture is enabled.
91    SCSI Appropriate SCSI support is enabled.
92            A lot of drivers have their options described inside
93            the Documentation/scsi/ sub-directory.
94    SECURITY Different security models are enabled.
95    SELINUX SELinux support is enabled.
96    APPARMOR AppArmor support is enabled.
97    SERIAL Serial support is enabled.
98    SH SuperH architecture is enabled.
99    SMP The kernel is an SMP kernel.
100    SPARC Sparc architecture is enabled.
101    SWSUSP Software suspend (hibernation) is enabled.
102    SUSPEND System suspend states are enabled.
103    FTRACE Function tracing enabled.
104    TPM TPM drivers are enabled.
105    TS Appropriate touchscreen support is enabled.
106    UMS USB Mass Storage support is enabled.
107    USB USB support is enabled.
108    USBHID USB Human Interface Device support is enabled.
109    V4L Video For Linux support is enabled.
110    VGA The VGA console has been enabled.
111    VT Virtual terminal support is enabled.
112    WDT Watchdog support is enabled.
113    XT IBM PC/XT MFM hard disk support is enabled.
114    X86-32 X86-32, aka i386 architecture is enabled.
115    X86-64 X86-64 architecture is enabled.
116            More X86-64 boot options can be found in
117            Documentation/x86/x86_64/boot-options.txt .
118    X86 Either 32bit or 64bit x86 (same as X86-32+X86-64)
119    XEN Xen support is enabled
120
121In addition, the following text indicates that the option:
122
123    BUGS= Relates to possible processor bugs on the said processor.
124    KNL Is a kernel start-up parameter.
125    BOOT Is a boot loader parameter.
126
127Parameters denoted with BOOT are actually interpreted by the boot
128loader, and have no meaning to the kernel directly.
129Do not modify the syntax of boot loader parameters without extreme
130need or coordination with <Documentation/x86/boot.txt>.
131
132There are also arch-specific kernel-parameters not documented here.
133See for example <Documentation/x86/x86_64/boot-options.txt>.
134
135Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
136a trailing = on the name of any parameter states that that parameter will
137be entered as an environment variable, whereas its absence indicates that
138it will appear as a kernel argument readable via /proc/cmdline by programs
139running once the system is up.
140
141The number of kernel parameters is not limited, but the length of the
142complete command line (parameters including spaces etc.) is limited to
143a fixed number of characters. This limit depends on the architecture
144and is between 256 and 4096 characters. It is defined in the file
145./include/asm/setup.h as COMMAND_LINE_SIZE.
146
147
148    acpi= [HW,ACPI,X86]
149            Advanced Configuration and Power Interface
150            Format: { force | off | strict | noirq | rsdt }
151            force -- enable ACPI if default was off
152            off -- disable ACPI if default was on
153            noirq -- do not use ACPI for IRQ routing
154            strict -- Be less tolerant of platforms that are not
155                strictly ACPI specification compliant.
156            rsdt -- prefer RSDT over (default) XSDT
157            copy_dsdt -- copy DSDT to memory
158
159            See also Documentation/power/pm.txt, pci=noacpi
160
161    acpi_apic_instance= [ACPI, IOAPIC]
162            Format: <int>
163            2: use 2nd APIC table, if available
164            1,0: use 1st APIC table
165            default: 0
166
167    acpi_backlight= [HW,ACPI]
168            acpi_backlight=vendor
169            acpi_backlight=video
170            If set to vendor, prefer vendor specific driver
171            (e.g. thinkpad_acpi, sony_acpi, etc.) instead
172            of the ACPI video.ko driver.
173
174    acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
175    acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
176            Format: <int>
177            CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
178            debug output. Bits in debug_layer correspond to a
179            _COMPONENT in an ACPI source file, e.g.,
180                #define _COMPONENT ACPI_PCI_COMPONENT
181            Bits in debug_level correspond to a level in
182            ACPI_DEBUG_PRINT statements, e.g.,
183                ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
184            The debug_level mask defaults to "info". See
185            Documentation/acpi/debug.txt for more information about
186            debug layers and levels.
187
188            Enable processor driver info messages:
189                acpi.debug_layer=0x20000000
190            Enable PCI/PCI interrupt routing info messages:
191                acpi.debug_layer=0x400000
192            Enable AML "Debug" output, i.e., stores to the Debug
193            object while interpreting AML:
194                acpi.debug_layer=0xffffffff acpi.debug_level=0x2
195            Enable all messages related to ACPI hardware:
196                acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
197
198            Some values produce so much output that the system is
199            unusable. The "log_buf_len" parameter may be useful
200            if you need to capture more output.
201
202    acpi_display_output= [HW,ACPI]
203            acpi_display_output=vendor
204            acpi_display_output=video
205            See above.
206
207    acpi_irq_balance [HW,ACPI]
208            ACPI will balance active IRQs
209            default in APIC mode
210
211    acpi_irq_nobalance [HW,ACPI]
212            ACPI will not move active IRQs (default)
213            default in PIC mode
214
215    acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
216            Format: <irq>,<irq>...
217
218    acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
219            use by PCI
220            Format: <irq>,<irq>...
221
222    acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT
223
224    acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
225            Format: To spoof as Windows 98: ="Microsoft Windows"
226
227    acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
228            acpi_osi="string1" # add string1 -- only one string
229            acpi_osi="!string2" # remove built-in string2
230            acpi_osi= # disable all strings
231
232    acpi_pm_good [X86]
233            Override the pmtimer bug detection: force the kernel
234            to assume that this machine's pmtimer latches its value
235            and always returns good values.
236
237    acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
238            Format: { level | edge | high | low }
239
240    acpi_serialize [HW,ACPI] force serialization of AML methods
241
242    acpi_skip_timer_override [HW,ACPI]
243            Recognize and ignore IRQ0/pin2 Interrupt Override.
244            For broken nForce2 BIOS resulting in XT-PIC timer.
245
246    acpi_sleep= [HW,ACPI] Sleep options
247            Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
248                  old_ordering, s4_nonvs, sci_force_enable }
249            See Documentation/power/video.txt for information on
250            s3_bios and s3_mode.
251            s3_beep is for debugging; it makes the PC's speaker beep
252            as soon as the kernel's real-mode entry point is called.
253            s4_nohwsig prevents ACPI hardware signature from being
254            used during resume from hibernation.
255            old_ordering causes the ACPI 1.0 ordering of the _PTS
256            control method, with respect to putting devices into
257            low power states, to be enforced (the ACPI 2.0 ordering
258            of _PTS is used by default).
259            nonvs prevents the kernel from saving/restoring the
260            ACPI NVS memory during suspend/hibernation and resume.
261            sci_force_enable causes the kernel to set SCI_EN directly
262            on resume from S1/S3 (which is against the ACPI spec,
263            but some broken systems don't work without it).
264
265    acpi_use_timer_override [HW,ACPI]
266            Use timer override. For some broken Nvidia NF5 boards
267            that require a timer override, but don't have HPET
268
269    acpi_enforce_resources= [ACPI]
270            { strict | lax | no }
271            Check for resource conflicts between native drivers
272            and ACPI OperationRegions (SystemIO and SystemMemory
273            only). IO ports and memory declared in ACPI might be
274            used by the ACPI subsystem in arbitrary AML code and
275            can interfere with legacy drivers.
276            strict (default): access to resources claimed by ACPI
277            is denied; legacy drivers trying to access reserved
278            resources will fail to bind to device using them.
279            lax: access to resources claimed by ACPI is allowed;
280            legacy drivers trying to access reserved resources
281            will bind successfully but a warning message is logged.
282            no: ACPI OperationRegions are not marked as reserved,
283            no further checks are performed.
284
285    add_efi_memmap [EFI; X86] Include EFI memory map in
286            kernel's map of available physical RAM.
287
288    agp= [AGP]
289            { off | try_unsupported }
290            off: disable AGP support
291            try_unsupported: try to drive unsupported chipsets
292                (may crash computer or cause data corruption)
293
294    ALSA [HW,ALSA]
295            See Documentation/sound/alsa/alsa-parameters.txt
296
297    alignment= [KNL,ARM]
298            Allow the default userspace alignment fault handler
299            behaviour to be specified. Bit 0 enables warnings,
300            bit 1 enables fixups, and bit 2 sends a segfault.
301
302    amd_iommu= [HW,X86-84]
303            Pass parameters to the AMD IOMMU driver in the system.
304            Possible values are:
305            fullflush - enable flushing of IO/TLB entries when
306                    they are unmapped. Otherwise they are
307                    flushed before they will be reused, which
308                    is a lot of faster
309            off - do not initialize any AMD IOMMU found in
310                    the system
311
312    amijoy.map= [HW,JOY] Amiga joystick support
313            Map of devices attached to JOY0DAT and JOY1DAT
314            Format: <a>,<b>
315            See also Documentation/kernel/input/joystick.txt
316
317    analog.map= [HW,JOY] Analog joystick and gamepad support
318            Specifies type or capabilities of an analog joystick
319            connected to one of 16 gameports
320            Format: <type1>,<type2>,..<type16>
321
322    apc= [HW,SPARC]
323            Power management functions (SPARCstation-4/5 + deriv.)
324            Format: noidle
325            Disable APC CPU standby support. SPARCstation-Fox does
326            not play well with APC CPU idle - disable it if you have
327            APC and your system crashes randomly.
328
329    apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
330            Change the output verbosity whilst booting
331            Format: { quiet (default) | verbose | debug }
332            Change the amount of debugging information output
333            when initialising the APIC and IO-APIC components.
334
335    autoconf= [IPV6]
336            See Documentation/networking/ipv6.txt.
337
338    show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
339            Limit apic dumping. The parameter defines the maximal
340            number of local apics being dumped. Also it is possible
341            to set it to "all" by meaning -- no limit here.
342            Format: { 1 (default) | 2 | ... | all }.
343            The parameter valid if only apic=debug or
344            apic=verbose is specified.
345            Example: apic=debug show_lapic=all
346
347    apm= [APM] Advanced Power Management
348            See header of arch/x86/kernel/apm_32.c.
349
350    arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
351            Format: <io>,<irq>,<nodeID>
352
353    ataflop= [HW,M68k]
354
355    atarimouse= [HW,MOUSE] Atari Mouse
356
357    atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
358            EzKey and similar keyboards
359
360    atkbd.reset= [HW] Reset keyboard during initialization
361
362    atkbd.set= [HW] Select keyboard code set
363            Format: <int> (2 = AT (default), 3 = PS/2)
364
365    atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
366            keyboards
367
368    atkbd.softraw= [HW] Choose between synthetic and real raw mode
369            Format: <bool> (0 = real, 1 = synthetic (default))
370
371    atkbd.softrepeat= [HW]
372            Use software keyboard repeat
373
374    autotest [IA64]
375
376    baycom_epp= [HW,AX25]
377            Format: <io>,<mode>
378
379    baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
380            Format: <io>,<mode>
381            See header of drivers/net/hamradio/baycom_par.c.
382
383    baycom_ser_fdx= [HW,AX25]
384            BayCom Serial Port AX.25 Modem (Full Duplex Mode)
385            Format: <io>,<irq>,<mode>[,<baud>]
386            See header of drivers/net/hamradio/baycom_ser_fdx.c.
387
388    baycom_ser_hdx= [HW,AX25]
389            BayCom Serial Port AX.25 Modem (Half Duplex Mode)
390            Format: <io>,<irq>,<mode>
391            See header of drivers/net/hamradio/baycom_ser_hdx.c.
392
393    boot_delay= Milliseconds to delay each printk during boot.
394            Values larger than 10 seconds (10000) are changed to
395            no delay (0).
396            Format: integer
397
398    bootmem_debug [KNL] Enable bootmem allocator debug messages.
399
400    bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
401    bttv.radio= Most important insmod options are available as
402            kernel args too.
403    bttv.pll= See Documentation/video4linux/bttv/Insmod-options
404    bttv.tuner= and Documentation/video4linux/bttv/CARDLIST
405
406    c101= [NET] Moxa C101 synchronous serial card
407
408    cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
409            Sometimes CPU hardware bugs make them report the cache
410            size incorrectly. The kernel will attempt work arounds
411            to fix known problems, but for some CPUs it is not
412            possible to determine what the correct size should be.
413            This option provides an override for these situations.
414
415    capability.disable=
416            [SECURITY] Disable capabilities. This would normally
417            be used only if an alternative security model is to be
418            configured. Potentially dangerous and should only be
419            used if you are entirely sure of the consequences.
420
421    ccw_timeout_log [S390]
422            See Documentation/s390/CommonIO for details.
423
424    cgroup_disable= [KNL] Disable a particular controller
425            Format: {name of the controller(s) to disable}
426                {Currently supported controllers - "memory"}
427
428    checkreqprot [SELINUX] Set initial checkreqprot flag value.
429            Format: { "0" | "1" }
430            See security/selinux/Kconfig help text.
431            0 -- check protection applied by kernel (includes
432                any implied execute protection).
433            1 -- check protection requested by application.
434            Default value is set via a kernel config option.
435            Value can be changed at runtime via
436                /selinux/checkreqprot.
437
438    cio_ignore= [S390]
439            See Documentation/s390/CommonIO for details.
440
441    clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
442            [Deprecated]
443            Forces specified clocksource (if available) to be used
444            when calculating gettimeofday(). If specified
445            clocksource is not available, it defaults to PIT.
446            Format: { pit | tsc | cyclone | pmtmr }
447
448    clocksource= Override the default clocksource
449            Format: <string>
450            Override the default clocksource and use the clocksource
451            with the name specified.
452            Some clocksource names to choose from, depending on
453            the platform:
454            [all] jiffies (this is the base, fallback clocksource)
455            [ACPI] acpi_pm
456            [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
457                pxa_timer,timer3,32k_counter,timer0_1
458            [AVR32] avr32
459            [X86-32] pit,hpet,tsc;
460                scx200_hrt on Geode; cyclone on IBM x440
461            [MIPS] MIPS
462            [PARISC] cr16
463            [S390] tod
464            [SH] SuperH
465            [SPARC64] tick
466            [X86-64] hpet,tsc
467
468    clearcpuid=BITNUM [X86]
469            Disable CPUID feature X for the kernel. See
470            arch/x86/include/asm/cpufeature.h for the valid bit
471            numbers. Note the Linux specific bits are not necessarily
472            stable over kernel options, but the vendor specific
473            ones should be.
474            Also note that user programs calling CPUID directly
475            or using the feature without checking anything
476            will still see it. This just prevents it from
477            being used by the kernel or shown in /proc/cpuinfo.
478            Also note the kernel might malfunction if you disable
479            some critical bits.
480
481    cmo_free_hint= [PPC] Format: { yes | no }
482            Specify whether pages are marked as being inactive
483            when they are freed. This is used in CMO environments
484            to determine OS memory pressure for page stealing by
485            a hypervisor.
486            Default: yes
487
488    code_bytes [X86] How many bytes of object code to print
489            in an oops report.
490            Range: 0 - 8192
491            Default: 64
492
493    com20020= [HW,NET] ARCnet - COM20020 chipset
494            Format:
495            <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
496
497    com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
498            Format: <io>[,<irq>]
499
500    com90xx= [HW,NET]
501            ARCnet - COM90xx chipset (memory-mapped buffers)
502            Format: <io>[,<irq>[,<memstart>]]
503
504    condev= [HW,S390] console device
505    conmode=
506
507    console= [KNL] Output console device and options.
508
509        tty<n> Use the virtual console device <n>.
510
511        ttyS<n>[,options]
512        ttyUSB0[,options]
513            Use the specified serial port. The options are of
514            the form "bbbbpnf", where "bbbb" is the baud rate,
515            "p" is parity ("n", "o", or "e"), "n" is number of
516            bits, and "f" is flow control ("r" for RTS or
517            omit it). Default is "9600n8".
518
519            See Documentation/serial-console.txt for more
520            information. See
521            Documentation/networking/netconsole.txt for an
522            alternative.
523
524        uart[8250],io,<addr>[,options]
525        uart[8250],mmio,<addr>[,options]
526            Start an early, polled-mode console on the 8250/16550
527            UART at the specified I/O port or MMIO address,
528            switching to the matching ttyS device later. The
529            options are the same as for ttyS, above.
530
531                If the device connected to the port is not a TTY but a braille
532                device, prepend "brl," before the device type, for instance
533            console=brl,ttyS0
534        For now, only VisioBraille is supported.
535
536    consoleblank= [KNL] The console blank (screen saver) timeout in
537            seconds. Defaults to 10*60 = 10mins. A value of 0
538            disables the blank timer.
539
540    coredump_filter=
541            [KNL] Change the default value for
542            /proc/<pid>/coredump_filter.
543            See also Documentation/filesystems/proc.txt.
544
545    cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
546            Format:
547            <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
548
549    crashkernel=nn[KMG]@ss[KMG]
550            [KNL] Reserve a chunk of physical memory to
551            hold a kernel to switch to with kexec on panic.
552
553    crashkernel=range1:size1[,range2:size2,...][@offset]
554            [KNL] Same as above, but depends on the memory
555            in the running system. The syntax of range is
556            start-[end] where start and end are both
557            a memory unit (amount[KMG]). See also
558            Documentation/kdump/kdump.txt for a example.
559
560    cs89x0_dma= [HW,NET]
561            Format: <dma>
562
563    cs89x0_media= [HW,NET]
564            Format: { rj45 | aui | bnc }
565
566    dasd= [HW,NET]
567            See header of drivers/s390/block/dasd_devmap.c.
568
569    db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
570            (one device per port)
571            Format: <port#>,<type>
572            See also Documentation/input/joystick-parport.txt
573
574    ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
575            time. See Documentation/dynamic-debug-howto.txt for
576            details.
577
578    debug [KNL] Enable kernel debugging (events log level).
579
580    debug_locks_verbose=
581            [KNL] verbose self-tests
582            Format=<0|1>
583            Print debugging info while doing the locking API
584            self-tests.
585            We default to 0 (no extra messages), setting it to
586            1 will print _a lot_ more information - normally
587            only useful to kernel developers.
588
589    debug_objects [KNL] Enable object debugging
590
591    no_debug_objects
592            [KNL] Disable object debugging
593
594    debugpat [X86] Enable PAT debugging
595
596    decnet.addr= [HW,NET]
597            Format: <area>[,<node>]
598            See also Documentation/networking/decnet.txt.
599
600    default_hugepagesz=
601            [same as hugepagesz=] The size of the default
602            HugeTLB page size. This is the size represented by
603            the legacy /proc/ hugepages APIs, used for SHM, and
604            default size when mounting hugetlbfs filesystems.
605            Defaults to the default architecture's huge page size
606            if not specified.
607
608    dhash_entries= [KNL]
609            Set number of hash buckets for dentry cache.
610
611    digi= [HW,SERIAL]
612            IO parameters + enable/disable command.
613
614    digiepca= [HW,SERIAL]
615            See drivers/char/README.epca and
616            Documentation/serial/digiepca.txt.
617
618    disable= [IPV6]
619            See Documentation/networking/ipv6.txt.
620
621    disable_ipv6= [IPV6]
622            See Documentation/networking/ipv6.txt.
623
624    disable_mtrr_cleanup [X86]
625            The kernel tries to adjust MTRR layout from continuous
626            to discrete, to make X server driver able to add WB
627            entry later. This parameter disables that.
628
629    disable_mtrr_trim [X86, Intel and AMD only]
630            By default the kernel will trim any uncacheable
631            memory out of your available memory pool based on
632            MTRR settings. This parameter disables that behavior,
633            possibly causing your machine to run very slowly.
634
635    disable_timer_pin_1 [X86]
636            Disable PIN 1 of APIC timer
637            Can be useful to work around chipset bugs.
638
639    dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
640            this option disables the debugging code at boot.
641
642    dma_debug_entries=<number>
643            This option allows to tune the number of preallocated
644            entries for DMA-API debugging code. One entry is
645            required per DMA-API allocation. Use this if the
646            DMA-API debugging code disables itself because the
647            architectural default is too low.
648
649    dma_debug_driver=<driver_name>
650            With this option the DMA-API debugging driver
651            filter feature can be enabled at boot time. Just
652            pass the driver to filter for as the parameter.
653            The filter can be disabled or changed to another
654            driver later using sysfs.
655
656    dscc4.setup= [NET]
657
658    dynamic_printk Enables pr_debug()/dev_dbg() calls if
659            CONFIG_DYNAMIC_PRINTK_DEBUG has been enabled.
660            These can also be switched on/off via
661            <debugfs>/dynamic_printk/modules
662
663    earlycon= [KNL] Output early console device and options.
664        uart[8250],io,<addr>[,options]
665        uart[8250],mmio,<addr>[,options]
666        uart[8250],mmio32,<addr>[,options]
667            Start an early, polled-mode console on the 8250/16550
668            UART at the specified I/O port or MMIO address.
669            MMIO inter-register address stride is either 8bit (mmio)
670                        or 32bit (mmio32).
671            The options are the same as for ttyS, above.
672
673    earlyprintk= [X86,SH,BLACKFIN]
674            earlyprintk=vga
675            earlyprintk=serial[,ttySn[,baudrate]]
676            earlyprintk=ttySn[,baudrate]
677            earlyprintk=dbgp[debugController#]
678
679            Append ",keep" to not disable it when the real console
680            takes over.
681
682            Only vga or serial or usb debug port at a time.
683
684            Currently only ttyS0 and ttyS1 are supported.
685
686            Interaction with the standard serial driver is not
687            very good.
688
689            The VGA output is eventually overwritten by the real
690            console.
691
692    ekgdboc= [X86,KGDB] Allow early kernel console debugging
693            ekgdboc=kbd
694
695            This is desgined to be used in conjunction with
696            the boot argument: earlyprintk=vga
697
698    edd= [EDD]
699            Format: {"off" | "on" | "skip[mbr]"}
700
701    eisa_irq_edge= [PARISC,HW]
702            See header of drivers/parisc/eisa.c.
703
704    elanfreq= [X86-32]
705            See comment before function elanfreq_setup() in
706            arch/x86/kernel/cpu/cpufreq/elanfreq.c.
707
708    elevator= [IOSCHED]
709            Format: {"cfq" | "deadline" | "noop"}
710            See Documentation/block/as-iosched.txt and
711            Documentation/block/deadline-iosched.txt for details.
712
713    elfcorehdr= [IA64,PPC,SH,X86]
714            Specifies physical address of start of kernel core
715            image elf header. Generally kexec loader will
716            pass this option to capture kernel.
717            See Documentation/kdump/kdump.txt for details.
718
719    enable_mtrr_cleanup [X86]
720            The kernel tries to adjust MTRR layout from continuous
721            to discrete, to make X server driver able to add WB
722            entry later. This parameter enables that.
723
724    enable_timer_pin_1 [X86]
725            Enable PIN 1 of APIC timer
726            Can be useful to work around chipset bugs
727            (in particular on some ATI chipsets).
728            The kernel tries to set a reasonable default.
729
730    enforcing [SELINUX] Set initial enforcing status.
731            Format: {"0" | "1"}
732            See security/selinux/Kconfig help text.
733            0 -- permissive (log only, no denials).
734            1 -- enforcing (deny and log).
735            Default value is 0.
736            Value can be changed at runtime via /selinux/enforce.
737
738    erst_disable [ACPI]
739            Disable Error Record Serialization Table (ERST)
740            support.
741
742    ether= [HW,NET] Ethernet cards parameters
743            This option is obsoleted by the "netdev=" option, which
744            has equivalent usage. See its documentation for details.
745
746    failslab=
747    fail_page_alloc=
748    fail_make_request=[KNL]
749            General fault injection mechanism.
750            Format: <interval>,<probability>,<space>,<times>
751            See also /Documentation/fault-injection/.
752
753    floppy= [HW]
754            See Documentation/blockdev/floppy.txt.
755
756    force_pal_cache_flush
757            [IA-64] Avoid check_sal_cache_flush which may hang on
758            buggy SAL_CACHE_FLUSH implementations. Using this
759            parameter will force ia64_sal_cache_flush to call
760            ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
761
762    ftrace=[tracer]
763            [FTRACE] will set and start the specified tracer
764            as early as possible in order to facilitate early
765            boot debugging.
766
767    ftrace_dump_on_oops[=orig_cpu]
768            [FTRACE] will dump the trace buffers on oops.
769            If no parameter is passed, ftrace will dump
770            buffers of all CPUs, but if you pass orig_cpu, it will
771            dump only the buffer of the CPU that triggered the
772            oops.
773
774    ftrace_filter=[function-list]
775            [FTRACE] Limit the functions traced by the function
776            tracer at boot up. function-list is a comma separated
777            list of functions. This list can be changed at run
778            time by the set_ftrace_filter file in the debugfs
779            tracing directory.
780
781    ftrace_notrace=[function-list]
782            [FTRACE] Do not trace the functions specified in
783            function-list. This list can be changed at run time
784            by the set_ftrace_notrace file in the debugfs
785            tracing directory.
786
787    ftrace_graph_filter=[function-list]
788            [FTRACE] Limit the top level callers functions traced
789            by the function graph tracer at boot up.
790            function-list is a comma separated list of functions
791            that can be changed at run time by the
792            set_graph_function file in the debugfs tracing directory.
793
794    gamecon.map[2|3]=
795            [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
796            support via parallel port (up to 5 devices per port)
797            Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
798            See also Documentation/input/joystick-parport.txt
799
800    gamma= [HW,DRM]
801
802    gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
803            Format: off | on
804            default: on
805
806    gcov_persist= [GCOV] When non-zero (default), profiling data for
807            kernel modules is saved and remains accessible via
808            debugfs, even when the module is unloaded/reloaded.
809            When zero, profiling data is discarded and associated
810            debugfs files are removed at module unload time.
811
812    gpt [EFI] Forces disk with valid GPT signature but
813            invalid Protective MBR to be treated as GPT.
814
815    hashdist= [KNL,NUMA] Large hashes allocated during boot
816            are distributed across NUMA nodes. Defaults on
817            for 64bit NUMA, off otherwise.
818            Format: 0 | 1 (for off | on)
819
820    hcl= [IA-64] SGI's Hardware Graph compatibility layer
821
822    hd= [EIDE] (E)IDE hard drive subsystem geometry
823            Format: <cyl>,<head>,<sect>
824
825    hest_disable [ACPI]
826            Disable Hardware Error Source Table (HEST) support;
827            corresponding firmware-first mode error processing
828            logic will be disabled.
829
830    highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
831            size of <nn>. This works even on boxes that have no
832            highmem otherwise. This also works to reduce highmem
833            size on bigger boxes.
834
835    highres= [KNL] Enable/disable high resolution timer mode.
836            Valid parameters: "on", "off"
837            Default: "on"
838
839    hisax= [HW,ISDN]
840            See Documentation/isdn/README.HiSax.
841
842    hlt [BUGS=ARM,SH]
843
844    hpet= [X86-32,HPET] option to control HPET usage
845            Format: { enable (default) | disable | force |
846                verbose }
847            disable: disable HPET and use PIT instead
848            force: allow force enabled of undocumented chips (ICH4,
849                VIA, nVidia)
850            verbose: show contents of HPET registers during setup
851
852    hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
853    hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
854            On x86-64 and powerpc, this option can be specified
855            multiple times interleaved with hugepages= to reserve
856            huge pages of different sizes. Valid pages sizes on
857            x86-64 are 2M (when the CPU supports "pse") and 1G
858            (when the CPU supports the "pdpe1gb" cpuinfo flag)
859            Note that 1GB pages can only be allocated at boot time
860            using hugepages= and not freed afterwards.
861
862    hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
863                   terminal devices. Valid values: 0..8
864    hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
865                   If specified, z/VM IUCV HVC accepts connections
866                   from listed z/VM user IDs only.
867
868    i2c_bus= [HW] Override the default board specific I2C bus speed
869                 or register an additional I2C bus that is not
870                 registered from board initialization code.
871                 Format:
872                 <bus_id>,<clkrate>
873
874    i8042.debug [HW] Toggle i8042 debug mode
875    i8042.direct [HW] Put keyboard port into non-translated mode
876    i8042.dumbkbd [HW] Pretend that controller can only read data from
877                 keyboard and cannot control its state
878                 (Don't attempt to blink the leds)
879    i8042.noaux [HW] Don't check for auxiliary (== mouse) port
880    i8042.nokbd [HW] Don't check/create keyboard port
881    i8042.noloop [HW] Disable the AUX Loopback command while probing
882                 for the AUX port
883    i8042.nomux [HW] Don't check presence of an active multiplexing
884                 controller
885    i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
886                 controllers
887    i8042.reset [HW] Reset the controller during init and cleanup
888    i8042.unlock [HW] Unlock (ignore) the keylock
889
890    i810= [HW,DRM]
891
892    i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
893            indicates that the driver is running on unsupported
894            hardware.
895    i8k.force [HW] Activate i8k driver even if SMM BIOS signature
896            does not match list of supported models.
897    i8k.power_status
898            [HW] Report power status in /proc/i8k
899            (disabled by default)
900    i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
901            capability is set.
902
903    icn= [HW,ISDN]
904            Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
905
906    ide-core.nodma= [HW] (E)IDE subsystem
907            Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
908            .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
909            .cdrom .chs .ignore_cable are additional options
910            See Documentation/ide/ide.txt.
911
912    ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
913            Claim all unknown PCI IDE storage controllers.
914
915    idle= [X86]
916            Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
917            Poll forces a polling idle loop that can slightly
918            improve the performance of waking up a idle CPU, but
919            will use a lot of power and make the system run hot.
920            Not recommended.
921            idle=mwait: On systems which support MONITOR/MWAIT but
922            the kernel chose to not use it because it doesn't save
923            as much power as a normal idle loop, use the
924            MONITOR/MWAIT idle loop anyways. Performance should be
925            the same as idle=poll.
926            idle=halt: Halt is forced to be used for CPU idle.
927            In such case C2/C3 won't be used again.
928            idle=nomwait: Disable mwait for CPU C-states
929
930    ignore_loglevel [KNL]
931            Ignore loglevel setting - this will print /all/
932            kernel messages to the console. Useful for debugging.
933
934    ihash_entries= [KNL]
935            Set number of hash buckets for inode cache.
936
937    ima_audit= [IMA]
938            Format: { "0" | "1" }
939            0 -- integrity auditing messages. (Default)
940            1 -- enable informational integrity auditing messages.
941
942    ima_hash= [IMA]
943            Format: { "sha1" | "md5" }
944            default: "sha1"
945
946    ima_tcb [IMA]
947            Load a policy which meets the needs of the Trusted
948            Computing Base. This means IMA will measure all
949            programs exec'd, files mmap'd for exec, and all files
950            opened for read by uid=0.
951
952    init= [KNL]
953            Format: <full_path>
954            Run specified binary instead of /sbin/init as init
955            process.
956
957    initcall_debug [KNL] Trace initcalls as they are executed. Useful
958            for working out where the kernel is dying during
959            startup.
960
961    initrd= [BOOT] Specify the location of the initial ramdisk
962
963    inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
964            Format: <irq>
965
966    intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
967        on
968            Enable intel iommu driver.
969        off
970            Disable intel iommu driver.
971        igfx_off [Default Off]
972            By default, gfx is mapped as normal device. If a gfx
973            device has a dedicated DMAR unit, the DMAR unit is
974            bypassed by not enabling DMAR with this option. In
975            this case, gfx device will use physical address for
976            DMA.
977        forcedac [x86_64]
978            With this option iommu will not optimize to look
979            for io virtual address below 32 bit forcing dual
980            address cycle on pci bus for cards supporting greater
981            than 32 bit addressing. The default is to look
982            for translation below 32 bit and if not available
983            then look in the higher range.
984        strict [Default Off]
985            With this option on every unmap_single operation will
986            result in a hardware IOTLB flush operation as opposed
987            to batching them for performance.
988
989    intremap= [X86-64, Intel-IOMMU]
990            Format: { on (default) | off | nosid }
991            on enable Interrupt Remapping (default)
992            off disable Interrupt Remapping
993            nosid disable Source ID checking
994
995    inttest= [IA64]
996
997    iomem= Disable strict checking of access to MMIO memory
998        strict regions from userspace.
999        relaxed
1000
1001    iommu= [x86]
1002        off
1003        force
1004        noforce
1005        biomerge
1006        panic
1007        nopanic
1008        merge
1009        nomerge
1010        forcesac
1011        soft
1012        pt [x86, IA64]
1013
1014    io7= [HW] IO7 for Marvel based alpha systems
1015            See comment before marvel_specify_io7 in
1016            arch/alpha/kernel/core_marvel.c.
1017
1018    io_delay= [X86] I/O delay method
1019        0x80
1020            Standard port 0x80 based delay
1021        0xed
1022            Alternate port 0xed based delay (needed on some systems)
1023        udelay
1024            Simple two microseconds delay
1025        none
1026            No delay
1027
1028    ip= [IP_PNP]
1029            See Documentation/filesystems/nfs/nfsroot.txt.
1030
1031    ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1032            See comment before ip2_setup() in
1033            drivers/char/ip2/ip2base.c.
1034
1035    irqfixup [HW]
1036            When an interrupt is not handled search all handlers
1037            for it. Intended to get systems with badly broken
1038            firmware running.
1039
1040    irqpoll [HW]
1041            When an interrupt is not handled search all handlers
1042            for it. Also check all handlers each timer
1043            interrupt. Intended to get systems with badly broken
1044            firmware running.
1045
1046    isapnp= [ISAPNP]
1047            Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1048
1049    isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1050            Format:
1051            <cpu number>,...,<cpu number>
1052            or
1053            <cpu number>-<cpu number>
1054            (must be a positive range in ascending order)
1055            or a mixture
1056            <cpu number>,...,<cpu number>-<cpu number>
1057
1058            This option can be used to specify one or more CPUs
1059            to isolate from the general SMP balancing and scheduling
1060            algorithms. You can move a process onto or off an
1061            "isolated" CPU via the CPU affinity syscalls or cpuset.
1062            <cpu number> begins at 0 and the maximum value is
1063            "number of CPUs in system - 1".
1064
1065            This option is the preferred way to isolate CPUs. The
1066            alternative -- manually setting the CPU mask of all
1067            tasks in the system -- can cause problems and
1068            suboptimal load balancer performance.
1069
1070    iucv= [HW,NET]
1071
1072    js= [HW,JOY] Analog joystick
1073            See Documentation/input/joystick.txt.
1074
1075    keepinitrd [HW,ARM]
1076
1077    kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1078            specifies the amount of memory usable by the kernel
1079            for non-movable allocations. The requested amount is
1080            spread evenly throughout all nodes in the system. The
1081            remaining memory in each node is used for Movable
1082            pages. In the event, a node is too small to have both
1083            kernelcore and Movable pages, kernelcore pages will
1084            take priority and other nodes will have a larger number
1085            of kernelcore pages. The Movable zone is used for the
1086            allocation of pages that may be reclaimed or moved
1087            by the page migration subsystem. This means that
1088            HugeTLB pages may not be allocated from this zone.
1089            Note that allocations like PTEs-from-HighMem still
1090            use the HighMem zone if it exists, and the Normal
1091            zone if it does not.
1092
1093    kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1094            Format: <Controller#>[,poll interval]
1095            The controller # is the number of the ehci usb debug
1096            port as it is probed via PCI. The poll interval is
1097            optional and is the number seconds in between
1098            each poll cycle to the debug port in case you need
1099            the functionality for interrupting the kernel with
1100            gdb or control-c on the dbgp connection. When
1101            not using this parameter you use sysrq-g to break into
1102            the kernel debugger.
1103
1104    kgdboc= [KGDB,HW] kgdb over consoles.
1105            Requires a tty driver that supports console polling,
1106            or a supported polling keyboard driver (non-usb).
1107             Serial only format: <serial_device>[,baud]
1108             keyboard only format: kbd
1109             keyboard and serial format: kbd,<serial_device>[,baud]
1110            Optional Kernel mode setting:
1111             kms, kbd format: kms,kbd
1112             kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1113
1114    kgdbwait [KGDB] Stop kernel execution and enter the
1115            kernel debugger at the earliest opportunity.
1116
1117    kmac= [MIPS] korina ethernet MAC address.
1118            Configure the RouterBoard 532 series on-chip
1119            Ethernet adapter MAC address.
1120
1121    kmemleak= [KNL] Boot-time kmemleak enable/disable
1122            Valid arguments: on, off
1123            Default: on
1124
1125    kstack=N [X86] Print N words from the kernel stack
1126            in oops dumps.
1127
1128    kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1129            Default is 0 (don't ignore, but inject #GP)
1130
1131    kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1132            Default is 1 (enabled)
1133
1134    kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1135            KVM MMU at runtime.
1136            Default is 0 (off)
1137
1138    kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1139            Default is 1 (enabled)
1140
1141    kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1142            for all guests.
1143            Default is 1 (enabled) if in 64bit or 32bit-PAE mode
1144
1145    kvm-intel.bypass_guest_pf=
1146            [KVM,Intel] Disables bypassing of guest page faults
1147            on Intel chips. Default is 1 (enabled)
1148
1149    kvm-intel.ept= [KVM,Intel] Disable extended page tables
1150            (virtualized MMU) support on capable Intel chips.
1151            Default is 1 (enabled)
1152
1153    kvm-intel.emulate_invalid_guest_state=
1154            [KVM,Intel] Enable emulation of invalid guest states
1155            Default is 0 (disabled)
1156
1157    kvm-intel.flexpriority=
1158            [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1159            Default is 1 (enabled)
1160
1161    kvm-intel.unrestricted_guest=
1162            [KVM,Intel] Disable unrestricted guest feature
1163            (virtualized real and unpaged mode) on capable
1164            Intel chips. Default is 1 (enabled)
1165
1166    kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1167            feature (tagged TLBs) on capable Intel chips.
1168            Default is 1 (enabled)
1169
1170    l2cr= [PPC]
1171
1172    l3cr= [PPC]
1173
1174    lapic [X86-32,APIC] Enable the local APIC even if BIOS
1175            disabled it.
1176
1177    lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1178            in C2 power state.
1179
1180    libata.dma= [LIBATA] DMA control
1181            libata.dma=0 Disable all PATA and SATA DMA
1182            libata.dma=1 PATA and SATA Disk DMA only
1183            libata.dma=2 ATAPI (CDROM) DMA only
1184            libata.dma=4 Compact Flash DMA only
1185            Combinations also work, so libata.dma=3 enables DMA
1186            for disks and CDROMs, but not CFs.
1187    
1188    libata.ignore_hpa= [LIBATA] Ignore HPA limit
1189            libata.ignore_hpa=0 keep BIOS limits (default)
1190            libata.ignore_hpa=1 ignore limits, using full disk
1191
1192    libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1193            when set.
1194            Format: <int>
1195
1196    libata.force= [LIBATA] Force configurations. The format is comma
1197            separated list of "[ID:]VAL" where ID is
1198            PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1199            matching port, link or device. Basically, it matches
1200            the ATA ID string printed on console by libata. If
1201            the whole ID part is omitted, the last PORT and DEVICE
1202            values are used. If ID hasn't been specified yet, the
1203            configuration applies to all ports, links and devices.
1204
1205            If only DEVICE is omitted, the parameter applies to
1206            the port and all links and devices behind it. DEVICE
1207            number of 0 either selects the first device or the
1208            first fan-out link behind PMP device. It does not
1209            select the host link. DEVICE number of 15 selects the
1210            host link and device attached to it.
1211
1212            The VAL specifies the configuration to force. As long
1213            as there's no ambiguity shortcut notation is allowed.
1214            For example, both 1.5 and 1.5G would work for 1.5Gbps.
1215            The following configurations can be forced.
1216
1217            * Cable type: 40c, 80c, short40c, unk, ign or sata.
1218              Any ID with matching PORT is used.
1219
1220            * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1221
1222            * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1223              udma[/][16,25,33,44,66,100,133] notation is also
1224              allowed.
1225
1226            * [no]ncq: Turn on or off NCQ.
1227
1228            * nohrst, nosrst, norst: suppress hard, soft
1229                          and both resets.
1230
1231            * dump_id: dump IDENTIFY data.
1232
1233            If there are multiple matching configurations changing
1234            the same attribute, the last one is used.
1235
1236    memblock=debug [KNL] Enable memblock debug messages.
1237
1238    load_ramdisk= [RAM] List of ramdisks to load from floppy
1239            See Documentation/blockdev/ramdisk.txt.
1240
1241    lockd.nlm_grace_period=P [NFS] Assign grace period.
1242            Format: <integer>
1243
1244    lockd.nlm_tcpport=N [NFS] Assign TCP port.
1245            Format: <integer>
1246
1247    lockd.nlm_timeout=T [NFS] Assign timeout value.
1248            Format: <integer>
1249
1250    lockd.nlm_udpport=M [NFS] Assign UDP port.
1251            Format: <integer>
1252
1253    logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1254            Format: <irq>
1255
1256    loglevel= All Kernel Messages with a loglevel smaller than the
1257            console loglevel will be printed to the console. It can
1258            also be changed with klogd or other programs. The
1259            loglevels are defined as follows:
1260
1261            0 (KERN_EMERG) system is unusable
1262            1 (KERN_ALERT) action must be taken immediately
1263            2 (KERN_CRIT) critical conditions
1264            3 (KERN_ERR) error conditions
1265            4 (KERN_WARNING) warning conditions
1266            5 (KERN_NOTICE) normal but significant condition
1267            6 (KERN_INFO) informational
1268            7 (KERN_DEBUG) debug-level messages
1269
1270    log_buf_len=n Sets the size of the printk ring buffer, in bytes.
1271            Format: { n | nk | nM }
1272            n must be a power of two. The default size
1273            is set in the kernel config file.
1274
1275    logo.nologo [FB] Disables display of the built-in Linux logo.
1276            This may be used to provide more screen space for
1277            kernel log messages and is useful when debugging
1278            kernel boot problems.
1279
1280    lp=0 [LP] Specify parallel ports to use, e.g,
1281    lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1282    lp=reset first parallel port). 'lp=0' disables the
1283    lp=auto printer driver. 'lp=reset' (which can be
1284                specified in addition to the ports) causes
1285                attached printers to be reset. Using
1286                lp=port1,port2,... specifies the parallel ports
1287                to associate lp devices with, starting with
1288                lp0. A port specification may be 'none' to skip
1289                that lp device, or a parport name such as
1290                'parport0'. Specifying 'lp=auto' instead of a
1291                port specification list means that device IDs
1292                from each port should be examined, to see if
1293                an IEEE 1284-compliant printer is attached; if
1294                so, the driver will manage that printer.
1295                See also header of drivers/char/lp.c.
1296
1297    lpj=n [KNL]
1298            Sets loops_per_jiffy to given constant, thus avoiding
1299            time-consuming boot-time autodetection (up to 250 ms per
1300            CPU). 0 enables autodetection (default). To determine
1301            the correct value for your kernel, boot with normal
1302            autodetection and see what value is printed. Note that
1303            on SMP systems the preset will be applied to all CPUs,
1304            which is likely to cause problems if your CPUs need
1305            significantly divergent settings. An incorrect value
1306            will cause delays in the kernel to be wrong, leading to
1307            unpredictable I/O errors and other breakage. Although
1308            unlikely, in the extreme case this might damage your
1309            hardware.
1310
1311    ltpc= [NET]
1312            Format: <io>,<irq>,<dma>
1313
1314    machvec= [IA64] Force the use of a particular machine-vector
1315            (machvec) in a generic kernel.
1316            Example: machvec=hpzx1_swiotlb
1317
1318    machtype= [Loongson] Share the same kernel image file between different
1319             yeeloong laptop.
1320            Example: machtype=lemote-yeeloong-2f-7inch
1321
1322    max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1323            than or equal to this physical address is ignored.
1324
1325    maxcpus= [SMP] Maximum number of processors that an SMP kernel
1326            should make use of. maxcpus=n : n >= 0 limits the
1327            kernel to using 'n' processors. n=0 is a special case,
1328            it is equivalent to "nosmp", which also disables
1329            the IO APIC.
1330
1331    max_loop= [LOOP] Maximum number of loopback devices that can
1332            be mounted
1333            Format: <1-256>
1334
1335    mcatest= [IA-64]
1336
1337    mce [X86-32] Machine Check Exception
1338
1339    mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1340
1341    md= [HW] RAID subsystems devices and level
1342            See Documentation/md.txt.
1343
1344    mdacon= [MDA]
1345            Format: <first>,<last>
1346            Specifies range of consoles to be captured by the MDA.
1347
1348    mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1349            Amount of memory to be used when the kernel is not able
1350            to see the whole system memory or for test.
1351            [X86-32] Use together with memmap= to avoid physical
1352            address space collisions. Without memmap= PCI devices
1353            could be placed at addresses belonging to unused RAM.
1354
1355    mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1356            memory.
1357
1358    memchunk=nn[KMG]
1359            [KNL,SH] Allow user to override the default size for
1360            per-device physically contiguous DMA buffers.
1361
1362    memmap=exactmap [KNL,X86] Enable setting of an exact
1363            E820 memory map, as specified by the user.
1364            Such memmap=exactmap lines can be constructed based on
1365            BIOS output or other requirements. See the memmap=nn@ss
1366            option description.
1367
1368    memmap=nn[KMG]@ss[KMG]
1369            [KNL] Force usage of a specific region of memory
1370            Region of memory to be used, from ss to ss+nn.
1371
1372    memmap=nn[KMG]#ss[KMG]
1373            [KNL,ACPI] Mark specific memory as ACPI data.
1374            Region of memory to be used, from ss to ss+nn.
1375
1376    memmap=nn[KMG]$ss[KMG]
1377            [KNL,ACPI] Mark specific memory as reserved.
1378            Region of memory to be used, from ss to ss+nn.
1379            Example: Exclude memory from 0x18690000-0x1869ffff
1380                     memmap=64K$0x18690000
1381                     or
1382                     memmap=0x10000$0x18690000
1383
1384    memory_corruption_check=0/1 [X86]
1385            Some BIOSes seem to corrupt the first 64k of
1386            memory when doing things like suspend/resume.
1387            Setting this option will scan the memory
1388            looking for corruption. Enabling this will
1389            both detect corruption and prevent the kernel
1390            from using the memory being corrupted.
1391            However, its intended as a diagnostic tool; if
1392            repeatable BIOS-originated corruption always
1393            affects the same memory, you can use memmap=
1394            to prevent the kernel from using that memory.
1395
1396    memory_corruption_check_size=size [X86]
1397            By default it checks for corruption in the low
1398            64k, making this memory unavailable for normal
1399            use. Use this parameter to scan for
1400            corruption in more or less memory.
1401
1402    memory_corruption_check_period=seconds [X86]
1403            By default it checks for corruption every 60
1404            seconds. Use this parameter to check at some
1405            other rate. 0 disables periodic checking.
1406
1407    memtest= [KNL,X86] Enable memtest
1408            Format: <integer>
1409            default : 0 <disable>
1410            Specifies the number of memtest passes to be
1411            performed. Each pass selects another test
1412            pattern from a given set of patterns. Memtest
1413            fills the memory with this pattern, validates
1414            memory contents and reserves bad memory
1415            regions that are detected.
1416
1417    meye.*= [HW] Set MotionEye Camera parameters
1418            See Documentation/video4linux/meye.txt.
1419
1420    mfgpt_irq= [IA-32] Specify the IRQ to use for the
1421            Multi-Function General Purpose Timers on AMD Geode
1422            platforms.
1423
1424    mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1425            the BIOS has incorrectly applied a workaround. TinyBIOS
1426            version 0.98 is known to be affected, 0.99 fixes the
1427            problem by letting the user disable the workaround.
1428
1429    mga= [HW,DRM]
1430
1431    min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1432            physical address is ignored.
1433
1434    mini2440= [ARM,HW,KNL]
1435            Format:[0..2][b][c][t]
1436            Default: "0tb"
1437            MINI2440 configuration specification:
1438            0 - The attached screen is the 3.5" TFT
1439            1 - The attached screen is the 7" TFT
1440            2 - The VGA Shield is attached (1024x768)
1441            Leaving out the screen size parameter will not load
1442            the TFT driver, and the framebuffer will be left
1443            unconfigured.
1444            b - Enable backlight. The TFT backlight pin will be
1445            linked to the kernel VESA blanking code and a GPIO
1446            LED. This parameter is not necessary when using the
1447            VGA shield.
1448            c - Enable the s3c camera interface.
1449            t - Reserved for enabling touchscreen support. The
1450            touchscreen support is not enabled in the mainstream
1451            kernel as of 2.6.30, a preliminary port can be found
1452            in the "bleeding edge" mini2440 support kernel at
1453            http://repo.or.cz/w/linux-2.6/mini2440.git
1454
1455    mminit_loglevel=
1456            [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1457            parameter allows control of the logging verbosity for
1458            the additional memory initialisation checks. A value
1459            of 0 disables mminit logging and a level of 4 will
1460            log everything. Information is printed at KERN_DEBUG
1461            so loglevel=8 may also need to be specified.
1462
1463    mousedev.tap_time=
1464            [MOUSE] Maximum time between finger touching and
1465            leaving touchpad surface for touch to be considered
1466            a tap and be reported as a left button click (for
1467            touchpads working in absolute mode only).
1468            Format: <msecs>
1469    mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1470            reporting absolute coordinates, such as tablets
1471    mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1472            reporting absolute coordinates, such as tablets
1473
1474    movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1475            is similar to kernelcore except it specifies the
1476            amount of memory used for migratable allocations.
1477            If both kernelcore and movablecore is specified,
1478            then kernelcore will be at *least* the specified
1479            value but may be more. If movablecore on its own
1480            is specified, the administrator must be careful
1481            that the amount of memory usable for all allocations
1482            is not too small.
1483
1484    MTD_Partition= [MTD]
1485            Format: <name>,<region-number>,<size>,<offset>
1486
1487    MTD_Region= [MTD] Format:
1488            <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1489
1490    mtdparts= [MTD]
1491            See drivers/mtd/cmdlinepart.c.
1492
1493    onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1494
1495            Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1496
1497            boundary - index of last SLC block on Flex-OneNAND.
1498                   The remaining blocks are configured as MLC blocks.
1499            lock - Configure if Flex-OneNAND boundary should be locked.
1500                   Once locked, the boundary cannot be changed.
1501                   1 indicates lock status, 0 indicates unlock status.
1502
1503    mtdset= [ARM]
1504            ARM/S3C2412 JIVE boot control
1505
1506            See arch/arm/mach-s3c2412/mach-jive.c
1507
1508    mtouchusb.raw_coordinates=
1509            [HW] Make the MicroTouch USB driver use raw coordinates
1510            ('y', default) or cooked coordinates ('n')
1511
1512    mtrr_chunk_size=nn[KMG] [X86]
1513            used for mtrr cleanup. It is largest continuous chunk
1514            that could hold holes aka. UC entries.
1515
1516    mtrr_gran_size=nn[KMG] [X86]
1517            Used for mtrr cleanup. It is granularity of mtrr block.
1518            Default is 1.
1519            Large value could prevent small alignment from
1520            using up MTRRs.
1521
1522    mtrr_spare_reg_nr=n [X86]
1523            Format: <integer>
1524            Range: 0,7 : spare reg number
1525            Default : 1
1526            Used for mtrr cleanup. It is spare mtrr entries number.
1527            Set to 2 or more if your graphical card needs more.
1528
1529    n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1530
1531    netdev= [NET] Network devices parameters
1532            Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1533            Note that mem_start is often overloaded to mean
1534            something different and driver-specific.
1535            This usage is only documented in each driver source
1536            file if at all.
1537
1538    nf_conntrack.acct=
1539            [NETFILTER] Enable connection tracking flow accounting
1540            0 to disable accounting
1541            1 to enable accounting
1542            Default value is 0.
1543
1544    nfsaddrs= [NFS] Deprecated. Use ip= instead.
1545            See Documentation/filesystems/nfs/nfsroot.txt.
1546
1547    nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1548            See Documentation/filesystems/nfs/nfsroot.txt.
1549
1550    nfsrootdebug [NFS] enable nfsroot debugging messages.
1551            See Documentation/filesystems/nfs/nfsroot.txt.
1552
1553    nfs.callback_tcpport=
1554            [NFS] set the TCP port on which the NFSv4 callback
1555            channel should listen.
1556
1557    nfs.cache_getent=
1558            [NFS] sets the pathname to the program which is used
1559            to update the NFS client cache entries.
1560
1561    nfs.cache_getent_timeout=
1562            [NFS] sets the timeout after which an attempt to
1563            update a cache entry is deemed to have failed.
1564
1565    nfs.idmap_cache_timeout=
1566            [NFS] set the maximum lifetime for idmapper cache
1567            entries.
1568
1569    nfs.enable_ino64=
1570            [NFS] enable 64-bit inode numbers.
1571            If zero, the NFS client will fake up a 32-bit inode
1572            number for the readdir() and stat() syscalls instead
1573            of returning the full 64-bit number.
1574            The default is to return 64-bit inode numbers.
1575
1576    nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1577            when a NMI is triggered.
1578            Format: [state][,regs][,debounce][,die]
1579
1580    nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1581            Format: [panic,][num]
1582            Valid num: 0,1,2
1583            0 - turn nmi_watchdog off
1584            1 - use the IO-APIC timer for the NMI watchdog
1585            2 - use the local APIC for the NMI watchdog using
1586            a performance counter. Note: This will use one
1587            performance counter and the local APIC's performance
1588            vector.
1589            When panic is specified, panic when an NMI watchdog
1590            timeout occurs.
1591            This is useful when you use a panic=... timeout and
1592            need the box quickly up again.
1593            Instead of 1 and 2 it is possible to use the following
1594            symbolic names: lapic and ioapic
1595            Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic
1596
1597    netpoll.carrier_timeout=
1598            [NET] Specifies amount of time (in seconds) that
1599            netpoll should wait for a carrier. By default netpoll
1600            waits 4 seconds.
1601
1602    no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1603            emulation library even if a 387 maths coprocessor
1604            is present.
1605
1606    no_console_suspend
1607            [HW] Never suspend the console
1608            Disable suspending of consoles during suspend and
1609            hibernate operations. Once disabled, debugging
1610            messages can reach various consoles while the rest
1611            of the system is being put to sleep (ie, while
1612            debugging driver suspend/resume hooks). This may
1613            not work reliably with all consoles, but is known
1614            to work with serial and VGA consoles.
1615
1616    noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1617            caches in the slab allocator. Saves per-node memory,
1618            but will impact performance.
1619
1620    noalign [KNL,ARM]
1621
1622    noapic [SMP,APIC] Tells the kernel to not make use of any
1623            IOAPICs that may be present in the system.
1624
1625    nobats [PPC] Do not use BATs for mapping kernel lowmem
1626            on "Classic" PPC cores.
1627
1628    nocache [ARM]
1629
1630    noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1631
1632    nodelayacct [KNL] Disable per-task delay accounting
1633
1634    nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1635
1636    nodsp [SH] Disable hardware DSP at boot time.
1637
1638    noefi [X86] Disable EFI runtime services support.
1639
1640    noexec [IA-64]
1641
1642    noexec [X86]
1643            On X86-32 available only on PAE configured kernels.
1644            noexec=on: enable non-executable mappings (default)
1645            noexec=off: disable non-executable mappings
1646
1647    noexec32 [X86-64]
1648            This affects only 32-bit executables.
1649            noexec32=on: enable non-executable mappings (default)
1650                read doesn't imply executable mappings
1651            noexec32=off: disable non-executable mappings
1652                read implies executable mappings
1653
1654    nofpu [SH] Disable hardware FPU at boot time.
1655
1656    nofxsr [BUGS=X86-32] Disables x86 floating point extended
1657            register save and restore. The kernel will only save
1658            legacy floating-point registers on task switch.
1659
1660    noxsave [BUGS=X86] Disables x86 extended register state save
1661            and restore using xsave. The kernel will fallback to
1662            enabling legacy floating-point and sse state.
1663
1664    nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1665            wfi(ARM) instruction doesn't work correctly and not to
1666            use it. This is also useful when using JTAG debugger.
1667
1668    no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1669            instruction doesn't work correctly and not to
1670            use it.
1671
1672    no_file_caps Tells the kernel not to honor file capabilities. The
1673            only way then for a file to be executed with privilege
1674            is to be setuid root or executed by root.
1675
1676    nohalt [IA-64] Tells the kernel not to use the power saving
1677            function PAL_HALT_LIGHT when idle. This increases
1678            power-consumption. On the positive side, it reduces
1679            interrupt wake-up latency, which may improve performance
1680            in certain environments such as networked servers or
1681            real-time systems.
1682
1683    nohz= [KNL] Boottime enable/disable dynamic ticks
1684            Valid arguments: on, off
1685            Default: on
1686
1687    noiotrap [SH] Disables trapped I/O port accesses.
1688
1689    noirqdebug [X86-32] Disables the code which attempts to detect and
1690            disable unhandled interrupt sources.
1691
1692    no_timer_check [X86,APIC] Disables the code which tests for
1693            broken timer IRQ sources.
1694
1695    noisapnp [ISAPNP] Disables ISA PnP code.
1696
1697    noinitrd [RAM] Tells the kernel not to load any configured
1698            initial RAM disk.
1699
1700    nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1701            remapping.
1702            [Deprecated - use intremap=off]
1703
1704    nointroute [IA-64]
1705
1706    nojitter [IA64] Disables jitter checking for ITC timers.
1707
1708    no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1709
1710    nolapic [X86-32,APIC] Do not enable or use the local APIC.
1711
1712    nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1713
1714    noltlbs [PPC] Do not use large page/tlb entries for kernel
1715            lowmem mapping on PPC40x.
1716
1717    nomca [IA-64] Disable machine check abort handling
1718
1719    nomce [X86-32] Machine Check Exception
1720
1721    nomfgpt [X86-32] Disable Multi-Function General Purpose
1722            Timer usage (for AMD Geode machines).
1723
1724    nopat [X86] Disable PAT (page attribute table extension of
1725            pagetables) support.
1726
1727    norandmaps Don't use address space randomization. Equivalent to
1728            echo 0 > /proc/sys/kernel/randomize_va_space
1729
1730    noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1731
1732    noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1733            with UP alternatives
1734
1735    noresidual [PPC] Don't use residual data on PReP machines.
1736
1737    noresume [SWSUSP] Disables resume and restores original swap
1738            space.
1739
1740    no-scroll [VGA] Disables scrollback.
1741            This is required for the Braillex ib80-piezo Braille
1742            reader made by F.H. Papenmeier (Germany).
1743
1744    nosbagart [IA-64]
1745
1746    nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1747
1748    nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1749            and disable the IO APIC. legacy for "maxcpus=0".
1750
1751    nosoftlockup [KNL] Disable the soft-lockup detector.
1752
1753    noswapaccount [KNL] Disable accounting of swap in memory resource
1754            controller. (See Documentation/cgroups/memory.txt)
1755
1756    nosync [HW,M68K] Disables sync negotiation for all devices.
1757
1758    notsc [BUGS=X86-32] Disable Time Stamp Counter
1759
1760    nousb [USB] Disable the USB subsystem
1761
1762    nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1763
1764    nowb [ARM]
1765
1766    nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1767
1768    nptcg= [IA64] Override max number of concurrent global TLB
1769            purges which is reported from either PAL_VM_SUMMARY or
1770            SAL PALO.
1771
1772    nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1773            could support. nr_cpus=n : n >= 1 limits the kernel to
1774            supporting 'n' processors. Later in runtime you can not
1775            use hotplug cpu feature to put more cpu back to online.
1776            just like you compile the kernel NR_CPUS=n
1777
1778    nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1779
1780    numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1781            one of ['zone', 'node', 'default'] can be specified
1782            This can be set from sysctl after boot.
1783            See Documentation/sysctl/vm.txt for details.
1784
1785    ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1786            See Documentation/debugging-via-ohci1394.txt for more
1787            info.
1788
1789    olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1790            Rather than timing out after 20 ms if an EC
1791            command is not properly ACKed, override the length
1792            of the timeout. We have interrupts disabled while
1793            waiting for the ACK, so if this is set too high
1794            interrupts *may* be lost!
1795
1796    omap_mux= [OMAP] Override bootloader pin multiplexing.
1797            Format: <mux_mode0.mode_name=value>...
1798            For example, to override I2C bus2:
1799            omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1800
1801    oprofile.timer= [HW]
1802            Use timer interrupt instead of performance counters
1803
1804    oprofile.cpu_type= Force an oprofile cpu type
1805            This might be useful if you have an older oprofile
1806            userland or if you want common events.
1807            Format: { arch_perfmon }
1808            arch_perfmon: [X86] Force use of architectural
1809                perfmon on Intel CPUs instead of the
1810                CPU specific event set.
1811
1812    OSS [HW,OSS]
1813            See Documentation/sound/oss/oss-parameters.txt
1814
1815    panic= [KNL] Kernel behaviour on panic
1816            Format: <timeout>
1817
1818    parkbd.port= [HW] Parallel port number the keyboard adapter is
1819            connected to, default is 0.
1820            Format: <parport#>
1821    parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1822            0 for XT, 1 for AT (default is AT).
1823            Format: <mode>
1824
1825    parport= [HW,PPT] Specify parallel ports. 0 disables.
1826            Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1827            Use 'auto' to force the driver to use any
1828            IRQ/DMA settings detected (the default is to
1829            ignore detected IRQ/DMA settings because of
1830            possible conflicts). You can specify the base
1831            address, IRQ, and DMA settings; IRQ and DMA
1832            should be numbers, or 'auto' (for using detected
1833            settings on that particular port), or 'nofifo'
1834            (to avoid using a FIFO even if it is detected).
1835            Parallel ports are assigned in the order they
1836            are specified on the command line, starting
1837            with parport0.
1838
1839    parport_init_mode= [HW,PPT]
1840            Configure VIA parallel port to operate in
1841            a specific mode. This is necessary on Pegasos
1842            computer where firmware has no options for setting
1843            up parallel port mode and sets it to spp.
1844            Currently this function knows 686a and 8231 chips.
1845            Format: [spp|ps2|epp|ecp|ecpepp]
1846
1847    pause_on_oops=
1848            Halt all CPUs after the first oops has been printed for
1849            the specified number of seconds. This is to be used if
1850            your oopses keep scrolling off the screen.
1851
1852    pcbit= [HW,ISDN]
1853
1854    pcd. [PARIDE]
1855            See header of drivers/block/paride/pcd.c.
1856            See also Documentation/blockdev/paride.txt.
1857
1858    pci=option[,option...] [PCI] various PCI subsystem options:
1859        earlydump [X86] dump PCI config space before the kernel
1860                    changes anything
1861        off [X86] don't probe for the PCI bus
1862        bios [X86-32] force use of PCI BIOS, don't access
1863                the hardware directly. Use this if your machine
1864                has a non-standard PCI host bridge.
1865        nobios [X86-32] disallow use of PCI BIOS, only direct
1866                hardware access methods are allowed. Use this
1867                if you experience crashes upon bootup and you
1868                suspect they are caused by the BIOS.
1869        conf1 [X86] Force use of PCI Configuration
1870                Mechanism 1.
1871        conf2 [X86] Force use of PCI Configuration
1872                Mechanism 2.
1873        noaer [PCIE] If the PCIEAER kernel config parameter is
1874                enabled, this kernel boot option can be used to
1875                disable the use of PCIE advanced error reporting.
1876        nodomains [PCI] Disable support for multiple PCI
1877                root domains (aka PCI segments, in ACPI-speak).
1878        nommconf [X86] Disable use of MMCONFIG for PCI
1879                Configuration
1880        check_enable_amd_mmconf [X86] check for and enable
1881                properly configured MMIO access to PCI
1882                config space on AMD family 10h CPU
1883        nomsi [MSI] If the PCI_MSI kernel config parameter is
1884                enabled, this kernel boot option can be used to
1885                disable the use of MSI interrupts system-wide.
1886        noioapicquirk [APIC] Disable all boot interrupt quirks.
1887                Safety option to keep boot IRQs enabled. This
1888                should never be necessary.
1889        ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1890                primary IO-APIC for bridges that cannot disable
1891                boot IRQs. This fixes a source of spurious IRQs
1892                when the system masks IRQs.
1893        noioapicreroute [APIC] Disable workaround that uses the
1894                boot IRQ equivalent of an IRQ that connects to
1895                a chipset where boot IRQs cannot be disabled.
1896                The opposite of ioapicreroute.
1897        biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1898                routing table. These calls are known to be buggy
1899                on several machines and they hang the machine
1900                when used, but on other computers it's the only
1901                way to get the interrupt routing table. Try
1902                this option if the kernel is unable to allocate
1903                IRQs or discover secondary PCI buses on your
1904                motherboard.
1905        rom [X86] Assign address space to expansion ROMs.
1906                Use with caution as certain devices share
1907                address decoders between ROMs and other
1908                resources.
1909        norom [X86] Do not assign address space to
1910                expansion ROMs that do not already have
1911                BIOS assigned address ranges.
1912        nobar [X86] Do not assign address space to the
1913                BARs that weren't assigned by the BIOS.
1914        irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1915                assigned automatically to PCI devices. You can
1916                make the kernel exclude IRQs of your ISA cards
1917                this way.
1918        pirqaddr=0xAAAAA [X86] Specify the physical address
1919                of the PIRQ table (normally generated
1920                by the BIOS) if it is outside the
1921                F0000h-100000h range.
1922        lastbus=N [X86] Scan all buses thru bus #N. Can be
1923                useful if the kernel is unable to find your
1924                secondary buses and you want to tell it
1925                explicitly which ones they are.
1926        assign-busses [X86] Always assign all PCI bus
1927                numbers ourselves, overriding
1928                whatever the firmware may have done.
1929        usepirqmask [X86] Honor the possible IRQ mask stored
1930                in the BIOS $PIR table. This is needed on
1931                some systems with broken BIOSes, notably
1932                some HP Pavilion N5400 and Omnibook XE3
1933                notebooks. This will have no effect if ACPI
1934                IRQ routing is enabled.
1935        noacpi [X86] Do not use ACPI for IRQ routing
1936                or for PCI scanning.
1937        use_crs [X86] Use PCI host bridge window information
1938                from ACPI. On BIOSes from 2008 or later, this
1939                is enabled by default. If you need to use this,
1940                please report a bug.
1941        nocrs [X86] Ignore PCI host bridge windows from ACPI.
1942                    If you need to use this, please report a bug.
1943        routeirq Do IRQ routing for all PCI devices.
1944                This is normally done in pci_enable_device(),
1945                so this option is a temporary workaround
1946                for broken drivers that don't call it.
1947        skip_isa_align [X86] do not align io start addr, so can
1948                handle more pci cards
1949        firmware [ARM] Do not re-enumerate the bus but instead
1950                just use the configuration from the
1951                bootloader. This is currently used on
1952                IXP2000 systems where the bus has to be
1953                configured a certain way for adjunct CPUs.
1954        noearly [X86] Don't do any early type 1 scanning.
1955                This might help on some broken boards which
1956                machine check when some devices' config space
1957                is read. But various workarounds are disabled
1958                and some IOMMU drivers will not work.
1959        bfsort Sort PCI devices into breadth-first order.
1960                This sorting is done to get a device
1961                order compatible with older (<= 2.4) kernels.
1962        nobfsort Don't sort PCI devices into breadth-first order.
1963        cbiosize=nn[KMG] The fixed amount of bus space which is
1964                reserved for the CardBus bridge's IO window.
1965                The default value is 256 bytes.
1966        cbmemsize=nn[KMG] The fixed amount of bus space which is
1967                reserved for the CardBus bridge's memory
1968                window. The default value is 64 megabytes.
1969        resource_alignment=
1970                Format:
1971                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
1972                Specifies alignment and device to reassign
1973                aligned memory resources.
1974                If <order of align> is not specified,
1975                PAGE_SIZE is used as alignment.
1976                PCI-PCI bridge can be specified, if resource
1977                windows need to be expanded.
1978        ecrc= Enable/disable PCIe ECRC (transaction layer
1979                end-to-end CRC checking).
1980                bios: Use BIOS/firmware settings. This is the
1981                the default.
1982                off: Turn ECRC off
1983                on: Turn ECRC on.
1984
1985    pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
1986            Management.
1987        off Disable ASPM.
1988        force Enable ASPM even on devices that claim not to support it.
1989            WARNING: Forcing ASPM on may cause system lockups.
1990
1991    pcie_ports= [PCIE] PCIe ports handling:
1992        auto Ask the BIOS whether or not to use native PCIe services
1993            associated with PCIe ports (PME, hot-plug, AER). Use
1994            them only if that is allowed by the BIOS.
1995        native Use native PCIe services associated with PCIe ports
1996            unconditionally.
1997        compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
1998            ports driver.
1999
2000    pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2001        nomsi Do not use MSI for native PCIe PME signaling (this makes
2002            all PCIe root ports use INTx for all services).
2003
2004    pcmv= [HW,PCMCIA] BadgePAD 4
2005
2006    pd. [PARIDE]
2007            See Documentation/blockdev/paride.txt.
2008
2009    pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2010            boot time.
2011            Format: { 0 | 1 }
2012            See arch/parisc/kernel/pdc_chassis.c
2013
2014    percpu_alloc= Select which percpu first chunk allocator to use.
2015            Currently supported values are "embed" and "page".
2016            Archs may support subset or none of the selections.
2017            See comments in mm/percpu.c for details on each
2018            allocator. This parameter is primarily for debugging
2019            and performance comparison.
2020
2021    pf. [PARIDE]
2022            See Documentation/blockdev/paride.txt.
2023
2024    pg. [PARIDE]
2025            See Documentation/blockdev/paride.txt.
2026
2027    pirq= [SMP,APIC] Manual mp-table setup
2028            See Documentation/x86/i386/IO-APIC.txt.
2029
2030    plip= [PPT,NET] Parallel port network link
2031            Format: { parport<nr> | timid | 0 }
2032            See also Documentation/parport.txt.
2033
2034    pmtmr= [X86] Manual setup of pmtmr I/O Port.
2035            Override pmtimer IOPort with a hex value.
2036            e.g. pmtmr=0x508
2037
2038    pnp.debug [PNP]
2039            Enable PNP debug messages. This depends on the
2040            CONFIG_PNP_DEBUG_MESSAGES option.
2041
2042    pnpacpi= [ACPI]
2043            { off }
2044
2045    pnpbios= [ISAPNP]
2046            { on | off | curr | res | no-curr | no-res }
2047
2048    pnp_reserve_irq=
2049            [ISAPNP] Exclude IRQs for the autoconfiguration
2050
2051    pnp_reserve_dma=
2052            [ISAPNP] Exclude DMAs for the autoconfiguration
2053
2054    pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2055            Ranges are in pairs (I/O port base and size).
2056
2057    pnp_reserve_mem=
2058            [ISAPNP] Exclude memory regions for the
2059            autoconfiguration.
2060            Ranges are in pairs (memory base and size).
2061
2062    ports= [IP_VS_FTP] IPVS ftp helper module
2063            Default is 21.
2064            Up to 8 (IP_VS_APP_MAX_PORTS) ports
2065            may be specified.
2066            Format: <port>,<port>....
2067
2068    print-fatal-signals=
2069            [KNL] debug: print fatal signals
2070
2071            If enabled, warn about various signal handling
2072            related application anomalies: too many signals,
2073            too many POSIX.1 timers, fatal signals causing a
2074            coredump - etc.
2075
2076            If you hit the warning due to signal overflow,
2077            you might want to try "ulimit -i unlimited".
2078
2079            default: off.
2080
2081    printk.time= Show timing data prefixed to each printk message line
2082            Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2083
2084    processor.max_cstate= [HW,ACPI]
2085            Limit processor to maximum C-state
2086            max_cstate=9 overrides any DMI blacklist limit.
2087
2088    processor.nocst [HW,ACPI]
2089            Ignore the _CST method to determine C-states,
2090            instead using the legacy FADT method
2091
2092    profile= [KNL] Enable kernel profiling via /proc/profile
2093            Format: [schedule,]<number>
2094            Param: "schedule" - profile schedule points.
2095            Param: <number> - step/bucket size as a power of 2 for
2096                statistical time based profiling.
2097            Param: "sleep" - profile D-state sleeping (millisecs).
2098                Requires CONFIG_SCHEDSTATS
2099            Param: "kvm" - profile VM exits.
2100
2101    prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2102            before loading.
2103            See Documentation/blockdev/ramdisk.txt.
2104
2105    psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2106            probe for; one of (bare|imps|exps|lifebook|any).
2107    psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2108            per second.
2109    psmouse.resetafter= [HW,MOUSE]
2110            Try to reset the device after so many bad packets
2111            (0 = never).
2112    psmouse.resolution=
2113            [HW,MOUSE] Set desired mouse resolution, in dpi.
2114    psmouse.smartscroll=
2115            [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2116            0 = disabled, 1 = enabled (default).
2117
2118    pt. [PARIDE]
2119            See Documentation/blockdev/paride.txt.
2120
2121    pty.legacy_count=
2122            [KNL] Number of legacy pty's. Overwrites compiled-in
2123            default number.
2124
2125    quiet [KNL] Disable most log messages
2126
2127    r128= [HW,DRM]
2128
2129    raid= [HW,RAID]
2130            See Documentation/md.txt.
2131
2132    ramdisk_blocksize= [RAM]
2133            See Documentation/blockdev/ramdisk.txt.
2134
2135    ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2136            See Documentation/blockdev/ramdisk.txt.
2137
2138    rcupdate.blimit= [KNL,BOOT]
2139            Set maximum number of finished RCU callbacks to process
2140            in one batch.
2141
2142    rcupdate.qhimark= [KNL,BOOT]
2143            Set threshold of queued
2144            RCU callbacks over which batch limiting is disabled.
2145
2146    rcupdate.qlowmark= [KNL,BOOT]
2147            Set threshold of queued RCU callbacks below which
2148            batch limiting is re-enabled.
2149
2150    rdinit= [KNL]
2151            Format: <full_path>
2152            Run specified binary instead of /init from the ramdisk,
2153            used for early userspace startup. See initrd.
2154
2155    reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2156            Format: <reboot_mode>[,<reboot_mode2>[,...]]
2157            See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2158
2159    relax_domain_level=
2160            [KNL, SMP] Set scheduler's default relax_domain_level.
2161            See Documentation/cgroups/cpusets.txt.
2162
2163    reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2164
2165    reservetop= [X86-32]
2166            Format: nn[KMG]
2167            Reserves a hole at the top of the kernel virtual
2168            address space.
2169
2170    reservelow= [X86]
2171            Format: nn[K]
2172            Set the amount of memory to reserve for BIOS at
2173            the bottom of the address space.
2174
2175    reset_devices [KNL] Force drivers to reset the underlying device
2176            during initialization.
2177
2178    resume= [SWSUSP]
2179            Specify the partition device for software suspend
2180
2181    resume_offset= [SWSUSP]
2182            Specify the offset from the beginning of the partition
2183            given by "resume=" at which the swap header is located,
2184            in <PAGE_SIZE> units (needed only for swap files).
2185            See Documentation/power/swsusp-and-swap-files.txt
2186
2187    hibernate= [HIBERNATION]
2188        noresume Don't check if there's a hibernation image
2189                present during boot.
2190        nocompress Don't compress/decompress hibernation images.
2191
2192    retain_initrd [RAM] Keep initrd memory after extraction
2193
2194    rhash_entries= [KNL,NET]
2195            Set number of hash buckets for route cache
2196
2197    riscom8= [HW,SERIAL]
2198            Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2199
2200    ro [KNL] Mount root device read-only on boot
2201
2202    root= [KNL] Root filesystem
2203
2204    rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2205            mount the root filesystem
2206
2207    rootflags= [KNL] Set root filesystem mount option string
2208
2209    rootfstype= [KNL] Set root filesystem type
2210
2211    rootwait [KNL] Wait (indefinitely) for root device to show up.
2212            Useful for devices that are detected asynchronously
2213            (e.g. USB and MMC devices).
2214
2215    rw [KNL] Mount root device read-write on boot
2216
2217    S [KNL] Run init in single mode
2218
2219    sa1100ir [NET]
2220            See drivers/net/irda/sa1100_ir.c.
2221
2222    sbni= [NET] Granch SBNI12 leased line adapter
2223
2224    sched_debug [KNL] Enables verbose scheduler debug messages.
2225
2226    security= [SECURITY] Choose a security module to enable at boot.
2227            If this boot parameter is not specified, only the first
2228            security module asking for security registration will be
2229            loaded. An invalid security module name will be treated
2230            as if no module has been chosen.
2231
2232    selinux= [SELINUX] Disable or enable SELinux at boot time.
2233            Format: { "0" | "1" }
2234            See security/selinux/Kconfig help text.
2235            0 -- disable.
2236            1 -- enable.
2237            Default value is set via kernel config option.
2238            If enabled at boot time, /selinux/disable can be used
2239            later to disable prior to initial policy load.
2240
2241    apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2242            Format: { "0" | "1" }
2243            See security/apparmor/Kconfig help text
2244            0 -- disable.
2245            1 -- enable.
2246            Default value is set via kernel config option.
2247
2248    serialnumber [BUGS=X86-32]
2249
2250    shapers= [NET]
2251            Maximal number of shapers.
2252
2253    show_msr= [x86] show boot-time MSR settings
2254            Format: { <integer> }
2255            Show boot-time (BIOS-initialized) MSR settings.
2256            The parameter means the number of CPUs to show,
2257            for example 1 means boot CPU only.
2258
2259    simeth= [IA-64]
2260    simscsi=
2261
2262    slram= [HW,MTD]
2263
2264    slub_debug[=options[,slabs]] [MM, SLUB]
2265            Enabling slub_debug allows one to determine the
2266            culprit if slab objects become corrupted. Enabling
2267            slub_debug can create guard zones around objects and
2268            may poison objects when not in use. Also tracks the
2269            last alloc / free. For more information see
2270            Documentation/vm/slub.txt.
2271
2272    slub_max_order= [MM, SLUB]
2273            Determines the maximum allowed order for slabs.
2274            A high setting may cause OOMs due to memory
2275            fragmentation. For more information see
2276            Documentation/vm/slub.txt.
2277
2278    slub_min_objects= [MM, SLUB]
2279            The minimum number of objects per slab. SLUB will
2280            increase the slab order up to slub_max_order to
2281            generate a sufficiently large slab able to contain
2282            the number of objects indicated. The higher the number
2283            of objects the smaller the overhead of tracking slabs
2284            and the less frequently locks need to be acquired.
2285            For more information see Documentation/vm/slub.txt.
2286
2287    slub_min_order= [MM, SLUB]
2288            Determines the mininum page order for slabs. Must be
2289            lower than slub_max_order.
2290            For more information see Documentation/vm/slub.txt.
2291
2292    slub_nomerge [MM, SLUB]
2293            Disable merging of slabs with similar size. May be
2294            necessary if there is some reason to distinguish
2295            allocs to different slabs. Debug options disable
2296            merging on their own.
2297            For more information see Documentation/vm/slub.txt.
2298
2299    smart2= [HW]
2300            Format: <io1>[,<io2>[,...,<io8>]]
2301
2302    smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2303            attempt to substitute SMP alternatives once at boot.
2304
2305    smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2306    smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2307    smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2308    smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2309    smsc-ircc2.ircc_irq= [HW] IRQ line
2310    smsc-ircc2.ircc_dma= [HW] DMA channel
2311    smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2312                0: Toshiba Satellite 1800 (GP data pin select)
2313                1: Fast pin select (default)
2314                2: ATC IRMode
2315
2316    softlockup_panic=
2317            [KNL] Should the soft-lockup detector generate panics.
2318
2319    sonypi.*= [HW] Sony Programmable I/O Control Device driver
2320            See Documentation/sonypi.txt
2321
2322    specialix= [HW,SERIAL] Specialix multi-serial port adapter
2323            See Documentation/serial/specialix.txt.
2324
2325    spia_io_base= [HW,MTD]
2326    spia_fio_base=
2327    spia_pedr=
2328    spia_peddr=
2329
2330    stacktrace [FTRACE]
2331            Enabled the stack tracer on boot up.
2332
2333    sti= [PARISC,HW]
2334            Format: <num>
2335            Set the STI (builtin display/keyboard on the HP-PARISC
2336            machines) console (graphic card) which should be used
2337            as the initial boot-console.
2338            See also comment in drivers/video/console/sticore.c.
2339
2340    sti_font= [HW]
2341            See comment in drivers/video/console/sticore.c.
2342
2343    stifb= [HW]
2344            Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2345
2346    sunrpc.min_resvport=
2347    sunrpc.max_resvport=
2348            [NFS,SUNRPC]
2349            SunRPC servers often require that client requests
2350            originate from a privileged port (i.e. a port in the
2351            range 0 < portnr < 1024).
2352            An administrator who wishes to reserve some of these
2353            ports for other uses may adjust the range that the
2354            kernel's sunrpc client considers to be privileged
2355            using these two parameters to set the minimum and
2356            maximum port values.
2357
2358    sunrpc.pool_mode=
2359            [NFS]
2360            Control how the NFS server code allocates CPUs to
2361            service thread pools. Depending on how many NICs
2362            you have and where their interrupts are bound, this
2363            option will affect which CPUs will do NFS serving.
2364            Note: this parameter cannot be changed while the
2365            NFS server is running.
2366
2367            auto the server chooses an appropriate mode
2368                    automatically using heuristics
2369            global a single global pool contains all CPUs
2370            percpu one pool for each CPU
2371            pernode one pool for each NUMA node (equivalent
2372                    to global on non-NUMA machines)
2373
2374    sunrpc.tcp_slot_table_entries=
2375    sunrpc.udp_slot_table_entries=
2376            [NFS,SUNRPC]
2377            Sets the upper limit on the number of simultaneous
2378            RPC calls that can be sent from the client to a
2379            server. Increasing these values may allow you to
2380            improve throughput, but will also increase the
2381            amount of memory reserved for use by the client.
2382
2383    swapaccount[=0|1]
2384            [KNL] Enable accounting of swap in memory resource
2385            controller if no parameter or 1 is given or disable
2386            it if 0 is given (See Documentation/cgroups/memory.txt)
2387
2388    swiotlb= [IA-64] Number of I/O TLB slabs
2389
2390    switches= [HW,M68k]
2391
2392    sysfs.deprecated=0|1 [KNL]
2393            Enable/disable old style sysfs layout for old udev
2394            on older distributions. When this option is enabled
2395            very new udev will not work anymore. When this option
2396            is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2397            in older udev will not work anymore.
2398            Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2399            the kernel configuration.
2400
2401    sysrq_always_enabled
2402            [KNL]
2403            Ignore sysrq setting - this boot parameter will
2404            neutralize any effect of /proc/sys/kernel/sysrq.
2405            Useful for debugging.
2406
2407    tdfx= [HW,DRM]
2408
2409    test_suspend= [SUSPEND]
2410            Specify "mem" (for Suspend-to-RAM) or "standby" (for
2411            standby suspend) as the system sleep state to briefly
2412            enter during system startup. The system is woken from
2413            this state using a wakeup-capable RTC alarm.
2414
2415    thash_entries= [KNL,NET]
2416            Set number of hash buckets for TCP connection
2417
2418    thermal.act= [HW,ACPI]
2419            -1: disable all active trip points in all thermal zones
2420            <degrees C>: override all lowest active trip points
2421
2422    thermal.crt= [HW,ACPI]
2423            -1: disable all critical trip points in all thermal zones
2424            <degrees C>: override all critical trip points
2425
2426    thermal.nocrt= [HW,ACPI]
2427            Set to disable actions on ACPI thermal zone
2428            critical and hot trip points.
2429
2430    thermal.off= [HW,ACPI]
2431            1: disable ACPI thermal control
2432
2433    thermal.psv= [HW,ACPI]
2434            -1: disable all passive trip points
2435            <degrees C>: override all passive trip points to this
2436            value
2437
2438    thermal.tzp= [HW,ACPI]
2439            Specify global default ACPI thermal zone polling rate
2440            <deci-seconds>: poll all this frequency
2441            0: no polling (default)
2442
2443    topology= [S390]
2444            Format: {off | on}
2445            Specify if the kernel should make use of the cpu
2446            topology informations if the hardware supports these.
2447            The scheduler will make use of these informations and
2448            e.g. base its process migration decisions on it.
2449            Default is on.
2450
2451    tp720= [HW,PS2]
2452
2453    tpm_suspend_pcr=[HW,TPM]
2454            Format: integer pcr id
2455            Specify that at suspend time, the tpm driver
2456            should extend the specified pcr with zeros,
2457            as a workaround for some chips which fail to
2458            flush the last written pcr on TPM_SaveState.
2459            This will guarantee that all the other pcrs
2460            are saved.
2461
2462    trace_buf_size=nn[KMG]
2463            [FTRACE] will set tracing buffer size.
2464
2465    trace_event=[event-list]
2466            [FTRACE] Set and start specified trace events in order
2467            to facilitate early boot debugging.
2468            See also Documentation/trace/events.txt
2469
2470    tsc= Disable clocksource-must-verify flag for TSC.
2471            Format: <string>
2472            [x86] reliable: mark tsc clocksource as reliable, this
2473            disables clocksource verification at runtime.
2474            Used to enable high-resolution timer mode on older
2475            hardware, and in virtualized environment.
2476            [x86] noirqtime: Do not use TSC to do irq accounting.
2477            Used to run time disable IRQ_TIME_ACCOUNTING on any
2478            platforms where RDTSC is slow and this accounting
2479            can add overhead.
2480
2481    turbografx.map[2|3]= [HW,JOY]
2482            TurboGraFX parallel port interface
2483            Format:
2484            <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2485            See also Documentation/input/joystick-parport.txt
2486
2487    uhash_entries= [KNL,NET]
2488            Set number of hash buckets for UDP/UDP-Lite connections
2489
2490    uhci-hcd.ignore_oc=
2491            [USB] Ignore overcurrent events (default N).
2492            Some badly-designed motherboards generate lots of
2493            bogus events, for ports that aren't wired to
2494            anything. Set this parameter to avoid log spamming.
2495            Note that genuine overcurrent events won't be
2496            reported either.
2497
2498    unknown_nmi_panic
2499            [X86]
2500            Set unknown_nmi_panic=1 early on boot.
2501
2502    usbcore.autosuspend=
2503            [USB] The autosuspend time delay (in seconds) used
2504            for newly-detected USB devices (default 2). This
2505            is the time required before an idle device will be
2506            autosuspended. Devices for which the delay is set
2507            to a negative value won't be autosuspended at all.
2508
2509    usbcore.usbfs_snoop=
2510            [USB] Set to log all usbfs traffic (default 0 = off).
2511
2512    usbcore.blinkenlights=
2513            [USB] Set to cycle leds on hubs (default 0 = off).
2514
2515    usbcore.old_scheme_first=
2516            [USB] Start with the old device initialization
2517            scheme (default 0 = off).
2518
2519    usbcore.use_both_schemes=
2520            [USB] Try the other device initialization scheme
2521            if the first one fails (default 1 = enabled).
2522
2523    usbcore.initial_descriptor_timeout=
2524            [USB] Specifies timeout for the initial 64-byte
2525                        USB_REQ_GET_DESCRIPTOR request in milliseconds
2526            (default 5000 = 5.0 seconds).
2527
2528    usbhid.mousepoll=
2529            [USBHID] The interval which mice are to be polled at.
2530
2531    usb-storage.delay_use=
2532            [UMS] The delay in seconds before a new device is
2533            scanned for Logical Units (default 5).
2534
2535    usb-storage.quirks=
2536            [UMS] A list of quirks entries to supplement or
2537            override the built-in unusual_devs list. List
2538            entries are separated by commas. Each entry has
2539            the form VID:PID:Flags where VID and PID are Vendor
2540            and Product ID values (4-digit hex numbers) and
2541            Flags is a set of characters, each corresponding
2542            to a common usb-storage quirk flag as follows:
2543                a = SANE_SENSE (collect more than 18 bytes
2544                    of sense data);
2545                b = BAD_SENSE (don't collect more than 18
2546                    bytes of sense data);
2547                c = FIX_CAPACITY (decrease the reported
2548                    device capacity by one sector);
2549                h = CAPACITY_HEURISTICS (decrease the
2550                    reported device capacity by one
2551                    sector if the number is odd);
2552                i = IGNORE_DEVICE (don't bind to this
2553                    device);
2554                l = NOT_LOCKABLE (don't try to lock and
2555                    unlock ejectable media);
2556                m = MAX_SECTORS_64 (don't transfer more
2557                    than 64 sectors = 32 KB at a time);
2558                o = CAPACITY_OK (accept the capacity
2559                    reported by the device);
2560                r = IGNORE_RESIDUE (the device reports
2561                    bogus residue values);
2562                s = SINGLE_LUN (the device has only one
2563                    Logical Unit);
2564                w = NO_WP_DETECT (don't test whether the
2565                    medium is write-protected).
2566            Example: quirks=0419:aaf5:rl,0421:0433:rc
2567
2568    userpte=
2569            [X86] Flags controlling user PTE allocations.
2570
2571                nohigh = do not allocate PTE pages in
2572                    HIGHMEM regardless of setting
2573                    of CONFIG_HIGHPTE.
2574
2575    vdso= [X86,SH]
2576            vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2577            vdso=1: enable VDSO (default)
2578            vdso=0: disable VDSO mapping
2579
2580    vdso32= [X86]
2581            vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2582            vdso32=1: enable 32-bit VDSO (default)
2583            vdso32=0: disable 32-bit VDSO mapping
2584
2585    vector= [IA-64,SMP]
2586            vector=percpu: enable percpu vector domain
2587
2588    video= [FB] Frame buffer configuration
2589            See Documentation/fb/modedb.txt.
2590
2591    vga= [BOOT,X86-32] Select a particular video mode
2592            See Documentation/x86/boot.txt and
2593            Documentation/svga.txt.
2594            Use vga=ask for menu.
2595            This is actually a boot loader parameter; the value is
2596            passed to the kernel using a special protocol.
2597
2598    vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2599            size of <nn>. This can be used to increase the
2600            minimum size (128MB on x86). It can also be used to
2601            decrease the size and leave more room for directly
2602            mapped kernel RAM.
2603
2604    vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2605            Format: <command>
2606
2607    vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2608            Format: <command>
2609
2610    vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2611            Format: <command>
2612
2613    vt.cur_default= [VT] Default cursor shape.
2614            Format: 0xCCBBAA, where AA, BB, and CC are the same as
2615            the parameters of the <Esc>[?A;B;Cc escape sequence;
2616            see VGA-softcursor.txt. Default: 2 = underline.
2617
2618    vt.default_blu= [VT]
2619            Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2620            Change the default blue palette of the console.
2621            This is a 16-member array composed of values
2622            ranging from 0-255.
2623
2624    vt.default_grn= [VT]
2625            Format: <green0>,<green1>,<green2>,...,<green15>
2626            Change the default green palette of the console.
2627            This is a 16-member array composed of values
2628            ranging from 0-255.
2629
2630    vt.default_red= [VT]
2631            Format: <red0>,<red1>,<red2>,...,<red15>
2632            Change the default red palette of the console.
2633            This is a 16-member array composed of values
2634            ranging from 0-255.
2635
2636    vt.default_utf8=
2637            [VT]
2638            Format=<0|1>
2639            Set system-wide default UTF-8 mode for all tty's.
2640            Default is 1, i.e. UTF-8 mode is enabled for all
2641            newly opened terminals.
2642
2643    vt.global_cursor_default=
2644            [VT]
2645            Format=<-1|0|1>
2646            Set system-wide default for whether a cursor
2647            is shown on new VTs. Default is -1,
2648            i.e. cursors will be created by default unless
2649            overridden by individual drivers. 0 will hide
2650            cursors, 1 will display them.
2651
2652    watchdog timers [HW,WDT] For information on watchdog timers,
2653            see Documentation/watchdog/watchdog-parameters.txt
2654            or other driver-specific files in the
2655            Documentation/watchdog/ directory.
2656
2657    x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2658            default x2apic cluster mode on platforms
2659            supporting x2apic.
2660
2661    x86_mrst_timer= [X86-32,APBT]
2662            Choose timer option for x86 Moorestown MID platform.
2663            Two valid options are apbt timer only and lapic timer
2664            plus one apbt timer for broadcast timer.
2665            x86_mrst_timer=apbt_only | lapic_and_apbt
2666
2667    xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2668    xd_geo= See header of drivers/block/xd.c.
2669
2670    xen_emul_unplug= [HW,X86,XEN]
2671            Unplug Xen emulated devices
2672            Format: [unplug0,][unplug1]
2673            ide-disks -- unplug primary master IDE devices
2674            aux-ide-disks -- unplug non-primary-master IDE devices
2675            nics -- unplug network devices
2676            all -- unplug all emulated devices (NICs and IDE disks)
2677            unnecessary -- unplugging emulated devices is
2678                unnecessary even if the host did not respond to
2679                the unplug protocol
2680            never -- do not unplug even if version check succeeds
2681
2682    xirc2ps_cs= [NET,PCMCIA]
2683            Format:
2684            <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2685
2686______________________________________________________________________
2687
2688TODO:
2689
2690    Add more DRM drivers.
2691

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