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    DRM Direct Rendering Management support is enabled.
47    DYNAMIC_DEBUG Build in debug messages and enable them at runtime
48    EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
49    EFI EFI Partitioning (GPT) is enabled
50    EIDE EIDE/ATAPI support is enabled.
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
147Finally, the [KMG] suffix is commonly described after a number of kernel
148parameter values. These 'K', 'M', and 'G' letters represent the _binary_
149multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
150bytes respectively. Such letter suffixes can also be entirely omitted.
151
152
153    acpi= [HW,ACPI,X86]
154            Advanced Configuration and Power Interface
155            Format: { force | off | strict | noirq | rsdt }
156            force -- enable ACPI if default was off
157            off -- disable ACPI if default was on
158            noirq -- do not use ACPI for IRQ routing
159            strict -- Be less tolerant of platforms that are not
160                strictly ACPI specification compliant.
161            rsdt -- prefer RSDT over (default) XSDT
162            copy_dsdt -- copy DSDT to memory
163
164            See also Documentation/power/pm.txt, pci=noacpi
165
166    acpi_apic_instance= [ACPI, IOAPIC]
167            Format: <int>
168            2: use 2nd APIC table, if available
169            1,0: use 1st APIC table
170            default: 0
171
172    acpi_backlight= [HW,ACPI]
173            acpi_backlight=vendor
174            acpi_backlight=video
175            If set to vendor, prefer vendor specific driver
176            (e.g. thinkpad_acpi, sony_acpi, etc.) instead
177            of the ACPI video.ko driver.
178
179    acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
180    acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
181            Format: <int>
182            CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
183            debug output. Bits in debug_layer correspond to a
184            _COMPONENT in an ACPI source file, e.g.,
185                #define _COMPONENT ACPI_PCI_COMPONENT
186            Bits in debug_level correspond to a level in
187            ACPI_DEBUG_PRINT statements, e.g.,
188                ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
189            The debug_level mask defaults to "info". See
190            Documentation/acpi/debug.txt for more information about
191            debug layers and levels.
192
193            Enable processor driver info messages:
194                acpi.debug_layer=0x20000000
195            Enable PCI/PCI interrupt routing info messages:
196                acpi.debug_layer=0x400000
197            Enable AML "Debug" output, i.e., stores to the Debug
198            object while interpreting AML:
199                acpi.debug_layer=0xffffffff acpi.debug_level=0x2
200            Enable all messages related to ACPI hardware:
201                acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
202
203            Some values produce so much output that the system is
204            unusable. The "log_buf_len" parameter may be useful
205            if you need to capture more output.
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, 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    bulk_remove=off [PPC] This parameter disables the use of the pSeries
407            firmware feature for flushing multiple hpte entries
408            at a time.
409
410    c101= [NET] Moxa C101 synchronous serial card
411
412    cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
413            Sometimes CPU hardware bugs make them report the cache
414            size incorrectly. The kernel will attempt work arounds
415            to fix known problems, but for some CPUs it is not
416            possible to determine what the correct size should be.
417            This option provides an override for these situations.
418
419    capability.disable=
420            [SECURITY] Disable capabilities. This would normally
421            be used only if an alternative security model is to be
422            configured. Potentially dangerous and should only be
423            used if you are entirely sure of the consequences.
424
425    ccw_timeout_log [S390]
426            See Documentation/s390/CommonIO for details.
427
428    cgroup_disable= [KNL] Disable a particular controller
429            Format: {name of the controller(s) to disable}
430                {Currently supported controllers - "memory"}
431
432    checkreqprot [SELINUX] Set initial checkreqprot flag value.
433            Format: { "0" | "1" }
434            See security/selinux/Kconfig help text.
435            0 -- check protection applied by kernel (includes
436                any implied execute protection).
437            1 -- check protection requested by application.
438            Default value is set via a kernel config option.
439            Value can be changed at runtime via
440                /selinux/checkreqprot.
441
442    cio_ignore= [S390]
443            See Documentation/s390/CommonIO for details.
444
445    clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
446            [Deprecated]
447            Forces specified clocksource (if available) to be used
448            when calculating gettimeofday(). If specified
449            clocksource is not available, it defaults to PIT.
450            Format: { pit | tsc | cyclone | pmtmr }
451
452    clocksource= Override the default clocksource
453            Format: <string>
454            Override the default clocksource and use the clocksource
455            with the name specified.
456            Some clocksource names to choose from, depending on
457            the platform:
458            [all] jiffies (this is the base, fallback clocksource)
459            [ACPI] acpi_pm
460            [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
461                pxa_timer,timer3,32k_counter,timer0_1
462            [AVR32] avr32
463            [X86-32] pit,hpet,tsc;
464                scx200_hrt on Geode; cyclone on IBM x440
465            [MIPS] MIPS
466            [PARISC] cr16
467            [S390] tod
468            [SH] SuperH
469            [SPARC64] tick
470            [X86-64] hpet,tsc
471
472    clearcpuid=BITNUM [X86]
473            Disable CPUID feature X for the kernel. See
474            arch/x86/include/asm/cpufeature.h for the valid bit
475            numbers. Note the Linux specific bits are not necessarily
476            stable over kernel options, but the vendor specific
477            ones should be.
478            Also note that user programs calling CPUID directly
479            or using the feature without checking anything
480            will still see it. This just prevents it from
481            being used by the kernel or shown in /proc/cpuinfo.
482            Also note the kernel might malfunction if you disable
483            some critical bits.
484
485    cmo_free_hint= [PPC] Format: { yes | no }
486            Specify whether pages are marked as being inactive
487            when they are freed. This is used in CMO environments
488            to determine OS memory pressure for page stealing by
489            a hypervisor.
490            Default: yes
491
492    code_bytes [X86] How many bytes of object code to print
493            in an oops report.
494            Range: 0 - 8192
495            Default: 64
496
497    com20020= [HW,NET] ARCnet - COM20020 chipset
498            Format:
499            <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
500
501    com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
502            Format: <io>[,<irq>]
503
504    com90xx= [HW,NET]
505            ARCnet - COM90xx chipset (memory-mapped buffers)
506            Format: <io>[,<irq>[,<memstart>]]
507
508    condev= [HW,S390] console device
509    conmode=
510
511    console= [KNL] Output console device and options.
512
513        tty<n> Use the virtual console device <n>.
514
515        ttyS<n>[,options]
516        ttyUSB0[,options]
517            Use the specified serial port. The options are of
518            the form "bbbbpnf", where "bbbb" is the baud rate,
519            "p" is parity ("n", "o", or "e"), "n" is number of
520            bits, and "f" is flow control ("r" for RTS or
521            omit it). Default is "9600n8".
522
523            See Documentation/serial-console.txt for more
524            information. See
525            Documentation/networking/netconsole.txt for an
526            alternative.
527
528        uart[8250],io,<addr>[,options]
529        uart[8250],mmio,<addr>[,options]
530            Start an early, polled-mode console on the 8250/16550
531            UART at the specified I/O port or MMIO address,
532            switching to the matching ttyS device later. The
533            options are the same as for ttyS, above.
534
535                If the device connected to the port is not a TTY but a braille
536                device, prepend "brl," before the device type, for instance
537            console=brl,ttyS0
538        For now, only VisioBraille is supported.
539
540    consoleblank= [KNL] The console blank (screen saver) timeout in
541            seconds. Defaults to 10*60 = 10mins. A value of 0
542            disables the blank timer.
543
544    coredump_filter=
545            [KNL] Change the default value for
546            /proc/<pid>/coredump_filter.
547            See also Documentation/filesystems/proc.txt.
548
549    cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
550            Format:
551            <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
552
553    crashkernel=size[KMG][@offset[KMG]]
554            [KNL] Using kexec, Linux can switch to a 'crash kernel'
555            upon panic. This parameter reserves the physical
556            memory region [offset, offset + size] for that kernel
557            image. If '@offset' is omitted, then a suitable offset
558            is selected automatically. Check
559            Documentation/kdump/kdump.txt for further details.
560
561    crashkernel=range1:size1[,range2:size2,...][@offset]
562            [KNL] Same as above, but depends on the memory
563            in the running system. The syntax of range is
564            start-[end] where start and end are both
565            a memory unit (amount[KMG]). See also
566            Documentation/kdump/kdump.txt for an example.
567
568    cs89x0_dma= [HW,NET]
569            Format: <dma>
570
571    cs89x0_media= [HW,NET]
572            Format: { rj45 | aui | bnc }
573
574    dasd= [HW,NET]
575            See header of drivers/s390/block/dasd_devmap.c.
576
577    db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
578            (one device per port)
579            Format: <port#>,<type>
580            See also Documentation/input/joystick-parport.txt
581
582    ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
583            time. See Documentation/dynamic-debug-howto.txt for
584            details.
585
586    debug [KNL] Enable kernel debugging (events log level).
587
588    debug_locks_verbose=
589            [KNL] verbose self-tests
590            Format=<0|1>
591            Print debugging info while doing the locking API
592            self-tests.
593            We default to 0 (no extra messages), setting it to
594            1 will print _a lot_ more information - normally
595            only useful to kernel developers.
596
597    debug_objects [KNL] Enable object debugging
598
599    no_debug_objects
600            [KNL] Disable object debugging
601
602    debugpat [X86] Enable PAT debugging
603
604    decnet.addr= [HW,NET]
605            Format: <area>[,<node>]
606            See also Documentation/networking/decnet.txt.
607
608    default_hugepagesz=
609            [same as hugepagesz=] The size of the default
610            HugeTLB page size. This is the size represented by
611            the legacy /proc/ hugepages APIs, used for SHM, and
612            default size when mounting hugetlbfs filesystems.
613            Defaults to the default architecture's huge page size
614            if not specified.
615
616    dhash_entries= [KNL]
617            Set number of hash buckets for dentry cache.
618
619    digi= [HW,SERIAL]
620            IO parameters + enable/disable command.
621
622    digiepca= [HW,SERIAL]
623            See drivers/char/README.epca and
624            Documentation/serial/digiepca.txt.
625
626    disable= [IPV6]
627            See Documentation/networking/ipv6.txt.
628
629    disable_ddw [PPC/PSERIES]
630            Disable Dynamic DMA Window support. Use this if
631            to workaround buggy firmware.
632
633    disable_ipv6= [IPV6]
634            See Documentation/networking/ipv6.txt.
635
636    disable_mtrr_cleanup [X86]
637            The kernel tries to adjust MTRR layout from continuous
638            to discrete, to make X server driver able to add WB
639            entry later. This parameter disables that.
640
641    disable_mtrr_trim [X86, Intel and AMD only]
642            By default the kernel will trim any uncacheable
643            memory out of your available memory pool based on
644            MTRR settings. This parameter disables that behavior,
645            possibly causing your machine to run very slowly.
646
647    disable_timer_pin_1 [X86]
648            Disable PIN 1 of APIC timer
649            Can be useful to work around chipset bugs.
650
651    dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
652            this option disables the debugging code at boot.
653
654    dma_debug_entries=<number>
655            This option allows to tune the number of preallocated
656            entries for DMA-API debugging code. One entry is
657            required per DMA-API allocation. Use this if the
658            DMA-API debugging code disables itself because the
659            architectural default is too low.
660
661    dma_debug_driver=<driver_name>
662            With this option the DMA-API debugging driver
663            filter feature can be enabled at boot time. Just
664            pass the driver to filter for as the parameter.
665            The filter can be disabled or changed to another
666            driver later using sysfs.
667
668    dscc4.setup= [NET]
669
670    earlycon= [KNL] Output early console device and options.
671        uart[8250],io,<addr>[,options]
672        uart[8250],mmio,<addr>[,options]
673        uart[8250],mmio32,<addr>[,options]
674            Start an early, polled-mode console on the 8250/16550
675            UART at the specified I/O port or MMIO address.
676            MMIO inter-register address stride is either 8bit (mmio)
677                        or 32bit (mmio32).
678            The options are the same as for ttyS, above.
679
680    earlyprintk= [X86,SH,BLACKFIN]
681            earlyprintk=vga
682            earlyprintk=serial[,ttySn[,baudrate]]
683            earlyprintk=ttySn[,baudrate]
684            earlyprintk=dbgp[debugController#]
685
686            Append ",keep" to not disable it when the real console
687            takes over.
688
689            Only vga or serial or usb debug port at a time.
690
691            Currently only ttyS0 and ttyS1 are supported.
692
693            Interaction with the standard serial driver is not
694            very good.
695
696            The VGA output is eventually overwritten by the real
697            console.
698
699    ekgdboc= [X86,KGDB] Allow early kernel console debugging
700            ekgdboc=kbd
701
702            This is designed to be used in conjunction with
703            the boot argument: earlyprintk=vga
704
705    edd= [EDD]
706            Format: {"off" | "on" | "skip[mbr]"}
707
708    eisa_irq_edge= [PARISC,HW]
709            See header of drivers/parisc/eisa.c.
710
711    elanfreq= [X86-32]
712            See comment before function elanfreq_setup() in
713            arch/x86/kernel/cpu/cpufreq/elanfreq.c.
714
715    elevator= [IOSCHED]
716            Format: {"cfq" | "deadline" | "noop"}
717            See Documentation/block/as-iosched.txt and
718            Documentation/block/deadline-iosched.txt for details.
719
720    elfcorehdr= [IA64,PPC,SH,X86]
721            Specifies physical address of start of kernel core
722            image elf header. Generally kexec loader will
723            pass this option to capture kernel.
724            See Documentation/kdump/kdump.txt for details.
725
726    enable_mtrr_cleanup [X86]
727            The kernel tries to adjust MTRR layout from continuous
728            to discrete, to make X server driver able to add WB
729            entry later. This parameter enables that.
730
731    enable_timer_pin_1 [X86]
732            Enable PIN 1 of APIC timer
733            Can be useful to work around chipset bugs
734            (in particular on some ATI chipsets).
735            The kernel tries to set a reasonable default.
736
737    enforcing [SELINUX] Set initial enforcing status.
738            Format: {"0" | "1"}
739            See security/selinux/Kconfig help text.
740            0 -- permissive (log only, no denials).
741            1 -- enforcing (deny and log).
742            Default value is 0.
743            Value can be changed at runtime via /selinux/enforce.
744
745    erst_disable [ACPI]
746            Disable Error Record Serialization Table (ERST)
747            support.
748
749    ether= [HW,NET] Ethernet cards parameters
750            This option is obsoleted by the "netdev=" option, which
751            has equivalent usage. See its documentation for details.
752
753    failslab=
754    fail_page_alloc=
755    fail_make_request=[KNL]
756            General fault injection mechanism.
757            Format: <interval>,<probability>,<space>,<times>
758            See also /Documentation/fault-injection/.
759
760    floppy= [HW]
761            See Documentation/blockdev/floppy.txt.
762
763    force_pal_cache_flush
764            [IA-64] Avoid check_sal_cache_flush which may hang on
765            buggy SAL_CACHE_FLUSH implementations. Using this
766            parameter will force ia64_sal_cache_flush to call
767            ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
768
769    ftrace=[tracer]
770            [FTRACE] will set and start the specified tracer
771            as early as possible in order to facilitate early
772            boot debugging.
773
774    ftrace_dump_on_oops[=orig_cpu]
775            [FTRACE] will dump the trace buffers on oops.
776            If no parameter is passed, ftrace will dump
777            buffers of all CPUs, but if you pass orig_cpu, it will
778            dump only the buffer of the CPU that triggered the
779            oops.
780
781    ftrace_filter=[function-list]
782            [FTRACE] Limit the functions traced by the function
783            tracer at boot up. function-list is a comma separated
784            list of functions. This list can be changed at run
785            time by the set_ftrace_filter file in the debugfs
786            tracing directory.
787
788    ftrace_notrace=[function-list]
789            [FTRACE] Do not trace the functions specified in
790            function-list. This list can be changed at run time
791            by the set_ftrace_notrace file in the debugfs
792            tracing directory.
793
794    ftrace_graph_filter=[function-list]
795            [FTRACE] Limit the top level callers functions traced
796            by the function graph tracer at boot up.
797            function-list is a comma separated list of functions
798            that can be changed at run time by the
799            set_graph_function file in the debugfs tracing directory.
800
801    gamecon.map[2|3]=
802            [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
803            support via parallel port (up to 5 devices per port)
804            Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
805            See also Documentation/input/joystick-parport.txt
806
807    gamma= [HW,DRM]
808
809    gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
810            Format: off | on
811            default: on
812
813    gcov_persist= [GCOV] When non-zero (default), profiling data for
814            kernel modules is saved and remains accessible via
815            debugfs, even when the module is unloaded/reloaded.
816            When zero, profiling data is discarded and associated
817            debugfs files are removed at module unload time.
818
819    gpt [EFI] Forces disk with valid GPT signature but
820            invalid Protective MBR to be treated as GPT.
821
822    hashdist= [KNL,NUMA] Large hashes allocated during boot
823            are distributed across NUMA nodes. Defaults on
824            for 64bit NUMA, off otherwise.
825            Format: 0 | 1 (for off | on)
826
827    hcl= [IA-64] SGI's Hardware Graph compatibility layer
828
829    hd= [EIDE] (E)IDE hard drive subsystem geometry
830            Format: <cyl>,<head>,<sect>
831
832    hest_disable [ACPI]
833            Disable Hardware Error Source Table (HEST) support;
834            corresponding firmware-first mode error processing
835            logic will be disabled.
836
837    highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
838            size of <nn>. This works even on boxes that have no
839            highmem otherwise. This also works to reduce highmem
840            size on bigger boxes.
841
842    highres= [KNL] Enable/disable high resolution timer mode.
843            Valid parameters: "on", "off"
844            Default: "on"
845
846    hisax= [HW,ISDN]
847            See Documentation/isdn/README.HiSax.
848
849    hlt [BUGS=ARM,SH]
850
851    hpet= [X86-32,HPET] option to control HPET usage
852            Format: { enable (default) | disable | force |
853                verbose }
854            disable: disable HPET and use PIT instead
855            force: allow force enabled of undocumented chips (ICH4,
856                VIA, nVidia)
857            verbose: show contents of HPET registers during setup
858
859    hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
860    hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
861            On x86-64 and powerpc, this option can be specified
862            multiple times interleaved with hugepages= to reserve
863            huge pages of different sizes. Valid pages sizes on
864            x86-64 are 2M (when the CPU supports "pse") and 1G
865            (when the CPU supports the "pdpe1gb" cpuinfo flag)
866            Note that 1GB pages can only be allocated at boot time
867            using hugepages= and not freed afterwards.
868
869    hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
870                   terminal devices. Valid values: 0..8
871    hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
872                   If specified, z/VM IUCV HVC accepts connections
873                   from listed z/VM user IDs only.
874
875    keep_bootcon [KNL]
876            Do not unregister boot console at start. This is only
877            useful for debugging when something happens in the window
878            between unregistering the boot console and initializing
879            the real console.
880
881    i2c_bus= [HW] Override the default board specific I2C bus speed
882                 or register an additional I2C bus that is not
883                 registered from board initialization code.
884                 Format:
885                 <bus_id>,<clkrate>
886
887    i8042.debug [HW] Toggle i8042 debug mode
888    i8042.direct [HW] Put keyboard port into non-translated mode
889    i8042.dumbkbd [HW] Pretend that controller can only read data from
890                 keyboard and cannot control its state
891                 (Don't attempt to blink the leds)
892    i8042.noaux [HW] Don't check for auxiliary (== mouse) port
893    i8042.nokbd [HW] Don't check/create keyboard port
894    i8042.noloop [HW] Disable the AUX Loopback command while probing
895                 for the AUX port
896    i8042.nomux [HW] Don't check presence of an active multiplexing
897                 controller
898    i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
899                 controllers
900    i8042.notimeout [HW] Ignore timeout condition signalled by conroller
901    i8042.reset [HW] Reset the controller during init and cleanup
902    i8042.unlock [HW] Unlock (ignore) the keylock
903
904    i810= [HW,DRM]
905
906    i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
907            indicates that the driver is running on unsupported
908            hardware.
909    i8k.force [HW] Activate i8k driver even if SMM BIOS signature
910            does not match list of supported models.
911    i8k.power_status
912            [HW] Report power status in /proc/i8k
913            (disabled by default)
914    i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
915            capability is set.
916
917    icn= [HW,ISDN]
918            Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
919
920    ide-core.nodma= [HW] (E)IDE subsystem
921            Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
922            .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
923            .cdrom .chs .ignore_cable are additional options
924            See Documentation/ide/ide.txt.
925
926    ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
927            Claim all unknown PCI IDE storage controllers.
928
929    idle= [X86]
930            Format: idle=poll, idle=mwait, idle=halt, idle=nomwait
931            Poll forces a polling idle loop that can slightly
932            improve the performance of waking up a idle CPU, but
933            will use a lot of power and make the system run hot.
934            Not recommended.
935            idle=mwait: On systems which support MONITOR/MWAIT but
936            the kernel chose to not use it because it doesn't save
937            as much power as a normal idle loop, use the
938            MONITOR/MWAIT idle loop anyways. Performance should be
939            the same as idle=poll.
940            idle=halt: Halt is forced to be used for CPU idle.
941            In such case C2/C3 won't be used again.
942            idle=nomwait: Disable mwait for CPU C-states
943
944    ignore_loglevel [KNL]
945            Ignore loglevel setting - this will print /all/
946            kernel messages to the console. Useful for debugging.
947
948    ihash_entries= [KNL]
949            Set number of hash buckets for inode cache.
950
951    ima_audit= [IMA]
952            Format: { "0" | "1" }
953            0 -- integrity auditing messages. (Default)
954            1 -- enable informational integrity auditing messages.
955
956    ima_hash= [IMA]
957            Format: { "sha1" | "md5" }
958            default: "sha1"
959
960    ima_tcb [IMA]
961            Load a policy which meets the needs of the Trusted
962            Computing Base. This means IMA will measure all
963            programs exec'd, files mmap'd for exec, and all files
964            opened for read by uid=0.
965
966    init= [KNL]
967            Format: <full_path>
968            Run specified binary instead of /sbin/init as init
969            process.
970
971    initcall_debug [KNL] Trace initcalls as they are executed. Useful
972            for working out where the kernel is dying during
973            startup.
974
975    initrd= [BOOT] Specify the location of the initial ramdisk
976
977    inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
978            Format: <irq>
979
980    intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
981        on
982            Enable intel iommu driver.
983        off
984            Disable intel iommu driver.
985        igfx_off [Default Off]
986            By default, gfx is mapped as normal device. If a gfx
987            device has a dedicated DMAR unit, the DMAR unit is
988            bypassed by not enabling DMAR with this option. In
989            this case, gfx device will use physical address for
990            DMA.
991        forcedac [x86_64]
992            With this option iommu will not optimize to look
993            for io virtual address below 32 bit forcing dual
994            address cycle on pci bus for cards supporting greater
995            than 32 bit addressing. The default is to look
996            for translation below 32 bit and if not available
997            then look in the higher range.
998        strict [Default Off]
999            With this option on every unmap_single operation will
1000            result in a hardware IOTLB flush operation as opposed
1001            to batching them for performance.
1002        sp_off [Default Off]
1003            By default, super page will be supported if Intel IOMMU
1004            has the capability. With this option, super page will
1005            not be supported.
1006    intremap= [X86-64, Intel-IOMMU]
1007            Format: { on (default) | off | nosid }
1008            on enable Interrupt Remapping (default)
1009            off disable Interrupt Remapping
1010            nosid disable Source ID checking
1011
1012    inttest= [IA64]
1013
1014    iomem= Disable strict checking of access to MMIO memory
1015        strict regions from userspace.
1016        relaxed
1017
1018    iommu= [x86]
1019        off
1020        force
1021        noforce
1022        biomerge
1023        panic
1024        nopanic
1025        merge
1026        nomerge
1027        forcesac
1028        soft
1029        pt [x86, IA64]
1030
1031    io7= [HW] IO7 for Marvel based alpha systems
1032            See comment before marvel_specify_io7 in
1033            arch/alpha/kernel/core_marvel.c.
1034
1035    io_delay= [X86] I/O delay method
1036        0x80
1037            Standard port 0x80 based delay
1038        0xed
1039            Alternate port 0xed based delay (needed on some systems)
1040        udelay
1041            Simple two microseconds delay
1042        none
1043            No delay
1044
1045    ip= [IP_PNP]
1046            See Documentation/filesystems/nfs/nfsroot.txt.
1047
1048    ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1049            See comment before ip2_setup() in
1050            drivers/char/ip2/ip2base.c.
1051
1052    irqfixup [HW]
1053            When an interrupt is not handled search all handlers
1054            for it. Intended to get systems with badly broken
1055            firmware running.
1056
1057    irqpoll [HW]
1058            When an interrupt is not handled search all handlers
1059            for it. Also check all handlers each timer
1060            interrupt. Intended to get systems with badly broken
1061            firmware running.
1062
1063    isapnp= [ISAPNP]
1064            Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1065
1066    isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1067            Format:
1068            <cpu number>,...,<cpu number>
1069            or
1070            <cpu number>-<cpu number>
1071            (must be a positive range in ascending order)
1072            or a mixture
1073            <cpu number>,...,<cpu number>-<cpu number>
1074
1075            This option can be used to specify one or more CPUs
1076            to isolate from the general SMP balancing and scheduling
1077            algorithms. You can move a process onto or off an
1078            "isolated" CPU via the CPU affinity syscalls or cpuset.
1079            <cpu number> begins at 0 and the maximum value is
1080            "number of CPUs in system - 1".
1081
1082            This option is the preferred way to isolate CPUs. The
1083            alternative -- manually setting the CPU mask of all
1084            tasks in the system -- can cause problems and
1085            suboptimal load balancer performance.
1086
1087    iucv= [HW,NET]
1088
1089    js= [HW,JOY] Analog joystick
1090            See Documentation/input/joystick.txt.
1091
1092    keepinitrd [HW,ARM]
1093
1094    kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1095            specifies the amount of memory usable by the kernel
1096            for non-movable allocations. The requested amount is
1097            spread evenly throughout all nodes in the system. The
1098            remaining memory in each node is used for Movable
1099            pages. In the event, a node is too small to have both
1100            kernelcore and Movable pages, kernelcore pages will
1101            take priority and other nodes will have a larger number
1102            of kernelcore pages. The Movable zone is used for the
1103            allocation of pages that may be reclaimed or moved
1104            by the page migration subsystem. This means that
1105            HugeTLB pages may not be allocated from this zone.
1106            Note that allocations like PTEs-from-HighMem still
1107            use the HighMem zone if it exists, and the Normal
1108            zone if it does not.
1109
1110    kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1111            Format: <Controller#>[,poll interval]
1112            The controller # is the number of the ehci usb debug
1113            port as it is probed via PCI. The poll interval is
1114            optional and is the number seconds in between
1115            each poll cycle to the debug port in case you need
1116            the functionality for interrupting the kernel with
1117            gdb or control-c on the dbgp connection. When
1118            not using this parameter you use sysrq-g to break into
1119            the kernel debugger.
1120
1121    kgdboc= [KGDB,HW] kgdb over consoles.
1122            Requires a tty driver that supports console polling,
1123            or a supported polling keyboard driver (non-usb).
1124             Serial only format: <serial_device>[,baud]
1125             keyboard only format: kbd
1126             keyboard and serial format: kbd,<serial_device>[,baud]
1127            Optional Kernel mode setting:
1128             kms, kbd format: kms,kbd
1129             kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1130
1131    kgdbwait [KGDB] Stop kernel execution and enter the
1132            kernel debugger at the earliest opportunity.
1133
1134    kmac= [MIPS] korina ethernet MAC address.
1135            Configure the RouterBoard 532 series on-chip
1136            Ethernet adapter MAC address.
1137
1138    kmemleak= [KNL] Boot-time kmemleak enable/disable
1139            Valid arguments: on, off
1140            Default: on
1141
1142    kstack=N [X86] Print N words from the kernel stack
1143            in oops dumps.
1144
1145    kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1146            Default is 0 (don't ignore, but inject #GP)
1147
1148    kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging.
1149            Default is 1 (enabled)
1150
1151    kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1152            KVM MMU at runtime.
1153            Default is 0 (off)
1154
1155    kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1156            Default is 1 (enabled)
1157
1158    kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1159            for all guests.
1160            Default is 1 (enabled) if in 64bit or 32bit-PAE mode
1161
1162    kvm-intel.bypass_guest_pf=
1163            [KVM,Intel] Disables bypassing of guest page faults
1164            on Intel chips. Default is 1 (enabled)
1165
1166    kvm-intel.ept= [KVM,Intel] Disable extended page tables
1167            (virtualized MMU) support on capable Intel chips.
1168            Default is 1 (enabled)
1169
1170    kvm-intel.emulate_invalid_guest_state=
1171            [KVM,Intel] Enable emulation of invalid guest states
1172            Default is 0 (disabled)
1173
1174    kvm-intel.flexpriority=
1175            [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1176            Default is 1 (enabled)
1177
1178    kvm-intel.unrestricted_guest=
1179            [KVM,Intel] Disable unrestricted guest feature
1180            (virtualized real and unpaged mode) on capable
1181            Intel chips. Default is 1 (enabled)
1182
1183    kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1184            feature (tagged TLBs) on capable Intel chips.
1185            Default is 1 (enabled)
1186
1187    l2cr= [PPC]
1188
1189    l3cr= [PPC]
1190
1191    lapic [X86-32,APIC] Enable the local APIC even if BIOS
1192            disabled it.
1193
1194    lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1195            in C2 power state.
1196
1197    libata.dma= [LIBATA] DMA control
1198            libata.dma=0 Disable all PATA and SATA DMA
1199            libata.dma=1 PATA and SATA Disk DMA only
1200            libata.dma=2 ATAPI (CDROM) DMA only
1201            libata.dma=4 Compact Flash DMA only
1202            Combinations also work, so libata.dma=3 enables DMA
1203            for disks and CDROMs, but not CFs.
1204    
1205    libata.ignore_hpa= [LIBATA] Ignore HPA limit
1206            libata.ignore_hpa=0 keep BIOS limits (default)
1207            libata.ignore_hpa=1 ignore limits, using full disk
1208
1209    libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1210            when set.
1211            Format: <int>
1212
1213    libata.force= [LIBATA] Force configurations. The format is comma
1214            separated list of "[ID:]VAL" where ID is
1215            PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1216            matching port, link or device. Basically, it matches
1217            the ATA ID string printed on console by libata. If
1218            the whole ID part is omitted, the last PORT and DEVICE
1219            values are used. If ID hasn't been specified yet, the
1220            configuration applies to all ports, links and devices.
1221
1222            If only DEVICE is omitted, the parameter applies to
1223            the port and all links and devices behind it. DEVICE
1224            number of 0 either selects the first device or the
1225            first fan-out link behind PMP device. It does not
1226            select the host link. DEVICE number of 15 selects the
1227            host link and device attached to it.
1228
1229            The VAL specifies the configuration to force. As long
1230            as there's no ambiguity shortcut notation is allowed.
1231            For example, both 1.5 and 1.5G would work for 1.5Gbps.
1232            The following configurations can be forced.
1233
1234            * Cable type: 40c, 80c, short40c, unk, ign or sata.
1235              Any ID with matching PORT is used.
1236
1237            * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1238
1239            * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1240              udma[/][16,25,33,44,66,100,133] notation is also
1241              allowed.
1242
1243            * [no]ncq: Turn on or off NCQ.
1244
1245            * nohrst, nosrst, norst: suppress hard, soft
1246                          and both resets.
1247
1248            * dump_id: dump IDENTIFY data.
1249
1250            If there are multiple matching configurations changing
1251            the same attribute, the last one is used.
1252
1253    memblock=debug [KNL] Enable memblock debug messages.
1254
1255    load_ramdisk= [RAM] List of ramdisks to load from floppy
1256            See Documentation/blockdev/ramdisk.txt.
1257
1258    lockd.nlm_grace_period=P [NFS] Assign grace period.
1259            Format: <integer>
1260
1261    lockd.nlm_tcpport=N [NFS] Assign TCP port.
1262            Format: <integer>
1263
1264    lockd.nlm_timeout=T [NFS] Assign timeout value.
1265            Format: <integer>
1266
1267    lockd.nlm_udpport=M [NFS] Assign UDP port.
1268            Format: <integer>
1269
1270    logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1271            Format: <irq>
1272
1273    loglevel= All Kernel Messages with a loglevel smaller than the
1274            console loglevel will be printed to the console. It can
1275            also be changed with klogd or other programs. The
1276            loglevels are defined as follows:
1277
1278            0 (KERN_EMERG) system is unusable
1279            1 (KERN_ALERT) action must be taken immediately
1280            2 (KERN_CRIT) critical conditions
1281            3 (KERN_ERR) error conditions
1282            4 (KERN_WARNING) warning conditions
1283            5 (KERN_NOTICE) normal but significant condition
1284            6 (KERN_INFO) informational
1285            7 (KERN_DEBUG) debug-level messages
1286
1287    log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1288            in bytes. n must be a power of two. The default
1289            size is set in the kernel config file.
1290
1291    logo.nologo [FB] Disables display of the built-in Linux logo.
1292            This may be used to provide more screen space for
1293            kernel log messages and is useful when debugging
1294            kernel boot problems.
1295
1296    lp=0 [LP] Specify parallel ports to use, e.g,
1297    lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1298    lp=reset first parallel port). 'lp=0' disables the
1299    lp=auto printer driver. 'lp=reset' (which can be
1300                specified in addition to the ports) causes
1301                attached printers to be reset. Using
1302                lp=port1,port2,... specifies the parallel ports
1303                to associate lp devices with, starting with
1304                lp0. A port specification may be 'none' to skip
1305                that lp device, or a parport name such as
1306                'parport0'. Specifying 'lp=auto' instead of a
1307                port specification list means that device IDs
1308                from each port should be examined, to see if
1309                an IEEE 1284-compliant printer is attached; if
1310                so, the driver will manage that printer.
1311                See also header of drivers/char/lp.c.
1312
1313    lpj=n [KNL]
1314            Sets loops_per_jiffy to given constant, thus avoiding
1315            time-consuming boot-time autodetection (up to 250 ms per
1316            CPU). 0 enables autodetection (default). To determine
1317            the correct value for your kernel, boot with normal
1318            autodetection and see what value is printed. Note that
1319            on SMP systems the preset will be applied to all CPUs,
1320            which is likely to cause problems if your CPUs need
1321            significantly divergent settings. An incorrect value
1322            will cause delays in the kernel to be wrong, leading to
1323            unpredictable I/O errors and other breakage. Although
1324            unlikely, in the extreme case this might damage your
1325            hardware.
1326
1327    ltpc= [NET]
1328            Format: <io>,<irq>,<dma>
1329
1330    machvec= [IA64] Force the use of a particular machine-vector
1331            (machvec) in a generic kernel.
1332            Example: machvec=hpzx1_swiotlb
1333
1334    machtype= [Loongson] Share the same kernel image file between different
1335             yeeloong laptop.
1336            Example: machtype=lemote-yeeloong-2f-7inch
1337
1338    max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1339            than or equal to this physical address is ignored.
1340
1341    maxcpus= [SMP] Maximum number of processors that an SMP kernel
1342            should make use of. maxcpus=n : n >= 0 limits the
1343            kernel to using 'n' processors. n=0 is a special case,
1344            it is equivalent to "nosmp", which also disables
1345            the IO APIC.
1346
1347    max_loop= [LOOP] Maximum number of loopback devices that can
1348            be mounted
1349            Format: <1-256>
1350
1351    mcatest= [IA-64]
1352
1353    mce [X86-32] Machine Check Exception
1354
1355    mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1356
1357    md= [HW] RAID subsystems devices and level
1358            See Documentation/md.txt.
1359
1360    mdacon= [MDA]
1361            Format: <first>,<last>
1362            Specifies range of consoles to be captured by the MDA.
1363
1364    mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1365            Amount of memory to be used when the kernel is not able
1366            to see the whole system memory or for test.
1367            [X86-32] Use together with memmap= to avoid physical
1368            address space collisions. Without memmap= PCI devices
1369            could be placed at addresses belonging to unused RAM.
1370
1371    mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1372            memory.
1373
1374    memchunk=nn[KMG]
1375            [KNL,SH] Allow user to override the default size for
1376            per-device physically contiguous DMA buffers.
1377
1378    memmap=exactmap [KNL,X86] Enable setting of an exact
1379            E820 memory map, as specified by the user.
1380            Such memmap=exactmap lines can be constructed based on
1381            BIOS output or other requirements. See the memmap=nn@ss
1382            option description.
1383
1384    memmap=nn[KMG]@ss[KMG]
1385            [KNL] Force usage of a specific region of memory
1386            Region of memory to be used, from ss to ss+nn.
1387
1388    memmap=nn[KMG]#ss[KMG]
1389            [KNL,ACPI] Mark specific memory as ACPI data.
1390            Region of memory to be used, from ss to ss+nn.
1391
1392    memmap=nn[KMG]$ss[KMG]
1393            [KNL,ACPI] Mark specific memory as reserved.
1394            Region of memory to be used, from ss to ss+nn.
1395            Example: Exclude memory from 0x18690000-0x1869ffff
1396                     memmap=64K$0x18690000
1397                     or
1398                     memmap=0x10000$0x18690000
1399
1400    memory_corruption_check=0/1 [X86]
1401            Some BIOSes seem to corrupt the first 64k of
1402            memory when doing things like suspend/resume.
1403            Setting this option will scan the memory
1404            looking for corruption. Enabling this will
1405            both detect corruption and prevent the kernel
1406            from using the memory being corrupted.
1407            However, its intended as a diagnostic tool; if
1408            repeatable BIOS-originated corruption always
1409            affects the same memory, you can use memmap=
1410            to prevent the kernel from using that memory.
1411
1412    memory_corruption_check_size=size [X86]
1413            By default it checks for corruption in the low
1414            64k, making this memory unavailable for normal
1415            use. Use this parameter to scan for
1416            corruption in more or less memory.
1417
1418    memory_corruption_check_period=seconds [X86]
1419            By default it checks for corruption every 60
1420            seconds. Use this parameter to check at some
1421            other rate. 0 disables periodic checking.
1422
1423    memtest= [KNL,X86] Enable memtest
1424            Format: <integer>
1425            default : 0 <disable>
1426            Specifies the number of memtest passes to be
1427            performed. Each pass selects another test
1428            pattern from a given set of patterns. Memtest
1429            fills the memory with this pattern, validates
1430            memory contents and reserves bad memory
1431            regions that are detected.
1432
1433    meye.*= [HW] Set MotionEye Camera parameters
1434            See Documentation/video4linux/meye.txt.
1435
1436    mfgpt_irq= [IA-32] Specify the IRQ to use for the
1437            Multi-Function General Purpose Timers on AMD Geode
1438            platforms.
1439
1440    mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1441            the BIOS has incorrectly applied a workaround. TinyBIOS
1442            version 0.98 is known to be affected, 0.99 fixes the
1443            problem by letting the user disable the workaround.
1444
1445    mga= [HW,DRM]
1446
1447    min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1448            physical address is ignored.
1449
1450    mini2440= [ARM,HW,KNL]
1451            Format:[0..2][b][c][t]
1452            Default: "0tb"
1453            MINI2440 configuration specification:
1454            0 - The attached screen is the 3.5" TFT
1455            1 - The attached screen is the 7" TFT
1456            2 - The VGA Shield is attached (1024x768)
1457            Leaving out the screen size parameter will not load
1458            the TFT driver, and the framebuffer will be left
1459            unconfigured.
1460            b - Enable backlight. The TFT backlight pin will be
1461            linked to the kernel VESA blanking code and a GPIO
1462            LED. This parameter is not necessary when using the
1463            VGA shield.
1464            c - Enable the s3c camera interface.
1465            t - Reserved for enabling touchscreen support. The
1466            touchscreen support is not enabled in the mainstream
1467            kernel as of 2.6.30, a preliminary port can be found
1468            in the "bleeding edge" mini2440 support kernel at
1469            http://repo.or.cz/w/linux-2.6/mini2440.git
1470
1471    mminit_loglevel=
1472            [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1473            parameter allows control of the logging verbosity for
1474            the additional memory initialisation checks. A value
1475            of 0 disables mminit logging and a level of 4 will
1476            log everything. Information is printed at KERN_DEBUG
1477            so loglevel=8 may also need to be specified.
1478
1479    mousedev.tap_time=
1480            [MOUSE] Maximum time between finger touching and
1481            leaving touchpad surface for touch to be considered
1482            a tap and be reported as a left button click (for
1483            touchpads working in absolute mode only).
1484            Format: <msecs>
1485    mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1486            reporting absolute coordinates, such as tablets
1487    mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1488            reporting absolute coordinates, such as tablets
1489
1490    movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1491            is similar to kernelcore except it specifies the
1492            amount of memory used for migratable allocations.
1493            If both kernelcore and movablecore is specified,
1494            then kernelcore will be at *least* the specified
1495            value but may be more. If movablecore on its own
1496            is specified, the administrator must be careful
1497            that the amount of memory usable for all allocations
1498            is not too small.
1499
1500    MTD_Partition= [MTD]
1501            Format: <name>,<region-number>,<size>,<offset>
1502
1503    MTD_Region= [MTD] Format:
1504            <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1505
1506    mtdparts= [MTD]
1507            See drivers/mtd/cmdlinepart.c.
1508
1509    multitce=off [PPC] This parameter disables the use of the pSeries
1510            firmware feature for updating multiple TCE entries
1511            at a time.
1512
1513    onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1514
1515            Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1516
1517            boundary - index of last SLC block on Flex-OneNAND.
1518                   The remaining blocks are configured as MLC blocks.
1519            lock - Configure if Flex-OneNAND boundary should be locked.
1520                   Once locked, the boundary cannot be changed.
1521                   1 indicates lock status, 0 indicates unlock status.
1522
1523    mtdset= [ARM]
1524            ARM/S3C2412 JIVE boot control
1525
1526            See arch/arm/mach-s3c2412/mach-jive.c
1527
1528    mtouchusb.raw_coordinates=
1529            [HW] Make the MicroTouch USB driver use raw coordinates
1530            ('y', default) or cooked coordinates ('n')
1531
1532    mtrr_chunk_size=nn[KMG] [X86]
1533            used for mtrr cleanup. It is largest continuous chunk
1534            that could hold holes aka. UC entries.
1535
1536    mtrr_gran_size=nn[KMG] [X86]
1537            Used for mtrr cleanup. It is granularity of mtrr block.
1538            Default is 1.
1539            Large value could prevent small alignment from
1540            using up MTRRs.
1541
1542    mtrr_spare_reg_nr=n [X86]
1543            Format: <integer>
1544            Range: 0,7 : spare reg number
1545            Default : 1
1546            Used for mtrr cleanup. It is spare mtrr entries number.
1547            Set to 2 or more if your graphical card needs more.
1548
1549    n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1550
1551    netdev= [NET] Network devices parameters
1552            Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1553            Note that mem_start is often overloaded to mean
1554            something different and driver-specific.
1555            This usage is only documented in each driver source
1556            file if at all.
1557
1558    nf_conntrack.acct=
1559            [NETFILTER] Enable connection tracking flow accounting
1560            0 to disable accounting
1561            1 to enable accounting
1562            Default value is 0.
1563
1564    nfsaddrs= [NFS] Deprecated. Use ip= instead.
1565            See Documentation/filesystems/nfs/nfsroot.txt.
1566
1567    nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1568            See Documentation/filesystems/nfs/nfsroot.txt.
1569
1570    nfsrootdebug [NFS] enable nfsroot debugging messages.
1571            See Documentation/filesystems/nfs/nfsroot.txt.
1572
1573    nfs.callback_tcpport=
1574            [NFS] set the TCP port on which the NFSv4 callback
1575            channel should listen.
1576
1577    nfs.cache_getent=
1578            [NFS] sets the pathname to the program which is used
1579            to update the NFS client cache entries.
1580
1581    nfs.cache_getent_timeout=
1582            [NFS] sets the timeout after which an attempt to
1583            update a cache entry is deemed to have failed.
1584
1585    nfs.idmap_cache_timeout=
1586            [NFS] set the maximum lifetime for idmapper cache
1587            entries.
1588
1589    nfs.enable_ino64=
1590            [NFS] enable 64-bit inode numbers.
1591            If zero, the NFS client will fake up a 32-bit inode
1592            number for the readdir() and stat() syscalls instead
1593            of returning the full 64-bit number.
1594            The default is to return 64-bit inode numbers.
1595
1596    nfs.nfs4_disable_idmapping=
1597            [NFSv4] When set, this option disables the NFSv4
1598            idmapper on the client, but only if the mount
1599            is using the 'sec=sys' security flavour. This may
1600            make migration from legacy NFSv2/v3 systems easier
1601            provided that the server has the appropriate support.
1602            The default is to always enable NFSv4 idmapping.
1603
1604    nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1605            when a NMI is triggered.
1606            Format: [state][,regs][,debounce][,die]
1607
1608    nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1609            Format: [panic,][nopanic,][num]
1610            Valid num: 0
1611            0 - turn nmi_watchdog off
1612            When panic is specified, panic when an NMI watchdog
1613            timeout occurs (or 'nopanic' to override the opposite
1614            default).
1615            This is useful when you use a panic=... timeout and
1616            need the box quickly up again.
1617
1618    netpoll.carrier_timeout=
1619            [NET] Specifies amount of time (in seconds) that
1620            netpoll should wait for a carrier. By default netpoll
1621            waits 4 seconds.
1622
1623    no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1624            emulation library even if a 387 maths coprocessor
1625            is present.
1626
1627    no_console_suspend
1628            [HW] Never suspend the console
1629            Disable suspending of consoles during suspend and
1630            hibernate operations. Once disabled, debugging
1631            messages can reach various consoles while the rest
1632            of the system is being put to sleep (ie, while
1633            debugging driver suspend/resume hooks). This may
1634            not work reliably with all consoles, but is known
1635            to work with serial and VGA consoles.
1636
1637    noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1638            caches in the slab allocator. Saves per-node memory,
1639            but will impact performance.
1640
1641    noalign [KNL,ARM]
1642
1643    noapic [SMP,APIC] Tells the kernel to not make use of any
1644            IOAPICs that may be present in the system.
1645
1646    noautogroup Disable scheduler automatic task group creation.
1647
1648    nobats [PPC] Do not use BATs for mapping kernel lowmem
1649            on "Classic" PPC cores.
1650
1651    nocache [ARM]
1652
1653    noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1654
1655    nodelayacct [KNL] Disable per-task delay accounting
1656
1657    nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1658
1659    nodsp [SH] Disable hardware DSP at boot time.
1660
1661    noefi [X86] Disable EFI runtime services support.
1662
1663    noexec [IA-64]
1664
1665    noexec [X86]
1666            On X86-32 available only on PAE configured kernels.
1667            noexec=on: enable non-executable mappings (default)
1668            noexec=off: disable non-executable mappings
1669
1670    nosmep [X86]
1671            Disable SMEP (Supervisor Mode Execution Protection)
1672            even if it is supported by processor.
1673
1674    noexec32 [X86-64]
1675            This affects only 32-bit executables.
1676            noexec32=on: enable non-executable mappings (default)
1677                read doesn't imply executable mappings
1678            noexec32=off: disable non-executable mappings
1679                read implies executable mappings
1680
1681    nofpu [SH] Disable hardware FPU at boot time.
1682
1683    nofxsr [BUGS=X86-32] Disables x86 floating point extended
1684            register save and restore. The kernel will only save
1685            legacy floating-point registers on task switch.
1686
1687    noxsave [BUGS=X86] Disables x86 extended register state save
1688            and restore using xsave. The kernel will fallback to
1689            enabling legacy floating-point and sse state.
1690
1691    nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1692            wfi(ARM) instruction doesn't work correctly and not to
1693            use it. This is also useful when using JTAG debugger.
1694
1695    no-hlt [BUGS=X86-32] Tells the kernel that the hlt
1696            instruction doesn't work correctly and not to
1697            use it.
1698
1699    no_file_caps Tells the kernel not to honor file capabilities. The
1700            only way then for a file to be executed with privilege
1701            is to be setuid root or executed by root.
1702
1703    nohalt [IA-64] Tells the kernel not to use the power saving
1704            function PAL_HALT_LIGHT when idle. This increases
1705            power-consumption. On the positive side, it reduces
1706            interrupt wake-up latency, which may improve performance
1707            in certain environments such as networked servers or
1708            real-time systems.
1709
1710    nohz= [KNL] Boottime enable/disable dynamic ticks
1711            Valid arguments: on, off
1712            Default: on
1713
1714    noiotrap [SH] Disables trapped I/O port accesses.
1715
1716    noirqdebug [X86-32] Disables the code which attempts to detect and
1717            disable unhandled interrupt sources.
1718
1719    no_timer_check [X86,APIC] Disables the code which tests for
1720            broken timer IRQ sources.
1721
1722    noisapnp [ISAPNP] Disables ISA PnP code.
1723
1724    noinitrd [RAM] Tells the kernel not to load any configured
1725            initial RAM disk.
1726
1727    nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1728            remapping.
1729            [Deprecated - use intremap=off]
1730
1731    nointroute [IA-64]
1732
1733    nojitter [IA64] Disables jitter checking for ITC timers.
1734
1735    no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1736
1737    no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1738            fault handling.
1739
1740    nolapic [X86-32,APIC] Do not enable or use the local APIC.
1741
1742    nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1743
1744    noltlbs [PPC] Do not use large page/tlb entries for kernel
1745            lowmem mapping on PPC40x.
1746
1747    nomca [IA-64] Disable machine check abort handling
1748
1749    nomce [X86-32] Machine Check Exception
1750
1751    nomfgpt [X86-32] Disable Multi-Function General Purpose
1752            Timer usage (for AMD Geode machines).
1753
1754    nopat [X86] Disable PAT (page attribute table extension of
1755            pagetables) support.
1756
1757    norandmaps Don't use address space randomization. Equivalent to
1758            echo 0 > /proc/sys/kernel/randomize_va_space
1759
1760    noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1761
1762    noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1763            with UP alternatives
1764
1765    noresidual [PPC] Don't use residual data on PReP machines.
1766
1767    noresume [SWSUSP] Disables resume and restores original swap
1768            space.
1769
1770    no-scroll [VGA] Disables scrollback.
1771            This is required for the Braillex ib80-piezo Braille
1772            reader made by F.H. Papenmeier (Germany).
1773
1774    nosbagart [IA-64]
1775
1776    nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
1777
1778    nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
1779            and disable the IO APIC. legacy for "maxcpus=0".
1780
1781    nosoftlockup [KNL] Disable the soft-lockup detector.
1782
1783    nosync [HW,M68K] Disables sync negotiation for all devices.
1784
1785    notsc [BUGS=X86-32] Disable Time Stamp Counter
1786
1787    nousb [USB] Disable the USB subsystem
1788
1789    nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
1790
1791    nowb [ARM]
1792
1793    nox2apic [X86-64,APIC] Do not enable x2APIC mode.
1794
1795    nptcg= [IA64] Override max number of concurrent global TLB
1796            purges which is reported from either PAL_VM_SUMMARY or
1797            SAL PALO.
1798
1799    nr_cpus= [SMP] Maximum number of processors that an SMP kernel
1800            could support. nr_cpus=n : n >= 1 limits the kernel to
1801            supporting 'n' processors. Later in runtime you can not
1802            use hotplug cpu feature to put more cpu back to online.
1803            just like you compile the kernel NR_CPUS=n
1804
1805    nr_uarts= [SERIAL] maximum number of UARTs to be registered.
1806
1807    numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
1808            one of ['zone', 'node', 'default'] can be specified
1809            This can be set from sysctl after boot.
1810            See Documentation/sysctl/vm.txt for details.
1811
1812    ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
1813            See Documentation/debugging-via-ohci1394.txt for more
1814            info.
1815
1816    olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
1817            Rather than timing out after 20 ms if an EC
1818            command is not properly ACKed, override the length
1819            of the timeout. We have interrupts disabled while
1820            waiting for the ACK, so if this is set too high
1821            interrupts *may* be lost!
1822
1823    omap_mux= [OMAP] Override bootloader pin multiplexing.
1824            Format: <mux_mode0.mode_name=value>...
1825            For example, to override I2C bus2:
1826            omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
1827
1828    oprofile.timer= [HW]
1829            Use timer interrupt instead of performance counters
1830
1831    oprofile.cpu_type= Force an oprofile cpu type
1832            This might be useful if you have an older oprofile
1833            userland or if you want common events.
1834            Format: { arch_perfmon }
1835            arch_perfmon: [X86] Force use of architectural
1836                perfmon on Intel CPUs instead of the
1837                CPU specific event set.
1838
1839    oops=panic Always panic on oopses. Default is to just kill the
1840            process, but there is a small probability of
1841            deadlocking the machine.
1842            This will also cause panics on machine check exceptions.
1843            Useful together with panic=30 to trigger a reboot.
1844
1845    OSS [HW,OSS]
1846            See Documentation/sound/oss/oss-parameters.txt
1847
1848    panic= [KNL] Kernel behaviour on panic: delay <timeout>
1849            seconds before rebooting
1850            Format: <timeout>
1851
1852    parkbd.port= [HW] Parallel port number the keyboard adapter is
1853            connected to, default is 0.
1854            Format: <parport#>
1855    parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
1856            0 for XT, 1 for AT (default is AT).
1857            Format: <mode>
1858
1859    parport= [HW,PPT] Specify parallel ports. 0 disables.
1860            Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
1861            Use 'auto' to force the driver to use any
1862            IRQ/DMA settings detected (the default is to
1863            ignore detected IRQ/DMA settings because of
1864            possible conflicts). You can specify the base
1865            address, IRQ, and DMA settings; IRQ and DMA
1866            should be numbers, or 'auto' (for using detected
1867            settings on that particular port), or 'nofifo'
1868            (to avoid using a FIFO even if it is detected).
1869            Parallel ports are assigned in the order they
1870            are specified on the command line, starting
1871            with parport0.
1872
1873    parport_init_mode= [HW,PPT]
1874            Configure VIA parallel port to operate in
1875            a specific mode. This is necessary on Pegasos
1876            computer where firmware has no options for setting
1877            up parallel port mode and sets it to spp.
1878            Currently this function knows 686a and 8231 chips.
1879            Format: [spp|ps2|epp|ecp|ecpepp]
1880
1881    pause_on_oops=
1882            Halt all CPUs after the first oops has been printed for
1883            the specified number of seconds. This is to be used if
1884            your oopses keep scrolling off the screen.
1885
1886    pcbit= [HW,ISDN]
1887
1888    pcd. [PARIDE]
1889            See header of drivers/block/paride/pcd.c.
1890            See also Documentation/blockdev/paride.txt.
1891
1892    pci=option[,option...] [PCI] various PCI subsystem options:
1893        earlydump [X86] dump PCI config space before the kernel
1894                    changes anything
1895        off [X86] don't probe for the PCI bus
1896        bios [X86-32] force use of PCI BIOS, don't access
1897                the hardware directly. Use this if your machine
1898                has a non-standard PCI host bridge.
1899        nobios [X86-32] disallow use of PCI BIOS, only direct
1900                hardware access methods are allowed. Use this
1901                if you experience crashes upon bootup and you
1902                suspect they are caused by the BIOS.
1903        conf1 [X86] Force use of PCI Configuration
1904                Mechanism 1.
1905        conf2 [X86] Force use of PCI Configuration
1906                Mechanism 2.
1907        noaer [PCIE] If the PCIEAER kernel config parameter is
1908                enabled, this kernel boot option can be used to
1909                disable the use of PCIE advanced error reporting.
1910        nodomains [PCI] Disable support for multiple PCI
1911                root domains (aka PCI segments, in ACPI-speak).
1912        nommconf [X86] Disable use of MMCONFIG for PCI
1913                Configuration
1914        check_enable_amd_mmconf [X86] check for and enable
1915                properly configured MMIO access to PCI
1916                config space on AMD family 10h CPU
1917        nomsi [MSI] If the PCI_MSI kernel config parameter is
1918                enabled, this kernel boot option can be used to
1919                disable the use of MSI interrupts system-wide.
1920        noioapicquirk [APIC] Disable all boot interrupt quirks.
1921                Safety option to keep boot IRQs enabled. This
1922                should never be necessary.
1923        ioapicreroute [APIC] Enable rerouting of boot IRQs to the
1924                primary IO-APIC for bridges that cannot disable
1925                boot IRQs. This fixes a source of spurious IRQs
1926                when the system masks IRQs.
1927        noioapicreroute [APIC] Disable workaround that uses the
1928                boot IRQ equivalent of an IRQ that connects to
1929                a chipset where boot IRQs cannot be disabled.
1930                The opposite of ioapicreroute.
1931        biosirq [X86-32] Use PCI BIOS calls to get the interrupt
1932                routing table. These calls are known to be buggy
1933                on several machines and they hang the machine
1934                when used, but on other computers it's the only
1935                way to get the interrupt routing table. Try
1936                this option if the kernel is unable to allocate
1937                IRQs or discover secondary PCI buses on your
1938                motherboard.
1939        rom [X86] Assign address space to expansion ROMs.
1940                Use with caution as certain devices share
1941                address decoders between ROMs and other
1942                resources.
1943        norom [X86] Do not assign address space to
1944                expansion ROMs that do not already have
1945                BIOS assigned address ranges.
1946        nobar [X86] Do not assign address space to the
1947                BARs that weren't assigned by the BIOS.
1948        irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
1949                assigned automatically to PCI devices. You can
1950                make the kernel exclude IRQs of your ISA cards
1951                this way.
1952        pirqaddr=0xAAAAA [X86] Specify the physical address
1953                of the PIRQ table (normally generated
1954                by the BIOS) if it is outside the
1955                F0000h-100000h range.
1956        lastbus=N [X86] Scan all buses thru bus #N. Can be
1957                useful if the kernel is unable to find your
1958                secondary buses and you want to tell it
1959                explicitly which ones they are.
1960        assign-busses [X86] Always assign all PCI bus
1961                numbers ourselves, overriding
1962                whatever the firmware may have done.
1963        usepirqmask [X86] Honor the possible IRQ mask stored
1964                in the BIOS $PIR table. This is needed on
1965                some systems with broken BIOSes, notably
1966                some HP Pavilion N5400 and Omnibook XE3
1967                notebooks. This will have no effect if ACPI
1968                IRQ routing is enabled.
1969        noacpi [X86] Do not use ACPI for IRQ routing
1970                or for PCI scanning.
1971        use_crs [X86] Use PCI host bridge window information
1972                from ACPI. On BIOSes from 2008 or later, this
1973                is enabled by default. If you need to use this,
1974                please report a bug.
1975        nocrs [X86] Ignore PCI host bridge windows from ACPI.
1976                    If you need to use this, please report a bug.
1977        routeirq Do IRQ routing for all PCI devices.
1978                This is normally done in pci_enable_device(),
1979                so this option is a temporary workaround
1980                for broken drivers that don't call it.
1981        skip_isa_align [X86] do not align io start addr, so can
1982                handle more pci cards
1983        firmware [ARM] Do not re-enumerate the bus but instead
1984                just use the configuration from the
1985                bootloader. This is currently used on
1986                IXP2000 systems where the bus has to be
1987                configured a certain way for adjunct CPUs.
1988        noearly [X86] Don't do any early type 1 scanning.
1989                This might help on some broken boards which
1990                machine check when some devices' config space
1991                is read. But various workarounds are disabled
1992                and some IOMMU drivers will not work.
1993        bfsort Sort PCI devices into breadth-first order.
1994                This sorting is done to get a device
1995                order compatible with older (<= 2.4) kernels.
1996        nobfsort Don't sort PCI devices into breadth-first order.
1997        cbiosize=nn[KMG] The fixed amount of bus space which is
1998                reserved for the CardBus bridge's IO window.
1999                The default value is 256 bytes.
2000        cbmemsize=nn[KMG] The fixed amount of bus space which is
2001                reserved for the CardBus bridge's memory
2002                window. The default value is 64 megabytes.
2003        resource_alignment=
2004                Format:
2005                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2006                Specifies alignment and device to reassign
2007                aligned memory resources.
2008                If <order of align> is not specified,
2009                PAGE_SIZE is used as alignment.
2010                PCI-PCI bridge can be specified, if resource
2011                windows need to be expanded.
2012        ecrc= Enable/disable PCIe ECRC (transaction layer
2013                end-to-end CRC checking).
2014                bios: Use BIOS/firmware settings. This is the
2015                the default.
2016                off: Turn ECRC off
2017                on: Turn ECRC on.
2018        realloc reallocate PCI resources if allocations done by BIOS
2019                are erroneous.
2020
2021    pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2022            Management.
2023        off Disable ASPM.
2024        force Enable ASPM even on devices that claim not to support it.
2025            WARNING: Forcing ASPM on may cause system lockups.
2026
2027    pcie_ports= [PCIE] PCIe ports handling:
2028        auto Ask the BIOS whether or not to use native PCIe services
2029            associated with PCIe ports (PME, hot-plug, AER). Use
2030            them only if that is allowed by the BIOS.
2031        native Use native PCIe services associated with PCIe ports
2032            unconditionally.
2033        compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2034            ports driver.
2035
2036    pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2037        nomsi Do not use MSI for native PCIe PME signaling (this makes
2038            all PCIe root ports use INTx for all services).
2039
2040    pcmv= [HW,PCMCIA] BadgePAD 4
2041
2042    pd. [PARIDE]
2043            See Documentation/blockdev/paride.txt.
2044
2045    pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2046            boot time.
2047            Format: { 0 | 1 }
2048            See arch/parisc/kernel/pdc_chassis.c
2049
2050    percpu_alloc= Select which percpu first chunk allocator to use.
2051            Currently supported values are "embed" and "page".
2052            Archs may support subset or none of the selections.
2053            See comments in mm/percpu.c for details on each
2054            allocator. This parameter is primarily for debugging
2055            and performance comparison.
2056
2057    pf. [PARIDE]
2058            See Documentation/blockdev/paride.txt.
2059
2060    pg. [PARIDE]
2061            See Documentation/blockdev/paride.txt.
2062
2063    pirq= [SMP,APIC] Manual mp-table setup
2064            See Documentation/x86/i386/IO-APIC.txt.
2065
2066    plip= [PPT,NET] Parallel port network link
2067            Format: { parport<nr> | timid | 0 }
2068            See also Documentation/parport.txt.
2069
2070    pmtmr= [X86] Manual setup of pmtmr I/O Port.
2071            Override pmtimer IOPort with a hex value.
2072            e.g. pmtmr=0x508
2073
2074    pnp.debug [PNP]
2075            Enable PNP debug messages. This depends on the
2076            CONFIG_PNP_DEBUG_MESSAGES option.
2077
2078    pnpacpi= [ACPI]
2079            { off }
2080
2081    pnpbios= [ISAPNP]
2082            { on | off | curr | res | no-curr | no-res }
2083
2084    pnp_reserve_irq=
2085            [ISAPNP] Exclude IRQs for the autoconfiguration
2086
2087    pnp_reserve_dma=
2088            [ISAPNP] Exclude DMAs for the autoconfiguration
2089
2090    pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2091            Ranges are in pairs (I/O port base and size).
2092
2093    pnp_reserve_mem=
2094            [ISAPNP] Exclude memory regions for the
2095            autoconfiguration.
2096            Ranges are in pairs (memory base and size).
2097
2098    ports= [IP_VS_FTP] IPVS ftp helper module
2099            Default is 21.
2100            Up to 8 (IP_VS_APP_MAX_PORTS) ports
2101            may be specified.
2102            Format: <port>,<port>....
2103
2104    print-fatal-signals=
2105            [KNL] debug: print fatal signals
2106
2107            If enabled, warn about various signal handling
2108            related application anomalies: too many signals,
2109            too many POSIX.1 timers, fatal signals causing a
2110            coredump - etc.
2111
2112            If you hit the warning due to signal overflow,
2113            you might want to try "ulimit -i unlimited".
2114
2115            default: off.
2116
2117    printk.time= Show timing data prefixed to each printk message line
2118            Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2119
2120    processor.max_cstate= [HW,ACPI]
2121            Limit processor to maximum C-state
2122            max_cstate=9 overrides any DMI blacklist limit.
2123
2124    processor.nocst [HW,ACPI]
2125            Ignore the _CST method to determine C-states,
2126            instead using the legacy FADT method
2127
2128    profile= [KNL] Enable kernel profiling via /proc/profile
2129            Format: [schedule,]<number>
2130            Param: "schedule" - profile schedule points.
2131            Param: <number> - step/bucket size as a power of 2 for
2132                statistical time based profiling.
2133            Param: "sleep" - profile D-state sleeping (millisecs).
2134                Requires CONFIG_SCHEDSTATS
2135            Param: "kvm" - profile VM exits.
2136
2137    prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2138            before loading.
2139            See Documentation/blockdev/ramdisk.txt.
2140
2141    psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2142            probe for; one of (bare|imps|exps|lifebook|any).
2143    psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2144            per second.
2145    psmouse.resetafter= [HW,MOUSE]
2146            Try to reset the device after so many bad packets
2147            (0 = never).
2148    psmouse.resolution=
2149            [HW,MOUSE] Set desired mouse resolution, in dpi.
2150    psmouse.smartscroll=
2151            [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2152            0 = disabled, 1 = enabled (default).
2153
2154    pt. [PARIDE]
2155            See Documentation/blockdev/paride.txt.
2156
2157    pty.legacy_count=
2158            [KNL] Number of legacy pty's. Overwrites compiled-in
2159            default number.
2160
2161    quiet [KNL] Disable most log messages
2162
2163    r128= [HW,DRM]
2164
2165    raid= [HW,RAID]
2166            See Documentation/md.txt.
2167
2168    ramdisk_blocksize= [RAM]
2169            See Documentation/blockdev/ramdisk.txt.
2170
2171    ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2172            See Documentation/blockdev/ramdisk.txt.
2173
2174    rcupdate.blimit= [KNL,BOOT]
2175            Set maximum number of finished RCU callbacks to process
2176            in one batch.
2177
2178    rcupdate.qhimark= [KNL,BOOT]
2179            Set threshold of queued
2180            RCU callbacks over which batch limiting is disabled.
2181
2182    rcupdate.qlowmark= [KNL,BOOT]
2183            Set threshold of queued RCU callbacks below which
2184            batch limiting is re-enabled.
2185
2186    rdinit= [KNL]
2187            Format: <full_path>
2188            Run specified binary instead of /init from the ramdisk,
2189            used for early userspace startup. See initrd.
2190
2191    reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2192            Format: <reboot_mode>[,<reboot_mode2>[,...]]
2193            See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2194
2195    relax_domain_level=
2196            [KNL, SMP] Set scheduler's default relax_domain_level.
2197            See Documentation/cgroups/cpusets.txt.
2198
2199    reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2200
2201    reservetop= [X86-32]
2202            Format: nn[KMG]
2203            Reserves a hole at the top of the kernel virtual
2204            address space.
2205
2206    reservelow= [X86]
2207            Format: nn[K]
2208            Set the amount of memory to reserve for BIOS at
2209            the bottom of the address space.
2210
2211    reset_devices [KNL] Force drivers to reset the underlying device
2212            during initialization.
2213
2214    resume= [SWSUSP]
2215            Specify the partition device for software suspend
2216
2217    resume_offset= [SWSUSP]
2218            Specify the offset from the beginning of the partition
2219            given by "resume=" at which the swap header is located,
2220            in <PAGE_SIZE> units (needed only for swap files).
2221            See Documentation/power/swsusp-and-swap-files.txt
2222
2223    hibernate= [HIBERNATION]
2224        noresume Don't check if there's a hibernation image
2225                present during boot.
2226        nocompress Don't compress/decompress hibernation images.
2227
2228    retain_initrd [RAM] Keep initrd memory after extraction
2229
2230    rhash_entries= [KNL,NET]
2231            Set number of hash buckets for route cache
2232
2233    riscom8= [HW,SERIAL]
2234            Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2235
2236    ro [KNL] Mount root device read-only on boot
2237
2238    root= [KNL] Root filesystem
2239
2240    rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2241            mount the root filesystem
2242
2243    rootflags= [KNL] Set root filesystem mount option string
2244
2245    rootfstype= [KNL] Set root filesystem type
2246
2247    rootwait [KNL] Wait (indefinitely) for root device to show up.
2248            Useful for devices that are detected asynchronously
2249            (e.g. USB and MMC devices).
2250
2251    rw [KNL] Mount root device read-write on boot
2252
2253    S [KNL] Run init in single mode
2254
2255    sa1100ir [NET]
2256            See drivers/net/irda/sa1100_ir.c.
2257
2258    sbni= [NET] Granch SBNI12 leased line adapter
2259
2260    sched_debug [KNL] Enables verbose scheduler debug messages.
2261
2262    security= [SECURITY] Choose a security module to enable at boot.
2263            If this boot parameter is not specified, only the first
2264            security module asking for security registration will be
2265            loaded. An invalid security module name will be treated
2266            as if no module has been chosen.
2267
2268    selinux= [SELINUX] Disable or enable SELinux at boot time.
2269            Format: { "0" | "1" }
2270            See security/selinux/Kconfig help text.
2271            0 -- disable.
2272            1 -- enable.
2273            Default value is set via kernel config option.
2274            If enabled at boot time, /selinux/disable can be used
2275            later to disable prior to initial policy load.
2276
2277    apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2278            Format: { "0" | "1" }
2279            See security/apparmor/Kconfig help text
2280            0 -- disable.
2281            1 -- enable.
2282            Default value is set via kernel config option.
2283
2284    serialnumber [BUGS=X86-32]
2285
2286    shapers= [NET]
2287            Maximal number of shapers.
2288
2289    show_msr= [x86] show boot-time MSR settings
2290            Format: { <integer> }
2291            Show boot-time (BIOS-initialized) MSR settings.
2292            The parameter means the number of CPUs to show,
2293            for example 1 means boot CPU only.
2294
2295    simeth= [IA-64]
2296    simscsi=
2297
2298    slram= [HW,MTD]
2299
2300    slub_debug[=options[,slabs]] [MM, SLUB]
2301            Enabling slub_debug allows one to determine the
2302            culprit if slab objects become corrupted. Enabling
2303            slub_debug can create guard zones around objects and
2304            may poison objects when not in use. Also tracks the
2305            last alloc / free. For more information see
2306            Documentation/vm/slub.txt.
2307
2308    slub_max_order= [MM, SLUB]
2309            Determines the maximum allowed order for slabs.
2310            A high setting may cause OOMs due to memory
2311            fragmentation. For more information see
2312            Documentation/vm/slub.txt.
2313
2314    slub_min_objects= [MM, SLUB]
2315            The minimum number of objects per slab. SLUB will
2316            increase the slab order up to slub_max_order to
2317            generate a sufficiently large slab able to contain
2318            the number of objects indicated. The higher the number
2319            of objects the smaller the overhead of tracking slabs
2320            and the less frequently locks need to be acquired.
2321            For more information see Documentation/vm/slub.txt.
2322
2323    slub_min_order= [MM, SLUB]
2324            Determines the mininum page order for slabs. Must be
2325            lower than slub_max_order.
2326            For more information see Documentation/vm/slub.txt.
2327
2328    slub_nomerge [MM, SLUB]
2329            Disable merging of slabs with similar size. May be
2330            necessary if there is some reason to distinguish
2331            allocs to different slabs. Debug options disable
2332            merging on their own.
2333            For more information see Documentation/vm/slub.txt.
2334
2335    smart2= [HW]
2336            Format: <io1>[,<io2>[,...,<io8>]]
2337
2338    smp-alt-once [X86-32,SMP] On a hotplug CPU system, only
2339            attempt to substitute SMP alternatives once at boot.
2340
2341    smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2342    smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2343    smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2344    smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2345    smsc-ircc2.ircc_irq= [HW] IRQ line
2346    smsc-ircc2.ircc_dma= [HW] DMA channel
2347    smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2348                0: Toshiba Satellite 1800 (GP data pin select)
2349                1: Fast pin select (default)
2350                2: ATC IRMode
2351
2352    softlockup_panic=
2353            [KNL] Should the soft-lockup detector generate panics.
2354            Format: <integer>
2355
2356    sonypi.*= [HW] Sony Programmable I/O Control Device driver
2357            See Documentation/sonypi.txt
2358
2359    specialix= [HW,SERIAL] Specialix multi-serial port adapter
2360            See Documentation/serial/specialix.txt.
2361
2362    spia_io_base= [HW,MTD]
2363    spia_fio_base=
2364    spia_pedr=
2365    spia_peddr=
2366
2367    stacktrace [FTRACE]
2368            Enabled the stack tracer on boot up.
2369
2370    sti= [PARISC,HW]
2371            Format: <num>
2372            Set the STI (builtin display/keyboard on the HP-PARISC
2373            machines) console (graphic card) which should be used
2374            as the initial boot-console.
2375            See also comment in drivers/video/console/sticore.c.
2376
2377    sti_font= [HW]
2378            See comment in drivers/video/console/sticore.c.
2379
2380    stifb= [HW]
2381            Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2382
2383    sunrpc.min_resvport=
2384    sunrpc.max_resvport=
2385            [NFS,SUNRPC]
2386            SunRPC servers often require that client requests
2387            originate from a privileged port (i.e. a port in the
2388            range 0 < portnr < 1024).
2389            An administrator who wishes to reserve some of these
2390            ports for other uses may adjust the range that the
2391            kernel's sunrpc client considers to be privileged
2392            using these two parameters to set the minimum and
2393            maximum port values.
2394
2395    sunrpc.pool_mode=
2396            [NFS]
2397            Control how the NFS server code allocates CPUs to
2398            service thread pools. Depending on how many NICs
2399            you have and where their interrupts are bound, this
2400            option will affect which CPUs will do NFS serving.
2401            Note: this parameter cannot be changed while the
2402            NFS server is running.
2403
2404            auto the server chooses an appropriate mode
2405                    automatically using heuristics
2406            global a single global pool contains all CPUs
2407            percpu one pool for each CPU
2408            pernode one pool for each NUMA node (equivalent
2409                    to global on non-NUMA machines)
2410
2411    sunrpc.tcp_slot_table_entries=
2412    sunrpc.udp_slot_table_entries=
2413            [NFS,SUNRPC]
2414            Sets the upper limit on the number of simultaneous
2415            RPC calls that can be sent from the client to a
2416            server. Increasing these values may allow you to
2417            improve throughput, but will also increase the
2418            amount of memory reserved for use by the client.
2419
2420    swapaccount[=0|1]
2421            [KNL] Enable accounting of swap in memory resource
2422            controller if no parameter or 1 is given or disable
2423            it if 0 is given (See Documentation/cgroups/memory.txt)
2424
2425    swiotlb= [IA-64] Number of I/O TLB slabs
2426
2427    switches= [HW,M68k]
2428
2429    sysfs.deprecated=0|1 [KNL]
2430            Enable/disable old style sysfs layout for old udev
2431            on older distributions. When this option is enabled
2432            very new udev will not work anymore. When this option
2433            is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2434            in older udev will not work anymore.
2435            Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2436            the kernel configuration.
2437
2438    sysrq_always_enabled
2439            [KNL]
2440            Ignore sysrq setting - this boot parameter will
2441            neutralize any effect of /proc/sys/kernel/sysrq.
2442            Useful for debugging.
2443
2444    tdfx= [HW,DRM]
2445
2446    test_suspend= [SUSPEND]
2447            Specify "mem" (for Suspend-to-RAM) or "standby" (for
2448            standby suspend) as the system sleep state to briefly
2449            enter during system startup. The system is woken from
2450            this state using a wakeup-capable RTC alarm.
2451
2452    thash_entries= [KNL,NET]
2453            Set number of hash buckets for TCP connection
2454
2455    thermal.act= [HW,ACPI]
2456            -1: disable all active trip points in all thermal zones
2457            <degrees C>: override all lowest active trip points
2458
2459    thermal.crt= [HW,ACPI]
2460            -1: disable all critical trip points in all thermal zones
2461            <degrees C>: override all critical trip points
2462
2463    thermal.nocrt= [HW,ACPI]
2464            Set to disable actions on ACPI thermal zone
2465            critical and hot trip points.
2466
2467    thermal.off= [HW,ACPI]
2468            1: disable ACPI thermal control
2469
2470    thermal.psv= [HW,ACPI]
2471            -1: disable all passive trip points
2472            <degrees C>: override all passive trip points to this
2473            value
2474
2475    thermal.tzp= [HW,ACPI]
2476            Specify global default ACPI thermal zone polling rate
2477            <deci-seconds>: poll all this frequency
2478            0: no polling (default)
2479
2480    threadirqs [KNL]
2481            Force threading of all interrupt handlers except those
2482            marked explicitely IRQF_NO_THREAD.
2483
2484    topology= [S390]
2485            Format: {off | on}
2486            Specify if the kernel should make use of the cpu
2487            topology information if the hardware supports this.
2488            The scheduler will make use of this information and
2489            e.g. base its process migration decisions on it.
2490            Default is on.
2491
2492    tp720= [HW,PS2]
2493
2494    tpm_suspend_pcr=[HW,TPM]
2495            Format: integer pcr id
2496            Specify that at suspend time, the tpm driver
2497            should extend the specified pcr with zeros,
2498            as a workaround for some chips which fail to
2499            flush the last written pcr on TPM_SaveState.
2500            This will guarantee that all the other pcrs
2501            are saved.
2502
2503    trace_buf_size=nn[KMG]
2504            [FTRACE] will set tracing buffer size.
2505
2506    trace_event=[event-list]
2507            [FTRACE] Set and start specified trace events in order
2508            to facilitate early boot debugging.
2509            See also Documentation/trace/events.txt
2510
2511    tsc= Disable clocksource stability checks for TSC.
2512            Format: <string>
2513            [x86] reliable: mark tsc clocksource as reliable, this
2514            disables clocksource verification at runtime, as well
2515            as the stability checks done at bootup. Used to enable
2516            high-resolution timer mode on older hardware, and in
2517            virtualized environment.
2518            [x86] noirqtime: Do not use TSC to do irq accounting.
2519            Used to run time disable IRQ_TIME_ACCOUNTING on any
2520            platforms where RDTSC is slow and this accounting
2521            can add overhead.
2522
2523    turbografx.map[2|3]= [HW,JOY]
2524            TurboGraFX parallel port interface
2525            Format:
2526            <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
2527            See also Documentation/input/joystick-parport.txt
2528
2529    uhash_entries= [KNL,NET]
2530            Set number of hash buckets for UDP/UDP-Lite connections
2531
2532    uhci-hcd.ignore_oc=
2533            [USB] Ignore overcurrent events (default N).
2534            Some badly-designed motherboards generate lots of
2535            bogus events, for ports that aren't wired to
2536            anything. Set this parameter to avoid log spamming.
2537            Note that genuine overcurrent events won't be
2538            reported either.
2539
2540    unknown_nmi_panic
2541            [X86] Cause panic on unknown NMI.
2542
2543    usbcore.autosuspend=
2544            [USB] The autosuspend time delay (in seconds) used
2545            for newly-detected USB devices (default 2). This
2546            is the time required before an idle device will be
2547            autosuspended. Devices for which the delay is set
2548            to a negative value won't be autosuspended at all.
2549
2550    usbcore.usbfs_snoop=
2551            [USB] Set to log all usbfs traffic (default 0 = off).
2552
2553    usbcore.blinkenlights=
2554            [USB] Set to cycle leds on hubs (default 0 = off).
2555
2556    usbcore.old_scheme_first=
2557            [USB] Start with the old device initialization
2558            scheme (default 0 = off).
2559
2560    usbcore.use_both_schemes=
2561            [USB] Try the other device initialization scheme
2562            if the first one fails (default 1 = enabled).
2563
2564    usbcore.initial_descriptor_timeout=
2565            [USB] Specifies timeout for the initial 64-byte
2566                        USB_REQ_GET_DESCRIPTOR request in milliseconds
2567            (default 5000 = 5.0 seconds).
2568
2569    usbhid.mousepoll=
2570            [USBHID] The interval which mice are to be polled at.
2571
2572    usb-storage.delay_use=
2573            [UMS] The delay in seconds before a new device is
2574            scanned for Logical Units (default 5).
2575
2576    usb-storage.quirks=
2577            [UMS] A list of quirks entries to supplement or
2578            override the built-in unusual_devs list. List
2579            entries are separated by commas. Each entry has
2580            the form VID:PID:Flags where VID and PID are Vendor
2581            and Product ID values (4-digit hex numbers) and
2582            Flags is a set of characters, each corresponding
2583            to a common usb-storage quirk flag as follows:
2584                a = SANE_SENSE (collect more than 18 bytes
2585                    of sense data);
2586                b = BAD_SENSE (don't collect more than 18
2587                    bytes of sense data);
2588                c = FIX_CAPACITY (decrease the reported
2589                    device capacity by one sector);
2590                d = NO_READ_DISC_INFO (don't use
2591                    READ_DISC_INFO command);
2592                e = NO_READ_CAPACITY_16 (don't use
2593                    READ_CAPACITY_16 command);
2594                h = CAPACITY_HEURISTICS (decrease the
2595                    reported device capacity by one
2596                    sector if the number is odd);
2597                i = IGNORE_DEVICE (don't bind to this
2598                    device);
2599                l = NOT_LOCKABLE (don't try to lock and
2600                    unlock ejectable media);
2601                m = MAX_SECTORS_64 (don't transfer more
2602                    than 64 sectors = 32 KB at a time);
2603                n = INITIAL_READ10 (force a retry of the
2604                    initial READ(10) command);
2605                o = CAPACITY_OK (accept the capacity
2606                    reported by the device);
2607                r = IGNORE_RESIDUE (the device reports
2608                    bogus residue values);
2609                s = SINGLE_LUN (the device has only one
2610                    Logical Unit);
2611                w = NO_WP_DETECT (don't test whether the
2612                    medium is write-protected).
2613            Example: quirks=0419:aaf5:rl,0421:0433:rc
2614
2615    userpte=
2616            [X86] Flags controlling user PTE allocations.
2617
2618                nohigh = do not allocate PTE pages in
2619                    HIGHMEM regardless of setting
2620                    of CONFIG_HIGHPTE.
2621
2622    vdso= [X86,SH]
2623            vdso=2: enable compat VDSO (default with COMPAT_VDSO)
2624            vdso=1: enable VDSO (default)
2625            vdso=0: disable VDSO mapping
2626
2627    vdso32= [X86]
2628            vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
2629            vdso32=1: enable 32-bit VDSO (default)
2630            vdso32=0: disable 32-bit VDSO mapping
2631
2632    vector= [IA-64,SMP]
2633            vector=percpu: enable percpu vector domain
2634
2635    video= [FB] Frame buffer configuration
2636            See Documentation/fb/modedb.txt.
2637
2638    vga= [BOOT,X86-32] Select a particular video mode
2639            See Documentation/x86/boot.txt and
2640            Documentation/svga.txt.
2641            Use vga=ask for menu.
2642            This is actually a boot loader parameter; the value is
2643            passed to the kernel using a special protocol.
2644
2645    vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
2646            size of <nn>. This can be used to increase the
2647            minimum size (128MB on x86). It can also be used to
2648            decrease the size and leave more room for directly
2649            mapped kernel RAM.
2650
2651    vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
2652            Format: <command>
2653
2654    vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
2655            Format: <command>
2656
2657    vmpoff= [KNL,S390] Perform z/VM CP command after power off.
2658            Format: <command>
2659
2660    vt.cur_default= [VT] Default cursor shape.
2661            Format: 0xCCBBAA, where AA, BB, and CC are the same as
2662            the parameters of the <Esc>[?A;B;Cc escape sequence;
2663            see VGA-softcursor.txt. Default: 2 = underline.
2664
2665    vt.default_blu= [VT]
2666            Format: <blue0>,<blue1>,<blue2>,...,<blue15>
2667            Change the default blue palette of the console.
2668            This is a 16-member array composed of values
2669            ranging from 0-255.
2670
2671    vt.default_grn= [VT]
2672            Format: <green0>,<green1>,<green2>,...,<green15>
2673            Change the default green palette of the console.
2674            This is a 16-member array composed of values
2675            ranging from 0-255.
2676
2677    vt.default_red= [VT]
2678            Format: <red0>,<red1>,<red2>,...,<red15>
2679            Change the default red palette of the console.
2680            This is a 16-member array composed of values
2681            ranging from 0-255.
2682
2683    vt.default_utf8=
2684            [VT]
2685            Format=<0|1>
2686            Set system-wide default UTF-8 mode for all tty's.
2687            Default is 1, i.e. UTF-8 mode is enabled for all
2688            newly opened terminals.
2689
2690    vt.global_cursor_default=
2691            [VT]
2692            Format=<-1|0|1>
2693            Set system-wide default for whether a cursor
2694            is shown on new VTs. Default is -1,
2695            i.e. cursors will be created by default unless
2696            overridden by individual drivers. 0 will hide
2697            cursors, 1 will display them.
2698
2699    watchdog timers [HW,WDT] For information on watchdog timers,
2700            see Documentation/watchdog/watchdog-parameters.txt
2701            or other driver-specific files in the
2702            Documentation/watchdog/ directory.
2703
2704    x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
2705            default x2apic cluster mode on platforms
2706            supporting x2apic.
2707
2708    x86_mrst_timer= [X86-32,APBT]
2709            Choose timer option for x86 Moorestown MID platform.
2710            Two valid options are apbt timer only and lapic timer
2711            plus one apbt timer for broadcast timer.
2712            x86_mrst_timer=apbt_only | lapic_and_apbt
2713
2714    xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
2715    xd_geo= See header of drivers/block/xd.c.
2716
2717    xen_emul_unplug= [HW,X86,XEN]
2718            Unplug Xen emulated devices
2719            Format: [unplug0,][unplug1]
2720            ide-disks -- unplug primary master IDE devices
2721            aux-ide-disks -- unplug non-primary-master IDE devices
2722            nics -- unplug network devices
2723            all -- unplug all emulated devices (NICs and IDE disks)
2724            unnecessary -- unplugging emulated devices is
2725                unnecessary even if the host did not respond to
2726                the unplug protocol
2727            never -- do not unplug even if version check succeeds
2728
2729    xirc2ps_cs= [NET,PCMCIA]
2730            Format:
2731            <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
2732
2733______________________________________________________________________
2734
2735TODO:
2736
2737    Add more DRM drivers.
2738

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