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

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