Root/Documentation/kernel-parameters.txt

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

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