Root/Documentation/kernel-parameters.txt

1                          Kernel Parameters
2                          ~~~~~~~~~~~~~~~~~
3
4The following is a consolidated list of the kernel parameters as implemented
5(mostly) by the __setup() macro and sorted into English Dictionary order
6(defined as ignoring all punctuation and sorting digits before letters in a
7case insensitive manner), and with descriptions where known.
8
9Module parameters for loadable modules are specified only as the
10parameter name with optional '=' and value as appropriate, such as:
11
12    modprobe usbcore blinkenlights=1
13
14Module parameters for modules that are built into the kernel image
15are specified on the kernel command line with the module name plus
16'.' plus parameter name, with '=' and value if appropriate, such as:
17
18    usbcore.blinkenlights=1
19
20Hyphens (dashes) and underscores are equivalent in parameter names, so
21    log_buf_len=1M print-fatal-signals=1
22can also be entered as
23    log-buf-len=1M print_fatal_signals=1
24
25
26This document may not be entirely up to date and comprehensive. The command
27"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
28module. Loadable modules, after being loaded into the running kernel, also
29reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
30parameters may be changed at runtime by the command
31"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
32
33The parameters listed below are only valid if certain kernel build options were
34enabled and if respective hardware is present. The text in square brackets at
35the beginning of each description states the restrictions within which a
36parameter is applicable:
37
38    ACPI ACPI support is enabled.
39    AGP AGP (Accelerated Graphics Port) is enabled.
40    ALSA ALSA sound support is enabled.
41    APIC APIC support is enabled.
42    APM Advanced Power Management support is enabled.
43    ARM ARM architecture is enabled.
44    AVR32 AVR32 architecture is enabled.
45    AX25 Appropriate AX.25 support is enabled.
46    BLACKFIN Blackfin architecture is enabled.
47    DRM Direct Rendering Management support is enabled.
48    DYNAMIC_DEBUG Build in debug messages and enable them at runtime
49    EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
50    EFI EFI Partitioning (GPT) is enabled
51    EIDE EIDE/ATAPI support is enabled.
52    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    MDA MDA console support is enabled.
74    MIPS MIPS architecture is enabled.
75    MOUSE Appropriate mouse support is enabled.
76    MSI Message Signaled Interrupts (PCI).
77    MTD MTD (Memory Technology Device) support is enabled.
78    NET Appropriate network support is enabled.
79    NUMA NUMA support is enabled.
80    NFS Appropriate NFS support is enabled.
81    OSS OSS sound support is enabled.
82    PV_OPS A paravirtualized kernel is enabled.
83    PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
84    PARISC The PA-RISC architecture is enabled.
85    PCI PCI bus support is enabled.
86    PCIE PCI Express support is enabled.
87    PCMCIA The PCMCIA subsystem is enabled.
88    PNP Plug & Play support is enabled.
89    PPC PowerPC architecture is enabled.
90    PPT Parallel port support is enabled.
91    PS2 Appropriate PS/2 support is enabled.
92    RAM RAM disk support is enabled.
93    S390 S390 architecture is enabled.
94    SCSI Appropriate SCSI support is enabled.
95            A lot of drivers have their options described inside
96            the Documentation/scsi/ sub-directory.
97    SECURITY Different security models are enabled.
98    SELINUX SELinux support is enabled.
99    APPARMOR AppArmor support is enabled.
100    SERIAL Serial support is enabled.
101    SH SuperH architecture is enabled.
102    SMP The kernel is an SMP kernel.
103    SPARC Sparc architecture is enabled.
104    SWSUSP Software suspend (hibernation) is enabled.
105    SUSPEND System suspend states are enabled.
106    TPM TPM drivers are enabled.
107    TS Appropriate touchscreen support is enabled.
108    UMS USB Mass Storage support is enabled.
109    USB USB support is enabled.
110    USBHID USB Human Interface Device support is enabled.
111    V4L Video For Linux support is enabled.
112    VMMIO Driver for memory mapped virtio devices 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    amd_iommu_dump= [HW,X86-64]
339            Enable AMD IOMMU driver option to dump the ACPI table
340            for AMD IOMMU. With this option enabled, AMD IOMMU
341            driver will print ACPI tables for AMD IOMMU during
342            IOMMU initialization.
343
344    amijoy.map= [HW,JOY] Amiga joystick support
345            Map of devices attached to JOY0DAT and JOY1DAT
346            Format: <a>,<b>
347            See also Documentation/input/joystick.txt
348
349    analog.map= [HW,JOY] Analog joystick and gamepad support
350            Specifies type or capabilities of an analog joystick
351            connected to one of 16 gameports
352            Format: <type1>,<type2>,..<type16>
353
354    apc= [HW,SPARC]
355            Power management functions (SPARCstation-4/5 + deriv.)
356            Format: noidle
357            Disable APC CPU standby support. SPARCstation-Fox does
358            not play well with APC CPU idle - disable it if you have
359            APC and your system crashes randomly.
360
361    apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
362            Change the output verbosity whilst booting
363            Format: { quiet (default) | verbose | debug }
364            Change the amount of debugging information output
365            when initialising the APIC and IO-APIC components.
366
367    autoconf= [IPV6]
368            See Documentation/networking/ipv6.txt.
369
370    show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
371            Limit apic dumping. The parameter defines the maximal
372            number of local apics being dumped. Also it is possible
373            to set it to "all" by meaning -- no limit here.
374            Format: { 1 (default) | 2 | ... | all }.
375            The parameter valid if only apic=debug or
376            apic=verbose is specified.
377            Example: apic=debug show_lapic=all
378
379    apm= [APM] Advanced Power Management
380            See header of arch/x86/kernel/apm_32.c.
381
382    arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
383            Format: <io>,<irq>,<nodeID>
384
385    ataflop= [HW,M68k]
386
387    atarimouse= [HW,MOUSE] Atari Mouse
388
389    atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
390            EzKey and similar keyboards
391
392    atkbd.reset= [HW] Reset keyboard during initialization
393
394    atkbd.set= [HW] Select keyboard code set
395            Format: <int> (2 = AT (default), 3 = PS/2)
396
397    atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
398            keyboards
399
400    atkbd.softraw= [HW] Choose between synthetic and real raw mode
401            Format: <bool> (0 = real, 1 = synthetic (default))
402
403    atkbd.softrepeat= [HW]
404            Use software keyboard repeat
405
406    baycom_epp= [HW,AX25]
407            Format: <io>,<mode>
408
409    baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
410            Format: <io>,<mode>
411            See header of drivers/net/hamradio/baycom_par.c.
412
413    baycom_ser_fdx= [HW,AX25]
414            BayCom Serial Port AX.25 Modem (Full Duplex Mode)
415            Format: <io>,<irq>,<mode>[,<baud>]
416            See header of drivers/net/hamradio/baycom_ser_fdx.c.
417
418    baycom_ser_hdx= [HW,AX25]
419            BayCom Serial Port AX.25 Modem (Half Duplex Mode)
420            Format: <io>,<irq>,<mode>
421            See header of drivers/net/hamradio/baycom_ser_hdx.c.
422
423    boot_delay= Milliseconds to delay each printk during boot.
424            Values larger than 10 seconds (10000) are changed to
425            no delay (0).
426            Format: integer
427
428    bootmem_debug [KNL] Enable bootmem allocator debug messages.
429
430    bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
431    bttv.radio= Most important insmod options are available as
432            kernel args too.
433    bttv.pll= See Documentation/video4linux/bttv/Insmod-options
434    bttv.tuner=
435
436    bulk_remove=off [PPC] This parameter disables the use of the pSeries
437            firmware feature for flushing multiple hpte entries
438            at a time.
439
440    c101= [NET] Moxa C101 synchronous serial card
441
442    cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
443            Sometimes CPU hardware bugs make them report the cache
444            size incorrectly. The kernel will attempt work arounds
445            to fix known problems, but for some CPUs it is not
446            possible to determine what the correct size should be.
447            This option provides an override for these situations.
448
449    ccw_timeout_log [S390]
450            See Documentation/s390/CommonIO for details.
451
452    cgroup_disable= [KNL] Disable a particular controller
453            Format: {name of the controller(s) to disable}
454                {Currently supported controllers - "memory"}
455
456    checkreqprot [SELINUX] Set initial checkreqprot flag value.
457            Format: { "0" | "1" }
458            See security/selinux/Kconfig help text.
459            0 -- check protection applied by kernel (includes
460                any implied execute protection).
461            1 -- check protection requested by application.
462            Default value is set via a kernel config option.
463            Value can be changed at runtime via
464                /selinux/checkreqprot.
465
466    cio_ignore= [S390]
467            See Documentation/s390/CommonIO for details.
468
469    clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
470            [Deprecated]
471            Forces specified clocksource (if available) to be used
472            when calculating gettimeofday(). If specified
473            clocksource is not available, it defaults to PIT.
474            Format: { pit | tsc | cyclone | pmtmr }
475
476    clocksource= Override the default clocksource
477            Format: <string>
478            Override the default clocksource and use the clocksource
479            with the name specified.
480            Some clocksource names to choose from, depending on
481            the platform:
482            [all] jiffies (this is the base, fallback clocksource)
483            [ACPI] acpi_pm
484            [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
485                pxa_timer,timer3,32k_counter,timer0_1
486            [AVR32] avr32
487            [X86-32] pit,hpet,tsc;
488                scx200_hrt on Geode; cyclone on IBM x440
489            [MIPS] MIPS
490            [PARISC] cr16
491            [S390] tod
492            [SH] SuperH
493            [SPARC64] tick
494            [X86-64] hpet,tsc
495
496    clearcpuid=BITNUM [X86]
497            Disable CPUID feature X for the kernel. See
498            arch/x86/include/asm/cpufeature.h for the valid bit
499            numbers. Note the Linux specific bits are not necessarily
500            stable over kernel options, but the vendor specific
501            ones should be.
502            Also note that user programs calling CPUID directly
503            or using the feature without checking anything
504            will still see it. This just prevents it from
505            being used by the kernel or shown in /proc/cpuinfo.
506            Also note the kernel might malfunction if you disable
507            some critical bits.
508
509    cma=nn[MG] [ARM,KNL]
510            Sets the size of kernel global memory area for contiguous
511            memory allocations. For more information, see
512            include/linux/dma-contiguous.h
513
514    cmo_free_hint= [PPC] Format: { yes | no }
515            Specify whether pages are marked as being inactive
516            when they are freed. This is used in CMO environments
517            to determine OS memory pressure for page stealing by
518            a hypervisor.
519            Default: yes
520
521    coherent_pool=nn[KMG] [ARM,KNL]
522            Sets the size of memory pool for coherent, atomic dma
523            allocations, by default set to 256K.
524
525    code_bytes [X86] How many bytes of object code to print
526            in an oops report.
527            Range: 0 - 8192
528            Default: 64
529
530    com20020= [HW,NET] ARCnet - COM20020 chipset
531            Format:
532            <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
533
534    com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
535            Format: <io>[,<irq>]
536
537    com90xx= [HW,NET]
538            ARCnet - COM90xx chipset (memory-mapped buffers)
539            Format: <io>[,<irq>[,<memstart>]]
540
541    condev= [HW,S390] console device
542    conmode=
543
544    console= [KNL] Output console device and options.
545
546        tty<n> Use the virtual console device <n>.
547
548        ttyS<n>[,options]
549        ttyUSB0[,options]
550            Use the specified serial port. The options are of
551            the form "bbbbpnf", where "bbbb" is the baud rate,
552            "p" is parity ("n", "o", or "e"), "n" is number of
553            bits, and "f" is flow control ("r" for RTS or
554            omit it). Default is "9600n8".
555
556            See Documentation/serial-console.txt for more
557            information. See
558            Documentation/networking/netconsole.txt for an
559            alternative.
560
561        uart[8250],io,<addr>[,options]
562        uart[8250],mmio,<addr>[,options]
563            Start an early, polled-mode console on the 8250/16550
564            UART at the specified I/O port or MMIO address,
565            switching to the matching ttyS device later. The
566            options are the same as for ttyS, above.
567        hvc<n> Use the hypervisor console device <n>. This is for
568            both Xen and PowerPC hypervisors.
569
570                If the device connected to the port is not a TTY but a braille
571                device, prepend "brl," before the device type, for instance
572            console=brl,ttyS0
573        For now, only VisioBraille is supported.
574
575    consoleblank= [KNL] The console blank (screen saver) timeout in
576            seconds. Defaults to 10*60 = 10mins. A value of 0
577            disables the blank timer.
578
579    coredump_filter=
580            [KNL] Change the default value for
581            /proc/<pid>/coredump_filter.
582            See also Documentation/filesystems/proc.txt.
583
584    cpuidle.off=1 [CPU_IDLE]
585            disable the cpuidle sub-system
586
587    cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
588            Format:
589            <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
590
591    crashkernel=size[KMG][@offset[KMG]]
592            [KNL] Using kexec, Linux can switch to a 'crash kernel'
593            upon panic. This parameter reserves the physical
594            memory region [offset, offset + size] for that kernel
595            image. If '@offset' is omitted, then a suitable offset
596            is selected automatically. Check
597            Documentation/kdump/kdump.txt for further details.
598
599    crashkernel=range1:size1[,range2:size2,...][@offset]
600            [KNL] Same as above, but depends on the memory
601            in the running system. The syntax of range is
602            start-[end] where start and end are both
603            a memory unit (amount[KMG]). See also
604            Documentation/kdump/kdump.txt for an example.
605
606    crashkernel=size[KMG],high
607            [KNL, x86_64] range could be above 4G. Allow kernel
608            to allocate physical memory region from top, so could
609            be above 4G if system have more than 4G ram installed.
610            Otherwise memory region will be allocated below 4G, if
611            available.
612            It will be ignored if crashkernel=X is specified.
613    crashkernel=size[KMG],low
614            [KNL, x86_64] range under 4G. When crashkernel=X,high
615            is passed, kernel could allocate physical memory region
616            above 4G, that cause second kernel crash on system
617            that require some amount of low memory, e.g. swiotlb
618            requires at least 64M+32K low memory. Kernel would
619            try to allocate 72M below 4G automatically.
620            This one let user to specify own low range under 4G
621            for second kernel instead.
622            0: to disable low allocation.
623            It will be ignored when crashkernel=X,high is not used
624            or memory reserved is below 4G.
625
626    cs89x0_dma= [HW,NET]
627            Format: <dma>
628
629    cs89x0_media= [HW,NET]
630            Format: { rj45 | aui | bnc }
631
632    dasd= [HW,NET]
633            See header of drivers/s390/block/dasd_devmap.c.
634
635    db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
636            (one device per port)
637            Format: <port#>,<type>
638            See also Documentation/input/joystick-parport.txt
639
640    ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
641            time. See Documentation/dynamic-debug-howto.txt for
642            details. Deprecated, see dyndbg.
643
644    debug [KNL] Enable kernel debugging (events log level).
645
646    debug_locks_verbose=
647            [KNL] verbose self-tests
648            Format=<0|1>
649            Print debugging info while doing the locking API
650            self-tests.
651            We default to 0 (no extra messages), setting it to
652            1 will print _a lot_ more information - normally
653            only useful to kernel developers.
654
655    debug_objects [KNL] Enable object debugging
656
657    no_debug_objects
658            [KNL] Disable object debugging
659
660    debug_guardpage_minorder=
661            [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
662            parameter allows control of the order of pages that will
663            be intentionally kept free (and hence protected) by the
664            buddy allocator. Bigger value increase the probability
665            of catching random memory corruption, but reduce the
666            amount of memory for normal system use. The maximum
667            possible value is MAX_ORDER/2. Setting this parameter
668            to 1 or 2 should be enough to identify most random
669            memory corruption problems caused by bugs in kernel or
670            driver code when a CPU writes to (or reads from) a
671            random memory location. Note that there exists a class
672            of memory corruptions problems caused by buggy H/W or
673            F/W or by drivers badly programing DMA (basically when
674            memory is written at bus level and the CPU MMU is
675            bypassed) which are not detectable by
676            CONFIG_DEBUG_PAGEALLOC, hence this option will not help
677            tracking down these problems.
678
679    debugpat [X86] Enable PAT debugging
680
681    decnet.addr= [HW,NET]
682            Format: <area>[,<node>]
683            See also Documentation/networking/decnet.txt.
684
685    default_hugepagesz=
686            [same as hugepagesz=] The size of the default
687            HugeTLB page size. This is the size represented by
688            the legacy /proc/ hugepages APIs, used for SHM, and
689            default size when mounting hugetlbfs filesystems.
690            Defaults to the default architecture's huge page size
691            if not specified.
692
693    dhash_entries= [KNL]
694            Set number of hash buckets for dentry cache.
695
696    digi= [HW,SERIAL]
697            IO parameters + enable/disable command.
698
699    digiepca= [HW,SERIAL]
700            See drivers/char/README.epca and
701            Documentation/serial/digiepca.txt.
702
703    disable= [IPV6]
704            See Documentation/networking/ipv6.txt.
705
706    disable_ddw [PPC/PSERIES]
707            Disable Dynamic DMA Window support. Use this if
708            to workaround buggy firmware.
709
710    disable_ipv6= [IPV6]
711            See Documentation/networking/ipv6.txt.
712
713    disable_mtrr_cleanup [X86]
714            The kernel tries to adjust MTRR layout from continuous
715            to discrete, to make X server driver able to add WB
716            entry later. This parameter disables that.
717
718    disable_mtrr_trim [X86, Intel and AMD only]
719            By default the kernel will trim any uncacheable
720            memory out of your available memory pool based on
721            MTRR settings. This parameter disables that behavior,
722            possibly causing your machine to run very slowly.
723
724    disable_timer_pin_1 [X86]
725            Disable PIN 1 of APIC timer
726            Can be useful to work around chipset bugs.
727
728    dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
729            this option disables the debugging code at boot.
730
731    dma_debug_entries=<number>
732            This option allows to tune the number of preallocated
733            entries for DMA-API debugging code. One entry is
734            required per DMA-API allocation. Use this if the
735            DMA-API debugging code disables itself because the
736            architectural default is too low.
737
738    dma_debug_driver=<driver_name>
739            With this option the DMA-API debugging driver
740            filter feature can be enabled at boot time. Just
741            pass the driver to filter for as the parameter.
742            The filter can be disabled or changed to another
743            driver later using sysfs.
744
745    drm_kms_helper.edid_firmware=[<connector>:]<file>
746            Broken monitors, graphic adapters and KVMs may
747            send no or incorrect EDID data sets. This parameter
748            allows to specify an EDID data set in the
749            /lib/firmware directory that is used instead.
750            Generic built-in EDID data sets are used, if one of
751            edid/1024x768.bin, edid/1280x1024.bin,
752            edid/1680x1050.bin, or edid/1920x1080.bin is given
753            and no file with the same name exists. Details and
754            instructions how to build your own EDID data are
755            available in Documentation/EDID/HOWTO.txt. An EDID
756            data set will only be used for a particular connector,
757            if its name and a colon are prepended to the EDID
758            name.
759
760    dscc4.setup= [NET]
761
762    dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
763    module.dyndbg[="val"]
764            Enable debug messages at boot time. See
765            Documentation/dynamic-debug-howto.txt for details.
766
767    earlycon= [KNL] Output early console device and options.
768        uart[8250],io,<addr>[,options]
769        uart[8250],mmio,<addr>[,options]
770        uart[8250],mmio32,<addr>[,options]
771            Start an early, polled-mode console on the 8250/16550
772            UART at the specified I/O port or MMIO address.
773            MMIO inter-register address stride is either 8-bit
774            (mmio) or 32-bit (mmio32).
775            The options are the same as for ttyS, above.
776
777    earlyprintk= [X86,SH,BLACKFIN]
778            earlyprintk=vga
779            earlyprintk=xen
780            earlyprintk=serial[,ttySn[,baudrate]]
781            earlyprintk=ttySn[,baudrate]
782            earlyprintk=dbgp[debugController#]
783
784            Append ",keep" to not disable it when the real console
785            takes over.
786
787            Only vga or serial or usb debug port at a time.
788
789            Currently only ttyS0 and ttyS1 are supported.
790
791            Interaction with the standard serial driver is not
792            very good.
793
794            The VGA output is eventually overwritten by the real
795            console.
796
797            The xen output can only be used by Xen PV guests.
798
799    ekgdboc= [X86,KGDB] Allow early kernel console debugging
800            ekgdboc=kbd
801
802            This is designed to be used in conjunction with
803            the boot argument: earlyprintk=vga
804
805    edd= [EDD]
806            Format: {"off" | "on" | "skip[mbr]"}
807
808    efi_no_storage_paranoia [EFI; X86]
809            Using this parameter you can use more than 50% of
810            your efi variable storage. Use this parameter only if
811            you are really sure that your UEFI does sane gc and
812            fulfills the spec otherwise your board may brick.
813
814    eisa_irq_edge= [PARISC,HW]
815            See header of drivers/parisc/eisa.c.
816
817    elanfreq= [X86-32]
818            See comment before function elanfreq_setup() in
819            arch/x86/kernel/cpu/cpufreq/elanfreq.c.
820
821    elevator= [IOSCHED]
822            Format: {"cfq" | "deadline" | "noop"}
823            See Documentation/block/cfq-iosched.txt and
824            Documentation/block/deadline-iosched.txt for details.
825
826    elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
827            Specifies physical address of start of kernel core
828            image elf header and optionally the size. Generally
829            kexec loader will pass this option to capture kernel.
830            See Documentation/kdump/kdump.txt for details.
831
832    enable_mtrr_cleanup [X86]
833            The kernel tries to adjust MTRR layout from continuous
834            to discrete, to make X server driver able to add WB
835            entry later. This parameter enables that.
836
837    enable_timer_pin_1 [X86]
838            Enable PIN 1 of APIC timer
839            Can be useful to work around chipset bugs
840            (in particular on some ATI chipsets).
841            The kernel tries to set a reasonable default.
842
843    enforcing [SELINUX] Set initial enforcing status.
844            Format: {"0" | "1"}
845            See security/selinux/Kconfig help text.
846            0 -- permissive (log only, no denials).
847            1 -- enforcing (deny and log).
848            Default value is 0.
849            Value can be changed at runtime via /selinux/enforce.
850
851    erst_disable [ACPI]
852            Disable Error Record Serialization Table (ERST)
853            support.
854
855    ether= [HW,NET] Ethernet cards parameters
856            This option is obsoleted by the "netdev=" option, which
857            has equivalent usage. See its documentation for details.
858
859    evm= [EVM]
860            Format: { "fix" }
861            Permit 'security.evm' to be updated regardless of
862            current integrity status.
863
864    failslab=
865    fail_page_alloc=
866    fail_make_request=[KNL]
867            General fault injection mechanism.
868            Format: <interval>,<probability>,<space>,<times>
869            See also Documentation/fault-injection/.
870
871    floppy= [HW]
872            See Documentation/blockdev/floppy.txt.
873
874    force_pal_cache_flush
875            [IA-64] Avoid check_sal_cache_flush which may hang on
876            buggy SAL_CACHE_FLUSH implementations. Using this
877            parameter will force ia64_sal_cache_flush to call
878            ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
879
880    ftrace=[tracer]
881            [FTRACE] will set and start the specified tracer
882            as early as possible in order to facilitate early
883            boot debugging.
884
885    ftrace_dump_on_oops[=orig_cpu]
886            [FTRACE] will dump the trace buffers on oops.
887            If no parameter is passed, ftrace will dump
888            buffers of all CPUs, but if you pass orig_cpu, it will
889            dump only the buffer of the CPU that triggered the
890            oops.
891
892    ftrace_filter=[function-list]
893            [FTRACE] Limit the functions traced by the function
894            tracer at boot up. function-list is a comma separated
895            list of functions. This list can be changed at run
896            time by the set_ftrace_filter file in the debugfs
897            tracing directory.
898
899    ftrace_notrace=[function-list]
900            [FTRACE] Do not trace the functions specified in
901            function-list. This list can be changed at run time
902            by the set_ftrace_notrace file in the debugfs
903            tracing directory.
904
905    ftrace_graph_filter=[function-list]
906            [FTRACE] Limit the top level callers functions traced
907            by the function graph tracer at boot up.
908            function-list is a comma separated list of functions
909            that can be changed at run time by the
910            set_graph_function file in the debugfs tracing directory.
911
912    gamecon.map[2|3]=
913            [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
914            support via parallel port (up to 5 devices per port)
915            Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
916            See also Documentation/input/joystick-parport.txt
917
918    gamma= [HW,DRM]
919
920    gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
921            Format: off | on
922            default: on
923
924    gcov_persist= [GCOV] When non-zero (default), profiling data for
925            kernel modules is saved and remains accessible via
926            debugfs, even when the module is unloaded/reloaded.
927            When zero, profiling data is discarded and associated
928            debugfs files are removed at module unload time.
929
930    gpt [EFI] Forces disk with valid GPT signature but
931            invalid Protective MBR to be treated as GPT.
932
933    grcan.enable0= [HW] Configuration of physical interface 0. Determines
934            the "Enable 0" bit of the configuration register.
935            Format: 0 | 1
936            Default: 0
937    grcan.enable1= [HW] Configuration of physical interface 1. Determines
938            the "Enable 0" bit of the configuration register.
939            Format: 0 | 1
940            Default: 0
941    grcan.select= [HW] Select which physical interface to use.
942            Format: 0 | 1
943            Default: 0
944    grcan.txsize= [HW] Sets the size of the tx buffer.
945            Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
946            Default: 1024
947    grcan.rxsize= [HW] Sets the size of the rx buffer.
948            Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
949            Default: 1024
950
951    hashdist= [KNL,NUMA] Large hashes allocated during boot
952            are distributed across NUMA nodes. Defaults on
953            for 64-bit NUMA, off otherwise.
954            Format: 0 | 1 (for off | on)
955
956    hcl= [IA-64] SGI's Hardware Graph compatibility layer
957
958    hd= [EIDE] (E)IDE hard drive subsystem geometry
959            Format: <cyl>,<head>,<sect>
960
961    hest_disable [ACPI]
962            Disable Hardware Error Source Table (HEST) support;
963            corresponding firmware-first mode error processing
964            logic will be disabled.
965
966    highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
967            size of <nn>. This works even on boxes that have no
968            highmem otherwise. This also works to reduce highmem
969            size on bigger boxes.
970
971    highres= [KNL] Enable/disable high resolution timer mode.
972            Valid parameters: "on", "off"
973            Default: "on"
974
975    hisax= [HW,ISDN]
976            See Documentation/isdn/README.HiSax.
977
978    hlt [BUGS=ARM,SH]
979
980    hpet= [X86-32,HPET] option to control HPET usage
981            Format: { enable (default) | disable | force |
982                verbose }
983            disable: disable HPET and use PIT instead
984            force: allow force enabled of undocumented chips (ICH4,
985                VIA, nVidia)
986            verbose: show contents of HPET registers during setup
987
988    hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
989    hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
990            On x86-64 and powerpc, this option can be specified
991            multiple times interleaved with hugepages= to reserve
992            huge pages of different sizes. Valid pages sizes on
993            x86-64 are 2M (when the CPU supports "pse") and 1G
994            (when the CPU supports the "pdpe1gb" cpuinfo flag)
995            Note that 1GB pages can only be allocated at boot time
996            using hugepages= and not freed afterwards.
997
998    hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
999                   terminal devices. Valid values: 0..8
1000    hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1001                   If specified, z/VM IUCV HVC accepts connections
1002                   from listed z/VM user IDs only.
1003
1004    hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1005                    hardware thread id mappings.
1006                Format: <cpu>:<hwthread>
1007
1008    keep_bootcon [KNL]
1009            Do not unregister boot console at start. This is only
1010            useful for debugging when something happens in the window
1011            between unregistering the boot console and initializing
1012            the real console.
1013
1014    i2c_bus= [HW] Override the default board specific I2C bus speed
1015                 or register an additional I2C bus that is not
1016                 registered from board initialization code.
1017                 Format:
1018                 <bus_id>,<clkrate>
1019
1020    i8042.debug [HW] Toggle i8042 debug mode
1021    i8042.direct [HW] Put keyboard port into non-translated mode
1022    i8042.dumbkbd [HW] Pretend that controller can only read data from
1023                 keyboard and cannot control its state
1024                 (Don't attempt to blink the leds)
1025    i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1026    i8042.nokbd [HW] Don't check/create keyboard port
1027    i8042.noloop [HW] Disable the AUX Loopback command while probing
1028                 for the AUX port
1029    i8042.nomux [HW] Don't check presence of an active multiplexing
1030                 controller
1031    i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1032                 controllers
1033    i8042.notimeout [HW] Ignore timeout condition signalled by controller
1034    i8042.reset [HW] Reset the controller during init and cleanup
1035    i8042.unlock [HW] Unlock (ignore) the keylock
1036
1037    i810= [HW,DRM]
1038
1039    i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1040            indicates that the driver is running on unsupported
1041            hardware.
1042    i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1043            does not match list of supported models.
1044    i8k.power_status
1045            [HW] Report power status in /proc/i8k
1046            (disabled by default)
1047    i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1048            capability is set.
1049
1050    i915.invert_brightness=
1051            [DRM] Invert the sense of the variable that is used to
1052            set the brightness of the panel backlight. Normally a
1053            brightness value of 0 indicates backlight switched off,
1054            and the maximum of the brightness value sets the backlight
1055            to maximum brightness. If this parameter is set to 0
1056            (default) and the machine requires it, or this parameter
1057            is set to 1, a brightness value of 0 sets the backlight
1058            to maximum brightness, and the maximum of the brightness
1059            value switches the backlight off.
1060            -1 -- never invert brightness
1061             0 -- machine default
1062             1 -- force brightness inversion
1063
1064    icn= [HW,ISDN]
1065            Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1066
1067    ide-core.nodma= [HW] (E)IDE subsystem
1068            Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1069            .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1070            .cdrom .chs .ignore_cable are additional options
1071            See Documentation/ide/ide.txt.
1072
1073    ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1074            Claim all unknown PCI IDE storage controllers.
1075
1076    idle= [X86]
1077            Format: idle=poll, idle=halt, idle=nomwait
1078            Poll forces a polling idle loop that can slightly
1079            improve the performance of waking up a idle CPU, but
1080            will use a lot of power and make the system run hot.
1081            Not recommended.
1082            idle=halt: Halt is forced to be used for CPU idle.
1083            In such case C2/C3 won't be used again.
1084            idle=nomwait: Disable mwait for CPU C-states
1085
1086    ignore_loglevel [KNL]
1087            Ignore loglevel setting - this will print /all/
1088            kernel messages to the console. Useful for debugging.
1089            We also add it as printk module parameter, so users
1090            could change it dynamically, usually by
1091            /sys/module/printk/parameters/ignore_loglevel.
1092
1093    ihash_entries= [KNL]
1094            Set number of hash buckets for inode cache.
1095
1096    ima_appraise= [IMA] appraise integrity measurements
1097            Format: { "off" | "enforce" | "fix" }
1098            default: "enforce"
1099
1100    ima_appraise_tcb [IMA]
1101            The builtin appraise policy appraises all files
1102            owned by uid=0.
1103
1104    ima_audit= [IMA]
1105            Format: { "0" | "1" }
1106            0 -- integrity auditing messages. (Default)
1107            1 -- enable informational integrity auditing messages.
1108
1109    ima_hash= [IMA]
1110            Format: { "sha1" | "md5" }
1111            default: "sha1"
1112
1113    ima_tcb [IMA]
1114            Load a policy which meets the needs of the Trusted
1115            Computing Base. This means IMA will measure all
1116            programs exec'd, files mmap'd for exec, and all files
1117            opened for read by uid=0.
1118
1119    init= [KNL]
1120            Format: <full_path>
1121            Run specified binary instead of /sbin/init as init
1122            process.
1123
1124    initcall_debug [KNL] Trace initcalls as they are executed. Useful
1125            for working out where the kernel is dying during
1126            startup.
1127
1128    initrd= [BOOT] Specify the location of the initial ramdisk
1129
1130    inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1131            Format: <irq>
1132
1133    intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1134        on
1135            Enable intel iommu driver.
1136        off
1137            Disable intel iommu driver.
1138        igfx_off [Default Off]
1139            By default, gfx is mapped as normal device. If a gfx
1140            device has a dedicated DMAR unit, the DMAR unit is
1141            bypassed by not enabling DMAR with this option. In
1142            this case, gfx device will use physical address for
1143            DMA.
1144        forcedac [x86_64]
1145            With this option iommu will not optimize to look
1146            for io virtual address below 32-bit forcing dual
1147            address cycle on pci bus for cards supporting greater
1148            than 32-bit addressing. The default is to look
1149            for translation below 32-bit and if not available
1150            then look in the higher range.
1151        strict [Default Off]
1152            With this option on every unmap_single operation will
1153            result in a hardware IOTLB flush operation as opposed
1154            to batching them for performance.
1155        sp_off [Default Off]
1156            By default, super page will be supported if Intel IOMMU
1157            has the capability. With this option, super page will
1158            not be supported.
1159
1160    intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1161            0 disables intel_idle and fall back on acpi_idle.
1162            1 to 6 specify maximum depth of C-state.
1163
1164    intel_pstate= [X86]
1165               disable
1166                 Do not enable intel_pstate as the default
1167                 scaling driver for the supported processors
1168
1169    intremap= [X86-64, Intel-IOMMU]
1170            on enable Interrupt Remapping (default)
1171            off disable Interrupt Remapping
1172            nosid disable Source ID checking
1173            no_x2apic_optout
1174                BIOS x2APIC opt-out request will be ignored
1175
1176    iomem= Disable strict checking of access to MMIO memory
1177        strict regions from userspace.
1178        relaxed
1179
1180    iommu= [x86]
1181        off
1182        force
1183        noforce
1184        biomerge
1185        panic
1186        nopanic
1187        merge
1188        nomerge
1189        forcesac
1190        soft
1191        pt [x86, IA-64]
1192
1193
1194    io7= [HW] IO7 for Marvel based alpha systems
1195            See comment before marvel_specify_io7 in
1196            arch/alpha/kernel/core_marvel.c.
1197
1198    io_delay= [X86] I/O delay method
1199        0x80
1200            Standard port 0x80 based delay
1201        0xed
1202            Alternate port 0xed based delay (needed on some systems)
1203        udelay
1204            Simple two microseconds delay
1205        none
1206            No delay
1207
1208    ip= [IP_PNP]
1209            See Documentation/filesystems/nfs/nfsroot.txt.
1210
1211    ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
1212            See comment before ip2_setup() in
1213            drivers/char/ip2/ip2base.c.
1214
1215    irqfixup [HW]
1216            When an interrupt is not handled search all handlers
1217            for it. Intended to get systems with badly broken
1218            firmware running.
1219
1220    irqpoll [HW]
1221            When an interrupt is not handled search all handlers
1222            for it. Also check all handlers each timer
1223            interrupt. Intended to get systems with badly broken
1224            firmware running.
1225
1226    isapnp= [ISAPNP]
1227            Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1228
1229    isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
1230            Format:
1231            <cpu number>,...,<cpu number>
1232            or
1233            <cpu number>-<cpu number>
1234            (must be a positive range in ascending order)
1235            or a mixture
1236            <cpu number>,...,<cpu number>-<cpu number>
1237
1238            This option can be used to specify one or more CPUs
1239            to isolate from the general SMP balancing and scheduling
1240            algorithms. You can move a process onto or off an
1241            "isolated" CPU via the CPU affinity syscalls or cpuset.
1242            <cpu number> begins at 0 and the maximum value is
1243            "number of CPUs in system - 1".
1244
1245            This option is the preferred way to isolate CPUs. The
1246            alternative -- manually setting the CPU mask of all
1247            tasks in the system -- can cause problems and
1248            suboptimal load balancer performance.
1249
1250    iucv= [HW,NET]
1251
1252    js= [HW,JOY] Analog joystick
1253            See Documentation/input/joystick.txt.
1254
1255    keepinitrd [HW,ARM]
1256
1257    kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1258            specifies the amount of memory usable by the kernel
1259            for non-movable allocations. The requested amount is
1260            spread evenly throughout all nodes in the system. The
1261            remaining memory in each node is used for Movable
1262            pages. In the event, a node is too small to have both
1263            kernelcore and Movable pages, kernelcore pages will
1264            take priority and other nodes will have a larger number
1265            of kernelcore pages. The Movable zone is used for the
1266            allocation of pages that may be reclaimed or moved
1267            by the page migration subsystem. This means that
1268            HugeTLB pages may not be allocated from this zone.
1269            Note that allocations like PTEs-from-HighMem still
1270            use the HighMem zone if it exists, and the Normal
1271            zone if it does not.
1272
1273    kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1274            Format: <Controller#>[,poll interval]
1275            The controller # is the number of the ehci usb debug
1276            port as it is probed via PCI. The poll interval is
1277            optional and is the number seconds in between
1278            each poll cycle to the debug port in case you need
1279            the functionality for interrupting the kernel with
1280            gdb or control-c on the dbgp connection. When
1281            not using this parameter you use sysrq-g to break into
1282            the kernel debugger.
1283
1284    kgdboc= [KGDB,HW] kgdb over consoles.
1285            Requires a tty driver that supports console polling,
1286            or a supported polling keyboard driver (non-usb).
1287             Serial only format: <serial_device>[,baud]
1288             keyboard only format: kbd
1289             keyboard and serial format: kbd,<serial_device>[,baud]
1290            Optional Kernel mode setting:
1291             kms, kbd format: kms,kbd
1292             kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1293
1294    kgdbwait [KGDB] Stop kernel execution and enter the
1295            kernel debugger at the earliest opportunity.
1296
1297    kmac= [MIPS] korina ethernet MAC address.
1298            Configure the RouterBoard 532 series on-chip
1299            Ethernet adapter MAC address.
1300
1301    kmemleak= [KNL] Boot-time kmemleak enable/disable
1302            Valid arguments: on, off
1303            Default: on
1304
1305    kstack=N [X86] Print N words from the kernel stack
1306            in oops dumps.
1307
1308    kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1309            Default is 0 (don't ignore, but inject #GP)
1310
1311    kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1312            KVM MMU at runtime.
1313            Default is 0 (off)
1314
1315    kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1316            Default is 1 (enabled)
1317
1318    kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1319            for all guests.
1320            Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1321
1322    kvm-intel.ept= [KVM,Intel] Disable extended page tables
1323            (virtualized MMU) support on capable Intel chips.
1324            Default is 1 (enabled)
1325
1326    kvm-intel.emulate_invalid_guest_state=
1327            [KVM,Intel] Enable emulation of invalid guest states
1328            Default is 0 (disabled)
1329
1330    kvm-intel.flexpriority=
1331            [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1332            Default is 1 (enabled)
1333
1334    kvm-intel.nested=
1335            [KVM,Intel] Enable VMX nesting (nVMX).
1336            Default is 0 (disabled)
1337
1338    kvm-intel.unrestricted_guest=
1339            [KVM,Intel] Disable unrestricted guest feature
1340            (virtualized real and unpaged mode) on capable
1341            Intel chips. Default is 1 (enabled)
1342
1343    kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1344            feature (tagged TLBs) on capable Intel chips.
1345            Default is 1 (enabled)
1346
1347    l2cr= [PPC]
1348
1349    l3cr= [PPC]
1350
1351    lapic [X86-32,APIC] Enable the local APIC even if BIOS
1352            disabled it.
1353
1354    lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1355            value for LAPIC timer one-shot implementation. Default
1356            back to the programmable timer unit in the LAPIC.
1357
1358    lapic_timer_c2_ok [X86,APIC] trust the local apic timer
1359            in C2 power state.
1360
1361    libata.dma= [LIBATA] DMA control
1362            libata.dma=0 Disable all PATA and SATA DMA
1363            libata.dma=1 PATA and SATA Disk DMA only
1364            libata.dma=2 ATAPI (CDROM) DMA only
1365            libata.dma=4 Compact Flash DMA only
1366            Combinations also work, so libata.dma=3 enables DMA
1367            for disks and CDROMs, but not CFs.
1368
1369    libata.ignore_hpa= [LIBATA] Ignore HPA limit
1370            libata.ignore_hpa=0 keep BIOS limits (default)
1371            libata.ignore_hpa=1 ignore limits, using full disk
1372
1373    libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1374            when set.
1375            Format: <int>
1376
1377    libata.force= [LIBATA] Force configurations. The format is comma
1378            separated list of "[ID:]VAL" where ID is
1379            PORT[.DEVICE]. PORT and DEVICE are decimal numbers
1380            matching port, link or device. Basically, it matches
1381            the ATA ID string printed on console by libata. If
1382            the whole ID part is omitted, the last PORT and DEVICE
1383            values are used. If ID hasn't been specified yet, the
1384            configuration applies to all ports, links and devices.
1385
1386            If only DEVICE is omitted, the parameter applies to
1387            the port and all links and devices behind it. DEVICE
1388            number of 0 either selects the first device or the
1389            first fan-out link behind PMP device. It does not
1390            select the host link. DEVICE number of 15 selects the
1391            host link and device attached to it.
1392
1393            The VAL specifies the configuration to force. As long
1394            as there's no ambiguity shortcut notation is allowed.
1395            For example, both 1.5 and 1.5G would work for 1.5Gbps.
1396            The following configurations can be forced.
1397
1398            * Cable type: 40c, 80c, short40c, unk, ign or sata.
1399              Any ID with matching PORT is used.
1400
1401            * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1402
1403            * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1404              udma[/][16,25,33,44,66,100,133] notation is also
1405              allowed.
1406
1407            * [no]ncq: Turn on or off NCQ.
1408
1409            * nohrst, nosrst, norst: suppress hard, soft
1410                          and both resets.
1411
1412            * rstonce: only attempt one reset during
1413              hot-unplug link recovery
1414
1415            * dump_id: dump IDENTIFY data.
1416
1417            If there are multiple matching configurations changing
1418            the same attribute, the last one is used.
1419
1420    memblock=debug [KNL] Enable memblock debug messages.
1421
1422    load_ramdisk= [RAM] List of ramdisks to load from floppy
1423            See Documentation/blockdev/ramdisk.txt.
1424
1425    lockd.nlm_grace_period=P [NFS] Assign grace period.
1426            Format: <integer>
1427
1428    lockd.nlm_tcpport=N [NFS] Assign TCP port.
1429            Format: <integer>
1430
1431    lockd.nlm_timeout=T [NFS] Assign timeout value.
1432            Format: <integer>
1433
1434    lockd.nlm_udpport=M [NFS] Assign UDP port.
1435            Format: <integer>
1436
1437    logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1438            Format: <irq>
1439
1440    loglevel= All Kernel Messages with a loglevel smaller than the
1441            console loglevel will be printed to the console. It can
1442            also be changed with klogd or other programs. The
1443            loglevels are defined as follows:
1444
1445            0 (KERN_EMERG) system is unusable
1446            1 (KERN_ALERT) action must be taken immediately
1447            2 (KERN_CRIT) critical conditions
1448            3 (KERN_ERR) error conditions
1449            4 (KERN_WARNING) warning conditions
1450            5 (KERN_NOTICE) normal but significant condition
1451            6 (KERN_INFO) informational
1452            7 (KERN_DEBUG) debug-level messages
1453
1454    log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1455            in bytes. n must be a power of two. The default
1456            size is set in the kernel config file.
1457
1458    logo.nologo [FB] Disables display of the built-in Linux logo.
1459            This may be used to provide more screen space for
1460            kernel log messages and is useful when debugging
1461            kernel boot problems.
1462
1463    lp=0 [LP] Specify parallel ports to use, e.g,
1464    lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1465    lp=reset first parallel port). 'lp=0' disables the
1466    lp=auto printer driver. 'lp=reset' (which can be
1467                specified in addition to the ports) causes
1468                attached printers to be reset. Using
1469                lp=port1,port2,... specifies the parallel ports
1470                to associate lp devices with, starting with
1471                lp0. A port specification may be 'none' to skip
1472                that lp device, or a parport name such as
1473                'parport0'. Specifying 'lp=auto' instead of a
1474                port specification list means that device IDs
1475                from each port should be examined, to see if
1476                an IEEE 1284-compliant printer is attached; if
1477                so, the driver will manage that printer.
1478                See also header of drivers/char/lp.c.
1479
1480    lpj=n [KNL]
1481            Sets loops_per_jiffy to given constant, thus avoiding
1482            time-consuming boot-time autodetection (up to 250 ms per
1483            CPU). 0 enables autodetection (default). To determine
1484            the correct value for your kernel, boot with normal
1485            autodetection and see what value is printed. Note that
1486            on SMP systems the preset will be applied to all CPUs,
1487            which is likely to cause problems if your CPUs need
1488            significantly divergent settings. An incorrect value
1489            will cause delays in the kernel to be wrong, leading to
1490            unpredictable I/O errors and other breakage. Although
1491            unlikely, in the extreme case this might damage your
1492            hardware.
1493
1494    ltpc= [NET]
1495            Format: <io>,<irq>,<dma>
1496
1497    machvec= [IA-64] Force the use of a particular machine-vector
1498            (machvec) in a generic kernel.
1499            Example: machvec=hpzx1_swiotlb
1500
1501    machtype= [Loongson] Share the same kernel image file between different
1502             yeeloong laptop.
1503            Example: machtype=lemote-yeeloong-2f-7inch
1504
1505    max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1506            than or equal to this physical address is ignored.
1507
1508    maxcpus= [SMP] Maximum number of processors that an SMP kernel
1509            should make use of. maxcpus=n : n >= 0 limits the
1510            kernel to using 'n' processors. n=0 is a special case,
1511            it is equivalent to "nosmp", which also disables
1512            the IO APIC.
1513
1514    max_loop= [LOOP] The number of loop block devices that get
1515    (loop.max_loop) unconditionally pre-created at init time. The default
1516            number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1517            of statically allocating a predefined number, loop
1518            devices can be requested on-demand with the
1519            /dev/loop-control interface.
1520
1521    mce [X86-32] Machine Check Exception
1522
1523    mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
1524
1525    md= [HW] RAID subsystems devices and level
1526            See Documentation/md.txt.
1527
1528    mdacon= [MDA]
1529            Format: <first>,<last>
1530            Specifies range of consoles to be captured by the MDA.
1531
1532    mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1533            Amount of memory to be used when the kernel is not able
1534            to see the whole system memory or for test.
1535            [X86] Work as limiting max address. Use together
1536            with memmap= to avoid physical address space collisions.
1537            Without memmap= PCI devices could be placed at addresses
1538            belonging to unused RAM.
1539
1540    mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1541            memory.
1542
1543    memchunk=nn[KMG]
1544            [KNL,SH] Allow user to override the default size for
1545            per-device physically contiguous DMA buffers.
1546
1547    memmap=exactmap [KNL,X86] Enable setting of an exact
1548            E820 memory map, as specified by the user.
1549            Such memmap=exactmap lines can be constructed based on
1550            BIOS output or other requirements. See the memmap=nn@ss
1551            option description.
1552
1553    memmap=nn[KMG]@ss[KMG]
1554            [KNL] Force usage of a specific region of memory
1555            Region of memory to be used, from ss to ss+nn.
1556
1557    memmap=nn[KMG]#ss[KMG]
1558            [KNL,ACPI] Mark specific memory as ACPI data.
1559            Region of memory to be used, from ss to ss+nn.
1560
1561    memmap=nn[KMG]$ss[KMG]
1562            [KNL,ACPI] Mark specific memory as reserved.
1563            Region of memory to be used, from ss to ss+nn.
1564            Example: Exclude memory from 0x18690000-0x1869ffff
1565                     memmap=64K$0x18690000
1566                     or
1567                     memmap=0x10000$0x18690000
1568
1569    memory_corruption_check=0/1 [X86]
1570            Some BIOSes seem to corrupt the first 64k of
1571            memory when doing things like suspend/resume.
1572            Setting this option will scan the memory
1573            looking for corruption. Enabling this will
1574            both detect corruption and prevent the kernel
1575            from using the memory being corrupted.
1576            However, its intended as a diagnostic tool; if
1577            repeatable BIOS-originated corruption always
1578            affects the same memory, you can use memmap=
1579            to prevent the kernel from using that memory.
1580
1581    memory_corruption_check_size=size [X86]
1582            By default it checks for corruption in the low
1583            64k, making this memory unavailable for normal
1584            use. Use this parameter to scan for
1585            corruption in more or less memory.
1586
1587    memory_corruption_check_period=seconds [X86]
1588            By default it checks for corruption every 60
1589            seconds. Use this parameter to check at some
1590            other rate. 0 disables periodic checking.
1591
1592    memtest= [KNL,X86] Enable memtest
1593            Format: <integer>
1594            default : 0 <disable>
1595            Specifies the number of memtest passes to be
1596            performed. Each pass selects another test
1597            pattern from a given set of patterns. Memtest
1598            fills the memory with this pattern, validates
1599            memory contents and reserves bad memory
1600            regions that are detected.
1601
1602    meye.*= [HW] Set MotionEye Camera parameters
1603            See Documentation/video4linux/meye.txt.
1604
1605    mfgpt_irq= [IA-32] Specify the IRQ to use for the
1606            Multi-Function General Purpose Timers on AMD Geode
1607            platforms.
1608
1609    mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1610            the BIOS has incorrectly applied a workaround. TinyBIOS
1611            version 0.98 is known to be affected, 0.99 fixes the
1612            problem by letting the user disable the workaround.
1613
1614    mga= [HW,DRM]
1615
1616    min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1617            physical address is ignored.
1618
1619    mini2440= [ARM,HW,KNL]
1620            Format:[0..2][b][c][t]
1621            Default: "0tb"
1622            MINI2440 configuration specification:
1623            0 - The attached screen is the 3.5" TFT
1624            1 - The attached screen is the 7" TFT
1625            2 - The VGA Shield is attached (1024x768)
1626            Leaving out the screen size parameter will not load
1627            the TFT driver, and the framebuffer will be left
1628            unconfigured.
1629            b - Enable backlight. The TFT backlight pin will be
1630            linked to the kernel VESA blanking code and a GPIO
1631            LED. This parameter is not necessary when using the
1632            VGA shield.
1633            c - Enable the s3c camera interface.
1634            t - Reserved for enabling touchscreen support. The
1635            touchscreen support is not enabled in the mainstream
1636            kernel as of 2.6.30, a preliminary port can be found
1637            in the "bleeding edge" mini2440 support kernel at
1638            http://repo.or.cz/w/linux-2.6/mini2440.git
1639
1640    mminit_loglevel=
1641            [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1642            parameter allows control of the logging verbosity for
1643            the additional memory initialisation checks. A value
1644            of 0 disables mminit logging and a level of 4 will
1645            log everything. Information is printed at KERN_DEBUG
1646            so loglevel=8 may also need to be specified.
1647
1648    module.sig_enforce
1649            [KNL] When CONFIG_MODULE_SIG is set, this means that
1650            modules without (valid) signatures will fail to load.
1651            Note that if CONFIG_MODULE_SIG_ENFORCE is set, that
1652            is always true, so this option does nothing.
1653
1654    mousedev.tap_time=
1655            [MOUSE] Maximum time between finger touching and
1656            leaving touchpad surface for touch to be considered
1657            a tap and be reported as a left button click (for
1658            touchpads working in absolute mode only).
1659            Format: <msecs>
1660    mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1661            reporting absolute coordinates, such as tablets
1662    mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1663            reporting absolute coordinates, such as tablets
1664
1665    movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
1666            is similar to kernelcore except it specifies the
1667            amount of memory used for migratable allocations.
1668            If both kernelcore and movablecore is specified,
1669            then kernelcore will be at *least* the specified
1670            value but may be more. If movablecore on its own
1671            is specified, the administrator must be careful
1672            that the amount of memory usable for all allocations
1673            is not too small.
1674
1675    MTD_Partition= [MTD]
1676            Format: <name>,<region-number>,<size>,<offset>
1677
1678    MTD_Region= [MTD] Format:
1679            <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1680
1681    mtdparts= [MTD]
1682            See drivers/mtd/cmdlinepart.c.
1683
1684    multitce=off [PPC] This parameter disables the use of the pSeries
1685            firmware feature for updating multiple TCE entries
1686            at a time.
1687
1688    onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1689
1690            Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1691
1692            boundary - index of last SLC block on Flex-OneNAND.
1693                   The remaining blocks are configured as MLC blocks.
1694            lock - Configure if Flex-OneNAND boundary should be locked.
1695                   Once locked, the boundary cannot be changed.
1696                   1 indicates lock status, 0 indicates unlock status.
1697
1698    mtdset= [ARM]
1699            ARM/S3C2412 JIVE boot control
1700
1701            See arch/arm/mach-s3c2412/mach-jive.c
1702
1703    mtouchusb.raw_coordinates=
1704            [HW] Make the MicroTouch USB driver use raw coordinates
1705            ('y', default) or cooked coordinates ('n')
1706
1707    mtrr_chunk_size=nn[KMG] [X86]
1708            used for mtrr cleanup. It is largest continuous chunk
1709            that could hold holes aka. UC entries.
1710
1711    mtrr_gran_size=nn[KMG] [X86]
1712            Used for mtrr cleanup. It is granularity of mtrr block.
1713            Default is 1.
1714            Large value could prevent small alignment from
1715            using up MTRRs.
1716
1717    mtrr_spare_reg_nr=n [X86]
1718            Format: <integer>
1719            Range: 0,7 : spare reg number
1720            Default : 1
1721            Used for mtrr cleanup. It is spare mtrr entries number.
1722            Set to 2 or more if your graphical card needs more.
1723
1724    n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1725
1726    netdev= [NET] Network devices parameters
1727            Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1728            Note that mem_start is often overloaded to mean
1729            something different and driver-specific.
1730            This usage is only documented in each driver source
1731            file if at all.
1732
1733    nf_conntrack.acct=
1734            [NETFILTER] Enable connection tracking flow accounting
1735            0 to disable accounting
1736            1 to enable accounting
1737            Default value is 0.
1738
1739    nfsaddrs= [NFS] Deprecated. Use ip= instead.
1740            See Documentation/filesystems/nfs/nfsroot.txt.
1741
1742    nfsroot= [NFS] nfs root filesystem for disk-less boxes.
1743            See Documentation/filesystems/nfs/nfsroot.txt.
1744
1745    nfsrootdebug [NFS] enable nfsroot debugging messages.
1746            See Documentation/filesystems/nfs/nfsroot.txt.
1747
1748    nfs.callback_tcpport=
1749            [NFS] set the TCP port on which the NFSv4 callback
1750            channel should listen.
1751
1752    nfs.cache_getent=
1753            [NFS] sets the pathname to the program which is used
1754            to update the NFS client cache entries.
1755
1756    nfs.cache_getent_timeout=
1757            [NFS] sets the timeout after which an attempt to
1758            update a cache entry is deemed to have failed.
1759
1760    nfs.idmap_cache_timeout=
1761            [NFS] set the maximum lifetime for idmapper cache
1762            entries.
1763
1764    nfs.enable_ino64=
1765            [NFS] enable 64-bit inode numbers.
1766            If zero, the NFS client will fake up a 32-bit inode
1767            number for the readdir() and stat() syscalls instead
1768            of returning the full 64-bit number.
1769            The default is to return 64-bit inode numbers.
1770
1771    nfs.max_session_slots=
1772            [NFSv4.1] Sets the maximum number of session slots
1773            the client will attempt to negotiate with the server.
1774            This limits the number of simultaneous RPC requests
1775            that the client can send to the NFSv4.1 server.
1776            Note that there is little point in setting this
1777            value higher than the max_tcp_slot_table_limit.
1778
1779    nfs.nfs4_disable_idmapping=
1780            [NFSv4] When set to the default of '1', this option
1781            ensures that both the RPC level authentication
1782            scheme and the NFS level operations agree to use
1783            numeric uids/gids if the mount is using the
1784            'sec=sys' security flavour. In effect it is
1785            disabling idmapping, which can make migration from
1786            legacy NFSv2/v3 systems to NFSv4 easier.
1787            Servers that do not support this mode of operation
1788            will be autodetected by the client, and it will fall
1789            back to using the idmapper.
1790            To turn off this behaviour, set the value to '0'.
1791    nfs.nfs4_unique_id=
1792            [NFS4] Specify an additional fixed unique ident-
1793            ification string that NFSv4 clients can insert into
1794            their nfs_client_id4 string. This is typically a
1795            UUID that is generated at system install time.
1796
1797    nfs.send_implementation_id =
1798            [NFSv4.1] Send client implementation identification
1799            information in exchange_id requests.
1800            If zero, no implementation identification information
1801            will be sent.
1802            The default is to send the implementation identification
1803            information.
1804
1805    nfsd.nfs4_disable_idmapping=
1806            [NFSv4] When set to the default of '1', the NFSv4
1807            server will return only numeric uids and gids to
1808            clients using auth_sys, and will accept numeric uids
1809            and gids from such clients. This is intended to ease
1810            migration from NFSv2/v3.
1811
1812    objlayoutdriver.osd_login_prog=
1813            [NFS] [OBJLAYOUT] sets the pathname to the program which
1814            is used to automatically discover and login into new
1815            osd-targets. Please see:
1816            Documentation/filesystems/pnfs.txt for more explanations
1817
1818    nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
1819            when a NMI is triggered.
1820            Format: [state][,regs][,debounce][,die]
1821
1822    nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
1823            Format: [panic,][nopanic,][num]
1824            Valid num: 0
1825            0 - turn nmi_watchdog off
1826            When panic is specified, panic when an NMI watchdog
1827            timeout occurs (or 'nopanic' to override the opposite
1828            default).
1829            This is useful when you use a panic=... timeout and
1830            need the box quickly up again.
1831
1832    netpoll.carrier_timeout=
1833            [NET] Specifies amount of time (in seconds) that
1834            netpoll should wait for a carrier. By default netpoll
1835            waits 4 seconds.
1836
1837    no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1838            emulation library even if a 387 maths coprocessor
1839            is present.
1840
1841    no_console_suspend
1842            [HW] Never suspend the console
1843            Disable suspending of consoles during suspend and
1844            hibernate operations. Once disabled, debugging
1845            messages can reach various consoles while the rest
1846            of the system is being put to sleep (ie, while
1847            debugging driver suspend/resume hooks). This may
1848            not work reliably with all consoles, but is known
1849            to work with serial and VGA consoles.
1850            To facilitate more flexible debugging, we also add
1851            console_suspend, a printk module parameter to control
1852            it. Users could use console_suspend (usually
1853            /sys/module/printk/parameters/console_suspend) to
1854            turn on/off it dynamically.
1855
1856    noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
1857            caches in the slab allocator. Saves per-node memory,
1858            but will impact performance.
1859
1860    noalign [KNL,ARM]
1861
1862    noapic [SMP,APIC] Tells the kernel to not make use of any
1863            IOAPICs that may be present in the system.
1864
1865    noautogroup Disable scheduler automatic task group creation.
1866
1867    nobats [PPC] Do not use BATs for mapping kernel lowmem
1868            on "Classic" PPC cores.
1869
1870    nocache [ARM]
1871
1872    noclflush [BUGS=X86] Don't use the CLFLUSH instruction
1873
1874    nodelayacct [KNL] Disable per-task delay accounting
1875
1876    nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
1877
1878    nodsp [SH] Disable hardware DSP at boot time.
1879
1880    noefi [X86] Disable EFI runtime services support.
1881
1882    noexec [IA-64]
1883
1884    noexec [X86]
1885            On X86-32 available only on PAE configured kernels.
1886            noexec=on: enable non-executable mappings (default)
1887            noexec=off: disable non-executable mappings
1888
1889    nosmap [X86]
1890            Disable SMAP (Supervisor Mode Access Prevention)
1891            even if it is supported by processor.
1892
1893    nosmep [X86]
1894            Disable SMEP (Supervisor Mode Execution Prevention)
1895            even if it is supported by processor.
1896
1897    noexec32 [X86-64]
1898            This affects only 32-bit executables.
1899            noexec32=on: enable non-executable mappings (default)
1900                read doesn't imply executable mappings
1901            noexec32=off: disable non-executable mappings
1902                read implies executable mappings
1903
1904    nofpu [SH] Disable hardware FPU at boot time.
1905
1906    nofxsr [BUGS=X86-32] Disables x86 floating point extended
1907            register save and restore. The kernel will only save
1908            legacy floating-point registers on task switch.
1909
1910    noxsave [BUGS=X86] Disables x86 extended register state save
1911            and restore using xsave. The kernel will fallback to
1912            enabling legacy floating-point and sse state.
1913
1914    eagerfpu= [X86]
1915            on enable eager fpu restore
1916            off disable eager fpu restore
1917            auto selects the default scheme, which automatically
1918                enables eagerfpu restore for xsaveopt.
1919
1920    nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
1921            wfi(ARM) instruction doesn't work correctly and not to
1922            use it. This is also useful when using JTAG debugger.
1923
1924    no_file_caps Tells the kernel not to honor file capabilities. The
1925            only way then for a file to be executed with privilege
1926            is to be setuid root or executed by root.
1927
1928    nohalt [IA-64] Tells the kernel not to use the power saving
1929            function PAL_HALT_LIGHT when idle. This increases
1930            power-consumption. On the positive side, it reduces
1931            interrupt wake-up latency, which may improve performance
1932            in certain environments such as networked servers or
1933            real-time systems.
1934
1935    nohz= [KNL] Boottime enable/disable dynamic ticks
1936            Valid arguments: on, off
1937            Default: on
1938
1939    noiotrap [SH] Disables trapped I/O port accesses.
1940
1941    noirqdebug [X86-32] Disables the code which attempts to detect and
1942            disable unhandled interrupt sources.
1943
1944    no_timer_check [X86,APIC] Disables the code which tests for
1945            broken timer IRQ sources.
1946
1947    noisapnp [ISAPNP] Disables ISA PnP code.
1948
1949    noinitrd [RAM] Tells the kernel not to load any configured
1950            initial RAM disk.
1951
1952    nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
1953            remapping.
1954            [Deprecated - use intremap=off]
1955
1956    nointroute [IA-64]
1957
1958    nojitter [IA-64] Disables jitter checking for ITC timers.
1959
1960    no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
1961
1962    no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
1963            fault handling.
1964
1965    no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
1966            steal time is computed, but won't influence scheduler
1967            behaviour
1968
1969    nolapic [X86-32,APIC] Do not enable or use the local APIC.
1970
1971    nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
1972
1973    noltlbs [PPC] Do not use large page/tlb entries for kernel
1974            lowmem mapping on PPC40x.
1975
1976    nomca [IA-64] Disable machine check abort handling
1977
1978    nomce [X86-32] Machine Check Exception
1979
1980    nomfgpt [X86-32] Disable Multi-Function General Purpose
1981            Timer usage (for AMD Geode machines).
1982
1983    nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
1984            shutdown the other cpus. Instead use the REBOOT_VECTOR
1985            irq.
1986
1987    nomodule Disable module load
1988
1989    nopat [X86] Disable PAT (page attribute table extension of
1990            pagetables) support.
1991
1992    norandmaps Don't use address space randomization. Equivalent to
1993            echo 0 > /proc/sys/kernel/randomize_va_space
1994
1995    noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
1996
1997    noreplace-smp [X86-32,SMP] Don't replace SMP instructions
1998            with UP alternatives
1999
2000    noresidual [PPC] Don't use residual data on PReP machines.
2001
2002    nordrand [X86] Disable the direct use of the RDRAND
2003            instruction even if it is supported by the
2004            processor. RDRAND is still available to user
2005            space applications.
2006
2007    noresume [SWSUSP] Disables resume and restores original swap
2008            space.
2009
2010    no-scroll [VGA] Disables scrollback.
2011            This is required for the Braillex ib80-piezo Braille
2012            reader made by F.H. Papenmeier (Germany).
2013
2014    nosbagart [IA-64]
2015
2016    nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2017
2018    nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2019            and disable the IO APIC. legacy for "maxcpus=0".
2020
2021    nosoftlockup [KNL] Disable the soft-lockup detector.
2022
2023    nosync [HW,M68K] Disables sync negotiation for all devices.
2024
2025    notsc [BUGS=X86-32] Disable Time Stamp Counter
2026
2027    nousb [USB] Disable the USB subsystem
2028
2029    nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
2030
2031    nowb [ARM]
2032
2033    nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2034
2035    cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2036            CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2037            Some features depend on CPU0. Known dependencies are:
2038            1. Resume from suspend/hibernate depends on CPU0.
2039            Suspend/hibernate will fail if CPU0 is offline and you
2040            need to online CPU0 before suspend/hibernate.
2041            2. PIC interrupts also depend on CPU0. CPU0 can't be
2042            removed if a PIC interrupt is detected.
2043            It's said poweroff/reboot may depend on CPU0 on some
2044            machines although I haven't seen such issues so far
2045            after CPU0 is offline on a few tested machines.
2046            If the dependencies are under your control, you can
2047            turn on cpu0_hotplug.
2048
2049    nptcg= [IA-64] Override max number of concurrent global TLB
2050            purges which is reported from either PAL_VM_SUMMARY or
2051            SAL PALO.
2052
2053    nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2054            could support. nr_cpus=n : n >= 1 limits the kernel to
2055            supporting 'n' processors. Later in runtime you can not
2056            use hotplug cpu feature to put more cpu back to online.
2057            just like you compile the kernel NR_CPUS=n
2058
2059    nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2060
2061    numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2062            Allowed values are enable and disable
2063
2064    numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2065            one of ['zone', 'node', 'default'] can be specified
2066            This can be set from sysctl after boot.
2067            See Documentation/sysctl/vm.txt for details.
2068
2069    ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2070            See Documentation/debugging-via-ohci1394.txt for more
2071            info.
2072
2073    olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2074            Rather than timing out after 20 ms if an EC
2075            command is not properly ACKed, override the length
2076            of the timeout. We have interrupts disabled while
2077            waiting for the ACK, so if this is set too high
2078            interrupts *may* be lost!
2079
2080    omap_mux= [OMAP] Override bootloader pin multiplexing.
2081            Format: <mux_mode0.mode_name=value>...
2082            For example, to override I2C bus2:
2083            omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2084
2085    oprofile.timer= [HW]
2086            Use timer interrupt instead of performance counters
2087
2088    oprofile.cpu_type= Force an oprofile cpu type
2089            This might be useful if you have an older oprofile
2090            userland or if you want common events.
2091            Format: { arch_perfmon }
2092            arch_perfmon: [X86] Force use of architectural
2093                perfmon on Intel CPUs instead of the
2094                CPU specific event set.
2095            timer: [X86] Force use of architectural NMI
2096                timer mode (see also oprofile.timer
2097                for generic hr timer mode)
2098                [s390] Force legacy basic mode sampling
2099                                (report cpu_type "timer")
2100
2101    oops=panic Always panic on oopses. Default is to just kill the
2102            process, but there is a small probability of
2103            deadlocking the machine.
2104            This will also cause panics on machine check exceptions.
2105            Useful together with panic=30 to trigger a reboot.
2106
2107    OSS [HW,OSS]
2108            See Documentation/sound/oss/oss-parameters.txt
2109
2110    panic= [KNL] Kernel behaviour on panic: delay <timeout>
2111            timeout > 0: seconds before rebooting
2112            timeout = 0: wait forever
2113            timeout < 0: reboot immediately
2114            Format: <timeout>
2115
2116    parkbd.port= [HW] Parallel port number the keyboard adapter is
2117            connected to, default is 0.
2118            Format: <parport#>
2119    parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2120            0 for XT, 1 for AT (default is AT).
2121            Format: <mode>
2122
2123    parport= [HW,PPT] Specify parallel ports. 0 disables.
2124            Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2125            Use 'auto' to force the driver to use any
2126            IRQ/DMA settings detected (the default is to
2127            ignore detected IRQ/DMA settings because of
2128            possible conflicts). You can specify the base
2129            address, IRQ, and DMA settings; IRQ and DMA
2130            should be numbers, or 'auto' (for using detected
2131            settings on that particular port), or 'nofifo'
2132            (to avoid using a FIFO even if it is detected).
2133            Parallel ports are assigned in the order they
2134            are specified on the command line, starting
2135            with parport0.
2136
2137    parport_init_mode= [HW,PPT]
2138            Configure VIA parallel port to operate in
2139            a specific mode. This is necessary on Pegasos
2140            computer where firmware has no options for setting
2141            up parallel port mode and sets it to spp.
2142            Currently this function knows 686a and 8231 chips.
2143            Format: [spp|ps2|epp|ecp|ecpepp]
2144
2145    pause_on_oops=
2146            Halt all CPUs after the first oops has been printed for
2147            the specified number of seconds. This is to be used if
2148            your oopses keep scrolling off the screen.
2149
2150    pcbit= [HW,ISDN]
2151
2152    pcd. [PARIDE]
2153            See header of drivers/block/paride/pcd.c.
2154            See also Documentation/blockdev/paride.txt.
2155
2156    pci=option[,option...] [PCI] various PCI subsystem options:
2157        earlydump [X86] dump PCI config space before the kernel
2158                    changes anything
2159        off [X86] don't probe for the PCI bus
2160        bios [X86-32] force use of PCI BIOS, don't access
2161                the hardware directly. Use this if your machine
2162                has a non-standard PCI host bridge.
2163        nobios [X86-32] disallow use of PCI BIOS, only direct
2164                hardware access methods are allowed. Use this
2165                if you experience crashes upon bootup and you
2166                suspect they are caused by the BIOS.
2167        conf1 [X86] Force use of PCI Configuration
2168                Mechanism 1.
2169        conf2 [X86] Force use of PCI Configuration
2170                Mechanism 2.
2171        noaer [PCIE] If the PCIEAER kernel config parameter is
2172                enabled, this kernel boot option can be used to
2173                disable the use of PCIE advanced error reporting.
2174        nodomains [PCI] Disable support for multiple PCI
2175                root domains (aka PCI segments, in ACPI-speak).
2176        nommconf [X86] Disable use of MMCONFIG for PCI
2177                Configuration
2178        check_enable_amd_mmconf [X86] check for and enable
2179                properly configured MMIO access to PCI
2180                config space on AMD family 10h CPU
2181        nomsi [MSI] If the PCI_MSI kernel config parameter is
2182                enabled, this kernel boot option can be used to
2183                disable the use of MSI interrupts system-wide.
2184        noioapicquirk [APIC] Disable all boot interrupt quirks.
2185                Safety option to keep boot IRQs enabled. This
2186                should never be necessary.
2187        ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2188                primary IO-APIC for bridges that cannot disable
2189                boot IRQs. This fixes a source of spurious IRQs
2190                when the system masks IRQs.
2191        noioapicreroute [APIC] Disable workaround that uses the
2192                boot IRQ equivalent of an IRQ that connects to
2193                a chipset where boot IRQs cannot be disabled.
2194                The opposite of ioapicreroute.
2195        biosirq [X86-32] Use PCI BIOS calls to get the interrupt
2196                routing table. These calls are known to be buggy
2197                on several machines and they hang the machine
2198                when used, but on other computers it's the only
2199                way to get the interrupt routing table. Try
2200                this option if the kernel is unable to allocate
2201                IRQs or discover secondary PCI buses on your
2202                motherboard.
2203        rom [X86] Assign address space to expansion ROMs.
2204                Use with caution as certain devices share
2205                address decoders between ROMs and other
2206                resources.
2207        norom [X86] Do not assign address space to
2208                expansion ROMs that do not already have
2209                BIOS assigned address ranges.
2210        nobar [X86] Do not assign address space to the
2211                BARs that weren't assigned by the BIOS.
2212        irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
2213                assigned automatically to PCI devices. You can
2214                make the kernel exclude IRQs of your ISA cards
2215                this way.
2216        pirqaddr=0xAAAAA [X86] Specify the physical address
2217                of the PIRQ table (normally generated
2218                by the BIOS) if it is outside the
2219                F0000h-100000h range.
2220        lastbus=N [X86] Scan all buses thru bus #N. Can be
2221                useful if the kernel is unable to find your
2222                secondary buses and you want to tell it
2223                explicitly which ones they are.
2224        assign-busses [X86] Always assign all PCI bus
2225                numbers ourselves, overriding
2226                whatever the firmware may have done.
2227        usepirqmask [X86] Honor the possible IRQ mask stored
2228                in the BIOS $PIR table. This is needed on
2229                some systems with broken BIOSes, notably
2230                some HP Pavilion N5400 and Omnibook XE3
2231                notebooks. This will have no effect if ACPI
2232                IRQ routing is enabled.
2233        noacpi [X86] Do not use ACPI for IRQ routing
2234                or for PCI scanning.
2235        use_crs [X86] Use PCI host bridge window information
2236                from ACPI. On BIOSes from 2008 or later, this
2237                is enabled by default. If you need to use this,
2238                please report a bug.
2239        nocrs [X86] Ignore PCI host bridge windows from ACPI.
2240                    If you need to use this, please report a bug.
2241        routeirq Do IRQ routing for all PCI devices.
2242                This is normally done in pci_enable_device(),
2243                so this option is a temporary workaround
2244                for broken drivers that don't call it.
2245        skip_isa_align [X86] do not align io start addr, so can
2246                handle more pci cards
2247        firmware [ARM] Do not re-enumerate the bus but instead
2248                just use the configuration from the
2249                bootloader. This is currently used on
2250                IXP2000 systems where the bus has to be
2251                configured a certain way for adjunct CPUs.
2252        noearly [X86] Don't do any early type 1 scanning.
2253                This might help on some broken boards which
2254                machine check when some devices' config space
2255                is read. But various workarounds are disabled
2256                and some IOMMU drivers will not work.
2257        bfsort Sort PCI devices into breadth-first order.
2258                This sorting is done to get a device
2259                order compatible with older (<= 2.4) kernels.
2260        nobfsort Don't sort PCI devices into breadth-first order.
2261        pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2262                tuning and use the BIOS-configured MPS defaults.
2263        pcie_bus_safe Set every device's MPS to the largest value
2264                supported by all devices below the root complex.
2265        pcie_bus_perf Set device MPS to the largest allowable MPS
2266                based on its parent bus. Also set MRRS (Max
2267                Read Request Size) to the largest supported
2268                value (no larger than the MPS that the device
2269                or bus can support) for best performance.
2270        pcie_bus_peer2peer Set every device's MPS to 128B, which
2271                every device is guaranteed to support. This
2272                configuration allows peer-to-peer DMA between
2273                any pair of devices, possibly at the cost of
2274                reduced performance. This also guarantees
2275                that hot-added devices will work.
2276        cbiosize=nn[KMG] The fixed amount of bus space which is
2277                reserved for the CardBus bridge's IO window.
2278                The default value is 256 bytes.
2279        cbmemsize=nn[KMG] The fixed amount of bus space which is
2280                reserved for the CardBus bridge's memory
2281                window. The default value is 64 megabytes.
2282        resource_alignment=
2283                Format:
2284                [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2285                Specifies alignment and device to reassign
2286                aligned memory resources.
2287                If <order of align> is not specified,
2288                PAGE_SIZE is used as alignment.
2289                PCI-PCI bridge can be specified, if resource
2290                windows need to be expanded.
2291        ecrc= Enable/disable PCIe ECRC (transaction layer
2292                end-to-end CRC checking).
2293                bios: Use BIOS/firmware settings. This is the
2294                the default.
2295                off: Turn ECRC off
2296                on: Turn ECRC on.
2297        hpiosize=nn[KMG] The fixed amount of bus space which is
2298                reserved for hotplug bridge's IO window.
2299                Default size is 256 bytes.
2300        hpmemsize=nn[KMG] The fixed amount of bus space which is
2301                reserved for hotplug bridge's memory window.
2302                Default size is 2 megabytes.
2303        realloc= Enable/disable reallocating PCI bridge resources
2304                if allocations done by BIOS are too small to
2305                accommodate resources required by all child
2306                devices.
2307                off: Turn realloc off
2308                on: Turn realloc on
2309        realloc same as realloc=on
2310        noari do not use PCIe ARI.
2311        pcie_scan_all Scan all possible PCIe devices. Otherwise we
2312                only look for one device below a PCIe downstream
2313                port.
2314
2315    pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2316            Management.
2317        off Disable ASPM.
2318        force Enable ASPM even on devices that claim not to support it.
2319            WARNING: Forcing ASPM on may cause system lockups.
2320
2321    pcie_hp= [PCIE] PCI Express Hotplug driver options:
2322        nomsi Do not use MSI for PCI Express Native Hotplug (this
2323            makes all PCIe ports use INTx for hotplug services).
2324
2325    pcie_ports= [PCIE] PCIe ports handling:
2326        auto Ask the BIOS whether or not to use native PCIe services
2327            associated with PCIe ports (PME, hot-plug, AER). Use
2328            them only if that is allowed by the BIOS.
2329        native Use native PCIe services associated with PCIe ports
2330            unconditionally.
2331        compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2332            ports driver.
2333
2334    pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
2335        nomsi Do not use MSI for native PCIe PME signaling (this makes
2336            all PCIe root ports use INTx for all services).
2337
2338    pcmv= [HW,PCMCIA] BadgePAD 4
2339
2340    pd. [PARIDE]
2341            See Documentation/blockdev/paride.txt.
2342
2343    pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2344            boot time.
2345            Format: { 0 | 1 }
2346            See arch/parisc/kernel/pdc_chassis.c
2347
2348    percpu_alloc= Select which percpu first chunk allocator to use.
2349            Currently supported values are "embed" and "page".
2350            Archs may support subset or none of the selections.
2351            See comments in mm/percpu.c for details on each
2352            allocator. This parameter is primarily for debugging
2353            and performance comparison.
2354
2355    pf. [PARIDE]
2356            See Documentation/blockdev/paride.txt.
2357
2358    pg. [PARIDE]
2359            See Documentation/blockdev/paride.txt.
2360
2361    pirq= [SMP,APIC] Manual mp-table setup
2362            See Documentation/x86/i386/IO-APIC.txt.
2363
2364    plip= [PPT,NET] Parallel port network link
2365            Format: { parport<nr> | timid | 0 }
2366            See also Documentation/parport.txt.
2367
2368    pmtmr= [X86] Manual setup of pmtmr I/O Port.
2369            Override pmtimer IOPort with a hex value.
2370            e.g. pmtmr=0x508
2371
2372    pnp.debug=1 [PNP]
2373            Enable PNP debug messages (depends on the
2374            CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2375            via /sys/module/pnp/parameters/debug. We always show
2376            current resource usage; turning this on also shows
2377            possible settings and some assignment information.
2378
2379    pnpacpi= [ACPI]
2380            { off }
2381
2382    pnpbios= [ISAPNP]
2383            { on | off | curr | res | no-curr | no-res }
2384
2385    pnp_reserve_irq=
2386            [ISAPNP] Exclude IRQs for the autoconfiguration
2387
2388    pnp_reserve_dma=
2389            [ISAPNP] Exclude DMAs for the autoconfiguration
2390
2391    pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
2392            Ranges are in pairs (I/O port base and size).
2393
2394    pnp_reserve_mem=
2395            [ISAPNP] Exclude memory regions for the
2396            autoconfiguration.
2397            Ranges are in pairs (memory base and size).
2398
2399    ports= [IP_VS_FTP] IPVS ftp helper module
2400            Default is 21.
2401            Up to 8 (IP_VS_APP_MAX_PORTS) ports
2402            may be specified.
2403            Format: <port>,<port>....
2404
2405    print-fatal-signals=
2406            [KNL] debug: print fatal signals
2407
2408            If enabled, warn about various signal handling
2409            related application anomalies: too many signals,
2410            too many POSIX.1 timers, fatal signals causing a
2411            coredump - etc.
2412
2413            If you hit the warning due to signal overflow,
2414            you might want to try "ulimit -i unlimited".
2415
2416            default: off.
2417
2418    printk.always_kmsg_dump=
2419            Trigger kmsg_dump for cases other than kernel oops or
2420            panics
2421            Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2422            default: disabled
2423
2424    printk.time= Show timing data prefixed to each printk message line
2425            Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2426
2427    processor.max_cstate= [HW,ACPI]
2428            Limit processor to maximum C-state
2429            max_cstate=9 overrides any DMI blacklist limit.
2430
2431    processor.nocst [HW,ACPI]
2432            Ignore the _CST method to determine C-states,
2433            instead using the legacy FADT method
2434
2435    profile= [KNL] Enable kernel profiling via /proc/profile
2436            Format: [schedule,]<number>
2437            Param: "schedule" - profile schedule points.
2438            Param: <number> - step/bucket size as a power of 2 for
2439                statistical time based profiling.
2440            Param: "sleep" - profile D-state sleeping (millisecs).
2441                Requires CONFIG_SCHEDSTATS
2442            Param: "kvm" - profile VM exits.
2443
2444    prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2445            before loading.
2446            See Documentation/blockdev/ramdisk.txt.
2447
2448    psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2449            probe for; one of (bare|imps|exps|lifebook|any).
2450    psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2451            per second.
2452    psmouse.resetafter= [HW,MOUSE]
2453            Try to reset the device after so many bad packets
2454            (0 = never).
2455    psmouse.resolution=
2456            [HW,MOUSE] Set desired mouse resolution, in dpi.
2457    psmouse.smartscroll=
2458            [HW,MOUSE] Controls Logitech smartscroll autorepeat.
2459            0 = disabled, 1 = enabled (default).
2460
2461    pstore.backend= Specify the name of the pstore backend to use
2462
2463    pt. [PARIDE]
2464            See Documentation/blockdev/paride.txt.
2465
2466    pty.legacy_count=
2467            [KNL] Number of legacy pty's. Overwrites compiled-in
2468            default number.
2469
2470    quiet [KNL] Disable most log messages
2471
2472    r128= [HW,DRM]
2473
2474    raid= [HW,RAID]
2475            See Documentation/md.txt.
2476
2477    ramdisk_blocksize= [RAM]
2478            See Documentation/blockdev/ramdisk.txt.
2479
2480    ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
2481            See Documentation/blockdev/ramdisk.txt.
2482
2483    rcu_nocbs= [KNL,BOOT]
2484            In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2485            the specified list of CPUs to be no-callback CPUs.
2486            Invocation of these CPUs' RCU callbacks will
2487            be offloaded to "rcuoN" kthreads created for
2488            that purpose. This reduces OS jitter on the
2489            offloaded CPUs, which can be useful for HPC and
2490            real-time workloads. It can also improve energy
2491            efficiency for asymmetric multiprocessors.
2492
2493    rcu_nocb_poll [KNL,BOOT]
2494            Rather than requiring that offloaded CPUs
2495            (specified by rcu_nocbs= above) explicitly
2496            awaken the corresponding "rcuoN" kthreads,
2497            make these kthreads poll for callbacks.
2498            This improves the real-time response for the
2499            offloaded CPUs by relieving them of the need to
2500            wake up the corresponding kthread, but degrades
2501            energy efficiency by requiring that the kthreads
2502            periodically wake up to do the polling.
2503
2504    rcutree.blimit= [KNL,BOOT]
2505            Set maximum number of finished RCU callbacks to process
2506            in one batch.
2507
2508    rcutree.fanout_leaf= [KNL,BOOT]
2509            Increase the number of CPUs assigned to each
2510            leaf rcu_node structure. Useful for very large
2511            systems.
2512
2513    rcutree.qhimark= [KNL,BOOT]
2514            Set threshold of queued
2515            RCU callbacks over which batch limiting is disabled.
2516
2517    rcutree.qlowmark= [KNL,BOOT]
2518            Set threshold of queued RCU callbacks below which
2519            batch limiting is re-enabled.
2520
2521    rcutree.rcu_cpu_stall_suppress= [KNL,BOOT]
2522            Suppress RCU CPU stall warning messages.
2523
2524    rcutree.rcu_cpu_stall_timeout= [KNL,BOOT]
2525            Set timeout for RCU CPU stall warning messages.
2526
2527    rcutree.jiffies_till_first_fqs= [KNL,BOOT]
2528            Set delay from grace-period initialization to
2529            first attempt to force quiescent states.
2530            Units are jiffies, minimum value is zero,
2531            and maximum value is HZ.
2532
2533    rcutree.jiffies_till_next_fqs= [KNL,BOOT]
2534            Set delay between subsequent attempts to force
2535            quiescent states. Units are jiffies, minimum
2536            value is one, and maximum value is HZ.
2537
2538    rcutorture.fqs_duration= [KNL,BOOT]
2539            Set duration of force_quiescent_state bursts.
2540
2541    rcutorture.fqs_holdoff= [KNL,BOOT]
2542            Set holdoff time within force_quiescent_state bursts.
2543
2544    rcutorture.fqs_stutter= [KNL,BOOT]
2545            Set wait time between force_quiescent_state bursts.
2546
2547    rcutorture.irqreader= [KNL,BOOT]
2548            Test RCU readers from irq handlers.
2549
2550    rcutorture.n_barrier_cbs= [KNL,BOOT]
2551            Set callbacks/threads for rcu_barrier() testing.
2552
2553    rcutorture.nfakewriters= [KNL,BOOT]
2554            Set number of concurrent RCU writers. These just
2555            stress RCU, they don't participate in the actual
2556            test, hence the "fake".
2557
2558    rcutorture.nreaders= [KNL,BOOT]
2559            Set number of RCU readers.
2560
2561    rcutorture.onoff_holdoff= [KNL,BOOT]
2562            Set time (s) after boot for CPU-hotplug testing.
2563
2564    rcutorture.onoff_interval= [KNL,BOOT]
2565            Set time (s) between CPU-hotplug operations, or
2566            zero to disable CPU-hotplug testing.
2567
2568    rcutorture.shuffle_interval= [KNL,BOOT]
2569            Set task-shuffle interval (s). Shuffling tasks
2570            allows some CPUs to go into dyntick-idle mode
2571            during the rcutorture test.
2572
2573    rcutorture.shutdown_secs= [KNL,BOOT]
2574            Set time (s) after boot system shutdown. This
2575            is useful for hands-off automated testing.
2576
2577    rcutorture.stall_cpu= [KNL,BOOT]
2578            Duration of CPU stall (s) to test RCU CPU stall
2579            warnings, zero to disable.
2580
2581    rcutorture.stall_cpu_holdoff= [KNL,BOOT]
2582            Time to wait (s) after boot before inducing stall.
2583
2584    rcutorture.stat_interval= [KNL,BOOT]
2585            Time (s) between statistics printk()s.
2586
2587    rcutorture.stutter= [KNL,BOOT]
2588            Time (s) to stutter testing, for example, specifying
2589            five seconds causes the test to run for five seconds,
2590            wait for five seconds, and so on. This tests RCU's
2591            ability to transition abruptly to and from idle.
2592
2593    rcutorture.test_boost= [KNL,BOOT]
2594            Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2595            "Maybe" means test if the RCU implementation
2596            under test support RCU priority boosting.
2597
2598    rcutorture.test_boost_duration= [KNL,BOOT]
2599            Duration (s) of each individual boost test.
2600
2601    rcutorture.test_boost_interval= [KNL,BOOT]
2602            Interval (s) between each boost test.
2603
2604    rcutorture.test_no_idle_hz= [KNL,BOOT]
2605            Test RCU's dyntick-idle handling. See also the
2606            rcutorture.shuffle_interval parameter.
2607
2608    rcutorture.torture_type= [KNL,BOOT]
2609            Specify the RCU implementation to test.
2610
2611    rcutorture.verbose= [KNL,BOOT]
2612            Enable additional printk() statements.
2613
2614    rdinit= [KNL]
2615            Format: <full_path>
2616            Run specified binary instead of /init from the ramdisk,
2617            used for early userspace startup. See initrd.
2618
2619    reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode
2620            Format: <reboot_mode>[,<reboot_mode2>[,...]]
2621            See arch/*/kernel/reboot.c or arch/*/kernel/process.c
2622
2623    relax_domain_level=
2624            [KNL, SMP] Set scheduler's default relax_domain_level.
2625            See Documentation/cgroups/cpusets.txt.
2626
2627    reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2628
2629    reservetop= [X86-32]
2630            Format: nn[KMG]
2631            Reserves a hole at the top of the kernel virtual
2632            address space.
2633
2634    reservelow= [X86]
2635            Format: nn[K]
2636            Set the amount of memory to reserve for BIOS at
2637            the bottom of the address space.
2638
2639    reset_devices [KNL] Force drivers to reset the underlying device
2640            during initialization.
2641
2642    resume= [SWSUSP]
2643            Specify the partition device for software suspend
2644            Format:
2645            {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
2646
2647    resume_offset= [SWSUSP]
2648            Specify the offset from the beginning of the partition
2649            given by "resume=" at which the swap header is located,
2650            in <PAGE_SIZE> units (needed only for swap files).
2651            See Documentation/power/swsusp-and-swap-files.txt
2652
2653    resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2654            read the resume files
2655
2656    resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2657            Useful for devices that are detected asynchronously
2658            (e.g. USB and MMC devices).
2659
2660    hibernate= [HIBERNATION]
2661        noresume Don't check if there's a hibernation image
2662                present during boot.
2663        nocompress Don't compress/decompress hibernation images.
2664
2665    retain_initrd [RAM] Keep initrd memory after extraction
2666
2667    rhash_entries= [KNL,NET]
2668            Set number of hash buckets for route cache
2669
2670    riscom8= [HW,SERIAL]
2671            Format: <io_board1>[,<io_board2>[,...<io_boardN>]]
2672
2673    ro [KNL] Mount root device read-only on boot
2674
2675    root= [KNL] Root filesystem
2676            See name_to_dev_t comment in init/do_mounts.c.
2677
2678    rootdelay= [KNL] Delay (in seconds) to pause before attempting to
2679            mount the root filesystem
2680
2681    rootflags= [KNL] Set root filesystem mount option string
2682
2683    rootfstype= [KNL] Set root filesystem type
2684
2685    rootwait [KNL] Wait (indefinitely) for root device to show up.
2686            Useful for devices that are detected asynchronously
2687            (e.g. USB and MMC devices).
2688
2689    rw [KNL] Mount root device read-write on boot
2690
2691    S [KNL] Run init in single mode
2692
2693    sa1100ir [NET]
2694            See drivers/net/irda/sa1100_ir.c.
2695
2696    sbni= [NET] Granch SBNI12 leased line adapter
2697
2698    sched_debug [KNL] Enables verbose scheduler debug messages.
2699
2700    skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
2701            xtime_lock contention on larger systems, and/or RCU lock
2702            contention on all systems with CONFIG_MAXSMP set.
2703            Format: { "0" | "1" }
2704            0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
2705            1 -- enable.
2706            Note: increases power consumption, thus should only be
2707            enabled if running jitter sensitive (HPC/RT) workloads.
2708
2709    security= [SECURITY] Choose a security module to enable at boot.
2710            If this boot parameter is not specified, only the first
2711            security module asking for security registration will be
2712            loaded. An invalid security module name will be treated
2713            as if no module has been chosen.
2714
2715    selinux= [SELINUX] Disable or enable SELinux at boot time.
2716            Format: { "0" | "1" }
2717            See security/selinux/Kconfig help text.
2718            0 -- disable.
2719            1 -- enable.
2720            Default value is set via kernel config option.
2721            If enabled at boot time, /selinux/disable can be used
2722            later to disable prior to initial policy load.
2723
2724    apparmor= [APPARMOR] Disable or enable AppArmor at boot time
2725            Format: { "0" | "1" }
2726            See security/apparmor/Kconfig help text
2727            0 -- disable.
2728            1 -- enable.
2729            Default value is set via kernel config option.
2730
2731    serialnumber [BUGS=X86-32]
2732
2733    shapers= [NET]
2734            Maximal number of shapers.
2735
2736    show_msr= [x86] show boot-time MSR settings
2737            Format: { <integer> }
2738            Show boot-time (BIOS-initialized) MSR settings.
2739            The parameter means the number of CPUs to show,
2740            for example 1 means boot CPU only.
2741
2742    simeth= [IA-64]
2743    simscsi=
2744
2745    slram= [HW,MTD]
2746
2747    slab_max_order= [MM, SLAB]
2748            Determines the maximum allowed order for slabs.
2749            A high setting may cause OOMs due to memory
2750            fragmentation. Defaults to 1 for systems with
2751            more than 32MB of RAM, 0 otherwise.
2752
2753    slub_debug[=options[,slabs]] [MM, SLUB]
2754            Enabling slub_debug allows one to determine the
2755            culprit if slab objects become corrupted. Enabling
2756            slub_debug can create guard zones around objects and
2757            may poison objects when not in use. Also tracks the
2758            last alloc / free. For more information see
2759            Documentation/vm/slub.txt.
2760
2761    slub_max_order= [MM, SLUB]
2762            Determines the maximum allowed order for slabs.
2763            A high setting may cause OOMs due to memory
2764            fragmentation. For more information see
2765            Documentation/vm/slub.txt.
2766
2767    slub_min_objects= [MM, SLUB]
2768            The minimum number of objects per slab. SLUB will
2769            increase the slab order up to slub_max_order to
2770            generate a sufficiently large slab able to contain
2771            the number of objects indicated. The higher the number
2772            of objects the smaller the overhead of tracking slabs
2773            and the less frequently locks need to be acquired.
2774            For more information see Documentation/vm/slub.txt.
2775
2776    slub_min_order= [MM, SLUB]
2777            Determines the minimum page order for slabs. Must be
2778            lower than slub_max_order.
2779            For more information see Documentation/vm/slub.txt.
2780
2781    slub_nomerge [MM, SLUB]
2782            Disable merging of slabs with similar size. May be
2783            necessary if there is some reason to distinguish
2784            allocs to different slabs. Debug options disable
2785            merging on their own.
2786            For more information see Documentation/vm/slub.txt.
2787
2788    smart2= [HW]
2789            Format: <io1>[,<io2>[,...,<io8>]]
2790
2791    smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
2792    smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
2793    smsc-ircc2.ircc_sir= [HW] SIR base I/O port
2794    smsc-ircc2.ircc_fir= [HW] FIR base I/O port
2795    smsc-ircc2.ircc_irq= [HW] IRQ line
2796    smsc-ircc2.ircc_dma= [HW] DMA channel
2797    smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
2798                0: Toshiba Satellite 1800 (GP data pin select)
2799                1: Fast pin select (default)
2800                2: ATC IRMode
2801
2802    softlockup_panic=
2803            [KNL] Should the soft-lockup detector generate panics.
2804            Format: <integer>
2805
2806    sonypi.*= [HW] Sony Programmable I/O Control Device driver
2807            See Documentation/laptops/sonypi.txt
2808
2809    specialix= [HW,SERIAL] Specialix multi-serial port adapter
2810            See Documentation/serial/specialix.txt.
2811
2812    spia_io_base= [HW,MTD]
2813    spia_fio_base=
2814    spia_pedr=
2815    spia_peddr=
2816
2817    stacktrace [FTRACE]
2818            Enabled the stack tracer on boot up.
2819
2820    stacktrace_filter=[function-list]
2821            [FTRACE] Limit the functions that the stack tracer
2822            will trace at boot up. function-list is a comma separated
2823            list of functions. This list can be changed at run
2824            time by the stack_trace_filter file in the debugfs
2825            tracing directory. Note, this enables stack tracing
2826            and the stacktrace above is not needed.
2827
2828    sti= [PARISC,HW]
2829            Format: <num>
2830            Set the STI (builtin display/keyboard on the HP-PARISC
2831            machines) console (graphic card) which should be used
2832            as the initial boot-console.
2833            See also comment in drivers/video/console/sticore.c.
2834
2835    sti_font= [HW]
2836            See comment in drivers/video/console/sticore.c.
2837
2838    stifb= [HW]
2839            Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
2840
2841    sunrpc.min_resvport=
2842    sunrpc.max_resvport=
2843            [NFS,SUNRPC]
2844            SunRPC servers often require that client requests
2845            originate from a privileged port (i.e. a port in the
2846            range 0 < portnr < 1024).
2847            An administrator who wishes to reserve some of these
2848            ports for other uses may adjust the range that the
2849            kernel's sunrpc client considers to be privileged
2850            using these two parameters to set the minimum and
2851            maximum port values.
2852
2853    sunrpc.pool_mode=
2854            [NFS]
2855            Control how the NFS server code allocates CPUs to
2856            service thread pools. Depending on how many NICs
2857            you have and where their interrupts are bound, this
2858            option will affect which CPUs will do NFS serving.
2859            Note: this parameter cannot be changed while the
2860            NFS server is running.
2861
2862            auto the server chooses an appropriate mode
2863                    automatically using heuristics
2864            global a single global pool contains all CPUs
2865            percpu one pool for each CPU
2866            pernode one pool for each NUMA node (equivalent
2867                    to global on non-NUMA machines)
2868
2869    sunrpc.tcp_slot_table_entries=
2870    sunrpc.udp_slot_table_entries=
2871            [NFS,SUNRPC]
2872            Sets the upper limit on the number of simultaneous
2873            RPC calls that can be sent from the client to a
2874            server. Increasing these values may allow you to
2875            improve throughput, but will also increase the
2876            amount of memory reserved for use by the client.
2877
2878    swapaccount[=0|1]
2879            [KNL] Enable accounting of swap in memory resource
2880            controller if no parameter or 1 is given or disable
2881            it if 0 is given (See Documentation/cgroups/memory.txt)
2882
2883    swiotlb= [IA-64] Number of I/O TLB slabs
2884
2885    switches= [HW,M68k]
2886
2887    sysfs.deprecated=0|1 [KNL]
2888            Enable/disable old style sysfs layout for old udev
2889            on older distributions. When this option is enabled
2890            very new udev will not work anymore. When this option
2891            is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
2892            in older udev will not work anymore.
2893            Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
2894            the kernel configuration.
2895
2896    sysrq_always_enabled
2897            [KNL]
2898            Ignore sysrq setting - this boot parameter will
2899            neutralize any effect of /proc/sys/kernel/sysrq.
2900            Useful for debugging.
2901
2902    tdfx= [HW,DRM]
2903
2904    test_suspend= [SUSPEND]
2905            Specify "mem" (for Suspend-to-RAM) or "standby" (for
2906            standby suspend) as the system sleep state to briefly
2907            enter during system startup. The system is woken from
2908            this state using a wakeup-capable RTC alarm.
2909
2910    thash_entries= [KNL,NET]
2911            Set number of hash buckets for TCP connection
2912
2913    thermal.act= [HW,ACPI]
2914            -1: disable all active trip points in all thermal zones
2915            <degrees C>: override all lowest active trip points
2916
2917    thermal.crt= [HW,ACPI]
2918            -1: disable all critical trip points in all thermal zones
2919            <degrees C>: override all critical trip points
2920
2921    thermal.nocrt= [HW,ACPI]
2922            Set to disable actions on ACPI thermal zone
2923            critical and hot trip points.
2924
2925    thermal.off= [HW,ACPI]
2926            1: disable ACPI thermal control
2927
2928    thermal.psv= [HW,ACPI]
2929            -1: disable all passive trip points
2930            <degrees C>: override all passive trip points to this
2931            value
2932
2933    thermal.tzp= [HW,ACPI]
2934            Specify global default ACPI thermal zone polling rate
2935            <deci-seconds>: poll all this frequency
2936            0: no polling (default)
2937
2938    threadirqs [KNL]
2939            Force threading of all interrupt handlers except those
2940            marked explicitly IRQF_NO_THREAD.
2941
2942    topology= [S390]
2943            Format: {off | on}
2944            Specify if the kernel should make use of the cpu
2945            topology information if the hardware supports this.
2946            The scheduler will make use of this information and
2947            e.g. base its process migration decisions on it.
2948            Default is on.
2949
2950    tp720= [HW,PS2]
2951
2952    tpm_suspend_pcr=[HW,TPM]
2953            Format: integer pcr id
2954            Specify that at suspend time, the tpm driver
2955            should extend the specified pcr with zeros,
2956            as a workaround for some chips which fail to
2957            flush the last written pcr on TPM_SaveState.
2958            This will guarantee that all the other pcrs
2959            are saved.
2960
2961    trace_buf_size=nn[KMG]
2962            [FTRACE] will set tracing buffer size.
2963
2964    trace_event=[event-list]
2965            [FTRACE] Set and start specified trace events in order
2966            to facilitate early boot debugging.
2967            See also Documentation/trace/events.txt
2968
2969    trace_options=[option-list]
2970            [FTRACE] Enable or disable tracer options at boot.
2971            The option-list is a comma delimited list of options
2972            that can be enabled or disabled just as if you were
2973            to echo the option name into
2974
2975                /sys/kernel/debug/tracing/trace_options
2976
2977            For example, to enable stacktrace option (to dump the
2978            stack trace of each event), add to the command line:
2979
2980                  trace_options=stacktrace
2981
2982            See also Documentation/trace/ftrace.txt "trace options"
2983            section.
2984
2985    transparent_hugepage=
2986            [KNL]
2987            Format: [always|madvise|never]
2988            Can be used to control the default behavior of the system
2989            with respect to transparent hugepages.
2990            See Documentation/vm/transhuge.txt for more details.
2991
2992    tsc= Disable clocksource stability checks for TSC.
2993            Format: <string>
2994            [x86] reliable: mark tsc clocksource as reliable, this
2995            disables clocksource verification at runtime, as well
2996            as the stability checks done at bootup. Used to enable
2997            high-resolution timer mode on older hardware, and in
2998            virtualized environment.
2999            [x86] noirqtime: Do not use TSC to do irq accounting.
3000            Used to run time disable IRQ_TIME_ACCOUNTING on any
3001            platforms where RDTSC is slow and this accounting
3002            can add overhead.
3003
3004    turbografx.map[2|3]= [HW,JOY]
3005            TurboGraFX parallel port interface
3006            Format:
3007            <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
3008            See also Documentation/input/joystick-parport.txt
3009
3010    udbg-immortal [PPC] When debugging early kernel crashes that
3011            happen after console_init() and before a proper
3012            console driver takes over, this boot options might
3013            help "seeing" what's going on.
3014
3015    uhash_entries= [KNL,NET]
3016            Set number of hash buckets for UDP/UDP-Lite connections
3017
3018    uhci-hcd.ignore_oc=
3019            [USB] Ignore overcurrent events (default N).
3020            Some badly-designed motherboards generate lots of
3021            bogus events, for ports that aren't wired to
3022            anything. Set this parameter to avoid log spamming.
3023            Note that genuine overcurrent events won't be
3024            reported either.
3025
3026    unknown_nmi_panic
3027            [X86] Cause panic on unknown NMI.
3028
3029    usbcore.authorized_default=
3030            [USB] Default USB device authorization:
3031            (default -1 = authorized except for wireless USB,
3032            0 = not authorized, 1 = authorized)
3033
3034    usbcore.autosuspend=
3035            [USB] The autosuspend time delay (in seconds) used
3036            for newly-detected USB devices (default 2). This
3037            is the time required before an idle device will be
3038            autosuspended. Devices for which the delay is set
3039            to a negative value won't be autosuspended at all.
3040
3041    usbcore.usbfs_snoop=
3042            [USB] Set to log all usbfs traffic (default 0 = off).
3043
3044    usbcore.blinkenlights=
3045            [USB] Set to cycle leds on hubs (default 0 = off).
3046
3047    usbcore.old_scheme_first=
3048            [USB] Start with the old device initialization
3049            scheme (default 0 = off).
3050
3051    usbcore.usbfs_memory_mb=
3052            [USB] Memory limit (in MB) for buffers allocated by
3053            usbfs (default = 16, 0 = max = 2047).
3054
3055    usbcore.use_both_schemes=
3056            [USB] Try the other device initialization scheme
3057            if the first one fails (default 1 = enabled).
3058
3059    usbcore.initial_descriptor_timeout=
3060            [USB] Specifies timeout for the initial 64-byte
3061                        USB_REQ_GET_DESCRIPTOR request in milliseconds
3062            (default 5000 = 5.0 seconds).
3063
3064    usbhid.mousepoll=
3065            [USBHID] The interval which mice are to be polled at.
3066
3067    usb-storage.delay_use=
3068            [UMS] The delay in seconds before a new device is
3069            scanned for Logical Units (default 5).
3070
3071    usb-storage.quirks=
3072            [UMS] A list of quirks entries to supplement or
3073            override the built-in unusual_devs list. List
3074            entries are separated by commas. Each entry has
3075            the form VID:PID:Flags where VID and PID are Vendor
3076            and Product ID values (4-digit hex numbers) and
3077            Flags is a set of characters, each corresponding
3078            to a common usb-storage quirk flag as follows:
3079                a = SANE_SENSE (collect more than 18 bytes
3080                    of sense data);
3081                b = BAD_SENSE (don't collect more than 18
3082                    bytes of sense data);
3083                c = FIX_CAPACITY (decrease the reported
3084                    device capacity by one sector);
3085                d = NO_READ_DISC_INFO (don't use
3086                    READ_DISC_INFO command);
3087                e = NO_READ_CAPACITY_16 (don't use
3088                    READ_CAPACITY_16 command);
3089                h = CAPACITY_HEURISTICS (decrease the
3090                    reported device capacity by one
3091                    sector if the number is odd);
3092                i = IGNORE_DEVICE (don't bind to this
3093                    device);
3094                l = NOT_LOCKABLE (don't try to lock and
3095                    unlock ejectable media);
3096                m = MAX_SECTORS_64 (don't transfer more
3097                    than 64 sectors = 32 KB at a time);
3098                n = INITIAL_READ10 (force a retry of the
3099                    initial READ(10) command);
3100                o = CAPACITY_OK (accept the capacity
3101                    reported by the device);
3102                p = WRITE_CACHE (the device cache is ON
3103                    by default);
3104                r = IGNORE_RESIDUE (the device reports
3105                    bogus residue values);
3106                s = SINGLE_LUN (the device has only one
3107                    Logical Unit);
3108                w = NO_WP_DETECT (don't test whether the
3109                    medium is write-protected).
3110            Example: quirks=0419:aaf5:rl,0421:0433:rc
3111
3112    user_debug= [KNL,ARM]
3113            Format: <int>
3114            See arch/arm/Kconfig.debug help text.
3115                 1 - undefined instruction events
3116                 2 - system calls
3117                 4 - invalid data aborts
3118                 8 - SIGSEGV faults
3119                16 - SIGBUS faults
3120            Example: user_debug=31
3121
3122    userpte=
3123            [X86] Flags controlling user PTE allocations.
3124
3125                nohigh = do not allocate PTE pages in
3126                    HIGHMEM regardless of setting
3127                    of CONFIG_HIGHPTE.
3128
3129    vdso= [X86,SH]
3130            vdso=2: enable compat VDSO (default with COMPAT_VDSO)
3131            vdso=1: enable VDSO (default)
3132            vdso=0: disable VDSO mapping
3133
3134    vdso32= [X86]
3135            vdso32=2: enable compat VDSO (default with COMPAT_VDSO)
3136            vdso32=1: enable 32-bit VDSO (default)
3137            vdso32=0: disable 32-bit VDSO mapping
3138
3139    vector= [IA-64,SMP]
3140            vector=percpu: enable percpu vector domain
3141
3142    video= [FB] Frame buffer configuration
3143            See Documentation/fb/modedb.txt.
3144
3145    virtio_mmio.device=
3146            [VMMIO] Memory mapped virtio (platform) device.
3147
3148                <size>@<baseaddr>:<irq>[:<id>]
3149            where:
3150                <size> := size (can use standard suffixes
3151                        like K, M and G)
3152                <baseaddr> := physical base address
3153                <irq> := interrupt number (as passed to
3154                        request_irq())
3155                <id> := (optional) platform device id
3156            example:
3157                virtio_mmio.device=1K@0x100b0000:48:7
3158
3159            Can be used multiple times for multiple devices.
3160
3161    vga= [BOOT,X86-32] Select a particular video mode
3162            See Documentation/x86/boot.txt and
3163            Documentation/svga.txt.
3164            Use vga=ask for menu.
3165            This is actually a boot loader parameter; the value is
3166            passed to the kernel using a special protocol.
3167
3168    vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
3169            size of <nn>. This can be used to increase the
3170            minimum size (128MB on x86). It can also be used to
3171            decrease the size and leave more room for directly
3172            mapped kernel RAM.
3173
3174    vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3175            Format: <command>
3176
3177    vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3178            Format: <command>
3179
3180    vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3181            Format: <command>
3182
3183    vsyscall= [X86-64]
3184            Controls the behavior of vsyscalls (i.e. calls to
3185            fixed addresses of 0xffffffffff600x00 from legacy
3186            code). Most statically-linked binaries and older
3187            versions of glibc use these calls. Because these
3188            functions are at fixed addresses, they make nice
3189            targets for exploits that can control RIP.
3190
3191            emulate [default] Vsyscalls turn into traps and are
3192                        emulated reasonably safely.
3193
3194            native Vsyscalls are native syscall instructions.
3195                        This is a little bit faster than trapping
3196                        and makes a few dynamic recompilers work
3197                        better than they would in emulation mode.
3198                        It also makes exploits much easier to write.
3199
3200            none Vsyscalls don't work at all. This makes
3201                        them quite hard to use for exploits but
3202                        might break your system.
3203
3204    vt.cur_default= [VT] Default cursor shape.
3205            Format: 0xCCBBAA, where AA, BB, and CC are the same as
3206            the parameters of the <Esc>[?A;B;Cc escape sequence;
3207            see VGA-softcursor.txt. Default: 2 = underline.
3208
3209    vt.default_blu= [VT]
3210            Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3211            Change the default blue palette of the console.
3212            This is a 16-member array composed of values
3213            ranging from 0-255.
3214
3215    vt.default_grn= [VT]
3216            Format: <green0>,<green1>,<green2>,...,<green15>
3217            Change the default green palette of the console.
3218            This is a 16-member array composed of values
3219            ranging from 0-255.
3220
3221    vt.default_red= [VT]
3222            Format: <red0>,<red1>,<red2>,...,<red15>
3223            Change the default red palette of the console.
3224            This is a 16-member array composed of values
3225            ranging from 0-255.
3226
3227    vt.default_utf8=
3228            [VT]
3229            Format=<0|1>
3230            Set system-wide default UTF-8 mode for all tty's.
3231            Default is 1, i.e. UTF-8 mode is enabled for all
3232            newly opened terminals.
3233
3234    vt.global_cursor_default=
3235            [VT]
3236            Format=<-1|0|1>
3237            Set system-wide default for whether a cursor
3238            is shown on new VTs. Default is -1,
3239            i.e. cursors will be created by default unless
3240            overridden by individual drivers. 0 will hide
3241            cursors, 1 will display them.
3242
3243    watchdog timers [HW,WDT] For information on watchdog timers,
3244            see Documentation/watchdog/watchdog-parameters.txt
3245            or other driver-specific files in the
3246            Documentation/watchdog/ directory.
3247
3248    x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3249            default x2apic cluster mode on platforms
3250            supporting x2apic.
3251
3252    x86_mrst_timer= [X86-32,APBT]
3253            Choose timer option for x86 Moorestown MID platform.
3254            Two valid options are apbt timer only and lapic timer
3255            plus one apbt timer for broadcast timer.
3256            x86_mrst_timer=apbt_only | lapic_and_apbt
3257
3258    xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks.
3259    xd_geo= See header of drivers/block/xd.c.
3260
3261    xen_emul_unplug= [HW,X86,XEN]
3262            Unplug Xen emulated devices
3263            Format: [unplug0,][unplug1]
3264            ide-disks -- unplug primary master IDE devices
3265            aux-ide-disks -- unplug non-primary-master IDE devices
3266            nics -- unplug network devices
3267            all -- unplug all emulated devices (NICs and IDE disks)
3268            unnecessary -- unplugging emulated devices is
3269                unnecessary even if the host did not respond to
3270                the unplug protocol
3271            never -- do not unplug even if version check succeeds
3272
3273    xirc2ps_cs= [NET,PCMCIA]
3274            Format:
3275            <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
3276
3277______________________________________________________________________
3278
3279TODO:
3280
3281    Add more DRM drivers.
3282

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