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

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