1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/driver-api/clk.rst.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
645 [KNL] Change console messages format
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
728 [KNL] Disable crypto self-tests
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
752 [KNL] Enable printing [hashed] pointers early in the
753 boot sequence. If enabled, we use a weak hash instead
754 of siphash to hash pointers. Use this option if you are
755 seeing instances of '(___ptrval___)') and need to see a
756 value (hashed pointer) instead. Cryptographically
757 insecure, please do not use on production kernels.
760 [KNL] verbose self-tests
762 Print debugging info while doing the locking API
764 We default to 0 (no extra messages), setting it to
765 1 will print _a lot_ more information - normally
766 only useful to kernel developers.
768 debug_objects [KNL] Enable object debugging
771 [KNL] Disable object debugging
773 debug_guardpage_minorder=
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter allows control of the order of pages that will
776 be intentionally kept free (and hence protected) by the
777 buddy allocator. Bigger value increase the probability
778 of catching random memory corruption, but reduce the
779 amount of memory for normal system use. The maximum
780 possible value is MAX_ORDER/2. Setting this parameter
781 to 1 or 2 should be enough to identify most random
782 memory corruption problems caused by bugs in kernel or
783 driver code when a CPU writes to (or reads from) a
784 random memory location. Note that there exists a class
785 of memory corruptions problems caused by buggy H/W or
786 F/W or by drivers badly programing DMA (basically when
787 memory is written at bus level and the CPU MMU is
788 bypassed) which are not detectable by
789 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
790 tracking down these problems.
793 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
794 parameter enables the feature at boot time. In
795 default, it is disabled. We can avoid allocating huge
796 chunk of memory for debug pagealloc if we don't enable
797 it at boot time and the system will work mostly same
798 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
799 on: enable the feature
801 debugpat [X86] Enable PAT debugging
803 decnet.addr= [HW,NET]
804 Format: <area>[,<node>]
805 See also Documentation/networking/decnet.txt.
808 [same as hugepagesz=] The size of the default
809 HugeTLB page size. This is the size represented by
810 the legacy /proc/ hugepages APIs, used for SHM, and
811 default size when mounting hugetlbfs filesystems.
812 Defaults to the default architecture's huge page size
815 deferred_probe_timeout=
816 [KNL] Debugging option to set a timeout in seconds for
817 deferred probe to give up waiting on dependencies to
818 probe. Only specific dependencies (subsystems or
819 drivers) that have opted in will be ignored. A timeout of 0
820 will timeout at the end of initcalls. This option will also
821 dump out devices still on the deferred probe list after
825 Set number of hash buckets for dentry cache.
827 disable_1tb_segments [PPC]
828 Disables the use of 1TB hash page table segments. This
829 causes the kernel to fall back to 256MB segments which
830 can be useful when debugging issues that require an SLB
834 See Documentation/networking/ipv6.txt.
837 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
838 hardening is enabled for this boot. Hardened
839 usercopy checking is used to protect the kernel
840 from reading or writing beyond known memory
841 allocation boundaries as a proactive defense
842 against bounds-checking flaws in the kernel's
843 copy_to_user()/copy_from_user() interface.
844 on Perform hardened usercopy checks (default).
845 off Disable hardened usercopy checks.
848 Disable RADIX MMU mode on POWER9
850 disable_cpu_apicid= [X86,APIC,SMP]
852 The number of initial APIC ID for the
853 corresponding CPU to be disabled at boot,
854 mostly used for the kdump 2nd kernel to
855 disable BSP to wake up multiple CPUs without
856 causing system reset or hang due to sending
859 disable_counter_freezing [HW]
860 Disable Intel PMU counter freezing feature.
861 The feature only exists starting from
862 Arch Perfmon v4 (Skylake and newer).
864 disable_ddw [PPC/PSERIES]
865 Disable Dynamic DMA Window support. Use this if
866 to workaround buggy firmware.
869 See Documentation/networking/ipv6.txt.
871 disable_mtrr_cleanup [X86]
872 The kernel tries to adjust MTRR layout from continuous
873 to discrete, to make X server driver able to add WB
874 entry later. This parameter disables that.
876 disable_mtrr_trim [X86, Intel and AMD only]
877 By default the kernel will trim any uncacheable
878 memory out of your available memory pool based on
879 MTRR settings. This parameter disables that behavior,
880 possibly causing your machine to run very slowly.
882 disable_timer_pin_1 [X86]
883 Disable PIN 1 of APIC timer
884 Can be useful to work around chipset bugs.
886 dis_ucode_ldr [X86] Disable the microcode loader.
888 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
889 this option disables the debugging code at boot.
891 dma_debug_entries=<number>
892 This option allows to tune the number of preallocated
893 entries for DMA-API debugging code. One entry is
894 required per DMA-API allocation. Use this if the
895 DMA-API debugging code disables itself because the
896 architectural default is too low.
898 dma_debug_driver=<driver_name>
899 With this option the DMA-API debugging driver
900 filter feature can be enabled at boot time. Just
901 pass the driver to filter for as the parameter.
902 The filter can be disabled or changed to another
903 driver later using sysfs.
905 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
906 Broken monitors, graphic adapters, KVMs and EDIDless
907 panels may send no or incorrect EDID data sets.
908 This parameter allows to specify an EDID data sets
909 in the /lib/firmware directory that are used instead.
910 Generic built-in EDID data sets are used, if one of
911 edid/1024x768.bin, edid/1280x1024.bin,
912 edid/1680x1050.bin, or edid/1920x1080.bin is given
913 and no file with the same name exists. Details and
914 instructions how to build your own EDID data are
915 available in Documentation/EDID/HOWTO.txt. An EDID
916 data set will only be used for a particular connector,
917 if its name and a colon are prepended to the EDID
918 name. Each connector may use a unique EDID data
919 set by separating the files with a comma. An EDID
920 data set with no connector name will be used for
921 any connectors not explicitly specified.
926 Format: {"off" | "known"}
927 Control how the dt_cpu_ftrs device-tree binding is
928 used for CPU feature discovery and setup (if it
930 off: Do not use it, fall back to legacy cpu table.
931 known: Do not pass through unknown features to guests
932 or userspace, only those that the kernel is aware of.
934 dump_apple_properties [X86]
935 Dump name and content of EFI device properties on
936 x86 Macs. Useful for driver authors to determine
937 what data is available or for reverse-engineering.
939 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
940 module.dyndbg[="val"]
941 Enable debug messages at boot time. See
942 Documentation/admin-guide/dynamic-debug-howto.rst
945 nompx [X86] Disables Intel Memory Protection Extensions.
946 See Documentation/x86/intel_mpx.txt for more
947 information about the feature.
949 nopku [X86] Disable Memory Protection Keys CPU feature found
952 module.async_probe [KNL]
953 Enable asynchronous probe on this module.
955 early_ioremap_debug [KNL]
956 Enable debug messages in early_ioremap support. This
957 is useful for tracking down temporary early mappings
958 which are not unmapped.
960 earlycon= [KNL] Output early console device and options.
962 [ARM64] The early console is determined by the
963 stdout-path property in device tree's chosen node,
964 or determined by the ACPI SPCR table.
966 [X86] When used with no options the early console is
967 determined by the ACPI SPCR table.
969 cdns,<addr>[,options]
970 Start an early, polled-mode console on a Cadence
971 (xuartps) serial port at the specified address. Only
972 supported option is baud rate. If baud rate is not
973 specified, the serial port must already be setup and
976 uart[8250],io,<addr>[,options]
977 uart[8250],mmio,<addr>[,options]
978 uart[8250],mmio32,<addr>[,options]
979 uart[8250],mmio32be,<addr>[,options]
980 uart[8250],0x<addr>[,options]
981 Start an early, polled-mode console on the 8250/16550
982 UART at the specified I/O port or MMIO address.
983 MMIO inter-register address stride is either 8-bit
984 (mmio) or 32-bit (mmio32 or mmio32be).
985 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
986 to be equivalent to 'mmio'. 'options' are specified
987 in the same format described for "console=ttyS<n>"; if
988 unspecified, the h/w is not initialized.
992 Start an early, polled-mode console on a pl011 serial
993 port at the specified address. The pl011 serial port
994 must already be setup and configured. Options are not
995 yet supported. If 'mmio32' is specified, then only
996 the driver will use only 32-bit accessors to read/write
997 the device registers.
1000 Start an early, polled-mode console on a meson serial
1001 port at the specified address. The serial port must
1002 already be setup and configured. Options are not yet
1006 Start an early, polled-mode console on an msm serial
1007 port at the specified address. The serial port
1008 must already be setup and configured. Options are not
1011 msm_serial_dm,<addr>
1012 Start an early, polled-mode console on an msm serial
1013 dm port at the specified address. The serial port
1014 must already be setup and configured. Options are not
1018 Start an early, polled-mode console on a serial port
1019 of an Actions Semi SoC, such as S500 or S900, at the
1020 specified address. The serial port must already be
1021 setup and configured. Options are not yet supported.
1023 smh Use ARM semihosting calls for early console.
1031 Use early console provided by serial driver available
1032 on Samsung SoCs, requires selecting proper type and
1033 a correct base address of the selected UART port. The
1034 serial port must already be setup and configured.
1035 Options are not yet supported.
1038 Start an early, polled-mode console on a lantiq serial
1039 (lqasc) port at the specified address. The serial port
1040 must already be setup and configured. Options are not
1045 Use early console provided by Freescale LP UART driver
1046 found on Freescale Vybrid and QorIQ LS1021A processors.
1047 A valid base address must be provided, and the serial
1048 port must already be setup and configured.
1051 Start an early, polled-mode console on the
1052 Armada 3700 serial port at the specified
1053 address. The serial port must already be setup
1054 and configured. Options are not yet supported.
1057 Start an early, polled-mode console on a Qualcomm
1058 Generic Interface (GENI) based serial port at the
1059 specified address. The serial port must already be
1060 setup and configured. Options are not yet supported.
1062 earlyprintk= [X86,SH,ARM,M68k,S390]
1067 earlyprintk=serial[,ttySn[,baudrate]]
1068 earlyprintk=serial[,0x...[,baudrate]]
1069 earlyprintk=ttySn[,baudrate]
1070 earlyprintk=dbgp[debugController#]
1071 earlyprintk=pciserial,bus:device.function[,baudrate]
1072 earlyprintk=xdbc[xhciController#]
1074 earlyprintk is useful when the kernel crashes before
1075 the normal console is initialized. It is not enabled by
1076 default because it has some cosmetic problems.
1078 Append ",keep" to not disable it when the real console
1081 Only one of vga, efi, serial, or usb debug port can
1084 Currently only ttyS0 and ttyS1 may be specified by
1085 name. Other I/O ports may be explicitly specified
1086 on some architectures (x86 and arm at least) by
1087 replacing ttySn with an I/O port address, like this:
1088 earlyprintk=serial,0x1008,115200
1089 You can find the port for a given device in
1090 /proc/tty/driver/serial:
1091 2: uart:ST16650V2 port:00001008 irq:18 ...
1093 Interaction with the standard serial driver is not
1096 The VGA and EFI output is eventually overwritten by
1099 The xen output can only be used by Xen PV guests.
1101 The sclp output can only be used on s390.
1103 edac_report= [HW,EDAC] Control how to report EDAC event
1104 Format: {"on" | "off" | "force"}
1105 on: enable EDAC to report H/W event. May be overridden
1106 by other higher priority error reporting module.
1107 off: disable H/W event reporting through EDAC.
1108 force: enforce the use of EDAC to report H/W event.
1111 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1114 This is designed to be used in conjunction with
1115 the boot argument: earlyprintk=vga
1118 Format: {"off" | "on" | "skip[mbr]"}
1121 Format: { "old_map", "nochunk", "noruntime", "debug" }
1122 old_map [X86-64]: switch to the old ioremap-based EFI
1123 runtime services mapping. 32-bit still uses this one by
1125 nochunk: disable reading files in "chunks" in the EFI
1126 boot stub, as chunking can cause problems with some
1127 firmware implementations.
1128 noruntime : disable EFI runtime services support
1129 debug: enable misc debug output
1131 efi_no_storage_paranoia [EFI; X86]
1132 Using this parameter you can use more than 50% of
1133 your efi variable storage. Use this parameter only if
1134 you are really sure that your UEFI does sane gc and
1135 fulfills the spec otherwise your board may brick.
1137 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1138 Add arbitrary attribute to specific memory range by
1139 updating original EFI memory map.
1140 Region of memory which aa attribute is added to is
1142 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1143 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1144 attribute is added to range 0x100000000-0x180000000 and
1145 0x10a0000000-0x1120000000.
1147 Using this parameter you can do debugging of EFI memmap
1148 related feature. For example, you can do debugging of
1149 Address Range Mirroring feature even if your box
1152 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1153 that is to be dynamically loaded by Linux. If there are
1154 multiple variables with the same name but with different
1155 vendor GUIDs, all of them will be loaded. See
1156 Documentation/acpi/ssdt-overlays.txt for details.
1159 eisa_irq_edge= [PARISC,HW]
1160 See header of drivers/parisc/eisa.c.
1163 See comment before function elanfreq_setup() in
1164 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1167 Format: {"cfq" | "deadline" | "noop"}
1168 See Documentation/block/cfq-iosched.txt and
1169 Documentation/block/deadline-iosched.txt for details.
1171 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1172 Specifies physical address of start of kernel core
1173 image elf header and optionally the size. Generally
1174 kexec loader will pass this option to capture kernel.
1175 See Documentation/kdump/kdump.txt for details.
1177 enable_mtrr_cleanup [X86]
1178 The kernel tries to adjust MTRR layout from continuous
1179 to discrete, to make X server driver able to add WB
1180 entry later. This parameter enables that.
1182 enable_timer_pin_1 [X86]
1183 Enable PIN 1 of APIC timer
1184 Can be useful to work around chipset bugs
1185 (in particular on some ATI chipsets).
1186 The kernel tries to set a reasonable default.
1188 enforcing [SELINUX] Set initial enforcing status.
1190 See security/selinux/Kconfig help text.
1191 0 -- permissive (log only, no denials).
1192 1 -- enforcing (deny and log).
1194 Value can be changed at runtime via /selinux/enforce.
1197 Disable Error Record Serialization Table (ERST)
1200 ether= [HW,NET] Ethernet cards parameters
1201 This option is obsoleted by the "netdev=" option, which
1202 has equivalent usage. See its documentation for details.
1206 Permit 'security.evm' to be updated regardless of
1207 current integrity status.
1211 fail_make_request=[KNL]
1212 General fault injection mechanism.
1213 Format: <interval>,<probability>,<space>,<times>
1214 See also Documentation/fault-injection/.
1217 See Documentation/blockdev/floppy.txt.
1219 force_pal_cache_flush
1220 [IA-64] Avoid check_sal_cache_flush which may hang on
1221 buggy SAL_CACHE_FLUSH implementations. Using this
1222 parameter will force ia64_sal_cache_flush to call
1223 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1226 Forcefully enable Physical Address Extension (PAE).
1227 Many Pentium M systems disable PAE but may have a
1228 functionally usable PAE implementation.
1229 Warning: use of this parameter will taint the kernel
1230 and may cause unknown problems.
1233 [FTRACE] will set and start the specified tracer
1234 as early as possible in order to facilitate early
1237 ftrace_dump_on_oops[=orig_cpu]
1238 [FTRACE] will dump the trace buffers on oops.
1239 If no parameter is passed, ftrace will dump
1240 buffers of all CPUs, but if you pass orig_cpu, it will
1241 dump only the buffer of the CPU that triggered the
1244 ftrace_filter=[function-list]
1245 [FTRACE] Limit the functions traced by the function
1246 tracer at boot up. function-list is a comma separated
1247 list of functions. This list can be changed at run
1248 time by the set_ftrace_filter file in the debugfs
1251 ftrace_notrace=[function-list]
1252 [FTRACE] Do not trace the functions specified in
1253 function-list. This list can be changed at run time
1254 by the set_ftrace_notrace file in the debugfs
1257 ftrace_graph_filter=[function-list]
1258 [FTRACE] Limit the top level callers functions traced
1259 by the function graph tracer at boot up.
1260 function-list is a comma separated list of functions
1261 that can be changed at run time by the
1262 set_graph_function file in the debugfs tracing directory.
1264 ftrace_graph_notrace=[function-list]
1265 [FTRACE] Do not trace from the functions specified in
1266 function-list. This list is a comma separated list of
1267 functions that can be changed at run time by the
1268 set_graph_notrace file in the debugfs tracing directory.
1270 ftrace_graph_max_depth=<uint>
1271 [FTRACE] Used with the function graph tracer. This is
1272 the max depth it will trace into a function. This value
1273 can be changed at run time by the max_graph_depth file
1274 in the tracefs tracing directory. default: 0 (no limit)
1277 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1278 support via parallel port (up to 5 devices per port)
1279 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1280 See also Documentation/input/devices/joystick-parport.rst
1284 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1288 gcov_persist= [GCOV] When non-zero (default), profiling data for
1289 kernel modules is saved and remains accessible via
1290 debugfs, even when the module is unloaded/reloaded.
1291 When zero, profiling data is discarded and associated
1292 debugfs files are removed at module unload time.
1294 goldfish [X86] Enable the goldfish android emulator platform.
1295 Don't use this when you are not running on the
1298 gpt [EFI] Forces disk with valid GPT signature but
1299 invalid Protective MBR to be treated as GPT. If the
1300 primary GPT is corrupted, it enables the backup/alternate
1301 GPT to be used instead.
1303 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1304 the "Enable 0" bit of the configuration register.
1307 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1308 the "Enable 0" bit of the configuration register.
1311 grcan.select= [HW] Select which physical interface to use.
1314 grcan.txsize= [HW] Sets the size of the tx buffer.
1315 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1317 grcan.rxsize= [HW] Sets the size of the rx buffer.
1318 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1321 gpio-mockup.gpio_mockup_ranges
1322 [HW] Sets the ranges of gpiochip of for this device.
1323 Format: <start1>,<end1>,<start2>,<end2>...
1325 hardlockup_all_cpu_backtrace=
1326 [KNL] Should the hard-lockup detector generate
1327 backtraces on all cpus.
1330 hashdist= [KNL,NUMA] Large hashes allocated during boot
1331 are distributed across NUMA nodes. Defaults on
1332 for 64-bit NUMA, off otherwise.
1333 Format: 0 | 1 (for off | on)
1335 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1337 hd= [EIDE] (E)IDE hard drive subsystem geometry
1338 Format: <cyl>,<head>,<sect>
1341 Disable Hardware Error Source Table (HEST) support;
1342 corresponding firmware-first mode error processing
1343 logic will be disabled.
1345 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1346 size of <nn>. This works even on boxes that have no
1347 highmem otherwise. This also works to reduce highmem
1348 size on bigger boxes.
1350 highres= [KNL] Enable/disable high resolution timer mode.
1351 Valid parameters: "on", "off"
1355 See Documentation/isdn/README.HiSax.
1359 hpet= [X86-32,HPET] option to control HPET usage
1360 Format: { enable (default) | disable | force |
1362 disable: disable HPET and use PIT instead
1363 force: allow force enabled of undocumented chips (ICH4,
1365 verbose: show contents of HPET registers during setup
1367 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1368 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1370 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1371 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1372 On x86-64 and powerpc, this option can be specified
1373 multiple times interleaved with hugepages= to reserve
1374 huge pages of different sizes. Valid pages sizes on
1375 x86-64 are 2M (when the CPU supports "pse") and 1G
1376 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1379 [KNL] Should the hung task detector generate panics.
1382 A nonzero value instructs the kernel to panic when a
1383 hung task is detected. The default value is controlled
1384 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1385 option. The value selected by this boot parameter can
1386 be changed later by the kernel.hung_task_panic sysctl.
1388 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1389 terminal devices. Valid values: 0..8
1390 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1391 If specified, z/VM IUCV HVC accepts connections
1392 from listed z/VM user IDs only.
1394 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1395 which allow the hypervisor to 'idle' the
1396 guest on lock contention.
1399 Do not unregister boot console at start. This is only
1400 useful for debugging when something happens in the window
1401 between unregistering the boot console and initializing
1404 i2c_bus= [HW] Override the default board specific I2C bus speed
1405 or register an additional I2C bus that is not
1406 registered from board initialization code.
1410 i8042.debug [HW] Toggle i8042 debug mode
1411 i8042.unmask_kbd_data
1412 [HW] Enable printing of interrupt data from the KBD port
1413 (disabled by default, and as a pre-condition
1414 requires that i8042.debug=1 be enabled)
1415 i8042.direct [HW] Put keyboard port into non-translated mode
1416 i8042.dumbkbd [HW] Pretend that controller can only read data from
1417 keyboard and cannot control its state
1418 (Don't attempt to blink the leds)
1419 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1420 i8042.nokbd [HW] Don't check/create keyboard port
1421 i8042.noloop [HW] Disable the AUX Loopback command while probing
1423 i8042.nomux [HW] Don't check presence of an active multiplexing
1425 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1427 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1428 i8042.reset [HW] Reset the controller during init, cleanup and
1429 suspend-to-ram transitions, only during s2r
1430 transitions, or never reset
1431 Format: { 1 | Y | y | 0 | N | n }
1432 1, Y, y: always reset controller
1433 0, N, n: don't ever reset controller
1434 Default: only on s2r transitions on x86; most other
1435 architectures force reset to be always executed
1436 i8042.unlock [HW] Unlock (ignore) the keylock
1437 i8042.kbdreset [HW] Reset device connected to KBD port
1441 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1442 indicates that the driver is running on unsupported
1444 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1445 does not match list of supported models.
1447 [HW] Report power status in /proc/i8k
1448 (disabled by default)
1449 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1452 i915.invert_brightness=
1453 [DRM] Invert the sense of the variable that is used to
1454 set the brightness of the panel backlight. Normally a
1455 brightness value of 0 indicates backlight switched off,
1456 and the maximum of the brightness value sets the backlight
1457 to maximum brightness. If this parameter is set to 0
1458 (default) and the machine requires it, or this parameter
1459 is set to 1, a brightness value of 0 sets the backlight
1460 to maximum brightness, and the maximum of the brightness
1461 value switches the backlight off.
1462 -1 -- never invert brightness
1463 0 -- machine default
1464 1 -- force brightness inversion
1467 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1469 ide-core.nodma= [HW] (E)IDE subsystem
1470 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1471 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1472 .cdrom .chs .ignore_cable are additional options
1473 See Documentation/ide/ide.txt.
1475 ide-generic.probe-mask= [HW] (E)IDE subsystem
1477 Probe mask for legacy ISA IDE ports. Depending on
1478 platform up to 6 ports are supported, enabled by
1479 setting corresponding bits in the mask to 1. The
1480 default value is 0x0, which has a special meaning.
1481 On systems that have PCI, it triggers scanning the
1482 PCI bus for the first and the second port, which
1483 are then probed. On systems without PCI the value
1484 of 0x0 enables probing the two first ports as if it
1487 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1488 Claim all unknown PCI IDE storage controllers.
1491 Format: idle=poll, idle=halt, idle=nomwait
1492 Poll forces a polling idle loop that can slightly
1493 improve the performance of waking up a idle CPU, but
1494 will use a lot of power and make the system run hot.
1496 idle=halt: Halt is forced to be used for CPU idle.
1497 In such case C2/C3 won't be used again.
1498 idle=nomwait: Disable mwait for CPU C-states
1500 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1501 Format: { strict | legacy | 2008 | relaxed }
1504 Choose which programs will be accepted for execution
1505 based on the IEEE 754 NaN encoding(s) supported by
1506 the FPU and the NaN encoding requested with the value
1507 of an ELF file header flag individually set by each
1508 binary. Hardware implementations are permitted to
1509 support either or both of the legacy and the 2008 NaN
1512 Available settings are as follows:
1513 strict accept binaries that request a NaN encoding
1514 supported by the FPU
1515 legacy only accept legacy-NaN binaries, if supported
1517 2008 only accept 2008-NaN binaries, if supported
1519 relaxed accept any binaries regardless of whether
1520 supported by the FPU
1522 The FPU emulator is always able to support both NaN
1523 encodings, so if no FPU hardware is present or it has
1524 been disabled with 'nofpu', then the settings of
1525 'legacy' and '2008' strap the emulator accordingly,
1526 'relaxed' straps the emulator for both legacy-NaN and
1527 2008-NaN, whereas 'strict' enables legacy-NaN only on
1528 legacy processors and both NaN encodings on MIPS32 or
1531 The setting for ABS.fmt/NEG.fmt instruction execution
1532 mode generally follows that for the NaN encoding,
1533 except where unsupported by hardware.
1535 ignore_loglevel [KNL]
1536 Ignore loglevel setting - this will print /all/
1537 kernel messages to the console. Useful for debugging.
1538 We also add it as printk module parameter, so users
1539 could change it dynamically, usually by
1540 /sys/module/printk/parameters/ignore_loglevel.
1543 Ignore RLIMIT_DATA setting for data mappings,
1544 print warning at first misuse. Can be changed via
1545 /sys/module/kernel/parameters/ignore_rlimit_data.
1547 ihash_entries= [KNL]
1548 Set number of hash buckets for inode cache.
1550 ima_appraise= [IMA] appraise integrity measurements
1551 Format: { "off" | "enforce" | "fix" | "log" }
1554 ima_appraise_tcb [IMA]
1555 The builtin appraise policy appraises all files
1558 ima_canonical_fmt [IMA]
1559 Use the canonical format for the binary runtime
1560 measurements, instead of host native format.
1563 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1567 The list of supported hash algorithms is defined
1568 in crypto/hash_info.h.
1571 The builtin policies to load during IMA setup.
1572 Format: "tcb | appraise_tcb | secure_boot |
1575 The "tcb" policy measures all programs exec'd, files
1576 mmap'd for exec, and all files opened with the read
1577 mode bit set by either the effective uid (euid=0) or
1580 The "appraise_tcb" policy appraises the integrity of
1581 all files owned by root. (This is the equivalent
1582 of ima_appraise_tcb.)
1584 The "secure_boot" policy appraises the integrity
1585 of files (eg. kexec kernel image, kernel modules,
1586 firmware, policy, etc) based on file signatures.
1588 The "fail_securely" policy forces file signature
1589 verification failure also on privileged mounted
1590 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1593 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1594 Load a policy which meets the needs of the Trusted
1595 Computing Base. This means IMA will measure all
1596 programs exec'd, files mmap'd for exec, and all files
1597 opened for read by uid=0.
1600 Select one of defined IMA measurements template formats.
1601 Formats: { "ima" | "ima-ng" | "ima-sig" }
1605 [IMA] Define a custom template format.
1606 Format: { "field1|...|fieldN" }
1608 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1609 Format: <min_file_size>
1610 Set the minimal file size for using asynchronous hash.
1611 If left unspecified, ahash usage is disabled.
1613 ahash performance varies for different data sizes on
1614 different crypto accelerators. This option can be used
1615 to achieve the best performance for a particular HW.
1617 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1619 Set hashing buffer size. Default: 4k.
1621 ahash performance varies for different chunk sizes on
1622 different crypto accelerators. This option can be used
1623 to achieve best performance for particular HW.
1627 Run specified binary instead of /sbin/init as init
1630 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1631 for working out where the kernel is dying during
1634 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1635 initcall functions. Useful for debugging built-in
1636 modules and initcalls.
1638 initrd= [BOOT] Specify the location of the initial ramdisk
1640 init_pkru= [x86] Specify the default memory protection keys rights
1641 register contents for all processes. 0x55555554 by
1642 default (disallow access to all but pkey 0). Can
1643 override in debugfs after boot.
1645 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1648 int_pln_enable [x86] Enable power limit notification interrupt
1650 integrity_audit=[IMA]
1651 Format: { "0" | "1" }
1652 0 -- basic integrity auditing messages. (Default)
1653 1 -- additional integrity auditing messages.
1655 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1657 Enable intel iommu driver.
1659 Disable intel iommu driver.
1660 igfx_off [Default Off]
1661 By default, gfx is mapped as normal device. If a gfx
1662 device has a dedicated DMAR unit, the DMAR unit is
1663 bypassed by not enabling DMAR with this option. In
1664 this case, gfx device will use physical address for
1667 With this option iommu will not optimize to look
1668 for io virtual address below 32-bit forcing dual
1669 address cycle on pci bus for cards supporting greater
1670 than 32-bit addressing. The default is to look
1671 for translation below 32-bit and if not available
1672 then look in the higher range.
1673 strict [Default Off]
1674 With this option on every unmap_single operation will
1675 result in a hardware IOTLB flush operation as opposed
1676 to batching them for performance.
1677 sp_off [Default Off]
1678 By default, super page will be supported if Intel IOMMU
1679 has the capability. With this option, super page will
1681 ecs_off [Default Off]
1682 By default, extended context tables will be supported if
1683 the hardware advertises that it has support both for the
1684 extended tables themselves, and also PASID support. With
1685 this option set, extended tables will not be used even
1686 on hardware which claims to support them.
1687 tboot_noforce [Default Off]
1688 Do not force the Intel IOMMU enabled under tboot.
1689 By default, tboot will force Intel IOMMU on, which
1690 could harm performance of some high-throughput
1691 devices like 40GBit network cards, even if identity
1693 Note that using this option lowers the security
1694 provided by tboot because it makes the system
1695 vulnerable to DMA attacks.
1697 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1698 0 disables intel_idle and fall back on acpi_idle.
1699 1 to 9 specify maximum depth of C-state.
1703 Do not enable intel_pstate as the default
1704 scaling driver for the supported processors
1706 Use intel_pstate as a scaling driver, but configure it
1707 to work with generic cpufreq governors (instead of
1708 enabling its internal governor). This mode cannot be
1709 used along with the hardware-managed P-states (HWP)
1712 Enable intel_pstate on systems that prohibit it by default
1713 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1714 instead of acpi-cpufreq may disable platform features, such
1715 as thermal controls and power capping, that rely on ACPI
1716 P-States information being indicated to OSPM and therefore
1717 should be used with caution. This option does not work with
1718 processors that aren't supported by the intel_pstate driver
1719 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1721 Do not enable hardware P state control (HWP)
1724 Only load intel_pstate on systems which support
1725 hardware P state control (HWP) if available.
1727 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1728 Description Table, specifies preferred power management
1729 profile as "Enterprise Server" or "Performance Server",
1730 then this feature is turned on by default.
1732 Allow per-logical-CPU P-State performance control limits using
1733 cpufreq sysfs interface
1735 intremap= [X86-64, Intel-IOMMU]
1736 on enable Interrupt Remapping (default)
1737 off disable Interrupt Remapping
1738 nosid disable Source ID checking
1740 BIOS x2APIC opt-out request will be ignored
1741 nopost disable Interrupt Posting
1743 iomem= Disable strict checking of access to MMIO memory
1744 strict regions from userspace.
1759 nobypass [PPC/POWERNV]
1760 Disable IOMMU bypass, using IOMMU for PCI devices.
1762 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1763 Format: { "0" | "1" }
1765 Request that DMA unmap operations use deferred
1766 invalidation of hardware TLBs, for increased
1767 throughput at the cost of reduced device isolation.
1768 Will fall back to strict mode if not supported by
1769 the relevant IOMMU driver.
1770 1 - Strict mode (default).
1771 DMA unmap operations invalidate IOMMU hardware TLBs
1775 [ARM64] Configure DMA to bypass the IOMMU by default.
1776 Format: { "0" | "1" }
1777 0 - Use IOMMU translation for DMA.
1778 1 - Bypass the IOMMU for DMA.
1779 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1781 io7= [HW] IO7 for Marvel based alpha systems
1782 See comment before marvel_specify_io7 in
1783 arch/alpha/kernel/core_marvel.c.
1785 io_delay= [X86] I/O delay method
1787 Standard port 0x80 based delay
1789 Alternate port 0xed based delay (needed on some systems)
1791 Simple two microseconds delay
1796 See Documentation/filesystems/nfs/nfsroot.txt.
1798 irqaffinity= [SMP] Set the default irq affinity mask
1799 The argument is a cpu list, as described above.
1801 irqchip.gicv2_force_probe=
1804 Force the kernel to look for the second 4kB page
1805 of a GICv2 controller even if the memory range
1806 exposed by the device tree is too small.
1808 irqchip.gicv3_nolpi=
1810 Force the kernel to ignore the availability of
1811 LPIs (and by consequence ITSs). Intended for system
1812 that use the kernel as a bootloader, and thus want
1813 to let secondary kernels in charge of setting up
1817 When an interrupt is not handled search all handlers
1818 for it. Intended to get systems with badly broken
1822 When an interrupt is not handled search all handlers
1823 for it. Also check all handlers each timer
1824 interrupt. Intended to get systems with badly broken
1828 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1830 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1831 [Deprecated - use cpusets instead]
1832 Format: [flag-list,]<cpu-list>
1834 Specify one or more CPUs to isolate from disturbances
1835 specified in the flag list (default: domain):
1838 Disable the tick when a single task runs.
1840 A residual 1Hz tick is offloaded to workqueues, which you
1841 need to affine to housekeeping through the global
1842 workqueue's affinity configured via the
1843 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1844 by using the 'domain' flag described below.
1846 NOTE: by default the global workqueue runs on all CPUs,
1847 so to protect individual CPUs the 'cpumask' file has to
1848 be configured manually after bootup.
1851 Isolate from the general SMP balancing and scheduling
1852 algorithms. Note that performing domain isolation this way
1853 is irreversible: it's not possible to bring back a CPU to
1854 the domains once isolated through isolcpus. It's strongly
1855 advised to use cpusets instead to disable scheduler load
1856 balancing through the "cpuset.sched_load_balance" file.
1857 It offers a much more flexible interface where CPUs can
1858 move in and out of an isolated set anytime.
1860 You can move a process onto or off an "isolated" CPU via
1861 the CPU affinity syscalls or cpuset.
1862 <cpu number> begins at 0 and the maximum value is
1863 "number of CPUs in system - 1".
1865 The format of <cpu-list> is described above.
1871 ivrs_ioapic [HW,X86_64]
1872 Provide an override to the IOAPIC-ID<->DEVICE-ID
1873 mapping provided in the IVRS ACPI table. For
1874 example, to map IOAPIC-ID decimal 10 to
1875 PCI device 00:14.0 write the parameter as:
1876 ivrs_ioapic[10]=00:14.0
1878 ivrs_hpet [HW,X86_64]
1879 Provide an override to the HPET-ID<->DEVICE-ID
1880 mapping provided in the IVRS ACPI table. For
1881 example, to map HPET-ID decimal 0 to
1882 PCI device 00:14.0 write the parameter as:
1883 ivrs_hpet[0]=00:14.0
1885 ivrs_acpihid [HW,X86_64]
1886 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1887 mapping provided in the IVRS ACPI table. For
1888 example, to map UART-HID:UID AMD0020:0 to
1889 PCI device 00:14.5 write the parameter as:
1890 ivrs_acpihid[00:14.5]=AMD0020:0
1892 js= [HW,JOY] Analog joystick
1893 See Documentation/input/joydev/joystick.rst.
1896 When CONFIG_RANDOMIZE_BASE is set, this disables
1897 kernel and module base offset ASLR (Address Space
1898 Layout Randomization).
1901 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1902 report on every invalid memory access. Without this
1903 parameter KASAN will print report only for the first
1908 kernelcore= [KNL,X86,IA-64,PPC]
1909 Format: nn[KMGTPE] | nn% | "mirror"
1910 This parameter specifies the amount of memory usable by
1911 the kernel for non-movable allocations. The requested
1912 amount is spread evenly throughout all nodes in the
1913 system as ZONE_NORMAL. The remaining memory is used for
1914 movable memory in its own zone, ZONE_MOVABLE. In the
1915 event, a node is too small to have both ZONE_NORMAL and
1916 ZONE_MOVABLE, kernelcore memory will take priority and
1917 other nodes will have a larger ZONE_MOVABLE.
1919 ZONE_MOVABLE is used for the allocation of pages that
1920 may be reclaimed or moved by the page migration
1921 subsystem. Note that allocations like PTEs-from-HighMem
1922 still use the HighMem zone if it exists, and the Normal
1923 zone if it does not.
1925 It is possible to specify the exact amount of memory in
1926 the form of "nn[KMGTPE]", a percentage of total system
1927 memory in the form of "nn%", or "mirror". If "mirror"
1928 option is specified, mirrored (reliable) memory is used
1929 for non-movable allocations and remaining memory is used
1930 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1931 are exclusive, so you cannot specify multiple forms.
1933 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1934 Format: <Controller#>[,poll interval]
1935 The controller # is the number of the ehci usb debug
1936 port as it is probed via PCI. The poll interval is
1937 optional and is the number seconds in between
1938 each poll cycle to the debug port in case you need
1939 the functionality for interrupting the kernel with
1940 gdb or control-c on the dbgp connection. When
1941 not using this parameter you use sysrq-g to break into
1942 the kernel debugger.
1944 kgdboc= [KGDB,HW] kgdb over consoles.
1945 Requires a tty driver that supports console polling,
1946 or a supported polling keyboard driver (non-usb).
1947 Serial only format: <serial_device>[,baud]
1948 keyboard only format: kbd
1949 keyboard and serial format: kbd,<serial_device>[,baud]
1950 Optional Kernel mode setting:
1951 kms, kbd format: kms,kbd
1952 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1954 kgdbwait [KGDB] Stop kernel execution and enter the
1955 kernel debugger at the earliest opportunity.
1957 kmac= [MIPS] korina ethernet MAC address.
1958 Configure the RouterBoard 532 series on-chip
1959 Ethernet adapter MAC address.
1961 kmemleak= [KNL] Boot-time kmemleak enable/disable
1962 Valid arguments: on, off
1964 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1967 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1968 Default is 0 (don't ignore, but inject #GP)
1970 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1971 Default is false (don't support).
1973 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1977 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1978 Default is 1 (enabled)
1980 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1982 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1984 kvm-arm.vgic_v3_group0_trap=
1985 [KVM,ARM] Trap guest accesses to GICv3 group-0
1988 kvm-arm.vgic_v3_group1_trap=
1989 [KVM,ARM] Trap guest accesses to GICv3 group-1
1992 kvm-arm.vgic_v3_common_trap=
1993 [KVM,ARM] Trap guest accesses to GICv3 common
1996 kvm-arm.vgic_v4_enable=
1997 [KVM,ARM] Allow use of GICv4 for direct injection of
2000 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2001 (virtualized MMU) support on capable Intel chips.
2002 Default is 1 (enabled)
2004 kvm-intel.emulate_invalid_guest_state=
2005 [KVM,Intel] Enable emulation of invalid guest states
2006 Default is 0 (disabled)
2008 kvm-intel.flexpriority=
2009 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2010 Default is 1 (enabled)
2013 [KVM,Intel] Enable VMX nesting (nVMX).
2014 Default is 0 (disabled)
2016 kvm-intel.unrestricted_guest=
2017 [KVM,Intel] Disable unrestricted guest feature
2018 (virtualized real and unpaged mode) on capable
2019 Intel chips. Default is 1 (enabled)
2021 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2024 Valid arguments: never, cond, always
2026 always: L1D cache flush on every VMENTER.
2027 cond: Flush L1D on VMENTER only when the code between
2028 VMEXIT and VMENTER can leak host memory.
2029 never: Disables the mitigation
2031 Default is cond (do L1 cache flush in specific instances)
2033 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2034 feature (tagged TLBs) on capable Intel chips.
2035 Default is 1 (enabled)
2037 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2040 The kernel PTE inversion protection is unconditionally
2041 enabled and cannot be disabled.
2044 Provides all available mitigations for the
2045 L1TF vulnerability. Disables SMT and
2046 enables all mitigations in the
2047 hypervisors, i.e. unconditional L1D flush.
2049 SMT control and L1D flush control via the
2050 sysfs interface is still possible after
2051 boot. Hypervisors will issue a warning
2052 when the first VM is started in a
2053 potentially insecure configuration,
2054 i.e. SMT enabled or L1D flush disabled.
2057 Same as 'full', but disables SMT and L1D
2058 flush runtime control. Implies the
2059 'nosmt=force' command line option.
2060 (i.e. sysfs control of SMT is disabled.)
2063 Leaves SMT enabled and enables the default
2064 hypervisor mitigation, i.e. conditional
2067 SMT control and L1D flush control via the
2068 sysfs interface is still possible after
2069 boot. Hypervisors will issue a warning
2070 when the first VM is started in a
2071 potentially insecure configuration,
2072 i.e. SMT enabled or L1D flush disabled.
2076 Disables SMT and enables the default
2077 hypervisor mitigation.
2079 SMT control and L1D flush control via the
2080 sysfs interface is still possible after
2081 boot. Hypervisors will issue a warning
2082 when the first VM is started in a
2083 potentially insecure configuration,
2084 i.e. SMT enabled or L1D flush disabled.
2087 Same as 'flush', but hypervisors will not
2088 warn when a VM is started in a potentially
2089 insecure configuration.
2092 Disables hypervisor mitigations and doesn't
2097 For details see: Documentation/admin-guide/l1tf.rst
2103 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2106 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2107 value for LAPIC timer one-shot implementation. Default
2108 back to the programmable timer unit in the LAPIC.
2110 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2113 libata.dma= [LIBATA] DMA control
2114 libata.dma=0 Disable all PATA and SATA DMA
2115 libata.dma=1 PATA and SATA Disk DMA only
2116 libata.dma=2 ATAPI (CDROM) DMA only
2117 libata.dma=4 Compact Flash DMA only
2118 Combinations also work, so libata.dma=3 enables DMA
2119 for disks and CDROMs, but not CFs.
2121 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2122 libata.ignore_hpa=0 keep BIOS limits (default)
2123 libata.ignore_hpa=1 ignore limits, using full disk
2125 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2129 libata.force= [LIBATA] Force configurations. The format is comma
2130 separated list of "[ID:]VAL" where ID is
2131 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2132 matching port, link or device. Basically, it matches
2133 the ATA ID string printed on console by libata. If
2134 the whole ID part is omitted, the last PORT and DEVICE
2135 values are used. If ID hasn't been specified yet, the
2136 configuration applies to all ports, links and devices.
2138 If only DEVICE is omitted, the parameter applies to
2139 the port and all links and devices behind it. DEVICE
2140 number of 0 either selects the first device or the
2141 first fan-out link behind PMP device. It does not
2142 select the host link. DEVICE number of 15 selects the
2143 host link and device attached to it.
2145 The VAL specifies the configuration to force. As long
2146 as there's no ambiguity shortcut notation is allowed.
2147 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2148 The following configurations can be forced.
2150 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2151 Any ID with matching PORT is used.
2153 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2155 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2156 udma[/][16,25,33,44,66,100,133] notation is also
2159 * [no]ncq: Turn on or off NCQ.
2161 * [no]ncqtrim: Turn off queued DSM TRIM.
2163 * nohrst, nosrst, norst: suppress hard, soft
2166 * rstonce: only attempt one reset during
2167 hot-unplug link recovery
2169 * dump_id: dump IDENTIFY data.
2171 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2173 * disable: Disable this device.
2175 If there are multiple matching configurations changing
2176 the same attribute, the last one is used.
2178 memblock=debug [KNL] Enable memblock debug messages.
2180 load_ramdisk= [RAM] List of ramdisks to load from floppy
2181 See Documentation/blockdev/ramdisk.txt.
2183 lockd.nlm_grace_period=P [NFS] Assign grace period.
2186 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2189 lockd.nlm_timeout=T [NFS] Assign timeout value.
2192 lockd.nlm_udpport=M [NFS] Assign UDP port.
2195 locktorture.nreaders_stress= [KNL]
2196 Set the number of locking read-acquisition kthreads.
2197 Defaults to being automatically set based on the
2198 number of online CPUs.
2200 locktorture.nwriters_stress= [KNL]
2201 Set the number of locking write-acquisition kthreads.
2203 locktorture.onoff_holdoff= [KNL]
2204 Set time (s) after boot for CPU-hotplug testing.
2206 locktorture.onoff_interval= [KNL]
2207 Set time (s) between CPU-hotplug operations, or
2208 zero to disable CPU-hotplug testing.
2210 locktorture.shuffle_interval= [KNL]
2211 Set task-shuffle interval (jiffies). Shuffling
2212 tasks allows some CPUs to go into dyntick-idle
2213 mode during the locktorture test.
2215 locktorture.shutdown_secs= [KNL]
2216 Set time (s) after boot system shutdown. This
2217 is useful for hands-off automated testing.
2219 locktorture.stat_interval= [KNL]
2220 Time (s) between statistics printk()s.
2222 locktorture.stutter= [KNL]
2223 Time (s) to stutter testing, for example,
2224 specifying five seconds causes the test to run for
2225 five seconds, wait for five seconds, and so on.
2226 This tests the locking primitive's ability to
2227 transition abruptly to and from idle.
2229 locktorture.torture_type= [KNL]
2230 Specify the locking implementation to test.
2232 locktorture.verbose= [KNL]
2233 Enable additional printk() statements.
2235 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2238 loglevel= All Kernel Messages with a loglevel smaller than the
2239 console loglevel will be printed to the console. It can
2240 also be changed with klogd or other programs. The
2241 loglevels are defined as follows:
2243 0 (KERN_EMERG) system is unusable
2244 1 (KERN_ALERT) action must be taken immediately
2245 2 (KERN_CRIT) critical conditions
2246 3 (KERN_ERR) error conditions
2247 4 (KERN_WARNING) warning conditions
2248 5 (KERN_NOTICE) normal but significant condition
2249 6 (KERN_INFO) informational
2250 7 (KERN_DEBUG) debug-level messages
2252 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2253 in bytes. n must be a power of two and greater
2254 than the minimal size. The minimal size is defined
2255 by LOG_BUF_SHIFT kernel config parameter. There is
2256 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2257 that allows to increase the default size depending on
2258 the number of CPUs. See init/Kconfig for more details.
2260 logo.nologo [FB] Disables display of the built-in Linux logo.
2261 This may be used to provide more screen space for
2262 kernel log messages and is useful when debugging
2263 kernel boot problems.
2265 lp=0 [LP] Specify parallel ports to use, e.g,
2266 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2267 lp=reset first parallel port). 'lp=0' disables the
2268 lp=auto printer driver. 'lp=reset' (which can be
2269 specified in addition to the ports) causes
2270 attached printers to be reset. Using
2271 lp=port1,port2,... specifies the parallel ports
2272 to associate lp devices with, starting with
2273 lp0. A port specification may be 'none' to skip
2274 that lp device, or a parport name such as
2275 'parport0'. Specifying 'lp=auto' instead of a
2276 port specification list means that device IDs
2277 from each port should be examined, to see if
2278 an IEEE 1284-compliant printer is attached; if
2279 so, the driver will manage that printer.
2280 See also header of drivers/char/lp.c.
2283 Sets loops_per_jiffy to given constant, thus avoiding
2284 time-consuming boot-time autodetection (up to 250 ms per
2285 CPU). 0 enables autodetection (default). To determine
2286 the correct value for your kernel, boot with normal
2287 autodetection and see what value is printed. Note that
2288 on SMP systems the preset will be applied to all CPUs,
2289 which is likely to cause problems if your CPUs need
2290 significantly divergent settings. An incorrect value
2291 will cause delays in the kernel to be wrong, leading to
2292 unpredictable I/O errors and other breakage. Although
2293 unlikely, in the extreme case this might damage your
2297 Format: <io>,<irq>,<dma>
2299 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2301 machvec= [IA-64] Force the use of a particular machine-vector
2302 (machvec) in a generic kernel.
2303 Example: machvec=hpzx1_swiotlb
2305 machtype= [Loongson] Share the same kernel image file between different
2307 Example: machtype=lemote-yeeloong-2f-7inch
2309 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2310 than or equal to this physical address is ignored.
2312 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2313 will bring up during bootup. maxcpus=n : n >= 0 limits
2314 the kernel to bring up 'n' processors. Surely after
2315 bootup you can bring up the other plugged cpu by executing
2316 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2317 only takes effect during system bootup.
2318 While n=0 is a special case, it is equivalent to "nosmp",
2319 which also disables the IO APIC.
2321 max_loop= [LOOP] The number of loop block devices that get
2322 (loop.max_loop) unconditionally pre-created at init time. The default
2323 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2324 of statically allocating a predefined number, loop
2325 devices can be requested on-demand with the
2326 /dev/loop-control interface.
2328 mce [X86-32] Machine Check Exception
2330 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2332 md= [HW] RAID subsystems devices and level
2333 See Documentation/admin-guide/md.rst.
2336 Format: <first>,<last>
2337 Specifies range of consoles to be captured by the MDA.
2339 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2340 Amount of memory to be used when the kernel is not able
2341 to see the whole system memory or for test.
2342 [X86] Work as limiting max address. Use together
2343 with memmap= to avoid physical address space collisions.
2344 Without memmap= PCI devices could be placed at addresses
2345 belonging to unused RAM.
2347 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2351 [KNL,SH] Allow user to override the default size for
2352 per-device physically contiguous DMA buffers.
2354 memhp_default_state=online/offline
2355 [KNL] Set the initial state for the memory hotplug
2356 onlining policy. If not specified, the default value is
2357 set according to the
2358 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2360 See Documentation/memory-hotplug.txt.
2362 memmap=exactmap [KNL,X86] Enable setting of an exact
2363 E820 memory map, as specified by the user.
2364 Such memmap=exactmap lines can be constructed based on
2365 BIOS output or other requirements. See the memmap=nn@ss
2368 memmap=nn[KMG]@ss[KMG]
2369 [KNL] Force usage of a specific region of memory.
2370 Region of memory to be used is from ss to ss+nn.
2371 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2372 which limits max address to nn[KMG].
2373 Multiple different regions can be specified,
2376 memmap=100M@2G,100M#3G,1G!1024G
2378 memmap=nn[KMG]#ss[KMG]
2379 [KNL,ACPI] Mark specific memory as ACPI data.
2380 Region of memory to be marked is from ss to ss+nn.
2382 memmap=nn[KMG]$ss[KMG]
2383 [KNL,ACPI] Mark specific memory as reserved.
2384 Region of memory to be reserved is from ss to ss+nn.
2385 Example: Exclude memory from 0x18690000-0x1869ffff
2386 memmap=64K$0x18690000
2388 memmap=0x10000$0x18690000
2389 Some bootloaders may need an escape character before '$',
2390 like Grub2, otherwise '$' and the following number
2393 memmap=nn[KMG]!ss[KMG]
2394 [KNL,X86] Mark specific memory as protected.
2395 Region of memory to be used, from ss to ss+nn.
2396 The memory region may be marked as e820 type 12 (0xc)
2397 and is NVDIMM or ADR memory.
2399 memmap=<size>%<offset>-<oldtype>+<newtype>
2400 [KNL,ACPI] Convert memory within the specified region
2401 from <oldtype> to <newtype>. If "-<oldtype>" is left
2402 out, the whole region will be marked as <newtype>,
2403 even if previously unavailable. If "+<newtype>" is left
2404 out, matching memory will be removed. Types are
2405 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2406 3 = ACPI, 12 = PRAM.
2408 memory_corruption_check=0/1 [X86]
2409 Some BIOSes seem to corrupt the first 64k of
2410 memory when doing things like suspend/resume.
2411 Setting this option will scan the memory
2412 looking for corruption. Enabling this will
2413 both detect corruption and prevent the kernel
2414 from using the memory being corrupted.
2415 However, its intended as a diagnostic tool; if
2416 repeatable BIOS-originated corruption always
2417 affects the same memory, you can use memmap=
2418 to prevent the kernel from using that memory.
2420 memory_corruption_check_size=size [X86]
2421 By default it checks for corruption in the low
2422 64k, making this memory unavailable for normal
2423 use. Use this parameter to scan for
2424 corruption in more or less memory.
2426 memory_corruption_check_period=seconds [X86]
2427 By default it checks for corruption every 60
2428 seconds. Use this parameter to check at some
2429 other rate. 0 disables periodic checking.
2431 memtest= [KNL,X86,ARM,PPC] Enable memtest
2433 default : 0 <disable>
2434 Specifies the number of memtest passes to be
2435 performed. Each pass selects another test
2436 pattern from a given set of patterns. Memtest
2437 fills the memory with this pattern, validates
2438 memory contents and reserves bad memory
2439 regions that are detected.
2441 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2442 Valid arguments: on, off
2443 Default (depends on kernel configuration option):
2444 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2445 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2446 mem_encrypt=on: Activate SME
2447 mem_encrypt=off: Do not activate SME
2449 Refer to Documentation/x86/amd-memory-encryption.txt
2450 for details on when memory encryption can be activated.
2452 mem_sleep_default= [SUSPEND] Default system suspend mode:
2453 s2idle - Suspend-To-Idle
2454 shallow - Power-On Suspend or equivalent (if supported)
2455 deep - Suspend-To-RAM or equivalent (if supported)
2456 See Documentation/admin-guide/pm/sleep-states.rst.
2458 meye.*= [HW] Set MotionEye Camera parameters
2459 See Documentation/media/v4l-drivers/meye.rst.
2461 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2462 Multi-Function General Purpose Timers on AMD Geode
2465 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2466 the BIOS has incorrectly applied a workaround. TinyBIOS
2467 version 0.98 is known to be affected, 0.99 fixes the
2468 problem by letting the user disable the workaround.
2472 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2473 physical address is ignored.
2475 mini2440= [ARM,HW,KNL]
2476 Format:[0..2][b][c][t]
2478 MINI2440 configuration specification:
2479 0 - The attached screen is the 3.5" TFT
2480 1 - The attached screen is the 7" TFT
2481 2 - The VGA Shield is attached (1024x768)
2482 Leaving out the screen size parameter will not load
2483 the TFT driver, and the framebuffer will be left
2485 b - Enable backlight. The TFT backlight pin will be
2486 linked to the kernel VESA blanking code and a GPIO
2487 LED. This parameter is not necessary when using the
2489 c - Enable the s3c camera interface.
2490 t - Reserved for enabling touchscreen support. The
2491 touchscreen support is not enabled in the mainstream
2492 kernel as of 2.6.30, a preliminary port can be found
2493 in the "bleeding edge" mini2440 support kernel at
2494 http://repo.or.cz/w/linux-2.6/mini2440.git
2497 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2498 parameter allows control of the logging verbosity for
2499 the additional memory initialisation checks. A value
2500 of 0 disables mminit logging and a level of 4 will
2501 log everything. Information is printed at KERN_DEBUG
2502 so loglevel=8 may also need to be specified.
2505 [KNL] When CONFIG_MODULE_SIG is set, this means that
2506 modules without (valid) signatures will fail to load.
2507 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2508 is always true, so this option does nothing.
2510 module_blacklist= [KNL] Do not load a comma-separated list of
2511 modules. Useful for debugging problem modules.
2514 [MOUSE] Maximum time between finger touching and
2515 leaving touchpad surface for touch to be considered
2516 a tap and be reported as a left button click (for
2517 touchpads working in absolute mode only).
2519 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2520 reporting absolute coordinates, such as tablets
2521 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2522 reporting absolute coordinates, such as tablets
2524 movablecore= [KNL,X86,IA-64,PPC]
2525 Format: nn[KMGTPE] | nn%
2526 This parameter is the complement to kernelcore=, it
2527 specifies the amount of memory used for migratable
2528 allocations. If both kernelcore and movablecore is
2529 specified, then kernelcore will be at *least* the
2530 specified value but may be more. If movablecore on its
2531 own is specified, the administrator must be careful
2532 that the amount of memory usable for all allocations
2535 movable_node [KNL] Boot-time switch to make hotplugable memory
2536 NUMA nodes to be movable. This means that the memory
2537 of such nodes will be usable only for movable
2538 allocations which rules out almost all kernel
2539 allocations. Use with caution!
2541 MTD_Partition= [MTD]
2542 Format: <name>,<region-number>,<size>,<offset>
2544 MTD_Region= [MTD] Format:
2545 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2548 See drivers/mtd/cmdlinepart.c.
2550 multitce=off [PPC] This parameter disables the use of the pSeries
2551 firmware feature for updating multiple TCE entries
2554 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2556 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2558 boundary - index of last SLC block on Flex-OneNAND.
2559 The remaining blocks are configured as MLC blocks.
2560 lock - Configure if Flex-OneNAND boundary should be locked.
2561 Once locked, the boundary cannot be changed.
2562 1 indicates lock status, 0 indicates unlock status.
2565 ARM/S3C2412 JIVE boot control
2567 See arch/arm/mach-s3c2412/mach-jive.c
2569 mtouchusb.raw_coordinates=
2570 [HW] Make the MicroTouch USB driver use raw coordinates
2571 ('y', default) or cooked coordinates ('n')
2573 mtrr_chunk_size=nn[KMG] [X86]
2574 used for mtrr cleanup. It is largest continuous chunk
2575 that could hold holes aka. UC entries.
2577 mtrr_gran_size=nn[KMG] [X86]
2578 Used for mtrr cleanup. It is granularity of mtrr block.
2580 Large value could prevent small alignment from
2583 mtrr_spare_reg_nr=n [X86]
2585 Range: 0,7 : spare reg number
2587 Used for mtrr cleanup. It is spare mtrr entries number.
2588 Set to 2 or more if your graphical card needs more.
2590 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2592 netdev= [NET] Network devices parameters
2593 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2594 Note that mem_start is often overloaded to mean
2595 something different and driver-specific.
2596 This usage is only documented in each driver source
2600 [NETFILTER] Enable connection tracking flow accounting
2601 0 to disable accounting
2602 1 to enable accounting
2605 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2606 See Documentation/filesystems/nfs/nfsroot.txt.
2608 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2609 See Documentation/filesystems/nfs/nfsroot.txt.
2611 nfsrootdebug [NFS] enable nfsroot debugging messages.
2612 See Documentation/filesystems/nfs/nfsroot.txt.
2614 nfs.callback_nr_threads=
2615 [NFSv4] set the total number of threads that the
2616 NFS client will assign to service NFSv4 callback
2619 nfs.callback_tcpport=
2620 [NFS] set the TCP port on which the NFSv4 callback
2621 channel should listen.
2624 [NFS] sets the pathname to the program which is used
2625 to update the NFS client cache entries.
2627 nfs.cache_getent_timeout=
2628 [NFS] sets the timeout after which an attempt to
2629 update a cache entry is deemed to have failed.
2631 nfs.idmap_cache_timeout=
2632 [NFS] set the maximum lifetime for idmapper cache
2636 [NFS] enable 64-bit inode numbers.
2637 If zero, the NFS client will fake up a 32-bit inode
2638 number for the readdir() and stat() syscalls instead
2639 of returning the full 64-bit number.
2640 The default is to return 64-bit inode numbers.
2642 nfs.max_session_cb_slots=
2643 [NFSv4.1] Sets the maximum number of session
2644 slots the client will assign to the callback
2645 channel. This determines the maximum number of
2646 callbacks the client will process in parallel for
2647 a particular server.
2649 nfs.max_session_slots=
2650 [NFSv4.1] Sets the maximum number of session slots
2651 the client will attempt to negotiate with the server.
2652 This limits the number of simultaneous RPC requests
2653 that the client can send to the NFSv4.1 server.
2654 Note that there is little point in setting this
2655 value higher than the max_tcp_slot_table_limit.
2657 nfs.nfs4_disable_idmapping=
2658 [NFSv4] When set to the default of '1', this option
2659 ensures that both the RPC level authentication
2660 scheme and the NFS level operations agree to use
2661 numeric uids/gids if the mount is using the
2662 'sec=sys' security flavour. In effect it is
2663 disabling idmapping, which can make migration from
2664 legacy NFSv2/v3 systems to NFSv4 easier.
2665 Servers that do not support this mode of operation
2666 will be autodetected by the client, and it will fall
2667 back to using the idmapper.
2668 To turn off this behaviour, set the value to '0'.
2670 [NFS4] Specify an additional fixed unique ident-
2671 ification string that NFSv4 clients can insert into
2672 their nfs_client_id4 string. This is typically a
2673 UUID that is generated at system install time.
2675 nfs.send_implementation_id =
2676 [NFSv4.1] Send client implementation identification
2677 information in exchange_id requests.
2678 If zero, no implementation identification information
2680 The default is to send the implementation identification
2683 nfs.recover_lost_locks =
2684 [NFSv4] Attempt to recover locks that were lost due
2685 to a lease timeout on the server. Please note that
2686 doing this risks data corruption, since there are
2687 no guarantees that the file will remain unchanged
2688 after the locks are lost.
2689 If you want to enable the kernel legacy behaviour of
2690 attempting to recover these locks, then set this
2692 The default parameter value of '0' causes the kernel
2693 not to attempt recovery of lost locks.
2695 nfs4.layoutstats_timer =
2696 [NFSv4.2] Change the rate at which the kernel sends
2697 layoutstats to the pNFS metadata server.
2699 Setting this to value to 0 causes the kernel to use
2700 whatever value is the default set by the layout
2701 driver. A non-zero value sets the minimum interval
2702 in seconds between layoutstats transmissions.
2704 nfsd.nfs4_disable_idmapping=
2705 [NFSv4] When set to the default of '1', the NFSv4
2706 server will return only numeric uids and gids to
2707 clients using auth_sys, and will accept numeric uids
2708 and gids from such clients. This is intended to ease
2709 migration from NFSv2/v3.
2711 nmi_debug= [KNL,SH] Specify one or more actions to take
2712 when a NMI is triggered.
2713 Format: [state][,regs][,debounce][,die]
2715 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2716 Format: [panic,][nopanic,][num]
2718 0 - turn hardlockup detector in nmi_watchdog off
2719 1 - turn hardlockup detector in nmi_watchdog on
2720 When panic is specified, panic when an NMI watchdog
2721 timeout occurs (or 'nopanic' to override the opposite
2722 default). To disable both hard and soft lockup detectors,
2723 please see 'nowatchdog'.
2724 This is useful when you use a panic=... timeout and
2725 need the box quickly up again.
2727 These settings can be accessed at runtime via
2728 the nmi_watchdog and hardlockup_panic sysctls.
2730 netpoll.carrier_timeout=
2731 [NET] Specifies amount of time (in seconds) that
2732 netpoll should wait for a carrier. By default netpoll
2735 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2736 emulation library even if a 387 maths coprocessor
2739 no5lvl [X86-64] Disable 5-level paging mode. Forces
2740 kernel to use 4-level paging instead.
2743 [HW] Never suspend the console
2744 Disable suspending of consoles during suspend and
2745 hibernate operations. Once disabled, debugging
2746 messages can reach various consoles while the rest
2747 of the system is being put to sleep (ie, while
2748 debugging driver suspend/resume hooks). This may
2749 not work reliably with all consoles, but is known
2750 to work with serial and VGA consoles.
2751 To facilitate more flexible debugging, we also add
2752 console_suspend, a printk module parameter to control
2753 it. Users could use console_suspend (usually
2754 /sys/module/printk/parameters/console_suspend) to
2755 turn on/off it dynamically.
2757 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2758 caches in the slab allocator. Saves per-node memory,
2759 but will impact performance.
2763 noaltinstr [S390] Disables alternative instructions patching
2764 (CPU alternatives feature).
2766 noapic [SMP,APIC] Tells the kernel to not make use of any
2767 IOAPICs that may be present in the system.
2769 noautogroup Disable scheduler automatic task group creation.
2771 nobats [PPC] Do not use BATs for mapping kernel lowmem
2772 on "Classic" PPC cores.
2776 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2778 nodelayacct [KNL] Disable per-task delay accounting
2780 nodsp [SH] Disable hardware DSP at boot time.
2782 noefi Disable EFI runtime services support.
2787 On X86-32 available only on PAE configured kernels.
2788 noexec=on: enable non-executable mappings (default)
2789 noexec=off: disable non-executable mappings
2792 Disable SMAP (Supervisor Mode Access Prevention)
2793 even if it is supported by processor.
2796 Disable SMEP (Supervisor Mode Execution Prevention)
2797 even if it is supported by processor.
2800 This affects only 32-bit executables.
2801 noexec32=on: enable non-executable mappings (default)
2802 read doesn't imply executable mappings
2803 noexec32=off: disable non-executable mappings
2804 read implies executable mappings
2806 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2808 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2809 register save and restore. The kernel will only save
2810 legacy floating-point registers on task switch.
2812 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2814 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2815 Equivalent to smt=1.
2817 [KNL,x86] Disable symmetric multithreading (SMT).
2818 nosmt=force: Force disable SMT, cannot be undone
2819 via the sysfs control file.
2821 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2822 check bypass). With this option data leaks are possible
2825 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2826 (indirect branch prediction) vulnerability. System may
2827 allow data leaks with this option, which is equivalent
2830 nospec_store_bypass_disable
2831 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2833 noxsave [BUGS=X86] Disables x86 extended register state save
2834 and restore using xsave. The kernel will fallback to
2835 enabling legacy floating-point and sse state.
2837 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2838 register states. The kernel will fall back to use
2839 xsave to save the states. By using this parameter,
2840 performance of saving the states is degraded because
2841 xsave doesn't support modified optimization while
2842 xsaveopt supports it on xsaveopt enabled systems.
2844 noxsaves [X86] Disables xsaves and xrstors used in saving and
2845 restoring x86 extended register state in compacted
2846 form of xsave area. The kernel will fall back to use
2847 xsaveopt and xrstor to save and restore the states
2848 in standard form of xsave area. By using this
2849 parameter, xsave area per process might occupy more
2850 memory on xsaves enabled systems.
2852 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2853 wfi(ARM) instruction doesn't work correctly and not to
2854 use it. This is also useful when using JTAG debugger.
2856 no_file_caps Tells the kernel not to honor file capabilities. The
2857 only way then for a file to be executed with privilege
2858 is to be setuid root or executed by root.
2860 nohalt [IA-64] Tells the kernel not to use the power saving
2861 function PAL_HALT_LIGHT when idle. This increases
2862 power-consumption. On the positive side, it reduces
2863 interrupt wake-up latency, which may improve performance
2864 in certain environments such as networked servers or
2867 nohibernate [HIBERNATION] Disable hibernation and resume.
2869 nohz= [KNL] Boottime enable/disable dynamic ticks
2870 Valid arguments: on, off
2873 nohz_full= [KNL,BOOT,SMP,ISOL]
2874 The argument is a cpu list, as described above.
2875 In kernels built with CONFIG_NO_HZ_FULL=y, set
2876 the specified list of CPUs whose tick will be stopped
2877 whenever possible. The boot CPU will be forced outside
2878 the range to maintain the timekeeping. Any CPUs
2879 in this list will have their RCU callbacks offloaded,
2880 just as if they had also been called out in the
2881 rcu_nocbs= boot parameter.
2883 noiotrap [SH] Disables trapped I/O port accesses.
2885 noirqdebug [X86-32] Disables the code which attempts to detect and
2886 disable unhandled interrupt sources.
2888 no_timer_check [X86,APIC] Disables the code which tests for
2889 broken timer IRQ sources.
2891 noisapnp [ISAPNP] Disables ISA PnP code.
2893 noinitrd [RAM] Tells the kernel not to load any configured
2896 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2898 [Deprecated - use intremap=off]
2902 noinvpcid [X86] Disable the INVPCID cpu feature.
2904 nojitter [IA-64] Disables jitter checking for ITC timers.
2906 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2908 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2912 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2913 clock and use the default one.
2915 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2916 steal time is computed, but won't influence scheduler
2919 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2921 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2923 noltlbs [PPC] Do not use large page/tlb entries for kernel
2924 lowmem mapping on PPC40x and PPC8xx
2926 nomca [IA-64] Disable machine check abort handling
2928 nomce [X86-32] Disable Machine Check Exception
2930 nomfgpt [X86-32] Disable Multi-Function General Purpose
2931 Timer usage (for AMD Geode machines).
2933 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2934 shutdown the other cpus. Instead use the REBOOT_VECTOR
2937 nomodule Disable module load
2939 nopat [X86] Disable PAT (page attribute table extension of
2940 pagetables) support.
2942 nopcid [X86-64] Disable the PCID cpu feature.
2944 norandmaps Don't use address space randomization. Equivalent to
2945 echo 0 > /proc/sys/kernel/randomize_va_space
2947 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2948 with UP alternatives
2950 nordrand [X86] Disable kernel use of the RDRAND and
2951 RDSEED instructions even if they are supported
2952 by the processor. RDRAND and RDSEED are still
2953 available to user space applications.
2955 noresume [SWSUSP] Disables resume and restores original swap
2958 no-scroll [VGA] Disables scrollback.
2959 This is required for the Braillex ib80-piezo Braille
2960 reader made by F.H. Papenmeier (Germany).
2964 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2966 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2967 and disable the IO APIC. legacy for "maxcpus=0".
2969 nosoftlockup [KNL] Disable the soft-lockup detector.
2971 nosync [HW,M68K] Disables sync negotiation for all devices.
2973 nowatchdog [KNL] Disable both lockup detectors, i.e.
2974 soft-lockup and NMI watchdog (hard-lockup).
2978 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2980 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2981 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2982 Some features depend on CPU0. Known dependencies are:
2983 1. Resume from suspend/hibernate depends on CPU0.
2984 Suspend/hibernate will fail if CPU0 is offline and you
2985 need to online CPU0 before suspend/hibernate.
2986 2. PIC interrupts also depend on CPU0. CPU0 can't be
2987 removed if a PIC interrupt is detected.
2988 It's said poweroff/reboot may depend on CPU0 on some
2989 machines although I haven't seen such issues so far
2990 after CPU0 is offline on a few tested machines.
2991 If the dependencies are under your control, you can
2992 turn on cpu0_hotplug.
2994 nps_mtm_hs_ctr= [KNL,ARC]
2995 This parameter sets the maximum duration, in
2996 cycles, each HW thread of the CTOP can run
2997 without interruptions, before HW switches it.
2998 The actual maximum duration is 16 times this
3000 Format: integer between 1 and 255
3003 nptcg= [IA-64] Override max number of concurrent global TLB
3004 purges which is reported from either PAL_VM_SUMMARY or
3007 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3008 could support. nr_cpus=n : n >= 1 limits the kernel to
3009 support 'n' processors. It could be larger than the
3010 number of already plugged CPU during bootup, later in
3011 runtime you can physically add extra cpu until it reaches
3012 n. So during boot up some boot time memory for per-cpu
3013 variables need be pre-allocated for later physical cpu
3016 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3018 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3019 Allowed values are enable and disable
3021 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3022 'node', 'default' can be specified
3023 This can be set from sysctl after boot.
3024 See Documentation/sysctl/vm.txt for details.
3026 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3027 See Documentation/debugging-via-ohci1394.txt for more
3030 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3031 Rather than timing out after 20 ms if an EC
3032 command is not properly ACKed, override the length
3033 of the timeout. We have interrupts disabled while
3034 waiting for the ACK, so if this is set too high
3035 interrupts *may* be lost!
3037 omap_mux= [OMAP] Override bootloader pin multiplexing.
3038 Format: <mux_mode0.mode_name=value>...
3039 For example, to override I2C bus2:
3040 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3042 oprofile.timer= [HW]
3043 Use timer interrupt instead of performance counters
3045 oprofile.cpu_type= Force an oprofile cpu type
3046 This might be useful if you have an older oprofile
3047 userland or if you want common events.
3048 Format: { arch_perfmon }
3049 arch_perfmon: [X86] Force use of architectural
3050 perfmon on Intel CPUs instead of the
3051 CPU specific event set.
3052 timer: [X86] Force use of architectural NMI
3053 timer mode (see also oprofile.timer
3054 for generic hr timer mode)
3056 oops=panic Always panic on oopses. Default is to just kill the
3057 process, but there is a small probability of
3058 deadlocking the machine.
3059 This will also cause panics on machine check exceptions.
3060 Useful together with panic=30 to trigger a reboot.
3062 page_owner= [KNL] Boot-time page_owner enabling option.
3063 Storage of the information about who allocated
3064 each page is disabled in default. With this switch,
3066 on: enable the feature
3068 page_poison= [KNL] Boot-time parameter changing the state of
3069 poisoning on the buddy allocator, available with
3070 CONFIG_PAGE_POISONING=y.
3071 off: turn off poisoning (default)
3072 on: turn on poisoning
3074 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3075 timeout > 0: seconds before rebooting
3076 timeout = 0: wait forever
3077 timeout < 0: reboot immediately
3080 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3083 crash_kexec_post_notifiers
3084 Run kdump after running panic-notifiers and dumping
3085 kmsg. This only for the users who doubt kdump always
3086 succeeds in any situation.
3087 Note that this also increases risks of kdump failure,
3088 because some panic notifiers can make the crashed
3089 kernel more unstable.
3091 parkbd.port= [HW] Parallel port number the keyboard adapter is
3092 connected to, default is 0.
3094 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3095 0 for XT, 1 for AT (default is AT).
3098 parport= [HW,PPT] Specify parallel ports. 0 disables.
3099 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3100 Use 'auto' to force the driver to use any
3101 IRQ/DMA settings detected (the default is to
3102 ignore detected IRQ/DMA settings because of
3103 possible conflicts). You can specify the base
3104 address, IRQ, and DMA settings; IRQ and DMA
3105 should be numbers, or 'auto' (for using detected
3106 settings on that particular port), or 'nofifo'
3107 (to avoid using a FIFO even if it is detected).
3108 Parallel ports are assigned in the order they
3109 are specified on the command line, starting
3112 parport_init_mode= [HW,PPT]
3113 Configure VIA parallel port to operate in
3114 a specific mode. This is necessary on Pegasos
3115 computer where firmware has no options for setting
3116 up parallel port mode and sets it to spp.
3117 Currently this function knows 686a and 8231 chips.
3118 Format: [spp|ps2|epp|ecp|ecpepp]
3121 Halt all CPUs after the first oops has been printed for
3122 the specified number of seconds. This is to be used if
3123 your oopses keep scrolling off the screen.
3128 See header of drivers/block/paride/pcd.c.
3129 See also Documentation/blockdev/paride.txt.
3131 pci=option[,option...] [PCI] various PCI subsystem options.
3133 Some options herein operate on a specific device
3134 or a set of devices (<pci_dev>). These are
3135 specified in one of the following formats:
3137 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3138 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3140 Note: the first format specifies a PCI
3141 bus/device/function address which may change
3142 if new hardware is inserted, if motherboard
3143 firmware changes, or due to changes caused
3144 by other kernel parameters. If the
3145 domain is left unspecified, it is
3146 taken to be zero. Optionally, a path
3147 to a device through multiple device/function
3148 addresses can be specified after the base
3149 address (this is more robust against
3150 renumbering issues). The second format
3151 selects devices using IDs from the
3152 configuration space which may match multiple
3153 devices in the system.
3155 earlydump dump PCI config space before the kernel
3157 off [X86] don't probe for the PCI bus
3158 bios [X86-32] force use of PCI BIOS, don't access
3159 the hardware directly. Use this if your machine
3160 has a non-standard PCI host bridge.
3161 nobios [X86-32] disallow use of PCI BIOS, only direct
3162 hardware access methods are allowed. Use this
3163 if you experience crashes upon bootup and you
3164 suspect they are caused by the BIOS.
3165 conf1 [X86] Force use of PCI Configuration Access
3166 Mechanism 1 (config address in IO port 0xCF8,
3167 data in IO port 0xCFC, both 32-bit).
3168 conf2 [X86] Force use of PCI Configuration Access
3169 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3170 the function, IO port 0xCFA, also 8-bit, sets
3171 bus number. The config space is then accessed
3172 through ports 0xC000-0xCFFF).
3173 See http://wiki.osdev.org/PCI for more info
3174 on the configuration access mechanisms.
3175 noaer [PCIE] If the PCIEAER kernel config parameter is
3176 enabled, this kernel boot option can be used to
3177 disable the use of PCIE advanced error reporting.
3178 nodomains [PCI] Disable support for multiple PCI
3179 root domains (aka PCI segments, in ACPI-speak).
3180 nommconf [X86] Disable use of MMCONFIG for PCI
3182 check_enable_amd_mmconf [X86] check for and enable
3183 properly configured MMIO access to PCI
3184 config space on AMD family 10h CPU
3185 nomsi [MSI] If the PCI_MSI kernel config parameter is
3186 enabled, this kernel boot option can be used to
3187 disable the use of MSI interrupts system-wide.
3188 noioapicquirk [APIC] Disable all boot interrupt quirks.
3189 Safety option to keep boot IRQs enabled. This
3190 should never be necessary.
3191 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3192 primary IO-APIC for bridges that cannot disable
3193 boot IRQs. This fixes a source of spurious IRQs
3194 when the system masks IRQs.
3195 noioapicreroute [APIC] Disable workaround that uses the
3196 boot IRQ equivalent of an IRQ that connects to
3197 a chipset where boot IRQs cannot be disabled.
3198 The opposite of ioapicreroute.
3199 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3200 routing table. These calls are known to be buggy
3201 on several machines and they hang the machine
3202 when used, but on other computers it's the only
3203 way to get the interrupt routing table. Try
3204 this option if the kernel is unable to allocate
3205 IRQs or discover secondary PCI buses on your
3207 rom [X86] Assign address space to expansion ROMs.
3208 Use with caution as certain devices share
3209 address decoders between ROMs and other
3211 norom [X86] Do not assign address space to
3212 expansion ROMs that do not already have
3213 BIOS assigned address ranges.
3214 nobar [X86] Do not assign address space to the
3215 BARs that weren't assigned by the BIOS.
3216 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3217 assigned automatically to PCI devices. You can
3218 make the kernel exclude IRQs of your ISA cards
3220 pirqaddr=0xAAAAA [X86] Specify the physical address
3221 of the PIRQ table (normally generated
3222 by the BIOS) if it is outside the
3223 F0000h-100000h range.
3224 lastbus=N [X86] Scan all buses thru bus #N. Can be
3225 useful if the kernel is unable to find your
3226 secondary buses and you want to tell it
3227 explicitly which ones they are.
3228 assign-busses [X86] Always assign all PCI bus
3229 numbers ourselves, overriding
3230 whatever the firmware may have done.
3231 usepirqmask [X86] Honor the possible IRQ mask stored
3232 in the BIOS $PIR table. This is needed on
3233 some systems with broken BIOSes, notably
3234 some HP Pavilion N5400 and Omnibook XE3
3235 notebooks. This will have no effect if ACPI
3236 IRQ routing is enabled.
3237 noacpi [X86] Do not use ACPI for IRQ routing
3238 or for PCI scanning.
3239 use_crs [X86] Use PCI host bridge window information
3240 from ACPI. On BIOSes from 2008 or later, this
3241 is enabled by default. If you need to use this,
3242 please report a bug.
3243 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3244 If you need to use this, please report a bug.
3245 routeirq Do IRQ routing for all PCI devices.
3246 This is normally done in pci_enable_device(),
3247 so this option is a temporary workaround
3248 for broken drivers that don't call it.
3249 skip_isa_align [X86] do not align io start addr, so can
3250 handle more pci cards
3251 noearly [X86] Don't do any early type 1 scanning.
3252 This might help on some broken boards which
3253 machine check when some devices' config space
3254 is read. But various workarounds are disabled
3255 and some IOMMU drivers will not work.
3256 bfsort Sort PCI devices into breadth-first order.
3257 This sorting is done to get a device
3258 order compatible with older (<= 2.4) kernels.
3259 nobfsort Don't sort PCI devices into breadth-first order.
3260 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3261 tuning and use the BIOS-configured MPS defaults.
3262 pcie_bus_safe Set every device's MPS to the largest value
3263 supported by all devices below the root complex.
3264 pcie_bus_perf Set device MPS to the largest allowable MPS
3265 based on its parent bus. Also set MRRS (Max
3266 Read Request Size) to the largest supported
3267 value (no larger than the MPS that the device
3268 or bus can support) for best performance.
3269 pcie_bus_peer2peer Set every device's MPS to 128B, which
3270 every device is guaranteed to support. This
3271 configuration allows peer-to-peer DMA between
3272 any pair of devices, possibly at the cost of
3273 reduced performance. This also guarantees
3274 that hot-added devices will work.
3275 cbiosize=nn[KMG] The fixed amount of bus space which is
3276 reserved for the CardBus bridge's IO window.
3277 The default value is 256 bytes.
3278 cbmemsize=nn[KMG] The fixed amount of bus space which is
3279 reserved for the CardBus bridge's memory
3280 window. The default value is 64 megabytes.
3283 [<order of align>@]<pci_dev>[; ...]
3284 Specifies alignment and device to reassign
3285 aligned memory resources. How to
3286 specify the device is described above.
3287 If <order of align> is not specified,
3288 PAGE_SIZE is used as alignment.
3289 PCI-PCI bridge can be specified, if resource
3290 windows need to be expanded.
3291 To specify the alignment for several
3292 instances of a device, the PCI vendor,
3293 device, subvendor, and subdevice may be
3294 specified, e.g., 4096@pci:8086:9c22:103c:198f
3295 ecrc= Enable/disable PCIe ECRC (transaction layer
3296 end-to-end CRC checking).
3297 bios: Use BIOS/firmware settings. This is the
3301 hpiosize=nn[KMG] The fixed amount of bus space which is
3302 reserved for hotplug bridge's IO window.
3303 Default size is 256 bytes.
3304 hpmemsize=nn[KMG] The fixed amount of bus space which is
3305 reserved for hotplug bridge's memory window.
3306 Default size is 2 megabytes.
3307 hpbussize=nn The minimum amount of additional bus numbers
3308 reserved for buses below a hotplug bridge.
3310 realloc= Enable/disable reallocating PCI bridge resources
3311 if allocations done by BIOS are too small to
3312 accommodate resources required by all child
3314 off: Turn realloc off
3316 realloc same as realloc=on
3317 noari do not use PCIe ARI.
3318 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3319 do not use PCIe ATS (and IOMMU device IOTLB).
3320 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3321 only look for one device below a PCIe downstream
3323 big_root_window Try to add a big 64bit memory window to the PCIe
3324 root complex on AMD CPUs. Some GFX hardware
3325 can resize a BAR to allow access to all VRAM.
3326 Adding the window is slightly risky (it may
3327 conflict with unreported devices), so this
3329 disable_acs_redir=<pci_dev>[; ...]
3330 Specify one or more PCI devices (in the format
3331 specified above) separated by semicolons.
3332 Each device specified will have the PCI ACS
3333 redirect capabilities forced off which will
3334 allow P2P traffic between devices through
3335 bridges without forcing it upstream. Note:
3336 this removes isolation between devices and
3337 may put more devices in an IOMMU group.
3339 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3342 force Enable ASPM even on devices that claim not to support it.
3343 WARNING: Forcing ASPM on may cause system lockups.
3345 pcie_ports= [PCIE] PCIe port services handling:
3346 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3347 even if the platform doesn't give the OS permission to
3348 use them. This may cause conflicts if the platform
3349 also tries to use these services.
3350 compat Disable native PCIe services (PME, AER, DPC, PCIe
3353 pcie_port_pm= [PCIE] PCIe port power management handling:
3354 off Disable power management of all PCIe ports
3355 force Forcibly enable power management of all PCIe ports
3357 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3358 nomsi Do not use MSI for native PCIe PME signaling (this makes
3359 all PCIe root ports use INTx for all services).
3361 pcmv= [HW,PCMCIA] BadgePAD 4
3365 Keep all power-domains already enabled by bootloader on,
3366 even if no driver has claimed them. This is useful
3367 for debug and development, but should not be
3368 needed on a platform with proper driver support.
3371 See Documentation/blockdev/paride.txt.
3373 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3376 See arch/parisc/kernel/pdc_chassis.c
3378 percpu_alloc= Select which percpu first chunk allocator to use.
3379 Currently supported values are "embed" and "page".
3380 Archs may support subset or none of the selections.
3381 See comments in mm/percpu.c for details on each
3382 allocator. This parameter is primarily for debugging
3383 and performance comparison.
3386 See Documentation/blockdev/paride.txt.
3389 See Documentation/blockdev/paride.txt.
3391 pirq= [SMP,APIC] Manual mp-table setup
3392 See Documentation/x86/i386/IO-APIC.txt.
3394 plip= [PPT,NET] Parallel port network link
3395 Format: { parport<nr> | timid | 0 }
3396 See also Documentation/admin-guide/parport.rst.
3398 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3399 Override pmtimer IOPort with a hex value.
3403 Enable PNP debug messages (depends on the
3404 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3405 via /sys/module/pnp/parameters/debug. We always show
3406 current resource usage; turning this on also shows
3407 possible settings and some assignment information.
3413 { on | off | curr | res | no-curr | no-res }
3416 [ISAPNP] Exclude IRQs for the autoconfiguration
3419 [ISAPNP] Exclude DMAs for the autoconfiguration
3421 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3422 Ranges are in pairs (I/O port base and size).
3425 [ISAPNP] Exclude memory regions for the
3427 Ranges are in pairs (memory base and size).
3429 ports= [IP_VS_FTP] IPVS ftp helper module
3431 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3433 Format: <port>,<port>....
3435 powersave=off [PPC] This option disables power saving features.
3436 It specifically disables cpuidle and sets the
3437 platform machine description specific power_save
3438 function to NULL. On Idle the CPU just reduces
3441 ppc_strict_facility_enable
3442 [PPC] This option catches any kernel floating point,
3443 Altivec, VSX and SPE outside of regions specifically
3444 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3445 There is some performance impact when enabling this.
3449 Disable Hardware Transactional Memory
3451 print-fatal-signals=
3452 [KNL] debug: print fatal signals
3454 If enabled, warn about various signal handling
3455 related application anomalies: too many signals,
3456 too many POSIX.1 timers, fatal signals causing a
3459 If you hit the warning due to signal overflow,
3460 you might want to try "ulimit -i unlimited".
3464 printk.always_kmsg_dump=
3465 Trigger kmsg_dump for cases other than kernel oops or
3467 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3470 printk.devkmsg={on,off,ratelimit}
3471 Control writing to /dev/kmsg.
3472 on - unlimited logging to /dev/kmsg from userspace
3473 off - logging to /dev/kmsg disabled
3474 ratelimit - ratelimit the logging
3477 printk.time= Show timing data prefixed to each printk message line
3478 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3480 processor.max_cstate= [HW,ACPI]
3481 Limit processor to maximum C-state
3482 max_cstate=9 overrides any DMI blacklist limit.
3484 processor.nocst [HW,ACPI]
3485 Ignore the _CST method to determine C-states,
3486 instead using the legacy FADT method
3488 profile= [KNL] Enable kernel profiling via /proc/profile
3489 Format: [<profiletype>,]<number>
3490 Param: <profiletype>: "schedule", "sleep", or "kvm"
3491 [defaults to kernel profiling]
3492 Param: "schedule" - profile schedule points.
3493 Param: "sleep" - profile D-state sleeping (millisecs).
3494 Requires CONFIG_SCHEDSTATS
3495 Param: "kvm" - profile VM exits.
3496 Param: <number> - step/bucket size as a power of 2 for
3497 statistical time based profiling.
3499 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3501 See Documentation/blockdev/ramdisk.txt.
3503 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3504 probe for; one of (bare|imps|exps|lifebook|any).
3505 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3507 psmouse.resetafter= [HW,MOUSE]
3508 Try to reset the device after so many bad packets
3511 [HW,MOUSE] Set desired mouse resolution, in dpi.
3512 psmouse.smartscroll=
3513 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3514 0 = disabled, 1 = enabled (default).
3516 pstore.backend= Specify the name of the pstore backend to use
3519 See Documentation/blockdev/paride.txt.
3521 pti= [X86_64] Control Page Table Isolation of user and
3522 kernel address spaces. Disabling this feature
3523 removes hardening, but improves performance of
3524 system calls and interrupts.
3526 on - unconditionally enable
3527 off - unconditionally disable
3528 auto - kernel detects whether your CPU model is
3529 vulnerable to issues that PTI mitigates
3531 Not specifying this option is equivalent to pti=auto.
3534 Equivalent to pti=off
3537 [KNL] Number of legacy pty's. Overwrites compiled-in
3540 quiet [KNL] Disable most log messages
3545 See Documentation/admin-guide/md.rst.
3547 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3548 See Documentation/blockdev/ramdisk.txt.
3550 random.trust_cpu={on,off}
3551 [KNL] Enable or disable trusting the use of the
3552 CPU's random number generator (if available) to
3553 fully seed the kernel's CRNG. Default is controlled
3554 by CONFIG_RANDOM_TRUST_CPU.
3556 ras=option[,option,...] [KNL] RAS-specific options
3559 Disable the Correctable Errors Collector,
3560 see CONFIG_RAS_CEC help text.
3563 The argument is a cpu list, as described above.
3565 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3566 the specified list of CPUs to be no-callback CPUs.
3567 Invocation of these CPUs' RCU callbacks will be
3568 offloaded to "rcuox/N" kthreads created for that
3569 purpose, where "x" is "p" for RCU-preempt, and
3570 "s" for RCU-sched, and "N" is the CPU number.
3571 This reduces OS jitter on the offloaded CPUs,
3572 which can be useful for HPC and real-time
3573 workloads. It can also improve energy efficiency
3574 for asymmetric multiprocessors.
3577 Rather than requiring that offloaded CPUs
3578 (specified by rcu_nocbs= above) explicitly
3579 awaken the corresponding "rcuoN" kthreads,
3580 make these kthreads poll for callbacks.
3581 This improves the real-time response for the
3582 offloaded CPUs by relieving them of the need to
3583 wake up the corresponding kthread, but degrades
3584 energy efficiency by requiring that the kthreads
3585 periodically wake up to do the polling.
3587 rcutree.blimit= [KNL]
3588 Set maximum number of finished RCU callbacks to
3589 process in one batch.
3591 rcutree.dump_tree= [KNL]
3592 Dump the structure of the rcu_node combining tree
3593 out at early boot. This is used for diagnostic
3594 purposes, to verify correct tree setup.
3596 rcutree.gp_cleanup_delay= [KNL]
3597 Set the number of jiffies to delay each step of
3598 RCU grace-period cleanup.
3600 rcutree.gp_init_delay= [KNL]
3601 Set the number of jiffies to delay each step of
3602 RCU grace-period initialization.
3604 rcutree.gp_preinit_delay= [KNL]
3605 Set the number of jiffies to delay each step of
3606 RCU grace-period pre-initialization, that is,
3607 the propagation of recent CPU-hotplug changes up
3608 the rcu_node combining tree.
3610 rcutree.rcu_fanout_exact= [KNL]
3611 Disable autobalancing of the rcu_node combining
3612 tree. This is used by rcutorture, and might
3613 possibly be useful for architectures having high
3614 cache-to-cache transfer latencies.
3616 rcutree.rcu_fanout_leaf= [KNL]
3617 Change the number of CPUs assigned to each
3618 leaf rcu_node structure. Useful for very
3619 large systems, which will choose the value 64,
3620 and for NUMA systems with large remote-access
3621 latencies, which will choose a value aligned
3622 with the appropriate hardware boundaries.
3624 rcutree.jiffies_till_sched_qs= [KNL]
3625 Set required age in jiffies for a
3626 given grace period before RCU starts
3627 soliciting quiescent-state help from
3628 rcu_note_context_switch(). If not specified, the
3629 kernel will calculate a value based on the most
3630 recent settings of rcutree.jiffies_till_first_fqs
3631 and rcutree.jiffies_till_next_fqs.
3632 This calculated value may be viewed in
3633 rcutree.jiffies_to_sched_qs. Any attempt to
3634 set rcutree.jiffies_to_sched_qs will be
3635 cheerfully overwritten.
3637 rcutree.jiffies_till_first_fqs= [KNL]
3638 Set delay from grace-period initialization to
3639 first attempt to force quiescent states.
3640 Units are jiffies, minimum value is zero,
3641 and maximum value is HZ.
3643 rcutree.jiffies_till_next_fqs= [KNL]
3644 Set delay between subsequent attempts to force
3645 quiescent states. Units are jiffies, minimum
3646 value is one, and maximum value is HZ.
3648 rcutree.kthread_prio= [KNL,BOOT]
3649 Set the SCHED_FIFO priority of the RCU per-CPU
3650 kthreads (rcuc/N). This value is also used for
3651 the priority of the RCU boost threads (rcub/N)
3652 and for the RCU grace-period kthreads (rcu_bh,
3653 rcu_preempt, and rcu_sched). If RCU_BOOST is
3654 set, valid values are 1-99 and the default is 1
3655 (the least-favored priority). Otherwise, when
3656 RCU_BOOST is not set, valid values are 0-99 and
3657 the default is zero (non-realtime operation).
3659 rcutree.rcu_nocb_leader_stride= [KNL]
3660 Set the number of NOCB kthread groups, which
3661 defaults to the square root of the number of
3662 CPUs. Larger numbers reduces the wakeup overhead
3663 on the per-CPU grace-period kthreads, but increases
3664 that same overhead on each group's leader.
3666 rcutree.qhimark= [KNL]
3667 Set threshold of queued RCU callbacks beyond which
3668 batch limiting is disabled.
3670 rcutree.qlowmark= [KNL]
3671 Set threshold of queued RCU callbacks below which
3672 batch limiting is re-enabled.
3674 rcutree.rcu_idle_gp_delay= [KNL]
3675 Set wakeup interval for idle CPUs that have
3676 RCU callbacks (RCU_FAST_NO_HZ=y).
3678 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3679 Set wakeup interval for idle CPUs that have
3680 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3681 Lazy RCU callbacks are those which RCU can
3682 prove do nothing more than free memory.
3684 rcutree.rcu_kick_kthreads= [KNL]
3685 Cause the grace-period kthread to get an extra
3686 wake_up() if it sleeps three times longer than
3687 it should at force-quiescent-state time.
3688 This wake_up() will be accompanied by a
3689 WARN_ONCE() splat and an ftrace_dump().
3691 rcuperf.gp_async= [KNL]
3692 Measure performance of asynchronous
3693 grace-period primitives such as call_rcu().
3695 rcuperf.gp_async_max= [KNL]
3696 Specify the maximum number of outstanding
3697 callbacks per writer thread. When a writer
3698 thread exceeds this limit, it invokes the
3699 corresponding flavor of rcu_barrier() to allow
3700 previously posted callbacks to drain.
3702 rcuperf.gp_exp= [KNL]
3703 Measure performance of expedited synchronous
3704 grace-period primitives.
3706 rcuperf.holdoff= [KNL]
3707 Set test-start holdoff period. The purpose of
3708 this parameter is to delay the start of the
3709 test until boot completes in order to avoid
3712 rcuperf.nreaders= [KNL]
3713 Set number of RCU readers. The value -1 selects
3714 N, where N is the number of CPUs. A value
3715 "n" less than -1 selects N-n+1, where N is again
3716 the number of CPUs. For example, -2 selects N
3717 (the number of CPUs), -3 selects N+1, and so on.
3718 A value of "n" less than or equal to -N selects
3721 rcuperf.nwriters= [KNL]
3722 Set number of RCU writers. The values operate
3723 the same as for rcuperf.nreaders.
3724 N, where N is the number of CPUs
3726 rcuperf.perf_type= [KNL]
3727 Specify the RCU implementation to test.
3729 rcuperf.shutdown= [KNL]
3730 Shut the system down after performance tests
3731 complete. This is useful for hands-off automated
3734 rcuperf.verbose= [KNL]
3735 Enable additional printk() statements.
3737 rcuperf.writer_holdoff= [KNL]
3738 Write-side holdoff between grace periods,
3739 in microseconds. The default of zero says
3742 rcutorture.cbflood_inter_holdoff= [KNL]
3743 Set holdoff time (jiffies) between successive
3744 callback-flood tests.
3746 rcutorture.cbflood_intra_holdoff= [KNL]
3747 Set holdoff time (jiffies) between successive
3748 bursts of callbacks within a given callback-flood
3751 rcutorture.cbflood_n_burst= [KNL]
3752 Set the number of bursts making up a given
3753 callback-flood test. Set this to zero to
3754 disable callback-flood testing.
3756 rcutorture.cbflood_n_per_burst= [KNL]
3757 Set the number of callbacks to be registered
3758 in a given burst of a callback-flood test.
3760 rcutorture.fqs_duration= [KNL]
3761 Set duration of force_quiescent_state bursts
3764 rcutorture.fqs_holdoff= [KNL]
3765 Set holdoff time within force_quiescent_state bursts
3768 rcutorture.fqs_stutter= [KNL]
3769 Set wait time between force_quiescent_state bursts
3772 rcutorture.gp_cond= [KNL]
3773 Use conditional/asynchronous update-side
3774 primitives, if available.
3776 rcutorture.gp_exp= [KNL]
3777 Use expedited update-side primitives, if available.
3779 rcutorture.gp_normal= [KNL]
3780 Use normal (non-expedited) asynchronous
3781 update-side primitives, if available.
3783 rcutorture.gp_sync= [KNL]
3784 Use normal (non-expedited) synchronous
3785 update-side primitives, if available. If all
3786 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3787 rcutorture.gp_normal=, and rcutorture.gp_sync=
3788 are zero, rcutorture acts as if is interpreted
3789 they are all non-zero.
3791 rcutorture.n_barrier_cbs= [KNL]
3792 Set callbacks/threads for rcu_barrier() testing.
3794 rcutorture.nfakewriters= [KNL]
3795 Set number of concurrent RCU writers. These just
3796 stress RCU, they don't participate in the actual
3797 test, hence the "fake".
3799 rcutorture.nreaders= [KNL]
3800 Set number of RCU readers. The value -1 selects
3801 N-1, where N is the number of CPUs. A value
3802 "n" less than -1 selects N-n-2, where N is again
3803 the number of CPUs. For example, -2 selects N
3804 (the number of CPUs), -3 selects N+1, and so on.
3806 rcutorture.object_debug= [KNL]
3807 Enable debug-object double-call_rcu() testing.
3809 rcutorture.onoff_holdoff= [KNL]
3810 Set time (s) after boot for CPU-hotplug testing.
3812 rcutorture.onoff_interval= [KNL]
3813 Set time (jiffies) between CPU-hotplug operations,
3814 or zero to disable CPU-hotplug testing.
3816 rcutorture.shuffle_interval= [KNL]
3817 Set task-shuffle interval (s). Shuffling tasks
3818 allows some CPUs to go into dyntick-idle mode
3819 during the rcutorture test.
3821 rcutorture.shutdown_secs= [KNL]
3822 Set time (s) after boot system shutdown. This
3823 is useful for hands-off automated testing.
3825 rcutorture.stall_cpu= [KNL]
3826 Duration of CPU stall (s) to test RCU CPU stall
3827 warnings, zero to disable.
3829 rcutorture.stall_cpu_holdoff= [KNL]
3830 Time to wait (s) after boot before inducing stall.
3832 rcutorture.stall_cpu_irqsoff= [KNL]
3833 Disable interrupts while stalling if set.
3835 rcutorture.stat_interval= [KNL]
3836 Time (s) between statistics printk()s.
3838 rcutorture.stutter= [KNL]
3839 Time (s) to stutter testing, for example, specifying
3840 five seconds causes the test to run for five seconds,
3841 wait for five seconds, and so on. This tests RCU's
3842 ability to transition abruptly to and from idle.
3844 rcutorture.test_boost= [KNL]
3845 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3846 "Maybe" means test if the RCU implementation
3847 under test support RCU priority boosting.
3849 rcutorture.test_boost_duration= [KNL]
3850 Duration (s) of each individual boost test.
3852 rcutorture.test_boost_interval= [KNL]
3853 Interval (s) between each boost test.
3855 rcutorture.test_no_idle_hz= [KNL]
3856 Test RCU's dyntick-idle handling. See also the
3857 rcutorture.shuffle_interval parameter.
3859 rcutorture.torture_type= [KNL]
3860 Specify the RCU implementation to test.
3862 rcutorture.verbose= [KNL]
3863 Enable additional printk() statements.
3865 rcupdate.rcu_cpu_stall_suppress= [KNL]
3866 Suppress RCU CPU stall warning messages.
3868 rcupdate.rcu_cpu_stall_timeout= [KNL]
3869 Set timeout for RCU CPU stall warning messages.
3871 rcupdate.rcu_expedited= [KNL]
3872 Use expedited grace-period primitives, for
3873 example, synchronize_rcu_expedited() instead
3874 of synchronize_rcu(). This reduces latency,
3875 but can increase CPU utilization, degrade
3876 real-time latency, and degrade energy efficiency.
3877 No effect on CONFIG_TINY_RCU kernels.
3879 rcupdate.rcu_normal= [KNL]
3880 Use only normal grace-period primitives,
3881 for example, synchronize_rcu() instead of
3882 synchronize_rcu_expedited(). This improves
3883 real-time latency, CPU utilization, and
3884 energy efficiency, but can expose users to
3885 increased grace-period latency. This parameter
3886 overrides rcupdate.rcu_expedited. No effect on
3887 CONFIG_TINY_RCU kernels.
3889 rcupdate.rcu_normal_after_boot= [KNL]
3890 Once boot has completed (that is, after
3891 rcu_end_inkernel_boot() has been invoked), use
3892 only normal grace-period primitives. No effect
3893 on CONFIG_TINY_RCU kernels.
3895 rcupdate.rcu_task_stall_timeout= [KNL]
3896 Set timeout in jiffies for RCU task stall warning
3897 messages. Disable with a value less than or equal
3900 rcupdate.rcu_self_test= [KNL]
3901 Run the RCU early boot self tests
3905 Run specified binary instead of /init from the ramdisk,
3906 used for early userspace startup. See initrd.
3909 Turn on/off individual RDT features. List is:
3910 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3912 E.g. to turn on cmt and turn off mba use:
3916 Format (x86 or x86_64):
3917 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3919 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3921 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3922 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3923 reboot_force is either force or not specified,
3924 reboot_cpu is s[mp]#### with #### being the processor
3925 to be used for rebooting.
3928 [KNL, SMP] Set scheduler's default relax_domain_level.
3929 See Documentation/cgroup-v1/cpusets.txt.
3931 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3932 Format: <base1>,<size1>[,<base2>,<size2>,...]
3933 Reserve I/O ports or memory so the kernel won't use
3934 them. If <base> is less than 0x10000, the region
3935 is assumed to be I/O ports; otherwise it is memory.
3937 reservetop= [X86-32]
3939 Reserves a hole at the top of the kernel virtual
3944 Set the amount of memory to reserve for BIOS at
3945 the bottom of the address space.
3947 reset_devices [KNL] Force drivers to reset the underlying device
3948 during initialization.
3951 Specify the partition device for software suspend
3953 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3955 resume_offset= [SWSUSP]
3956 Specify the offset from the beginning of the partition
3957 given by "resume=" at which the swap header is located,
3958 in <PAGE_SIZE> units (needed only for swap files).
3959 See Documentation/power/swsusp-and-swap-files.txt
3961 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3962 read the resume files
3964 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3965 Useful for devices that are detected asynchronously
3966 (e.g. USB and MMC devices).
3968 hibernate= [HIBERNATION]
3969 noresume Don't check if there's a hibernation image
3970 present during boot.
3971 nocompress Don't compress/decompress hibernation images.
3972 no Disable hibernation and resume.
3973 protect_image Turn on image protection during restoration
3974 (that will set all pages holding image data
3975 during restoration read-only).
3977 retain_initrd [RAM] Keep initrd memory after extraction
3979 rfkill.default_state=
3980 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3981 etc. communication is blocked by default.
3984 rfkill.master_switch_mode=
3985 0 The "airplane mode" button does nothing.
3986 1 The "airplane mode" button toggles between everything
3987 blocked and the previous configuration.
3988 2 The "airplane mode" button toggles between everything
3989 blocked and everything unblocked.
3991 rhash_entries= [KNL,NET]
3992 Set number of hash buckets for route cache
3995 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3998 ro [KNL] Mount root device read-only on boot
4001 on Mark read-only kernel memory as read-only (default).
4002 off Leave read-only kernel memory writable for debugging.
4005 Enable the uart passthrough on the designated usb port
4006 on Rockchip SoCs. When active, the signals of the
4007 debug-uart get routed to the D+ and D- pins of the usb
4008 port and the regular usb controller gets disabled.
4010 root= [KNL] Root filesystem
4011 See name_to_dev_t comment in init/do_mounts.c.
4013 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4014 mount the root filesystem
4016 rootflags= [KNL] Set root filesystem mount option string
4018 rootfstype= [KNL] Set root filesystem type
4020 rootwait [KNL] Wait (indefinitely) for root device to show up.
4021 Useful for devices that are detected asynchronously
4022 (e.g. USB and MMC devices).
4024 rproc_mem=nn[KMG][@address]
4025 [KNL,ARM,CMA] Remoteproc physical memory block.
4026 Memory area to be used by remote processor image,
4029 rw [KNL] Mount root device read-write on boot
4031 S [KNL] Run init in single mode
4033 s390_iommu= [HW,S390]
4034 Set s390 IOTLB flushing mode
4036 With strict flushing every unmap operation will result in
4037 an IOTLB flush. Default is lazy flushing before reuse,
4041 See drivers/net/irda/sa1100_ir.c.
4043 sbni= [NET] Granch SBNI12 leased line adapter
4045 sched_debug [KNL] Enables verbose scheduler debug messages.
4047 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4048 Allowed values are enable and disable. This feature
4049 incurs a small amount of overhead in the scheduler
4050 but is useful for debugging and performance tuning.
4052 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4053 xtime_lock contention on larger systems, and/or RCU lock
4054 contention on all systems with CONFIG_MAXSMP set.
4055 Format: { "0" | "1" }
4056 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4058 Note: increases power consumption, thus should only be
4059 enabled if running jitter sensitive (HPC/RT) workloads.
4061 security= [SECURITY] Choose a security module to enable at boot.
4062 If this boot parameter is not specified, only the first
4063 security module asking for security registration will be
4064 loaded. An invalid security module name will be treated
4065 as if no module has been chosen.
4067 selinux= [SELINUX] Disable or enable SELinux at boot time.
4068 Format: { "0" | "1" }
4069 See security/selinux/Kconfig help text.
4072 Default value is set via kernel config option.
4073 If enabled at boot time, /selinux/disable can be used
4074 later to disable prior to initial policy load.
4076 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4077 Format: { "0" | "1" }
4078 See security/apparmor/Kconfig help text
4081 Default value is set via kernel config option.
4083 serialnumber [BUGS=X86-32]
4086 Maximal number of shapers.
4094 Disable merging of slabs with similar size. May be
4095 necessary if there is some reason to distinguish
4096 allocs to different slabs, especially in hardened
4097 environments where the risk of heap overflows and
4098 layout control by attackers can usually be
4099 frustrated by disabling merging. This will reduce
4100 most of the exposure of a heap attack to a single
4101 cache (risks via metadata attacks are mostly
4102 unchanged). Debug options disable merging on their
4104 For more information see Documentation/vm/slub.rst.
4106 slab_max_order= [MM, SLAB]
4107 Determines the maximum allowed order for slabs.
4108 A high setting may cause OOMs due to memory
4109 fragmentation. Defaults to 1 for systems with
4110 more than 32MB of RAM, 0 otherwise.
4112 slub_debug[=options[,slabs]] [MM, SLUB]
4113 Enabling slub_debug allows one to determine the
4114 culprit if slab objects become corrupted. Enabling
4115 slub_debug can create guard zones around objects and
4116 may poison objects when not in use. Also tracks the
4117 last alloc / free. For more information see
4118 Documentation/vm/slub.rst.
4120 slub_memcg_sysfs= [MM, SLUB]
4121 Determines whether to enable sysfs directories for
4122 memory cgroup sub-caches. 1 to enable, 0 to disable.
4123 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4124 Enabling this can lead to a very high number of debug
4125 directories and files being created under
4128 slub_max_order= [MM, SLUB]
4129 Determines the maximum allowed order for slabs.
4130 A high setting may cause OOMs due to memory
4131 fragmentation. For more information see
4132 Documentation/vm/slub.rst.
4134 slub_min_objects= [MM, SLUB]
4135 The minimum number of objects per slab. SLUB will
4136 increase the slab order up to slub_max_order to
4137 generate a sufficiently large slab able to contain
4138 the number of objects indicated. The higher the number
4139 of objects the smaller the overhead of tracking slabs
4140 and the less frequently locks need to be acquired.
4141 For more information see Documentation/vm/slub.rst.
4143 slub_min_order= [MM, SLUB]
4144 Determines the minimum page order for slabs. Must be
4145 lower than slub_max_order.
4146 For more information see Documentation/vm/slub.rst.
4148 slub_nomerge [MM, SLUB]
4149 Same with slab_nomerge. This is supported for legacy.
4150 See slab_nomerge for more information.
4153 Format: <io1>[,<io2>[,...,<io8>]]
4155 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4156 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4157 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4158 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4159 smsc-ircc2.ircc_irq= [HW] IRQ line
4160 smsc-ircc2.ircc_dma= [HW] DMA channel
4161 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4162 0: Toshiba Satellite 1800 (GP data pin select)
4163 1: Fast pin select (default)
4166 smt [KNL,S390] Set the maximum number of threads (logical
4167 CPUs) to use per physical CPU on systems capable of
4168 symmetric multithreading (SMT). Will be capped to the
4169 actual hardware limit.
4171 Default: -1 (no limit)
4174 [KNL] Should the soft-lockup detector generate panics.
4177 A nonzero value instructs the soft-lockup detector
4178 to panic the machine when a soft-lockup occurs. This
4179 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4180 which is the respective build-time switch to that
4183 softlockup_all_cpu_backtrace=
4184 [KNL] Should the soft-lockup detector generate
4185 backtraces on all cpus.
4188 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4189 See Documentation/laptops/sonypi.txt
4191 spectre_v2= [X86] Control mitigation of Spectre variant 2
4192 (indirect branch speculation) vulnerability.
4194 on - unconditionally enable
4195 off - unconditionally disable
4196 auto - kernel detects whether your CPU model is
4199 Selecting 'on' will, and 'auto' may, choose a
4200 mitigation method at run time according to the
4201 CPU, the available microcode, the setting of the
4202 CONFIG_RETPOLINE configuration option, and the
4203 compiler with which the kernel was built.
4205 Specific mitigations can also be selected manually:
4207 retpoline - replace indirect branches
4208 retpoline,generic - google's original retpoline
4209 retpoline,amd - AMD-specific minimal thunk
4211 Not specifying this option is equivalent to
4214 spec_store_bypass_disable=
4215 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4216 (Speculative Store Bypass vulnerability)
4218 Certain CPUs are vulnerable to an exploit against a
4219 a common industry wide performance optimization known
4220 as "Speculative Store Bypass" in which recent stores
4221 to the same memory location may not be observed by
4222 later loads during speculative execution. The idea
4223 is that such stores are unlikely and that they can
4224 be detected prior to instruction retirement at the
4225 end of a particular speculation execution window.
4227 In vulnerable processors, the speculatively forwarded
4228 store can be used in a cache side channel attack, for
4229 example to read memory to which the attacker does not
4230 directly have access (e.g. inside sandboxed code).
4232 This parameter controls whether the Speculative Store
4233 Bypass optimization is used.
4235 On x86 the options are:
4237 on - Unconditionally disable Speculative Store Bypass
4238 off - Unconditionally enable Speculative Store Bypass
4239 auto - Kernel detects whether the CPU model contains an
4240 implementation of Speculative Store Bypass and
4241 picks the most appropriate mitigation. If the
4242 CPU is not vulnerable, "off" is selected. If the
4243 CPU is vulnerable the default mitigation is
4244 architecture and Kconfig dependent. See below.
4245 prctl - Control Speculative Store Bypass per thread
4246 via prctl. Speculative Store Bypass is enabled
4247 for a process by default. The state of the control
4248 is inherited on fork.
4249 seccomp - Same as "prctl" above, but all seccomp threads
4250 will disable SSB unless they explicitly opt out.
4252 Default mitigations:
4253 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4255 On powerpc the options are:
4257 on,auto - On Power8 and Power9 insert a store-forwarding
4258 barrier on kernel entry and exit. On Power7
4259 perform a software flush on kernel entry and
4263 Not specifying this option is equivalent to
4264 spec_store_bypass_disable=auto.
4266 spia_io_base= [HW,MTD]
4271 srcutree.counter_wrap_check [KNL]
4272 Specifies how frequently to check for
4273 grace-period sequence counter wrap for the
4274 srcu_data structure's ->srcu_gp_seq_needed field.
4275 The greater the number of bits set in this kernel
4276 parameter, the less frequently counter wrap will
4277 be checked for. Note that the bottom two bits
4280 srcutree.exp_holdoff [KNL]
4281 Specifies how many nanoseconds must elapse
4282 since the end of the last SRCU grace period for
4283 a given srcu_struct until the next normal SRCU
4284 grace period will be considered for automatic
4285 expediting. Set to zero to disable automatic
4289 Speculative Store Bypass Disable control
4291 On CPUs that are vulnerable to the Speculative
4292 Store Bypass vulnerability and offer a
4293 firmware based mitigation, this parameter
4294 indicates how the mitigation should be used:
4296 force-on: Unconditionally enable mitigation for
4297 for both kernel and userspace
4298 force-off: Unconditionally disable mitigation for
4299 for both kernel and userspace
4300 kernel: Always enable mitigation in the
4301 kernel, and offer a prctl interface
4302 to allow userspace to register its
4303 interest in being mitigated too.
4305 stack_guard_gap= [MM]
4306 override the default stack gap protection. The value
4307 is in page units and it defines how many pages prior
4308 to (for stacks growing down) resp. after (for stacks
4309 growing up) the main stack are reserved for no other
4310 mapping. Default value is 256 pages.
4313 Enabled the stack tracer on boot up.
4315 stacktrace_filter=[function-list]
4316 [FTRACE] Limit the functions that the stack tracer
4317 will trace at boot up. function-list is a comma separated
4318 list of functions. This list can be changed at run
4319 time by the stack_trace_filter file in the debugfs
4320 tracing directory. Note, this enables stack tracing
4321 and the stacktrace above is not needed.
4325 Set the STI (builtin display/keyboard on the HP-PARISC
4326 machines) console (graphic card) which should be used
4327 as the initial boot-console.
4328 See also comment in drivers/video/console/sticore.c.
4331 See comment in drivers/video/console/sticore.c.
4334 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4336 sunrpc.min_resvport=
4337 sunrpc.max_resvport=
4339 SunRPC servers often require that client requests
4340 originate from a privileged port (i.e. a port in the
4341 range 0 < portnr < 1024).
4342 An administrator who wishes to reserve some of these
4343 ports for other uses may adjust the range that the
4344 kernel's sunrpc client considers to be privileged
4345 using these two parameters to set the minimum and
4346 maximum port values.
4348 sunrpc.svc_rpc_per_connection_limit=
4350 Limit the number of requests that the server will
4351 process in parallel from a single connection.
4352 The default value is 0 (no limit).
4356 Control how the NFS server code allocates CPUs to
4357 service thread pools. Depending on how many NICs
4358 you have and where their interrupts are bound, this
4359 option will affect which CPUs will do NFS serving.
4360 Note: this parameter cannot be changed while the
4361 NFS server is running.
4363 auto the server chooses an appropriate mode
4364 automatically using heuristics
4365 global a single global pool contains all CPUs
4366 percpu one pool for each CPU
4367 pernode one pool for each NUMA node (equivalent
4368 to global on non-NUMA machines)
4370 sunrpc.tcp_slot_table_entries=
4371 sunrpc.udp_slot_table_entries=
4373 Sets the upper limit on the number of simultaneous
4374 RPC calls that can be sent from the client to a
4375 server. Increasing these values may allow you to
4376 improve throughput, but will also increase the
4377 amount of memory reserved for use by the client.
4379 suspend.pm_test_delay=
4381 Sets the number of seconds to remain in a suspend test
4382 mode before resuming the system (see
4383 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4384 is set. Default value is 5.
4387 [KNL] Enable accounting of swap in memory resource
4388 controller if no parameter or 1 is given or disable
4389 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4391 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4392 Format: { <int> | force | noforce }
4393 <int> -- Number of I/O TLB slabs
4394 force -- force using of bounce buffers even if they
4395 wouldn't be automatically used by the kernel
4396 noforce -- Never use bounce buffers (for debugging)
4400 sysfs.deprecated=0|1 [KNL]
4401 Enable/disable old style sysfs layout for old udev
4402 on older distributions. When this option is enabled
4403 very new udev will not work anymore. When this option
4404 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4405 in older udev will not work anymore.
4406 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4407 the kernel configuration.
4409 sysrq_always_enabled
4411 Ignore sysrq setting - this boot parameter will
4412 neutralize any effect of /proc/sys/kernel/sysrq.
4413 Useful for debugging.
4415 tcpmhash_entries= [KNL,NET]
4416 Set the number of tcp_metrics_hash slots.
4417 Default value is 8192 or 16384 depending on total
4418 ram pages. This is used to specify the TCP metrics
4419 cache size. See Documentation/networking/ip-sysctl.txt
4420 "tcp_no_metrics_save" section for more details.
4424 test_suspend= [SUSPEND][,N]
4425 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4426 standby suspend) or "freeze" (for suspend type freeze)
4427 as the system sleep state during system startup with
4428 the optional capability to repeat N number of times.
4429 The system is woken from this state using a
4430 wakeup-capable RTC alarm.
4432 thash_entries= [KNL,NET]
4433 Set number of hash buckets for TCP connection
4435 thermal.act= [HW,ACPI]
4436 -1: disable all active trip points in all thermal zones
4437 <degrees C>: override all lowest active trip points
4439 thermal.crt= [HW,ACPI]
4440 -1: disable all critical trip points in all thermal zones
4441 <degrees C>: override all critical trip points
4443 thermal.nocrt= [HW,ACPI]
4444 Set to disable actions on ACPI thermal zone
4445 critical and hot trip points.
4447 thermal.off= [HW,ACPI]
4448 1: disable ACPI thermal control
4450 thermal.psv= [HW,ACPI]
4451 -1: disable all passive trip points
4452 <degrees C>: override all passive trip points to this
4455 thermal.tzp= [HW,ACPI]
4456 Specify global default ACPI thermal zone polling rate
4457 <deci-seconds>: poll all this frequency
4458 0: no polling (default)
4461 Force threading of all interrupt handlers except those
4462 marked explicitly IRQF_NO_THREAD.
4465 Enable the Transcendent memory driver if built-in.
4467 tmem.cleancache=0|1 [KNL, XEN]
4468 Default is on (1). Disable the usage of the cleancache
4469 API to send anonymous pages to the hypervisor.
4471 tmem.frontswap=0|1 [KNL, XEN]
4472 Default is on (1). Disable the usage of the frontswap
4473 API to send swap pages to the hypervisor. If disabled
4474 the selfballooning and selfshrinking are force disabled.
4476 tmem.selfballooning=0|1 [KNL, XEN]
4477 Default is on (1). Disable the driving of swap pages
4480 tmem.selfshrinking=0|1 [KNL, XEN]
4481 Default is on (1). Partial swapoff that immediately
4482 transfers pages from Xen hypervisor back to the
4483 kernel based on different criteria.
4487 Specify if the kernel should make use of the cpu
4488 topology information if the hardware supports this.
4489 The scheduler will make use of this information and
4490 e.g. base its process migration decisions on it.
4493 topology_updates= [KNL, PPC, NUMA]
4495 Specify if the kernel should ignore (off)
4496 topology updates sent by the hypervisor to this
4501 tpm_suspend_pcr=[HW,TPM]
4502 Format: integer pcr id
4503 Specify that at suspend time, the tpm driver
4504 should extend the specified pcr with zeros,
4505 as a workaround for some chips which fail to
4506 flush the last written pcr on TPM_SaveState.
4507 This will guarantee that all the other pcrs
4510 trace_buf_size=nn[KMG]
4511 [FTRACE] will set tracing buffer size on each cpu.
4513 trace_event=[event-list]
4514 [FTRACE] Set and start specified trace events in order
4515 to facilitate early boot debugging. The event-list is a
4516 comma separated list of trace events to enable. See
4517 also Documentation/trace/events.rst
4519 trace_options=[option-list]
4520 [FTRACE] Enable or disable tracer options at boot.
4521 The option-list is a comma delimited list of options
4522 that can be enabled or disabled just as if you were
4523 to echo the option name into
4525 /sys/kernel/debug/tracing/trace_options
4527 For example, to enable stacktrace option (to dump the
4528 stack trace of each event), add to the command line:
4530 trace_options=stacktrace
4532 See also Documentation/trace/ftrace.rst "trace options"
4536 Have the tracepoints sent to printk as well as the
4537 tracing ring buffer. This is useful for early boot up
4538 where the system hangs or reboots and does not give the
4539 option for reading the tracing buffer or performing a
4540 ftrace_dump_on_oops.
4542 To turn off having tracepoints sent to printk,
4543 echo 0 > /proc/sys/kernel/tracepoint_printk
4544 Note, echoing 1 into this file without the
4545 tracepoint_printk kernel cmdline option has no effect.
4549 Having tracepoints sent to printk() and activating high
4550 frequency tracepoints such as irq or sched, can cause
4551 the system to live lock.
4554 [FTRACE] enable this option to disable tracing when a
4555 warning is hit. This turns off "tracing_on". Tracing can
4556 be enabled again by echoing '1' into the "tracing_on"
4557 file located in /sys/kernel/debug/tracing/
4559 This option is useful, as it disables the trace before
4560 the WARNING dump is called, which prevents the trace to
4561 be filled with content caused by the warning output.
4563 This option can also be set at run time via the sysctl
4564 option: kernel/traceoff_on_warning
4566 transparent_hugepage=
4568 Format: [always|madvise|never]
4569 Can be used to control the default behavior of the system
4570 with respect to transparent hugepages.
4571 See Documentation/admin-guide/mm/transhuge.rst
4574 tsc= Disable clocksource stability checks for TSC.
4576 [x86] reliable: mark tsc clocksource as reliable, this
4577 disables clocksource verification at runtime, as well
4578 as the stability checks done at bootup. Used to enable
4579 high-resolution timer mode on older hardware, and in
4580 virtualized environment.
4581 [x86] noirqtime: Do not use TSC to do irq accounting.
4582 Used to run time disable IRQ_TIME_ACCOUNTING on any
4583 platforms where RDTSC is slow and this accounting
4585 [x86] unstable: mark the TSC clocksource as unstable, this
4586 marks the TSC unconditionally unstable at bootup and
4587 avoids any further wobbles once the TSC watchdog notices.
4589 turbografx.map[2|3]= [HW,JOY]
4590 TurboGraFX parallel port interface
4592 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4593 See also Documentation/input/devices/joystick-parport.rst
4595 udbg-immortal [PPC] When debugging early kernel crashes that
4596 happen after console_init() and before a proper
4597 console driver takes over, this boot options might
4598 help "seeing" what's going on.
4600 uhash_entries= [KNL,NET]
4601 Set number of hash buckets for UDP/UDP-Lite connections
4604 [USB] Ignore overcurrent events (default N).
4605 Some badly-designed motherboards generate lots of
4606 bogus events, for ports that aren't wired to
4607 anything. Set this parameter to avoid log spamming.
4608 Note that genuine overcurrent events won't be
4612 [X86] Cause panic on unknown NMI.
4614 usbcore.authorized_default=
4615 [USB] Default USB device authorization:
4616 (default -1 = authorized except for wireless USB,
4617 0 = not authorized, 1 = authorized)
4619 usbcore.autosuspend=
4620 [USB] The autosuspend time delay (in seconds) used
4621 for newly-detected USB devices (default 2). This
4622 is the time required before an idle device will be
4623 autosuspended. Devices for which the delay is set
4624 to a negative value won't be autosuspended at all.
4626 usbcore.usbfs_snoop=
4627 [USB] Set to log all usbfs traffic (default 0 = off).
4629 usbcore.usbfs_snoop_max=
4630 [USB] Maximum number of bytes to snoop in each URB
4633 usbcore.blinkenlights=
4634 [USB] Set to cycle leds on hubs (default 0 = off).
4636 usbcore.old_scheme_first=
4637 [USB] Start with the old device initialization
4638 scheme, applies only to low and full-speed devices
4641 usbcore.usbfs_memory_mb=
4642 [USB] Memory limit (in MB) for buffers allocated by
4643 usbfs (default = 16, 0 = max = 2047).
4645 usbcore.use_both_schemes=
4646 [USB] Try the other device initialization scheme
4647 if the first one fails (default 1 = enabled).
4649 usbcore.initial_descriptor_timeout=
4650 [USB] Specifies timeout for the initial 64-byte
4651 USB_REQ_GET_DESCRIPTOR request in milliseconds
4652 (default 5000 = 5.0 seconds).
4654 usbcore.nousb [USB] Disable the USB subsystem
4657 [USB] A list of quirk entries to augment the built-in
4658 usb core quirk list. List entries are separated by
4659 commas. Each entry has the form
4660 VendorID:ProductID:Flags. The IDs are 4-digit hex
4661 numbers and Flags is a set of letters. Each letter
4662 will change the built-in quirk; setting it if it is
4663 clear and clearing it if it is set. The letters have
4664 the following meanings:
4665 a = USB_QUIRK_STRING_FETCH_255 (string
4666 descriptors must not be fetched using
4668 b = USB_QUIRK_RESET_RESUME (device can't resume
4669 correctly so reset it instead);
4670 c = USB_QUIRK_NO_SET_INTF (device can't handle
4671 Set-Interface requests);
4672 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4673 handle its Configuration or Interface
4675 e = USB_QUIRK_RESET (device can't be reset
4676 (e.g morph devices), don't use reset);
4677 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4678 more interface descriptions than the
4679 bNumInterfaces count, and can't handle
4680 talking to these interfaces);
4681 g = USB_QUIRK_DELAY_INIT (device needs a pause
4682 during initialization, after we read
4683 the device descriptor);
4684 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4685 high speed and super speed interrupt
4686 endpoints, the USB 2.0 and USB 3.0 spec
4687 require the interval in microframes (1
4688 microframe = 125 microseconds) to be
4689 calculated as interval = 2 ^
4691 Devices with this quirk report their
4692 bInterval as the result of this
4693 calculation instead of the exponent
4694 variable used in the calculation);
4695 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4696 handle device_qualifier descriptor
4698 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4699 generates spurious wakeup, ignore
4700 remote wakeup capability);
4701 k = USB_QUIRK_NO_LPM (device can't handle Link
4703 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4704 (Device reports its bInterval as linear
4705 frames instead of the USB 2.0
4707 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4708 to be disconnected before suspend to
4709 prevent spurious wakeup);
4710 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4711 pause after every control message);
4712 Example: quirks=0781:5580:bk,0a5c:5834:gij
4715 [USBHID] The interval which mice are to be polled at.
4718 [USBHID] The interval which joysticks are to be polled at.
4721 [USBHID] The interval which keyboards are to be polled at.
4723 usb-storage.delay_use=
4724 [UMS] The delay in seconds before a new device is
4725 scanned for Logical Units (default 1).
4728 [UMS] A list of quirks entries to supplement or
4729 override the built-in unusual_devs list. List
4730 entries are separated by commas. Each entry has
4731 the form VID:PID:Flags where VID and PID are Vendor
4732 and Product ID values (4-digit hex numbers) and
4733 Flags is a set of characters, each corresponding
4734 to a common usb-storage quirk flag as follows:
4735 a = SANE_SENSE (collect more than 18 bytes
4737 b = BAD_SENSE (don't collect more than 18
4738 bytes of sense data);
4739 c = FIX_CAPACITY (decrease the reported
4740 device capacity by one sector);
4741 d = NO_READ_DISC_INFO (don't use
4742 READ_DISC_INFO command);
4743 e = NO_READ_CAPACITY_16 (don't use
4744 READ_CAPACITY_16 command);
4745 f = NO_REPORT_OPCODES (don't use report opcodes
4747 g = MAX_SECTORS_240 (don't transfer more than
4748 240 sectors at a time, uas only);
4749 h = CAPACITY_HEURISTICS (decrease the
4750 reported device capacity by one
4751 sector if the number is odd);
4752 i = IGNORE_DEVICE (don't bind to this
4754 j = NO_REPORT_LUNS (don't use report luns
4756 l = NOT_LOCKABLE (don't try to lock and
4757 unlock ejectable media);
4758 m = MAX_SECTORS_64 (don't transfer more
4759 than 64 sectors = 32 KB at a time);
4760 n = INITIAL_READ10 (force a retry of the
4761 initial READ(10) command);
4762 o = CAPACITY_OK (accept the capacity
4763 reported by the device);
4764 p = WRITE_CACHE (the device cache is ON
4766 r = IGNORE_RESIDUE (the device reports
4767 bogus residue values);
4768 s = SINGLE_LUN (the device has only one
4770 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4771 commands, uas only);
4772 u = IGNORE_UAS (don't bind to the uas driver);
4773 w = NO_WP_DETECT (don't test whether the
4774 medium is write-protected).
4775 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4776 even if the device claims no cache)
4777 Example: quirks=0419:aaf5:rl,0421:0433:rc
4779 user_debug= [KNL,ARM]
4781 See arch/arm/Kconfig.debug help text.
4782 1 - undefined instruction events
4784 4 - invalid data aborts
4787 Example: user_debug=31
4790 [X86] Flags controlling user PTE allocations.
4792 nohigh = do not allocate PTE pages in
4793 HIGHMEM regardless of setting
4797 On X86_32, this is an alias for vdso32=. Otherwise:
4799 vdso=1: enable VDSO (the default)
4800 vdso=0: disable VDSO mapping
4802 vdso32= [X86] Control the 32-bit vDSO
4803 vdso32=1: enable 32-bit VDSO
4804 vdso32=0 or vdso32=2: disable 32-bit VDSO
4806 See the help text for CONFIG_COMPAT_VDSO for more
4807 details. If CONFIG_COMPAT_VDSO is set, the default is
4808 vdso32=0; otherwise, the default is vdso32=1.
4810 For compatibility with older kernels, vdso32=2 is an
4813 Try vdso32=0 if you encounter an error that says:
4814 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4817 vector=percpu: enable percpu vector domain
4819 video= [FB] Frame buffer configuration
4820 See Documentation/fb/modedb.txt.
4822 video.brightness_switch_enabled= [0,1]
4823 If set to 1, on receiving an ACPI notify event
4824 generated by hotkey, video driver will adjust brightness
4825 level and then send out the event to user space through
4826 the allocated input device; If set to 0, video driver
4827 will only send out the event without touching backlight
4832 [VMMIO] Memory mapped virtio (platform) device.
4834 <size>@<baseaddr>:<irq>[:<id>]
4836 <size> := size (can use standard suffixes
4838 <baseaddr> := physical base address
4839 <irq> := interrupt number (as passed to
4841 <id> := (optional) platform device id
4843 virtio_mmio.device=1K@0x100b0000:48:7
4845 Can be used multiple times for multiple devices.
4847 vga= [BOOT,X86-32] Select a particular video mode
4848 See Documentation/x86/boot.txt and
4849 Documentation/svga.txt.
4850 Use vga=ask for menu.
4851 This is actually a boot loader parameter; the value is
4852 passed to the kernel using a special protocol.
4854 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
4855 May slow down system boot speed, especially when
4856 enabled on systems with a large amount of memory.
4857 All options are enabled by default, and this
4858 interface is meant to allow for selectively
4859 enabling or disabling specific virtual memory
4862 Available options are:
4863 P Enable page structure init time poisoning
4864 - Disable all of the above options
4866 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4867 size of <nn>. This can be used to increase the
4868 minimum size (128MB on x86). It can also be used to
4869 decrease the size and leave more room for directly
4872 vmcp_cma=nn[MG] [KNL,S390]
4873 Sets the memory size reserved for contiguous memory
4874 allocations for the vmcp device driver.
4876 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4879 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4882 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4886 Controls the behavior of vsyscalls (i.e. calls to
4887 fixed addresses of 0xffffffffff600x00 from legacy
4888 code). Most statically-linked binaries and older
4889 versions of glibc use these calls. Because these
4890 functions are at fixed addresses, they make nice
4891 targets for exploits that can control RIP.
4893 emulate [default] Vsyscalls turn into traps and are
4894 emulated reasonably safely.
4896 native Vsyscalls are native syscall instructions.
4897 This is a little bit faster than trapping
4898 and makes a few dynamic recompilers work
4899 better than they would in emulation mode.
4900 It also makes exploits much easier to write.
4902 none Vsyscalls don't work at all. This makes
4903 them quite hard to use for exploits but
4904 might break your system.
4906 vt.color= [VT] Default text color.
4907 Format: 0xYX, X = foreground, Y = background.
4908 Default: 0x07 = light gray on black.
4910 vt.cur_default= [VT] Default cursor shape.
4911 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4912 the parameters of the <Esc>[?A;B;Cc escape sequence;
4913 see VGA-softcursor.txt. Default: 2 = underline.
4915 vt.default_blu= [VT]
4916 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4917 Change the default blue palette of the console.
4918 This is a 16-member array composed of values
4921 vt.default_grn= [VT]
4922 Format: <green0>,<green1>,<green2>,...,<green15>
4923 Change the default green palette of the console.
4924 This is a 16-member array composed of values
4927 vt.default_red= [VT]
4928 Format: <red0>,<red1>,<red2>,...,<red15>
4929 Change the default red palette of the console.
4930 This is a 16-member array composed of values
4936 Set system-wide default UTF-8 mode for all tty's.
4937 Default is 1, i.e. UTF-8 mode is enabled for all
4938 newly opened terminals.
4940 vt.global_cursor_default=
4943 Set system-wide default for whether a cursor
4944 is shown on new VTs. Default is -1,
4945 i.e. cursors will be created by default unless
4946 overridden by individual drivers. 0 will hide
4947 cursors, 1 will display them.
4949 vt.italic= [VT] Default color for italic text; 0-15.
4952 vt.underline= [VT] Default color for underlined text; 0-15.
4955 watchdog timers [HW,WDT] For information on watchdog timers,
4956 see Documentation/watchdog/watchdog-parameters.txt
4957 or other driver-specific files in the
4958 Documentation/watchdog/ directory.
4960 workqueue.watchdog_thresh=
4961 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4962 warn stall conditions and dump internal state to
4963 help debugging. 0 disables workqueue stall
4964 detection; otherwise, it's the stall threshold
4965 duration in seconds. The default value is 30 and
4966 it can be updated at runtime by writing to the
4967 corresponding sysfs file.
4969 workqueue.disable_numa
4970 By default, all work items queued to unbound
4971 workqueues are affine to the NUMA nodes they're
4972 issued on, which results in better behavior in
4973 general. If NUMA affinity needs to be disabled for
4974 whatever reason, this option can be used. Note
4975 that this also can be controlled per-workqueue for
4976 workqueues visible under /sys/bus/workqueue/.
4978 workqueue.power_efficient
4979 Per-cpu workqueues are generally preferred because
4980 they show better performance thanks to cache
4981 locality; unfortunately, per-cpu workqueues tend to
4982 be more power hungry than unbound workqueues.
4984 Enabling this makes the per-cpu workqueues which
4985 were observed to contribute significantly to power
4986 consumption unbound, leading to measurably lower
4987 power usage at the cost of small performance
4990 The default value of this parameter is determined by
4991 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4993 workqueue.debug_force_rr_cpu
4994 Workqueue used to implicitly guarantee that work
4995 items queued without explicit CPU specified are put
4996 on the local CPU. This guarantee is no longer true
4997 and while local CPU is still preferred work items
4998 may be put on foreign CPUs. This debug option
4999 forces round-robin CPU selection to flush out
5000 usages which depend on the now broken guarantee.
5001 When enabled, memory and cache locality will be
5004 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5005 default x2apic cluster mode on platforms
5008 x86_intel_mid_timer= [X86-32,APBT]
5009 Choose timer option for x86 Intel MID platform.
5010 Two valid options are apbt timer only and lapic timer
5011 plus one apbt timer for broadcast timer.
5012 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5014 xen_512gb_limit [KNL,X86-64,XEN]
5015 Restricts the kernel running paravirtualized under Xen
5016 to use only up to 512 GB of RAM. The reason to do so is
5017 crash analysis tools and Xen tools for doing domain
5018 save/restore/migration must be enabled to handle larger
5021 xen_emul_unplug= [HW,X86,XEN]
5022 Unplug Xen emulated devices
5023 Format: [unplug0,][unplug1]
5024 ide-disks -- unplug primary master IDE devices
5025 aux-ide-disks -- unplug non-primary-master IDE devices
5026 nics -- unplug network devices
5027 all -- unplug all emulated devices (NICs and IDE disks)
5028 unnecessary -- unplugging emulated devices is
5029 unnecessary even if the host did not respond to
5031 never -- do not unplug even if version check succeeds
5033 xen_nopvspin [X86,XEN]
5034 Disables the ticketlock slowpath using Xen PV
5038 Disables the PV optimizations forcing the HVM guest to
5039 run as generic HVM guest with no PV drivers.
5041 xen_scrub_pages= [XEN]
5042 Boolean option to control scrubbing pages before giving them back
5043 to Xen, for use by other domains. Can be also changed at runtime
5044 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5045 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5047 xirc2ps_cs= [NET,PCMCIA]
5049 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5051 xhci-hcd.quirks [USB,KNL]
5052 A hex value specifying bitmask with supplemental xhci
5053 host controller quirks. Meaning of each bit can be
5054 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob