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
816 Set number of hash buckets for dentry cache.
818 disable_1tb_segments [PPC]
819 Disables the use of 1TB hash page table segments. This
820 causes the kernel to fall back to 256MB segments which
821 can be useful when debugging issues that require an SLB
825 See Documentation/networking/ipv6.txt.
828 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
829 hardening is enabled for this boot. Hardened
830 usercopy checking is used to protect the kernel
831 from reading or writing beyond known memory
832 allocation boundaries as a proactive defense
833 against bounds-checking flaws in the kernel's
834 copy_to_user()/copy_from_user() interface.
835 on Perform hardened usercopy checks (default).
836 off Disable hardened usercopy checks.
839 Disable RADIX MMU mode on POWER9
841 disable_cpu_apicid= [X86,APIC,SMP]
843 The number of initial APIC ID for the
844 corresponding CPU to be disabled at boot,
845 mostly used for the kdump 2nd kernel to
846 disable BSP to wake up multiple CPUs without
847 causing system reset or hang due to sending
850 disable_ddw [PPC/PSERIES]
851 Disable Dynamic DMA Window support. Use this if
852 to workaround buggy firmware.
855 See Documentation/networking/ipv6.txt.
857 disable_mtrr_cleanup [X86]
858 The kernel tries to adjust MTRR layout from continuous
859 to discrete, to make X server driver able to add WB
860 entry later. This parameter disables that.
862 disable_mtrr_trim [X86, Intel and AMD only]
863 By default the kernel will trim any uncacheable
864 memory out of your available memory pool based on
865 MTRR settings. This parameter disables that behavior,
866 possibly causing your machine to run very slowly.
868 disable_timer_pin_1 [X86]
869 Disable PIN 1 of APIC timer
870 Can be useful to work around chipset bugs.
872 dis_ucode_ldr [X86] Disable the microcode loader.
874 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
875 this option disables the debugging code at boot.
877 dma_debug_entries=<number>
878 This option allows to tune the number of preallocated
879 entries for DMA-API debugging code. One entry is
880 required per DMA-API allocation. Use this if the
881 DMA-API debugging code disables itself because the
882 architectural default is too low.
884 dma_debug_driver=<driver_name>
885 With this option the DMA-API debugging driver
886 filter feature can be enabled at boot time. Just
887 pass the driver to filter for as the parameter.
888 The filter can be disabled or changed to another
889 driver later using sysfs.
891 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
892 Broken monitors, graphic adapters, KVMs and EDIDless
893 panels may send no or incorrect EDID data sets.
894 This parameter allows to specify an EDID data sets
895 in the /lib/firmware directory that are used instead.
896 Generic built-in EDID data sets are used, if one of
897 edid/1024x768.bin, edid/1280x1024.bin,
898 edid/1680x1050.bin, or edid/1920x1080.bin is given
899 and no file with the same name exists. Details and
900 instructions how to build your own EDID data are
901 available in Documentation/EDID/HOWTO.txt. An EDID
902 data set will only be used for a particular connector,
903 if its name and a colon are prepended to the EDID
904 name. Each connector may use a unique EDID data
905 set by separating the files with a comma. An EDID
906 data set with no connector name will be used for
907 any connectors not explicitly specified.
912 Format: {"off" | "known"}
913 Control how the dt_cpu_ftrs device-tree binding is
914 used for CPU feature discovery and setup (if it
916 off: Do not use it, fall back to legacy cpu table.
917 known: Do not pass through unknown features to guests
918 or userspace, only those that the kernel is aware of.
920 dump_apple_properties [X86]
921 Dump name and content of EFI device properties on
922 x86 Macs. Useful for driver authors to determine
923 what data is available or for reverse-engineering.
925 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
926 module.dyndbg[="val"]
927 Enable debug messages at boot time. See
928 Documentation/admin-guide/dynamic-debug-howto.rst
931 nompx [X86] Disables Intel Memory Protection Extensions.
932 See Documentation/x86/intel_mpx.txt for more
933 information about the feature.
935 nopku [X86] Disable Memory Protection Keys CPU feature found
938 module.async_probe [KNL]
939 Enable asynchronous probe on this module.
941 early_ioremap_debug [KNL]
942 Enable debug messages in early_ioremap support. This
943 is useful for tracking down temporary early mappings
944 which are not unmapped.
946 earlycon= [KNL] Output early console device and options.
948 [ARM64] The early console is determined by the
949 stdout-path property in device tree's chosen node,
950 or determined by the ACPI SPCR table.
952 [X86] When used with no options the early console is
953 determined by the ACPI SPCR table.
955 cdns,<addr>[,options]
956 Start an early, polled-mode console on a Cadence
957 (xuartps) serial port at the specified address. Only
958 supported option is baud rate. If baud rate is not
959 specified, the serial port must already be setup and
962 uart[8250],io,<addr>[,options]
963 uart[8250],mmio,<addr>[,options]
964 uart[8250],mmio32,<addr>[,options]
965 uart[8250],mmio32be,<addr>[,options]
966 uart[8250],0x<addr>[,options]
967 Start an early, polled-mode console on the 8250/16550
968 UART at the specified I/O port or MMIO address.
969 MMIO inter-register address stride is either 8-bit
970 (mmio) or 32-bit (mmio32 or mmio32be).
971 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
972 to be equivalent to 'mmio'. 'options' are specified
973 in the same format described for "console=ttyS<n>"; if
974 unspecified, the h/w is not initialized.
978 Start an early, polled-mode console on a pl011 serial
979 port at the specified address. The pl011 serial port
980 must already be setup and configured. Options are not
981 yet supported. If 'mmio32' is specified, then only
982 the driver will use only 32-bit accessors to read/write
983 the device registers.
986 Start an early, polled-mode console on a meson serial
987 port at the specified address. The serial port must
988 already be setup and configured. Options are not yet
992 Start an early, polled-mode console on an msm serial
993 port at the specified address. The serial port
994 must already be setup and configured. Options are not
998 Start an early, polled-mode console on an msm serial
999 dm port at the specified address. The serial port
1000 must already be setup and configured. Options are not
1004 Start an early, polled-mode console on a serial port
1005 of an Actions Semi SoC, such as S500 or S900, at the
1006 specified address. The serial port must already be
1007 setup and configured. Options are not yet supported.
1009 smh Use ARM semihosting calls for early console.
1017 Use early console provided by serial driver available
1018 on Samsung SoCs, requires selecting proper type and
1019 a correct base address of the selected UART port. The
1020 serial port must already be setup and configured.
1021 Options are not yet supported.
1024 Start an early, polled-mode console on a lantiq serial
1025 (lqasc) port at the specified address. The serial port
1026 must already be setup and configured. Options are not
1031 Use early console provided by Freescale LP UART driver
1032 found on Freescale Vybrid and QorIQ LS1021A processors.
1033 A valid base address must be provided, and the serial
1034 port must already be setup and configured.
1037 Start an early, polled-mode console on the
1038 Armada 3700 serial port at the specified
1039 address. The serial port must already be setup
1040 and configured. Options are not yet supported.
1043 Start an early, polled-mode console on a Qualcomm
1044 Generic Interface (GENI) based serial port at the
1045 specified address. The serial port must already be
1046 setup and configured. Options are not yet supported.
1048 earlyprintk= [X86,SH,ARM,M68k,S390]
1053 earlyprintk=serial[,ttySn[,baudrate]]
1054 earlyprintk=serial[,0x...[,baudrate]]
1055 earlyprintk=ttySn[,baudrate]
1056 earlyprintk=dbgp[debugController#]
1057 earlyprintk=pciserial,bus:device.function[,baudrate]
1058 earlyprintk=xdbc[xhciController#]
1060 earlyprintk is useful when the kernel crashes before
1061 the normal console is initialized. It is not enabled by
1062 default because it has some cosmetic problems.
1064 Append ",keep" to not disable it when the real console
1067 Only one of vga, efi, serial, or usb debug port can
1070 Currently only ttyS0 and ttyS1 may be specified by
1071 name. Other I/O ports may be explicitly specified
1072 on some architectures (x86 and arm at least) by
1073 replacing ttySn with an I/O port address, like this:
1074 earlyprintk=serial,0x1008,115200
1075 You can find the port for a given device in
1076 /proc/tty/driver/serial:
1077 2: uart:ST16650V2 port:00001008 irq:18 ...
1079 Interaction with the standard serial driver is not
1082 The VGA and EFI output is eventually overwritten by
1085 The xen output can only be used by Xen PV guests.
1087 The sclp output can only be used on s390.
1089 edac_report= [HW,EDAC] Control how to report EDAC event
1090 Format: {"on" | "off" | "force"}
1091 on: enable EDAC to report H/W event. May be overridden
1092 by other higher priority error reporting module.
1093 off: disable H/W event reporting through EDAC.
1094 force: enforce the use of EDAC to report H/W event.
1097 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1100 This is designed to be used in conjunction with
1101 the boot argument: earlyprintk=vga
1104 Format: {"off" | "on" | "skip[mbr]"}
1107 Format: { "old_map", "nochunk", "noruntime", "debug" }
1108 old_map [X86-64]: switch to the old ioremap-based EFI
1109 runtime services mapping. 32-bit still uses this one by
1111 nochunk: disable reading files in "chunks" in the EFI
1112 boot stub, as chunking can cause problems with some
1113 firmware implementations.
1114 noruntime : disable EFI runtime services support
1115 debug: enable misc debug output
1117 efi_no_storage_paranoia [EFI; X86]
1118 Using this parameter you can use more than 50% of
1119 your efi variable storage. Use this parameter only if
1120 you are really sure that your UEFI does sane gc and
1121 fulfills the spec otherwise your board may brick.
1123 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1124 Add arbitrary attribute to specific memory range by
1125 updating original EFI memory map.
1126 Region of memory which aa attribute is added to is
1128 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1129 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1130 attribute is added to range 0x100000000-0x180000000 and
1131 0x10a0000000-0x1120000000.
1133 Using this parameter you can do debugging of EFI memmap
1134 related feature. For example, you can do debugging of
1135 Address Range Mirroring feature even if your box
1138 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1139 that is to be dynamically loaded by Linux. If there are
1140 multiple variables with the same name but with different
1141 vendor GUIDs, all of them will be loaded. See
1142 Documentation/acpi/ssdt-overlays.txt for details.
1145 eisa_irq_edge= [PARISC,HW]
1146 See header of drivers/parisc/eisa.c.
1149 See comment before function elanfreq_setup() in
1150 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1153 Format: {"cfq" | "deadline" | "noop"}
1154 See Documentation/block/cfq-iosched.txt and
1155 Documentation/block/deadline-iosched.txt for details.
1157 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1158 Specifies physical address of start of kernel core
1159 image elf header and optionally the size. Generally
1160 kexec loader will pass this option to capture kernel.
1161 See Documentation/kdump/kdump.txt for details.
1163 enable_mtrr_cleanup [X86]
1164 The kernel tries to adjust MTRR layout from continuous
1165 to discrete, to make X server driver able to add WB
1166 entry later. This parameter enables that.
1168 enable_timer_pin_1 [X86]
1169 Enable PIN 1 of APIC timer
1170 Can be useful to work around chipset bugs
1171 (in particular on some ATI chipsets).
1172 The kernel tries to set a reasonable default.
1174 enforcing [SELINUX] Set initial enforcing status.
1176 See security/selinux/Kconfig help text.
1177 0 -- permissive (log only, no denials).
1178 1 -- enforcing (deny and log).
1180 Value can be changed at runtime via /selinux/enforce.
1183 Disable Error Record Serialization Table (ERST)
1186 ether= [HW,NET] Ethernet cards parameters
1187 This option is obsoleted by the "netdev=" option, which
1188 has equivalent usage. See its documentation for details.
1192 Permit 'security.evm' to be updated regardless of
1193 current integrity status.
1197 fail_make_request=[KNL]
1198 General fault injection mechanism.
1199 Format: <interval>,<probability>,<space>,<times>
1200 See also Documentation/fault-injection/.
1203 See Documentation/blockdev/floppy.txt.
1205 force_pal_cache_flush
1206 [IA-64] Avoid check_sal_cache_flush which may hang on
1207 buggy SAL_CACHE_FLUSH implementations. Using this
1208 parameter will force ia64_sal_cache_flush to call
1209 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1212 Forcefully enable Physical Address Extension (PAE).
1213 Many Pentium M systems disable PAE but may have a
1214 functionally usable PAE implementation.
1215 Warning: use of this parameter will taint the kernel
1216 and may cause unknown problems.
1219 [FTRACE] will set and start the specified tracer
1220 as early as possible in order to facilitate early
1223 ftrace_dump_on_oops[=orig_cpu]
1224 [FTRACE] will dump the trace buffers on oops.
1225 If no parameter is passed, ftrace will dump
1226 buffers of all CPUs, but if you pass orig_cpu, it will
1227 dump only the buffer of the CPU that triggered the
1230 ftrace_filter=[function-list]
1231 [FTRACE] Limit the functions traced by the function
1232 tracer at boot up. function-list is a comma separated
1233 list of functions. This list can be changed at run
1234 time by the set_ftrace_filter file in the debugfs
1237 ftrace_notrace=[function-list]
1238 [FTRACE] Do not trace the functions specified in
1239 function-list. This list can be changed at run time
1240 by the set_ftrace_notrace file in the debugfs
1243 ftrace_graph_filter=[function-list]
1244 [FTRACE] Limit the top level callers functions traced
1245 by the function graph tracer at boot up.
1246 function-list is a comma separated list of functions
1247 that can be changed at run time by the
1248 set_graph_function file in the debugfs tracing directory.
1250 ftrace_graph_notrace=[function-list]
1251 [FTRACE] Do not trace from the functions specified in
1252 function-list. This list is a comma separated list of
1253 functions that can be changed at run time by the
1254 set_graph_notrace file in the debugfs tracing directory.
1256 ftrace_graph_max_depth=<uint>
1257 [FTRACE] Used with the function graph tracer. This is
1258 the max depth it will trace into a function. This value
1259 can be changed at run time by the max_graph_depth file
1260 in the tracefs tracing directory. default: 0 (no limit)
1263 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1264 support via parallel port (up to 5 devices per port)
1265 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1266 See also Documentation/input/devices/joystick-parport.rst
1270 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1274 gcov_persist= [GCOV] When non-zero (default), profiling data for
1275 kernel modules is saved and remains accessible via
1276 debugfs, even when the module is unloaded/reloaded.
1277 When zero, profiling data is discarded and associated
1278 debugfs files are removed at module unload time.
1280 goldfish [X86] Enable the goldfish android emulator platform.
1281 Don't use this when you are not running on the
1284 gpt [EFI] Forces disk with valid GPT signature but
1285 invalid Protective MBR to be treated as GPT. If the
1286 primary GPT is corrupted, it enables the backup/alternate
1287 GPT to be used instead.
1289 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1290 the "Enable 0" bit of the configuration register.
1293 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1294 the "Enable 0" bit of the configuration register.
1297 grcan.select= [HW] Select which physical interface to use.
1300 grcan.txsize= [HW] Sets the size of the tx buffer.
1301 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1303 grcan.rxsize= [HW] Sets the size of the rx buffer.
1304 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1307 gpio-mockup.gpio_mockup_ranges
1308 [HW] Sets the ranges of gpiochip of for this device.
1309 Format: <start1>,<end1>,<start2>,<end2>...
1311 hardlockup_all_cpu_backtrace=
1312 [KNL] Should the hard-lockup detector generate
1313 backtraces on all cpus.
1316 hashdist= [KNL,NUMA] Large hashes allocated during boot
1317 are distributed across NUMA nodes. Defaults on
1318 for 64-bit NUMA, off otherwise.
1319 Format: 0 | 1 (for off | on)
1321 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1323 hd= [EIDE] (E)IDE hard drive subsystem geometry
1324 Format: <cyl>,<head>,<sect>
1327 Disable Hardware Error Source Table (HEST) support;
1328 corresponding firmware-first mode error processing
1329 logic will be disabled.
1331 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1332 size of <nn>. This works even on boxes that have no
1333 highmem otherwise. This also works to reduce highmem
1334 size on bigger boxes.
1336 highres= [KNL] Enable/disable high resolution timer mode.
1337 Valid parameters: "on", "off"
1341 See Documentation/isdn/README.HiSax.
1345 hpet= [X86-32,HPET] option to control HPET usage
1346 Format: { enable (default) | disable | force |
1348 disable: disable HPET and use PIT instead
1349 force: allow force enabled of undocumented chips (ICH4,
1351 verbose: show contents of HPET registers during setup
1353 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1354 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1356 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1357 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1358 On x86-64 and powerpc, this option can be specified
1359 multiple times interleaved with hugepages= to reserve
1360 huge pages of different sizes. Valid pages sizes on
1361 x86-64 are 2M (when the CPU supports "pse") and 1G
1362 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1365 [KNL] Should the hung task detector generate panics.
1368 A nonzero value instructs the kernel to panic when a
1369 hung task is detected. The default value is controlled
1370 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1371 option. The value selected by this boot parameter can
1372 be changed later by the kernel.hung_task_panic sysctl.
1374 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1375 terminal devices. Valid values: 0..8
1376 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1377 If specified, z/VM IUCV HVC accepts connections
1378 from listed z/VM user IDs only.
1380 Do not unregister boot console at start. This is only
1381 useful for debugging when something happens in the window
1382 between unregistering the boot console and initializing
1385 i2c_bus= [HW] Override the default board specific I2C bus speed
1386 or register an additional I2C bus that is not
1387 registered from board initialization code.
1391 i8042.debug [HW] Toggle i8042 debug mode
1392 i8042.unmask_kbd_data
1393 [HW] Enable printing of interrupt data from the KBD port
1394 (disabled by default, and as a pre-condition
1395 requires that i8042.debug=1 be enabled)
1396 i8042.direct [HW] Put keyboard port into non-translated mode
1397 i8042.dumbkbd [HW] Pretend that controller can only read data from
1398 keyboard and cannot control its state
1399 (Don't attempt to blink the leds)
1400 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1401 i8042.nokbd [HW] Don't check/create keyboard port
1402 i8042.noloop [HW] Disable the AUX Loopback command while probing
1404 i8042.nomux [HW] Don't check presence of an active multiplexing
1406 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1408 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1409 i8042.reset [HW] Reset the controller during init, cleanup and
1410 suspend-to-ram transitions, only during s2r
1411 transitions, or never reset
1412 Format: { 1 | Y | y | 0 | N | n }
1413 1, Y, y: always reset controller
1414 0, N, n: don't ever reset controller
1415 Default: only on s2r transitions on x86; most other
1416 architectures force reset to be always executed
1417 i8042.unlock [HW] Unlock (ignore) the keylock
1418 i8042.kbdreset [HW] Reset device connected to KBD port
1422 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1423 indicates that the driver is running on unsupported
1425 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1426 does not match list of supported models.
1428 [HW] Report power status in /proc/i8k
1429 (disabled by default)
1430 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1433 i915.invert_brightness=
1434 [DRM] Invert the sense of the variable that is used to
1435 set the brightness of the panel backlight. Normally a
1436 brightness value of 0 indicates backlight switched off,
1437 and the maximum of the brightness value sets the backlight
1438 to maximum brightness. If this parameter is set to 0
1439 (default) and the machine requires it, or this parameter
1440 is set to 1, a brightness value of 0 sets the backlight
1441 to maximum brightness, and the maximum of the brightness
1442 value switches the backlight off.
1443 -1 -- never invert brightness
1444 0 -- machine default
1445 1 -- force brightness inversion
1448 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1450 ide-core.nodma= [HW] (E)IDE subsystem
1451 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1452 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1453 .cdrom .chs .ignore_cable are additional options
1454 See Documentation/ide/ide.txt.
1456 ide-generic.probe-mask= [HW] (E)IDE subsystem
1458 Probe mask for legacy ISA IDE ports. Depending on
1459 platform up to 6 ports are supported, enabled by
1460 setting corresponding bits in the mask to 1. The
1461 default value is 0x0, which has a special meaning.
1462 On systems that have PCI, it triggers scanning the
1463 PCI bus for the first and the second port, which
1464 are then probed. On systems without PCI the value
1465 of 0x0 enables probing the two first ports as if it
1468 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1469 Claim all unknown PCI IDE storage controllers.
1472 Format: idle=poll, idle=halt, idle=nomwait
1473 Poll forces a polling idle loop that can slightly
1474 improve the performance of waking up a idle CPU, but
1475 will use a lot of power and make the system run hot.
1477 idle=halt: Halt is forced to be used for CPU idle.
1478 In such case C2/C3 won't be used again.
1479 idle=nomwait: Disable mwait for CPU C-states
1481 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1482 Format: { strict | legacy | 2008 | relaxed }
1485 Choose which programs will be accepted for execution
1486 based on the IEEE 754 NaN encoding(s) supported by
1487 the FPU and the NaN encoding requested with the value
1488 of an ELF file header flag individually set by each
1489 binary. Hardware implementations are permitted to
1490 support either or both of the legacy and the 2008 NaN
1493 Available settings are as follows:
1494 strict accept binaries that request a NaN encoding
1495 supported by the FPU
1496 legacy only accept legacy-NaN binaries, if supported
1498 2008 only accept 2008-NaN binaries, if supported
1500 relaxed accept any binaries regardless of whether
1501 supported by the FPU
1503 The FPU emulator is always able to support both NaN
1504 encodings, so if no FPU hardware is present or it has
1505 been disabled with 'nofpu', then the settings of
1506 'legacy' and '2008' strap the emulator accordingly,
1507 'relaxed' straps the emulator for both legacy-NaN and
1508 2008-NaN, whereas 'strict' enables legacy-NaN only on
1509 legacy processors and both NaN encodings on MIPS32 or
1512 The setting for ABS.fmt/NEG.fmt instruction execution
1513 mode generally follows that for the NaN encoding,
1514 except where unsupported by hardware.
1516 ignore_loglevel [KNL]
1517 Ignore loglevel setting - this will print /all/
1518 kernel messages to the console. Useful for debugging.
1519 We also add it as printk module parameter, so users
1520 could change it dynamically, usually by
1521 /sys/module/printk/parameters/ignore_loglevel.
1524 Ignore RLIMIT_DATA setting for data mappings,
1525 print warning at first misuse. Can be changed via
1526 /sys/module/kernel/parameters/ignore_rlimit_data.
1528 ihash_entries= [KNL]
1529 Set number of hash buckets for inode cache.
1531 ima_appraise= [IMA] appraise integrity measurements
1532 Format: { "off" | "enforce" | "fix" | "log" }
1535 ima_appraise_tcb [IMA]
1536 The builtin appraise policy appraises all files
1539 ima_canonical_fmt [IMA]
1540 Use the canonical format for the binary runtime
1541 measurements, instead of host native format.
1544 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1548 The list of supported hash algorithms is defined
1549 in crypto/hash_info.h.
1552 The builtin policies to load during IMA setup.
1553 Format: "tcb | appraise_tcb | secure_boot |
1556 The "tcb" policy measures all programs exec'd, files
1557 mmap'd for exec, and all files opened with the read
1558 mode bit set by either the effective uid (euid=0) or
1561 The "appraise_tcb" policy appraises the integrity of
1562 all files owned by root. (This is the equivalent
1563 of ima_appraise_tcb.)
1565 The "secure_boot" policy appraises the integrity
1566 of files (eg. kexec kernel image, kernel modules,
1567 firmware, policy, etc) based on file signatures.
1569 The "fail_securely" policy forces file signature
1570 verification failure also on privileged mounted
1571 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1574 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1575 Load a policy which meets the needs of the Trusted
1576 Computing Base. This means IMA will measure all
1577 programs exec'd, files mmap'd for exec, and all files
1578 opened for read by uid=0.
1581 Select one of defined IMA measurements template formats.
1582 Formats: { "ima" | "ima-ng" | "ima-sig" }
1586 [IMA] Define a custom template format.
1587 Format: { "field1|...|fieldN" }
1589 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1590 Format: <min_file_size>
1591 Set the minimal file size for using asynchronous hash.
1592 If left unspecified, ahash usage is disabled.
1594 ahash performance varies for different data sizes on
1595 different crypto accelerators. This option can be used
1596 to achieve the best performance for a particular HW.
1598 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1600 Set hashing buffer size. Default: 4k.
1602 ahash performance varies for different chunk sizes on
1603 different crypto accelerators. This option can be used
1604 to achieve best performance for particular HW.
1608 Run specified binary instead of /sbin/init as init
1611 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1612 for working out where the kernel is dying during
1615 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1616 initcall functions. Useful for debugging built-in
1617 modules and initcalls.
1619 initrd= [BOOT] Specify the location of the initial ramdisk
1621 init_pkru= [x86] Specify the default memory protection keys rights
1622 register contents for all processes. 0x55555554 by
1623 default (disallow access to all but pkey 0). Can
1624 override in debugfs after boot.
1626 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1629 int_pln_enable [x86] Enable power limit notification interrupt
1631 integrity_audit=[IMA]
1632 Format: { "0" | "1" }
1633 0 -- basic integrity auditing messages. (Default)
1634 1 -- additional integrity auditing messages.
1636 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1638 Enable intel iommu driver.
1640 Disable intel iommu driver.
1641 igfx_off [Default Off]
1642 By default, gfx is mapped as normal device. If a gfx
1643 device has a dedicated DMAR unit, the DMAR unit is
1644 bypassed by not enabling DMAR with this option. In
1645 this case, gfx device will use physical address for
1648 With this option iommu will not optimize to look
1649 for io virtual address below 32-bit forcing dual
1650 address cycle on pci bus for cards supporting greater
1651 than 32-bit addressing. The default is to look
1652 for translation below 32-bit and if not available
1653 then look in the higher range.
1654 strict [Default Off]
1655 With this option on every unmap_single operation will
1656 result in a hardware IOTLB flush operation as opposed
1657 to batching them for performance.
1658 sp_off [Default Off]
1659 By default, super page will be supported if Intel IOMMU
1660 has the capability. With this option, super page will
1662 ecs_off [Default Off]
1663 By default, extended context tables will be supported if
1664 the hardware advertises that it has support both for the
1665 extended tables themselves, and also PASID support. With
1666 this option set, extended tables will not be used even
1667 on hardware which claims to support them.
1668 tboot_noforce [Default Off]
1669 Do not force the Intel IOMMU enabled under tboot.
1670 By default, tboot will force Intel IOMMU on, which
1671 could harm performance of some high-throughput
1672 devices like 40GBit network cards, even if identity
1674 Note that using this option lowers the security
1675 provided by tboot because it makes the system
1676 vulnerable to DMA attacks.
1678 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1679 0 disables intel_idle and fall back on acpi_idle.
1680 1 to 9 specify maximum depth of C-state.
1684 Do not enable intel_pstate as the default
1685 scaling driver for the supported processors
1687 Use intel_pstate as a scaling driver, but configure it
1688 to work with generic cpufreq governors (instead of
1689 enabling its internal governor). This mode cannot be
1690 used along with the hardware-managed P-states (HWP)
1693 Enable intel_pstate on systems that prohibit it by default
1694 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1695 instead of acpi-cpufreq may disable platform features, such
1696 as thermal controls and power capping, that rely on ACPI
1697 P-States information being indicated to OSPM and therefore
1698 should be used with caution. This option does not work with
1699 processors that aren't supported by the intel_pstate driver
1700 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1702 Do not enable hardware P state control (HWP)
1705 Only load intel_pstate on systems which support
1706 hardware P state control (HWP) if available.
1708 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1709 Description Table, specifies preferred power management
1710 profile as "Enterprise Server" or "Performance Server",
1711 then this feature is turned on by default.
1713 Allow per-logical-CPU P-State performance control limits using
1714 cpufreq sysfs interface
1716 intremap= [X86-64, Intel-IOMMU]
1717 on enable Interrupt Remapping (default)
1718 off disable Interrupt Remapping
1719 nosid disable Source ID checking
1721 BIOS x2APIC opt-out request will be ignored
1722 nopost disable Interrupt Posting
1724 iomem= Disable strict checking of access to MMIO memory
1725 strict regions from userspace.
1739 nobypass [PPC/POWERNV]
1740 Disable IOMMU bypass, using IOMMU for PCI devices.
1743 [ARM64] Configure DMA to bypass the IOMMU by default.
1744 Format: { "0" | "1" }
1745 0 - Use IOMMU translation for DMA.
1746 1 - Bypass the IOMMU for DMA.
1747 unset - Use IOMMU translation for DMA.
1749 io7= [HW] IO7 for Marvel based alpha systems
1750 See comment before marvel_specify_io7 in
1751 arch/alpha/kernel/core_marvel.c.
1753 io_delay= [X86] I/O delay method
1755 Standard port 0x80 based delay
1757 Alternate port 0xed based delay (needed on some systems)
1759 Simple two microseconds delay
1764 See Documentation/filesystems/nfs/nfsroot.txt.
1766 irqaffinity= [SMP] Set the default irq affinity mask
1767 The argument is a cpu list, as described above.
1769 irqchip.gicv2_force_probe=
1772 Force the kernel to look for the second 4kB page
1773 of a GICv2 controller even if the memory range
1774 exposed by the device tree is too small.
1776 irqchip.gicv3_nolpi=
1778 Force the kernel to ignore the availability of
1779 LPIs (and by consequence ITSs). Intended for system
1780 that use the kernel as a bootloader, and thus want
1781 to let secondary kernels in charge of setting up
1785 When an interrupt is not handled search all handlers
1786 for it. Intended to get systems with badly broken
1790 When an interrupt is not handled search all handlers
1791 for it. Also check all handlers each timer
1792 interrupt. Intended to get systems with badly broken
1796 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1798 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1799 [Deprecated - use cpusets instead]
1800 Format: [flag-list,]<cpu-list>
1802 Specify one or more CPUs to isolate from disturbances
1803 specified in the flag list (default: domain):
1806 Disable the tick when a single task runs.
1808 A residual 1Hz tick is offloaded to workqueues, which you
1809 need to affine to housekeeping through the global
1810 workqueue's affinity configured via the
1811 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1812 by using the 'domain' flag described below.
1814 NOTE: by default the global workqueue runs on all CPUs,
1815 so to protect individual CPUs the 'cpumask' file has to
1816 be configured manually after bootup.
1819 Isolate from the general SMP balancing and scheduling
1820 algorithms. Note that performing domain isolation this way
1821 is irreversible: it's not possible to bring back a CPU to
1822 the domains once isolated through isolcpus. It's strongly
1823 advised to use cpusets instead to disable scheduler load
1824 balancing through the "cpuset.sched_load_balance" file.
1825 It offers a much more flexible interface where CPUs can
1826 move in and out of an isolated set anytime.
1828 You can move a process onto or off an "isolated" CPU via
1829 the CPU affinity syscalls or cpuset.
1830 <cpu number> begins at 0 and the maximum value is
1831 "number of CPUs in system - 1".
1833 The format of <cpu-list> is described above.
1839 ivrs_ioapic [HW,X86_64]
1840 Provide an override to the IOAPIC-ID<->DEVICE-ID
1841 mapping provided in the IVRS ACPI table. For
1842 example, to map IOAPIC-ID decimal 10 to
1843 PCI device 00:14.0 write the parameter as:
1844 ivrs_ioapic[10]=00:14.0
1846 ivrs_hpet [HW,X86_64]
1847 Provide an override to the HPET-ID<->DEVICE-ID
1848 mapping provided in the IVRS ACPI table. For
1849 example, to map HPET-ID decimal 0 to
1850 PCI device 00:14.0 write the parameter as:
1851 ivrs_hpet[0]=00:14.0
1853 ivrs_acpihid [HW,X86_64]
1854 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1855 mapping provided in the IVRS ACPI table. For
1856 example, to map UART-HID:UID AMD0020:0 to
1857 PCI device 00:14.5 write the parameter as:
1858 ivrs_acpihid[00:14.5]=AMD0020:0
1860 js= [HW,JOY] Analog joystick
1861 See Documentation/input/joydev/joystick.rst.
1864 When CONFIG_RANDOMIZE_BASE is set, this disables
1865 kernel and module base offset ASLR (Address Space
1866 Layout Randomization).
1869 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1870 report on every invalid memory access. Without this
1871 parameter KASAN will print report only for the first
1876 kernelcore= [KNL,X86,IA-64,PPC]
1877 Format: nn[KMGTPE] | nn% | "mirror"
1878 This parameter specifies the amount of memory usable by
1879 the kernel for non-movable allocations. The requested
1880 amount is spread evenly throughout all nodes in the
1881 system as ZONE_NORMAL. The remaining memory is used for
1882 movable memory in its own zone, ZONE_MOVABLE. In the
1883 event, a node is too small to have both ZONE_NORMAL and
1884 ZONE_MOVABLE, kernelcore memory will take priority and
1885 other nodes will have a larger ZONE_MOVABLE.
1887 ZONE_MOVABLE is used for the allocation of pages that
1888 may be reclaimed or moved by the page migration
1889 subsystem. Note that allocations like PTEs-from-HighMem
1890 still use the HighMem zone if it exists, and the Normal
1891 zone if it does not.
1893 It is possible to specify the exact amount of memory in
1894 the form of "nn[KMGTPE]", a percentage of total system
1895 memory in the form of "nn%", or "mirror". If "mirror"
1896 option is specified, mirrored (reliable) memory is used
1897 for non-movable allocations and remaining memory is used
1898 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1899 are exclusive, so you cannot specify multiple forms.
1901 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1902 Format: <Controller#>[,poll interval]
1903 The controller # is the number of the ehci usb debug
1904 port as it is probed via PCI. The poll interval is
1905 optional and is the number seconds in between
1906 each poll cycle to the debug port in case you need
1907 the functionality for interrupting the kernel with
1908 gdb or control-c on the dbgp connection. When
1909 not using this parameter you use sysrq-g to break into
1910 the kernel debugger.
1912 kgdboc= [KGDB,HW] kgdb over consoles.
1913 Requires a tty driver that supports console polling,
1914 or a supported polling keyboard driver (non-usb).
1915 Serial only format: <serial_device>[,baud]
1916 keyboard only format: kbd
1917 keyboard and serial format: kbd,<serial_device>[,baud]
1918 Optional Kernel mode setting:
1919 kms, kbd format: kms,kbd
1920 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1922 kgdbwait [KGDB] Stop kernel execution and enter the
1923 kernel debugger at the earliest opportunity.
1925 kmac= [MIPS] korina ethernet MAC address.
1926 Configure the RouterBoard 532 series on-chip
1927 Ethernet adapter MAC address.
1929 kmemleak= [KNL] Boot-time kmemleak enable/disable
1930 Valid arguments: on, off
1932 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1935 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1936 Default is 0 (don't ignore, but inject #GP)
1938 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1939 Default is false (don't support).
1941 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1945 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1946 Default is 1 (enabled)
1948 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1950 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1952 kvm-arm.vgic_v3_group0_trap=
1953 [KVM,ARM] Trap guest accesses to GICv3 group-0
1956 kvm-arm.vgic_v3_group1_trap=
1957 [KVM,ARM] Trap guest accesses to GICv3 group-1
1960 kvm-arm.vgic_v3_common_trap=
1961 [KVM,ARM] Trap guest accesses to GICv3 common
1964 kvm-arm.vgic_v4_enable=
1965 [KVM,ARM] Allow use of GICv4 for direct injection of
1968 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1969 (virtualized MMU) support on capable Intel chips.
1970 Default is 1 (enabled)
1972 kvm-intel.emulate_invalid_guest_state=
1973 [KVM,Intel] Enable emulation of invalid guest states
1974 Default is 0 (disabled)
1976 kvm-intel.flexpriority=
1977 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1978 Default is 1 (enabled)
1981 [KVM,Intel] Enable VMX nesting (nVMX).
1982 Default is 0 (disabled)
1984 kvm-intel.unrestricted_guest=
1985 [KVM,Intel] Disable unrestricted guest feature
1986 (virtualized real and unpaged mode) on capable
1987 Intel chips. Default is 1 (enabled)
1989 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
1992 Valid arguments: never, cond, always
1994 always: L1D cache flush on every VMENTER.
1995 cond: Flush L1D on VMENTER only when the code between
1996 VMEXIT and VMENTER can leak host memory.
1997 never: Disables the mitigation
1999 Default is cond (do L1 cache flush in specific instances)
2001 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2002 feature (tagged TLBs) on capable Intel chips.
2003 Default is 1 (enabled)
2005 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2008 The kernel PTE inversion protection is unconditionally
2009 enabled and cannot be disabled.
2012 Provides all available mitigations for the
2013 L1TF vulnerability. Disables SMT and
2014 enables all mitigations in the
2015 hypervisors, i.e. unconditional L1D flush.
2017 SMT control and L1D flush control via the
2018 sysfs interface is still possible after
2019 boot. Hypervisors will issue a warning
2020 when the first VM is started in a
2021 potentially insecure configuration,
2022 i.e. SMT enabled or L1D flush disabled.
2025 Same as 'full', but disables SMT and L1D
2026 flush runtime control. Implies the
2027 'nosmt=force' command line option.
2028 (i.e. sysfs control of SMT is disabled.)
2031 Leaves SMT enabled and enables the default
2032 hypervisor mitigation, i.e. conditional
2035 SMT control and L1D flush control via the
2036 sysfs interface is still possible after
2037 boot. Hypervisors will issue a warning
2038 when the first VM is started in a
2039 potentially insecure configuration,
2040 i.e. SMT enabled or L1D flush disabled.
2044 Disables SMT and enables the default
2045 hypervisor mitigation.
2047 SMT control and L1D flush control via the
2048 sysfs interface is still possible after
2049 boot. Hypervisors will issue a warning
2050 when the first VM is started in a
2051 potentially insecure configuration,
2052 i.e. SMT enabled or L1D flush disabled.
2055 Same as 'flush', but hypervisors will not
2056 warn when a VM is started in a potentially
2057 insecure configuration.
2060 Disables hypervisor mitigations and doesn't
2065 For details see: Documentation/admin-guide/l1tf.rst
2071 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2074 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2075 value for LAPIC timer one-shot implementation. Default
2076 back to the programmable timer unit in the LAPIC.
2078 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2081 libata.dma= [LIBATA] DMA control
2082 libata.dma=0 Disable all PATA and SATA DMA
2083 libata.dma=1 PATA and SATA Disk DMA only
2084 libata.dma=2 ATAPI (CDROM) DMA only
2085 libata.dma=4 Compact Flash DMA only
2086 Combinations also work, so libata.dma=3 enables DMA
2087 for disks and CDROMs, but not CFs.
2089 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2090 libata.ignore_hpa=0 keep BIOS limits (default)
2091 libata.ignore_hpa=1 ignore limits, using full disk
2093 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2097 libata.force= [LIBATA] Force configurations. The format is comma
2098 separated list of "[ID:]VAL" where ID is
2099 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2100 matching port, link or device. Basically, it matches
2101 the ATA ID string printed on console by libata. If
2102 the whole ID part is omitted, the last PORT and DEVICE
2103 values are used. If ID hasn't been specified yet, the
2104 configuration applies to all ports, links and devices.
2106 If only DEVICE is omitted, the parameter applies to
2107 the port and all links and devices behind it. DEVICE
2108 number of 0 either selects the first device or the
2109 first fan-out link behind PMP device. It does not
2110 select the host link. DEVICE number of 15 selects the
2111 host link and device attached to it.
2113 The VAL specifies the configuration to force. As long
2114 as there's no ambiguity shortcut notation is allowed.
2115 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2116 The following configurations can be forced.
2118 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2119 Any ID with matching PORT is used.
2121 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2123 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2124 udma[/][16,25,33,44,66,100,133] notation is also
2127 * [no]ncq: Turn on or off NCQ.
2129 * [no]ncqtrim: Turn off queued DSM TRIM.
2131 * nohrst, nosrst, norst: suppress hard, soft
2134 * rstonce: only attempt one reset during
2135 hot-unplug link recovery
2137 * dump_id: dump IDENTIFY data.
2139 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2141 * disable: Disable this device.
2143 If there are multiple matching configurations changing
2144 the same attribute, the last one is used.
2146 memblock=debug [KNL] Enable memblock debug messages.
2148 load_ramdisk= [RAM] List of ramdisks to load from floppy
2149 See Documentation/blockdev/ramdisk.txt.
2151 lockd.nlm_grace_period=P [NFS] Assign grace period.
2154 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2157 lockd.nlm_timeout=T [NFS] Assign timeout value.
2160 lockd.nlm_udpport=M [NFS] Assign UDP port.
2163 locktorture.nreaders_stress= [KNL]
2164 Set the number of locking read-acquisition kthreads.
2165 Defaults to being automatically set based on the
2166 number of online CPUs.
2168 locktorture.nwriters_stress= [KNL]
2169 Set the number of locking write-acquisition kthreads.
2171 locktorture.onoff_holdoff= [KNL]
2172 Set time (s) after boot for CPU-hotplug testing.
2174 locktorture.onoff_interval= [KNL]
2175 Set time (s) between CPU-hotplug operations, or
2176 zero to disable CPU-hotplug testing.
2178 locktorture.shuffle_interval= [KNL]
2179 Set task-shuffle interval (jiffies). Shuffling
2180 tasks allows some CPUs to go into dyntick-idle
2181 mode during the locktorture test.
2183 locktorture.shutdown_secs= [KNL]
2184 Set time (s) after boot system shutdown. This
2185 is useful for hands-off automated testing.
2187 locktorture.stat_interval= [KNL]
2188 Time (s) between statistics printk()s.
2190 locktorture.stutter= [KNL]
2191 Time (s) to stutter testing, for example,
2192 specifying five seconds causes the test to run for
2193 five seconds, wait for five seconds, and so on.
2194 This tests the locking primitive's ability to
2195 transition abruptly to and from idle.
2197 locktorture.torture_type= [KNL]
2198 Specify the locking implementation to test.
2200 locktorture.verbose= [KNL]
2201 Enable additional printk() statements.
2203 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2206 loglevel= All Kernel Messages with a loglevel smaller than the
2207 console loglevel will be printed to the console. It can
2208 also be changed with klogd or other programs. The
2209 loglevels are defined as follows:
2211 0 (KERN_EMERG) system is unusable
2212 1 (KERN_ALERT) action must be taken immediately
2213 2 (KERN_CRIT) critical conditions
2214 3 (KERN_ERR) error conditions
2215 4 (KERN_WARNING) warning conditions
2216 5 (KERN_NOTICE) normal but significant condition
2217 6 (KERN_INFO) informational
2218 7 (KERN_DEBUG) debug-level messages
2220 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2221 in bytes. n must be a power of two and greater
2222 than the minimal size. The minimal size is defined
2223 by LOG_BUF_SHIFT kernel config parameter. There is
2224 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2225 that allows to increase the default size depending on
2226 the number of CPUs. See init/Kconfig for more details.
2228 logo.nologo [FB] Disables display of the built-in Linux logo.
2229 This may be used to provide more screen space for
2230 kernel log messages and is useful when debugging
2231 kernel boot problems.
2233 lp=0 [LP] Specify parallel ports to use, e.g,
2234 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2235 lp=reset first parallel port). 'lp=0' disables the
2236 lp=auto printer driver. 'lp=reset' (which can be
2237 specified in addition to the ports) causes
2238 attached printers to be reset. Using
2239 lp=port1,port2,... specifies the parallel ports
2240 to associate lp devices with, starting with
2241 lp0. A port specification may be 'none' to skip
2242 that lp device, or a parport name such as
2243 'parport0'. Specifying 'lp=auto' instead of a
2244 port specification list means that device IDs
2245 from each port should be examined, to see if
2246 an IEEE 1284-compliant printer is attached; if
2247 so, the driver will manage that printer.
2248 See also header of drivers/char/lp.c.
2251 Sets loops_per_jiffy to given constant, thus avoiding
2252 time-consuming boot-time autodetection (up to 250 ms per
2253 CPU). 0 enables autodetection (default). To determine
2254 the correct value for your kernel, boot with normal
2255 autodetection and see what value is printed. Note that
2256 on SMP systems the preset will be applied to all CPUs,
2257 which is likely to cause problems if your CPUs need
2258 significantly divergent settings. An incorrect value
2259 will cause delays in the kernel to be wrong, leading to
2260 unpredictable I/O errors and other breakage. Although
2261 unlikely, in the extreme case this might damage your
2265 Format: <io>,<irq>,<dma>
2267 machvec= [IA-64] Force the use of a particular machine-vector
2268 (machvec) in a generic kernel.
2269 Example: machvec=hpzx1_swiotlb
2271 machtype= [Loongson] Share the same kernel image file between different
2273 Example: machtype=lemote-yeeloong-2f-7inch
2275 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2276 than or equal to this physical address is ignored.
2278 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2279 will bring up during bootup. maxcpus=n : n >= 0 limits
2280 the kernel to bring up 'n' processors. Surely after
2281 bootup you can bring up the other plugged cpu by executing
2282 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2283 only takes effect during system bootup.
2284 While n=0 is a special case, it is equivalent to "nosmp",
2285 which also disables the IO APIC.
2287 max_loop= [LOOP] The number of loop block devices that get
2288 (loop.max_loop) unconditionally pre-created at init time. The default
2289 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2290 of statically allocating a predefined number, loop
2291 devices can be requested on-demand with the
2292 /dev/loop-control interface.
2294 mce [X86-32] Machine Check Exception
2296 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2298 md= [HW] RAID subsystems devices and level
2299 See Documentation/admin-guide/md.rst.
2302 Format: <first>,<last>
2303 Specifies range of consoles to be captured by the MDA.
2305 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2306 Amount of memory to be used when the kernel is not able
2307 to see the whole system memory or for test.
2308 [X86] Work as limiting max address. Use together
2309 with memmap= to avoid physical address space collisions.
2310 Without memmap= PCI devices could be placed at addresses
2311 belonging to unused RAM.
2313 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2317 [KNL,SH] Allow user to override the default size for
2318 per-device physically contiguous DMA buffers.
2320 memhp_default_state=online/offline
2321 [KNL] Set the initial state for the memory hotplug
2322 onlining policy. If not specified, the default value is
2323 set according to the
2324 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2326 See Documentation/memory-hotplug.txt.
2328 memmap=exactmap [KNL,X86] Enable setting of an exact
2329 E820 memory map, as specified by the user.
2330 Such memmap=exactmap lines can be constructed based on
2331 BIOS output or other requirements. See the memmap=nn@ss
2334 memmap=nn[KMG]@ss[KMG]
2335 [KNL] Force usage of a specific region of memory.
2336 Region of memory to be used is from ss to ss+nn.
2337 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2338 which limits max address to nn[KMG].
2339 Multiple different regions can be specified,
2342 memmap=100M@2G,100M#3G,1G!1024G
2344 memmap=nn[KMG]#ss[KMG]
2345 [KNL,ACPI] Mark specific memory as ACPI data.
2346 Region of memory to be marked is from ss to ss+nn.
2348 memmap=nn[KMG]$ss[KMG]
2349 [KNL,ACPI] Mark specific memory as reserved.
2350 Region of memory to be reserved is from ss to ss+nn.
2351 Example: Exclude memory from 0x18690000-0x1869ffff
2352 memmap=64K$0x18690000
2354 memmap=0x10000$0x18690000
2355 Some bootloaders may need an escape character before '$',
2356 like Grub2, otherwise '$' and the following number
2359 memmap=nn[KMG]!ss[KMG]
2360 [KNL,X86] Mark specific memory as protected.
2361 Region of memory to be used, from ss to ss+nn.
2362 The memory region may be marked as e820 type 12 (0xc)
2363 and is NVDIMM or ADR memory.
2365 memmap=<size>%<offset>-<oldtype>+<newtype>
2366 [KNL,ACPI] Convert memory within the specified region
2367 from <oldtype> to <newtype>. If "-<oldtype>" is left
2368 out, the whole region will be marked as <newtype>,
2369 even if previously unavailable. If "+<newtype>" is left
2370 out, matching memory will be removed. Types are
2371 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2372 3 = ACPI, 12 = PRAM.
2374 memory_corruption_check=0/1 [X86]
2375 Some BIOSes seem to corrupt the first 64k of
2376 memory when doing things like suspend/resume.
2377 Setting this option will scan the memory
2378 looking for corruption. Enabling this will
2379 both detect corruption and prevent the kernel
2380 from using the memory being corrupted.
2381 However, its intended as a diagnostic tool; if
2382 repeatable BIOS-originated corruption always
2383 affects the same memory, you can use memmap=
2384 to prevent the kernel from using that memory.
2386 memory_corruption_check_size=size [X86]
2387 By default it checks for corruption in the low
2388 64k, making this memory unavailable for normal
2389 use. Use this parameter to scan for
2390 corruption in more or less memory.
2392 memory_corruption_check_period=seconds [X86]
2393 By default it checks for corruption every 60
2394 seconds. Use this parameter to check at some
2395 other rate. 0 disables periodic checking.
2397 memtest= [KNL,X86,ARM] Enable memtest
2399 default : 0 <disable>
2400 Specifies the number of memtest passes to be
2401 performed. Each pass selects another test
2402 pattern from a given set of patterns. Memtest
2403 fills the memory with this pattern, validates
2404 memory contents and reserves bad memory
2405 regions that are detected.
2407 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2408 Valid arguments: on, off
2409 Default (depends on kernel configuration option):
2410 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2411 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2412 mem_encrypt=on: Activate SME
2413 mem_encrypt=off: Do not activate SME
2415 Refer to Documentation/x86/amd-memory-encryption.txt
2416 for details on when memory encryption can be activated.
2418 mem_sleep_default= [SUSPEND] Default system suspend mode:
2419 s2idle - Suspend-To-Idle
2420 shallow - Power-On Suspend or equivalent (if supported)
2421 deep - Suspend-To-RAM or equivalent (if supported)
2422 See Documentation/admin-guide/pm/sleep-states.rst.
2424 meye.*= [HW] Set MotionEye Camera parameters
2425 See Documentation/media/v4l-drivers/meye.rst.
2427 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2428 Multi-Function General Purpose Timers on AMD Geode
2431 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2432 the BIOS has incorrectly applied a workaround. TinyBIOS
2433 version 0.98 is known to be affected, 0.99 fixes the
2434 problem by letting the user disable the workaround.
2438 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2439 physical address is ignored.
2441 mini2440= [ARM,HW,KNL]
2442 Format:[0..2][b][c][t]
2444 MINI2440 configuration specification:
2445 0 - The attached screen is the 3.5" TFT
2446 1 - The attached screen is the 7" TFT
2447 2 - The VGA Shield is attached (1024x768)
2448 Leaving out the screen size parameter will not load
2449 the TFT driver, and the framebuffer will be left
2451 b - Enable backlight. The TFT backlight pin will be
2452 linked to the kernel VESA blanking code and a GPIO
2453 LED. This parameter is not necessary when using the
2455 c - Enable the s3c camera interface.
2456 t - Reserved for enabling touchscreen support. The
2457 touchscreen support is not enabled in the mainstream
2458 kernel as of 2.6.30, a preliminary port can be found
2459 in the "bleeding edge" mini2440 support kernel at
2460 http://repo.or.cz/w/linux-2.6/mini2440.git
2463 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2464 parameter allows control of the logging verbosity for
2465 the additional memory initialisation checks. A value
2466 of 0 disables mminit logging and a level of 4 will
2467 log everything. Information is printed at KERN_DEBUG
2468 so loglevel=8 may also need to be specified.
2471 [KNL] When CONFIG_MODULE_SIG is set, this means that
2472 modules without (valid) signatures will fail to load.
2473 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2474 is always true, so this option does nothing.
2476 module_blacklist= [KNL] Do not load a comma-separated list of
2477 modules. Useful for debugging problem modules.
2480 [MOUSE] Maximum time between finger touching and
2481 leaving touchpad surface for touch to be considered
2482 a tap and be reported as a left button click (for
2483 touchpads working in absolute mode only).
2485 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2486 reporting absolute coordinates, such as tablets
2487 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2488 reporting absolute coordinates, such as tablets
2490 movablecore= [KNL,X86,IA-64,PPC]
2491 Format: nn[KMGTPE] | nn%
2492 This parameter is the complement to kernelcore=, it
2493 specifies the amount of memory used for migratable
2494 allocations. If both kernelcore and movablecore is
2495 specified, then kernelcore will be at *least* the
2496 specified value but may be more. If movablecore on its
2497 own is specified, the administrator must be careful
2498 that the amount of memory usable for all allocations
2501 movable_node [KNL] Boot-time switch to make hotplugable memory
2502 NUMA nodes to be movable. This means that the memory
2503 of such nodes will be usable only for movable
2504 allocations which rules out almost all kernel
2505 allocations. Use with caution!
2507 MTD_Partition= [MTD]
2508 Format: <name>,<region-number>,<size>,<offset>
2510 MTD_Region= [MTD] Format:
2511 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2514 See drivers/mtd/cmdlinepart.c.
2516 multitce=off [PPC] This parameter disables the use of the pSeries
2517 firmware feature for updating multiple TCE entries
2520 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2522 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2524 boundary - index of last SLC block on Flex-OneNAND.
2525 The remaining blocks are configured as MLC blocks.
2526 lock - Configure if Flex-OneNAND boundary should be locked.
2527 Once locked, the boundary cannot be changed.
2528 1 indicates lock status, 0 indicates unlock status.
2531 ARM/S3C2412 JIVE boot control
2533 See arch/arm/mach-s3c2412/mach-jive.c
2535 mtouchusb.raw_coordinates=
2536 [HW] Make the MicroTouch USB driver use raw coordinates
2537 ('y', default) or cooked coordinates ('n')
2539 mtrr_chunk_size=nn[KMG] [X86]
2540 used for mtrr cleanup. It is largest continuous chunk
2541 that could hold holes aka. UC entries.
2543 mtrr_gran_size=nn[KMG] [X86]
2544 Used for mtrr cleanup. It is granularity of mtrr block.
2546 Large value could prevent small alignment from
2549 mtrr_spare_reg_nr=n [X86]
2551 Range: 0,7 : spare reg number
2553 Used for mtrr cleanup. It is spare mtrr entries number.
2554 Set to 2 or more if your graphical card needs more.
2556 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2558 netdev= [NET] Network devices parameters
2559 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2560 Note that mem_start is often overloaded to mean
2561 something different and driver-specific.
2562 This usage is only documented in each driver source
2566 [NETFILTER] Enable connection tracking flow accounting
2567 0 to disable accounting
2568 1 to enable accounting
2571 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2572 See Documentation/filesystems/nfs/nfsroot.txt.
2574 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2575 See Documentation/filesystems/nfs/nfsroot.txt.
2577 nfsrootdebug [NFS] enable nfsroot debugging messages.
2578 See Documentation/filesystems/nfs/nfsroot.txt.
2580 nfs.callback_nr_threads=
2581 [NFSv4] set the total number of threads that the
2582 NFS client will assign to service NFSv4 callback
2585 nfs.callback_tcpport=
2586 [NFS] set the TCP port on which the NFSv4 callback
2587 channel should listen.
2590 [NFS] sets the pathname to the program which is used
2591 to update the NFS client cache entries.
2593 nfs.cache_getent_timeout=
2594 [NFS] sets the timeout after which an attempt to
2595 update a cache entry is deemed to have failed.
2597 nfs.idmap_cache_timeout=
2598 [NFS] set the maximum lifetime for idmapper cache
2602 [NFS] enable 64-bit inode numbers.
2603 If zero, the NFS client will fake up a 32-bit inode
2604 number for the readdir() and stat() syscalls instead
2605 of returning the full 64-bit number.
2606 The default is to return 64-bit inode numbers.
2608 nfs.max_session_cb_slots=
2609 [NFSv4.1] Sets the maximum number of session
2610 slots the client will assign to the callback
2611 channel. This determines the maximum number of
2612 callbacks the client will process in parallel for
2613 a particular server.
2615 nfs.max_session_slots=
2616 [NFSv4.1] Sets the maximum number of session slots
2617 the client will attempt to negotiate with the server.
2618 This limits the number of simultaneous RPC requests
2619 that the client can send to the NFSv4.1 server.
2620 Note that there is little point in setting this
2621 value higher than the max_tcp_slot_table_limit.
2623 nfs.nfs4_disable_idmapping=
2624 [NFSv4] When set to the default of '1', this option
2625 ensures that both the RPC level authentication
2626 scheme and the NFS level operations agree to use
2627 numeric uids/gids if the mount is using the
2628 'sec=sys' security flavour. In effect it is
2629 disabling idmapping, which can make migration from
2630 legacy NFSv2/v3 systems to NFSv4 easier.
2631 Servers that do not support this mode of operation
2632 will be autodetected by the client, and it will fall
2633 back to using the idmapper.
2634 To turn off this behaviour, set the value to '0'.
2636 [NFS4] Specify an additional fixed unique ident-
2637 ification string that NFSv4 clients can insert into
2638 their nfs_client_id4 string. This is typically a
2639 UUID that is generated at system install time.
2641 nfs.send_implementation_id =
2642 [NFSv4.1] Send client implementation identification
2643 information in exchange_id requests.
2644 If zero, no implementation identification information
2646 The default is to send the implementation identification
2649 nfs.recover_lost_locks =
2650 [NFSv4] Attempt to recover locks that were lost due
2651 to a lease timeout on the server. Please note that
2652 doing this risks data corruption, since there are
2653 no guarantees that the file will remain unchanged
2654 after the locks are lost.
2655 If you want to enable the kernel legacy behaviour of
2656 attempting to recover these locks, then set this
2658 The default parameter value of '0' causes the kernel
2659 not to attempt recovery of lost locks.
2661 nfs4.layoutstats_timer =
2662 [NFSv4.2] Change the rate at which the kernel sends
2663 layoutstats to the pNFS metadata server.
2665 Setting this to value to 0 causes the kernel to use
2666 whatever value is the default set by the layout
2667 driver. A non-zero value sets the minimum interval
2668 in seconds between layoutstats transmissions.
2670 nfsd.nfs4_disable_idmapping=
2671 [NFSv4] When set to the default of '1', the NFSv4
2672 server will return only numeric uids and gids to
2673 clients using auth_sys, and will accept numeric uids
2674 and gids from such clients. This is intended to ease
2675 migration from NFSv2/v3.
2677 nmi_debug= [KNL,SH] Specify one or more actions to take
2678 when a NMI is triggered.
2679 Format: [state][,regs][,debounce][,die]
2681 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2682 Format: [panic,][nopanic,][num]
2684 0 - turn hardlockup detector in nmi_watchdog off
2685 1 - turn hardlockup detector in nmi_watchdog on
2686 When panic is specified, panic when an NMI watchdog
2687 timeout occurs (or 'nopanic' to override the opposite
2688 default). To disable both hard and soft lockup detectors,
2689 please see 'nowatchdog'.
2690 This is useful when you use a panic=... timeout and
2691 need the box quickly up again.
2693 These settings can be accessed at runtime via
2694 the nmi_watchdog and hardlockup_panic sysctls.
2696 netpoll.carrier_timeout=
2697 [NET] Specifies amount of time (in seconds) that
2698 netpoll should wait for a carrier. By default netpoll
2701 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2702 emulation library even if a 387 maths coprocessor
2705 no5lvl [X86-64] Disable 5-level paging mode. Forces
2706 kernel to use 4-level paging instead.
2709 [HW] Never suspend the console
2710 Disable suspending of consoles during suspend and
2711 hibernate operations. Once disabled, debugging
2712 messages can reach various consoles while the rest
2713 of the system is being put to sleep (ie, while
2714 debugging driver suspend/resume hooks). This may
2715 not work reliably with all consoles, but is known
2716 to work with serial and VGA consoles.
2717 To facilitate more flexible debugging, we also add
2718 console_suspend, a printk module parameter to control
2719 it. Users could use console_suspend (usually
2720 /sys/module/printk/parameters/console_suspend) to
2721 turn on/off it dynamically.
2723 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2724 caches in the slab allocator. Saves per-node memory,
2725 but will impact performance.
2729 noaltinstr [S390] Disables alternative instructions patching
2730 (CPU alternatives feature).
2732 noapic [SMP,APIC] Tells the kernel to not make use of any
2733 IOAPICs that may be present in the system.
2735 noautogroup Disable scheduler automatic task group creation.
2737 nobats [PPC] Do not use BATs for mapping kernel lowmem
2738 on "Classic" PPC cores.
2742 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2744 nodelayacct [KNL] Disable per-task delay accounting
2746 nodsp [SH] Disable hardware DSP at boot time.
2748 noefi Disable EFI runtime services support.
2753 On X86-32 available only on PAE configured kernels.
2754 noexec=on: enable non-executable mappings (default)
2755 noexec=off: disable non-executable mappings
2758 Disable SMAP (Supervisor Mode Access Prevention)
2759 even if it is supported by processor.
2762 Disable SMEP (Supervisor Mode Execution Prevention)
2763 even if it is supported by processor.
2766 This affects only 32-bit executables.
2767 noexec32=on: enable non-executable mappings (default)
2768 read doesn't imply executable mappings
2769 noexec32=off: disable non-executable mappings
2770 read implies executable mappings
2772 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2774 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2775 register save and restore. The kernel will only save
2776 legacy floating-point registers on task switch.
2778 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2780 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2781 Equivalent to smt=1.
2783 [KNL,x86] Disable symmetric multithreading (SMT).
2784 nosmt=force: Force disable SMT, cannot be undone
2785 via the sysfs control file.
2787 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2788 (indirect branch prediction) vulnerability. System may
2789 allow data leaks with this option, which is equivalent
2792 nospec_store_bypass_disable
2793 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2795 noxsave [BUGS=X86] Disables x86 extended register state save
2796 and restore using xsave. The kernel will fallback to
2797 enabling legacy floating-point and sse state.
2799 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2800 register states. The kernel will fall back to use
2801 xsave to save the states. By using this parameter,
2802 performance of saving the states is degraded because
2803 xsave doesn't support modified optimization while
2804 xsaveopt supports it on xsaveopt enabled systems.
2806 noxsaves [X86] Disables xsaves and xrstors used in saving and
2807 restoring x86 extended register state in compacted
2808 form of xsave area. The kernel will fall back to use
2809 xsaveopt and xrstor to save and restore the states
2810 in standard form of xsave area. By using this
2811 parameter, xsave area per process might occupy more
2812 memory on xsaves enabled systems.
2814 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2815 wfi(ARM) instruction doesn't work correctly and not to
2816 use it. This is also useful when using JTAG debugger.
2818 no_file_caps Tells the kernel not to honor file capabilities. The
2819 only way then for a file to be executed with privilege
2820 is to be setuid root or executed by root.
2822 nohalt [IA-64] Tells the kernel not to use the power saving
2823 function PAL_HALT_LIGHT when idle. This increases
2824 power-consumption. On the positive side, it reduces
2825 interrupt wake-up latency, which may improve performance
2826 in certain environments such as networked servers or
2829 nohibernate [HIBERNATION] Disable hibernation and resume.
2831 nohz= [KNL] Boottime enable/disable dynamic ticks
2832 Valid arguments: on, off
2835 nohz_full= [KNL,BOOT,SMP,ISOL]
2836 The argument is a cpu list, as described above.
2837 In kernels built with CONFIG_NO_HZ_FULL=y, set
2838 the specified list of CPUs whose tick will be stopped
2839 whenever possible. The boot CPU will be forced outside
2840 the range to maintain the timekeeping. Any CPUs
2841 in this list will have their RCU callbacks offloaded,
2842 just as if they had also been called out in the
2843 rcu_nocbs= boot parameter.
2845 noiotrap [SH] Disables trapped I/O port accesses.
2847 noirqdebug [X86-32] Disables the code which attempts to detect and
2848 disable unhandled interrupt sources.
2850 no_timer_check [X86,APIC] Disables the code which tests for
2851 broken timer IRQ sources.
2853 noisapnp [ISAPNP] Disables ISA PnP code.
2855 noinitrd [RAM] Tells the kernel not to load any configured
2858 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2860 [Deprecated - use intremap=off]
2864 noinvpcid [X86] Disable the INVPCID cpu feature.
2866 nojitter [IA-64] Disables jitter checking for ITC timers.
2868 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2870 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2874 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2875 clock and use the default one.
2877 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2878 steal time is computed, but won't influence scheduler
2881 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2883 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2885 noltlbs [PPC] Do not use large page/tlb entries for kernel
2886 lowmem mapping on PPC40x and PPC8xx
2888 nomca [IA-64] Disable machine check abort handling
2890 nomce [X86-32] Disable Machine Check Exception
2892 nomfgpt [X86-32] Disable Multi-Function General Purpose
2893 Timer usage (for AMD Geode machines).
2895 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2896 shutdown the other cpus. Instead use the REBOOT_VECTOR
2899 nomodule Disable module load
2901 nopat [X86] Disable PAT (page attribute table extension of
2902 pagetables) support.
2904 nopcid [X86-64] Disable the PCID cpu feature.
2906 norandmaps Don't use address space randomization. Equivalent to
2907 echo 0 > /proc/sys/kernel/randomize_va_space
2909 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2910 with UP alternatives
2912 nordrand [X86] Disable kernel use of the RDRAND and
2913 RDSEED instructions even if they are supported
2914 by the processor. RDRAND and RDSEED are still
2915 available to user space applications.
2917 noresume [SWSUSP] Disables resume and restores original swap
2920 no-scroll [VGA] Disables scrollback.
2921 This is required for the Braillex ib80-piezo Braille
2922 reader made by F.H. Papenmeier (Germany).
2926 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2928 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2929 and disable the IO APIC. legacy for "maxcpus=0".
2931 nosoftlockup [KNL] Disable the soft-lockup detector.
2933 nosync [HW,M68K] Disables sync negotiation for all devices.
2935 nowatchdog [KNL] Disable both lockup detectors, i.e.
2936 soft-lockup and NMI watchdog (hard-lockup).
2940 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2942 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2943 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2944 Some features depend on CPU0. Known dependencies are:
2945 1. Resume from suspend/hibernate depends on CPU0.
2946 Suspend/hibernate will fail if CPU0 is offline and you
2947 need to online CPU0 before suspend/hibernate.
2948 2. PIC interrupts also depend on CPU0. CPU0 can't be
2949 removed if a PIC interrupt is detected.
2950 It's said poweroff/reboot may depend on CPU0 on some
2951 machines although I haven't seen such issues so far
2952 after CPU0 is offline on a few tested machines.
2953 If the dependencies are under your control, you can
2954 turn on cpu0_hotplug.
2956 nps_mtm_hs_ctr= [KNL,ARC]
2957 This parameter sets the maximum duration, in
2958 cycles, each HW thread of the CTOP can run
2959 without interruptions, before HW switches it.
2960 The actual maximum duration is 16 times this
2962 Format: integer between 1 and 255
2965 nptcg= [IA-64] Override max number of concurrent global TLB
2966 purges which is reported from either PAL_VM_SUMMARY or
2969 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2970 could support. nr_cpus=n : n >= 1 limits the kernel to
2971 support 'n' processors. It could be larger than the
2972 number of already plugged CPU during bootup, later in
2973 runtime you can physically add extra cpu until it reaches
2974 n. So during boot up some boot time memory for per-cpu
2975 variables need be pre-allocated for later physical cpu
2978 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2980 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2981 Allowed values are enable and disable
2983 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2984 'node', 'default' can be specified
2985 This can be set from sysctl after boot.
2986 See Documentation/sysctl/vm.txt for details.
2988 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2989 See Documentation/debugging-via-ohci1394.txt for more
2992 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2993 Rather than timing out after 20 ms if an EC
2994 command is not properly ACKed, override the length
2995 of the timeout. We have interrupts disabled while
2996 waiting for the ACK, so if this is set too high
2997 interrupts *may* be lost!
2999 omap_mux= [OMAP] Override bootloader pin multiplexing.
3000 Format: <mux_mode0.mode_name=value>...
3001 For example, to override I2C bus2:
3002 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3004 oprofile.timer= [HW]
3005 Use timer interrupt instead of performance counters
3007 oprofile.cpu_type= Force an oprofile cpu type
3008 This might be useful if you have an older oprofile
3009 userland or if you want common events.
3010 Format: { arch_perfmon }
3011 arch_perfmon: [X86] Force use of architectural
3012 perfmon on Intel CPUs instead of the
3013 CPU specific event set.
3014 timer: [X86] Force use of architectural NMI
3015 timer mode (see also oprofile.timer
3016 for generic hr timer mode)
3018 oops=panic Always panic on oopses. Default is to just kill the
3019 process, but there is a small probability of
3020 deadlocking the machine.
3021 This will also cause panics on machine check exceptions.
3022 Useful together with panic=30 to trigger a reboot.
3024 page_owner= [KNL] Boot-time page_owner enabling option.
3025 Storage of the information about who allocated
3026 each page is disabled in default. With this switch,
3028 on: enable the feature
3030 page_poison= [KNL] Boot-time parameter changing the state of
3031 poisoning on the buddy allocator.
3032 off: turn off poisoning
3033 on: turn on poisoning
3035 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3036 timeout > 0: seconds before rebooting
3037 timeout = 0: wait forever
3038 timeout < 0: reboot immediately
3041 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3044 crash_kexec_post_notifiers
3045 Run kdump after running panic-notifiers and dumping
3046 kmsg. This only for the users who doubt kdump always
3047 succeeds in any situation.
3048 Note that this also increases risks of kdump failure,
3049 because some panic notifiers can make the crashed
3050 kernel more unstable.
3052 parkbd.port= [HW] Parallel port number the keyboard adapter is
3053 connected to, default is 0.
3055 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3056 0 for XT, 1 for AT (default is AT).
3059 parport= [HW,PPT] Specify parallel ports. 0 disables.
3060 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3061 Use 'auto' to force the driver to use any
3062 IRQ/DMA settings detected (the default is to
3063 ignore detected IRQ/DMA settings because of
3064 possible conflicts). You can specify the base
3065 address, IRQ, and DMA settings; IRQ and DMA
3066 should be numbers, or 'auto' (for using detected
3067 settings on that particular port), or 'nofifo'
3068 (to avoid using a FIFO even if it is detected).
3069 Parallel ports are assigned in the order they
3070 are specified on the command line, starting
3073 parport_init_mode= [HW,PPT]
3074 Configure VIA parallel port to operate in
3075 a specific mode. This is necessary on Pegasos
3076 computer where firmware has no options for setting
3077 up parallel port mode and sets it to spp.
3078 Currently this function knows 686a and 8231 chips.
3079 Format: [spp|ps2|epp|ecp|ecpepp]
3082 Halt all CPUs after the first oops has been printed for
3083 the specified number of seconds. This is to be used if
3084 your oopses keep scrolling off the screen.
3089 See header of drivers/block/paride/pcd.c.
3090 See also Documentation/blockdev/paride.txt.
3092 pci=option[,option...] [PCI] various PCI subsystem options:
3093 earlydump [X86] dump PCI config space before the kernel
3095 off [X86] don't probe for the PCI bus
3096 bios [X86-32] force use of PCI BIOS, don't access
3097 the hardware directly. Use this if your machine
3098 has a non-standard PCI host bridge.
3099 nobios [X86-32] disallow use of PCI BIOS, only direct
3100 hardware access methods are allowed. Use this
3101 if you experience crashes upon bootup and you
3102 suspect they are caused by the BIOS.
3103 conf1 [X86] Force use of PCI Configuration Access
3104 Mechanism 1 (config address in IO port 0xCF8,
3105 data in IO port 0xCFC, both 32-bit).
3106 conf2 [X86] Force use of PCI Configuration Access
3107 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3108 the function, IO port 0xCFA, also 8-bit, sets
3109 bus number. The config space is then accessed
3110 through ports 0xC000-0xCFFF).
3111 See http://wiki.osdev.org/PCI for more info
3112 on the configuration access mechanisms.
3113 noaer [PCIE] If the PCIEAER kernel config parameter is
3114 enabled, this kernel boot option can be used to
3115 disable the use of PCIE advanced error reporting.
3116 nodomains [PCI] Disable support for multiple PCI
3117 root domains (aka PCI segments, in ACPI-speak).
3118 nommconf [X86] Disable use of MMCONFIG for PCI
3120 check_enable_amd_mmconf [X86] check for and enable
3121 properly configured MMIO access to PCI
3122 config space on AMD family 10h CPU
3123 nomsi [MSI] If the PCI_MSI kernel config parameter is
3124 enabled, this kernel boot option can be used to
3125 disable the use of MSI interrupts system-wide.
3126 noioapicquirk [APIC] Disable all boot interrupt quirks.
3127 Safety option to keep boot IRQs enabled. This
3128 should never be necessary.
3129 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3130 primary IO-APIC for bridges that cannot disable
3131 boot IRQs. This fixes a source of spurious IRQs
3132 when the system masks IRQs.
3133 noioapicreroute [APIC] Disable workaround that uses the
3134 boot IRQ equivalent of an IRQ that connects to
3135 a chipset where boot IRQs cannot be disabled.
3136 The opposite of ioapicreroute.
3137 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3138 routing table. These calls are known to be buggy
3139 on several machines and they hang the machine
3140 when used, but on other computers it's the only
3141 way to get the interrupt routing table. Try
3142 this option if the kernel is unable to allocate
3143 IRQs or discover secondary PCI buses on your
3145 rom [X86] Assign address space to expansion ROMs.
3146 Use with caution as certain devices share
3147 address decoders between ROMs and other
3149 norom [X86] Do not assign address space to
3150 expansion ROMs that do not already have
3151 BIOS assigned address ranges.
3152 nobar [X86] Do not assign address space to the
3153 BARs that weren't assigned by the BIOS.
3154 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3155 assigned automatically to PCI devices. You can
3156 make the kernel exclude IRQs of your ISA cards
3158 pirqaddr=0xAAAAA [X86] Specify the physical address
3159 of the PIRQ table (normally generated
3160 by the BIOS) if it is outside the
3161 F0000h-100000h range.
3162 lastbus=N [X86] Scan all buses thru bus #N. Can be
3163 useful if the kernel is unable to find your
3164 secondary buses and you want to tell it
3165 explicitly which ones they are.
3166 assign-busses [X86] Always assign all PCI bus
3167 numbers ourselves, overriding
3168 whatever the firmware may have done.
3169 usepirqmask [X86] Honor the possible IRQ mask stored
3170 in the BIOS $PIR table. This is needed on
3171 some systems with broken BIOSes, notably
3172 some HP Pavilion N5400 and Omnibook XE3
3173 notebooks. This will have no effect if ACPI
3174 IRQ routing is enabled.
3175 noacpi [X86] Do not use ACPI for IRQ routing
3176 or for PCI scanning.
3177 use_crs [X86] Use PCI host bridge window information
3178 from ACPI. On BIOSes from 2008 or later, this
3179 is enabled by default. If you need to use this,
3180 please report a bug.
3181 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3182 If you need to use this, please report a bug.
3183 routeirq Do IRQ routing for all PCI devices.
3184 This is normally done in pci_enable_device(),
3185 so this option is a temporary workaround
3186 for broken drivers that don't call it.
3187 skip_isa_align [X86] do not align io start addr, so can
3188 handle more pci cards
3189 noearly [X86] Don't do any early type 1 scanning.
3190 This might help on some broken boards which
3191 machine check when some devices' config space
3192 is read. But various workarounds are disabled
3193 and some IOMMU drivers will not work.
3194 bfsort Sort PCI devices into breadth-first order.
3195 This sorting is done to get a device
3196 order compatible with older (<= 2.4) kernels.
3197 nobfsort Don't sort PCI devices into breadth-first order.
3198 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3199 tuning and use the BIOS-configured MPS defaults.
3200 pcie_bus_safe Set every device's MPS to the largest value
3201 supported by all devices below the root complex.
3202 pcie_bus_perf Set device MPS to the largest allowable MPS
3203 based on its parent bus. Also set MRRS (Max
3204 Read Request Size) to the largest supported
3205 value (no larger than the MPS that the device
3206 or bus can support) for best performance.
3207 pcie_bus_peer2peer Set every device's MPS to 128B, which
3208 every device is guaranteed to support. This
3209 configuration allows peer-to-peer DMA between
3210 any pair of devices, possibly at the cost of
3211 reduced performance. This also guarantees
3212 that hot-added devices will work.
3213 cbiosize=nn[KMG] The fixed amount of bus space which is
3214 reserved for the CardBus bridge's IO window.
3215 The default value is 256 bytes.
3216 cbmemsize=nn[KMG] The fixed amount of bus space which is
3217 reserved for the CardBus bridge's memory
3218 window. The default value is 64 megabytes.
3221 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
3222 [<order of align>@]pci:<vendor>:<device>\
3223 [:<subvendor>:<subdevice>][; ...]
3224 Specifies alignment and device to reassign
3225 aligned memory resources.
3226 If <order of align> is not specified,
3227 PAGE_SIZE is used as alignment.
3228 PCI-PCI bridge can be specified, if resource
3229 windows need to be expanded.
3230 To specify the alignment for several
3231 instances of a device, the PCI vendor,
3232 device, subvendor, and subdevice may be
3233 specified, e.g., 4096@pci:8086:9c22:103c:198f
3234 ecrc= Enable/disable PCIe ECRC (transaction layer
3235 end-to-end CRC checking).
3236 bios: Use BIOS/firmware settings. This is the
3240 hpiosize=nn[KMG] The fixed amount of bus space which is
3241 reserved for hotplug bridge's IO window.
3242 Default size is 256 bytes.
3243 hpmemsize=nn[KMG] The fixed amount of bus space which is
3244 reserved for hotplug bridge's memory window.
3245 Default size is 2 megabytes.
3246 hpbussize=nn The minimum amount of additional bus numbers
3247 reserved for buses below a hotplug bridge.
3249 realloc= Enable/disable reallocating PCI bridge resources
3250 if allocations done by BIOS are too small to
3251 accommodate resources required by all child
3253 off: Turn realloc off
3255 realloc same as realloc=on
3256 noari do not use PCIe ARI.
3257 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3258 do not use PCIe ATS (and IOMMU device IOTLB).
3259 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3260 only look for one device below a PCIe downstream
3262 big_root_window Try to add a big 64bit memory window to the PCIe
3263 root complex on AMD CPUs. Some GFX hardware
3264 can resize a BAR to allow access to all VRAM.
3265 Adding the window is slightly risky (it may
3266 conflict with unreported devices), so this
3269 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3272 force Enable ASPM even on devices that claim not to support it.
3273 WARNING: Forcing ASPM on may cause system lockups.
3275 pcie_ports= [PCIE] PCIe port services handling:
3276 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3277 even if the platform doesn't give the OS permission to
3278 use them. This may cause conflicts if the platform
3279 also tries to use these services.
3280 compat Disable native PCIe services (PME, AER, DPC, PCIe
3283 pcie_port_pm= [PCIE] PCIe port power management handling:
3284 off Disable power management of all PCIe ports
3285 force Forcibly enable power management of all PCIe ports
3287 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3288 nomsi Do not use MSI for native PCIe PME signaling (this makes
3289 all PCIe root ports use INTx for all services).
3291 pcmv= [HW,PCMCIA] BadgePAD 4
3295 Keep all power-domains already enabled by bootloader on,
3296 even if no driver has claimed them. This is useful
3297 for debug and development, but should not be
3298 needed on a platform with proper driver support.
3301 See Documentation/blockdev/paride.txt.
3303 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3306 See arch/parisc/kernel/pdc_chassis.c
3308 percpu_alloc= Select which percpu first chunk allocator to use.
3309 Currently supported values are "embed" and "page".
3310 Archs may support subset or none of the selections.
3311 See comments in mm/percpu.c for details on each
3312 allocator. This parameter is primarily for debugging
3313 and performance comparison.
3316 See Documentation/blockdev/paride.txt.
3319 See Documentation/blockdev/paride.txt.
3321 pirq= [SMP,APIC] Manual mp-table setup
3322 See Documentation/x86/i386/IO-APIC.txt.
3324 plip= [PPT,NET] Parallel port network link
3325 Format: { parport<nr> | timid | 0 }
3326 See also Documentation/admin-guide/parport.rst.
3328 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3329 Override pmtimer IOPort with a hex value.
3333 Enable PNP debug messages (depends on the
3334 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3335 via /sys/module/pnp/parameters/debug. We always show
3336 current resource usage; turning this on also shows
3337 possible settings and some assignment information.
3343 { on | off | curr | res | no-curr | no-res }
3346 [ISAPNP] Exclude IRQs for the autoconfiguration
3349 [ISAPNP] Exclude DMAs for the autoconfiguration
3351 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3352 Ranges are in pairs (I/O port base and size).
3355 [ISAPNP] Exclude memory regions for the
3357 Ranges are in pairs (memory base and size).
3359 ports= [IP_VS_FTP] IPVS ftp helper module
3361 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3363 Format: <port>,<port>....
3365 powersave=off [PPC] This option disables power saving features.
3366 It specifically disables cpuidle and sets the
3367 platform machine description specific power_save
3368 function to NULL. On Idle the CPU just reduces
3371 ppc_strict_facility_enable
3372 [PPC] This option catches any kernel floating point,
3373 Altivec, VSX and SPE outside of regions specifically
3374 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3375 There is some performance impact when enabling this.
3379 Disable Hardware Transactional Memory
3381 print-fatal-signals=
3382 [KNL] debug: print fatal signals
3384 If enabled, warn about various signal handling
3385 related application anomalies: too many signals,
3386 too many POSIX.1 timers, fatal signals causing a
3389 If you hit the warning due to signal overflow,
3390 you might want to try "ulimit -i unlimited".
3394 printk.always_kmsg_dump=
3395 Trigger kmsg_dump for cases other than kernel oops or
3397 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3400 printk.devkmsg={on,off,ratelimit}
3401 Control writing to /dev/kmsg.
3402 on - unlimited logging to /dev/kmsg from userspace
3403 off - logging to /dev/kmsg disabled
3404 ratelimit - ratelimit the logging
3407 printk.time= Show timing data prefixed to each printk message line
3408 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3410 processor.max_cstate= [HW,ACPI]
3411 Limit processor to maximum C-state
3412 max_cstate=9 overrides any DMI blacklist limit.
3414 processor.nocst [HW,ACPI]
3415 Ignore the _CST method to determine C-states,
3416 instead using the legacy FADT method
3418 profile= [KNL] Enable kernel profiling via /proc/profile
3419 Format: [<profiletype>,]<number>
3420 Param: <profiletype>: "schedule", "sleep", or "kvm"
3421 [defaults to kernel profiling]
3422 Param: "schedule" - profile schedule points.
3423 Param: "sleep" - profile D-state sleeping (millisecs).
3424 Requires CONFIG_SCHEDSTATS
3425 Param: "kvm" - profile VM exits.
3426 Param: <number> - step/bucket size as a power of 2 for
3427 statistical time based profiling.
3429 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3431 See Documentation/blockdev/ramdisk.txt.
3433 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3434 probe for; one of (bare|imps|exps|lifebook|any).
3435 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3437 psmouse.resetafter= [HW,MOUSE]
3438 Try to reset the device after so many bad packets
3441 [HW,MOUSE] Set desired mouse resolution, in dpi.
3442 psmouse.smartscroll=
3443 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3444 0 = disabled, 1 = enabled (default).
3446 pstore.backend= Specify the name of the pstore backend to use
3449 See Documentation/blockdev/paride.txt.
3451 pti= [X86_64] Control Page Table Isolation of user and
3452 kernel address spaces. Disabling this feature
3453 removes hardening, but improves performance of
3454 system calls and interrupts.
3456 on - unconditionally enable
3457 off - unconditionally disable
3458 auto - kernel detects whether your CPU model is
3459 vulnerable to issues that PTI mitigates
3461 Not specifying this option is equivalent to pti=auto.
3464 Equivalent to pti=off
3467 [KNL] Number of legacy pty's. Overwrites compiled-in
3470 quiet [KNL] Disable most log messages
3475 See Documentation/admin-guide/md.rst.
3477 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3478 See Documentation/blockdev/ramdisk.txt.
3480 ras=option[,option,...] [KNL] RAS-specific options
3483 Disable the Correctable Errors Collector,
3484 see CONFIG_RAS_CEC help text.
3487 The argument is a cpu list, as described above.
3489 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3490 the specified list of CPUs to be no-callback CPUs.
3491 Invocation of these CPUs' RCU callbacks will
3492 be offloaded to "rcuox/N" kthreads created for
3493 that purpose, where "x" is "b" for RCU-bh, "p"
3494 for RCU-preempt, and "s" for RCU-sched, and "N"
3495 is the CPU number. This reduces OS jitter on the
3496 offloaded CPUs, which can be useful for HPC and
3497 real-time workloads. It can also improve energy
3498 efficiency for asymmetric multiprocessors.
3501 Rather than requiring that offloaded CPUs
3502 (specified by rcu_nocbs= above) explicitly
3503 awaken the corresponding "rcuoN" kthreads,
3504 make these kthreads poll for callbacks.
3505 This improves the real-time response for the
3506 offloaded CPUs by relieving them of the need to
3507 wake up the corresponding kthread, but degrades
3508 energy efficiency by requiring that the kthreads
3509 periodically wake up to do the polling.
3511 rcutree.blimit= [KNL]
3512 Set maximum number of finished RCU callbacks to
3513 process in one batch.
3515 rcutree.dump_tree= [KNL]
3516 Dump the structure of the rcu_node combining tree
3517 out at early boot. This is used for diagnostic
3518 purposes, to verify correct tree setup.
3520 rcutree.gp_cleanup_delay= [KNL]
3521 Set the number of jiffies to delay each step of
3522 RCU grace-period cleanup.
3524 rcutree.gp_init_delay= [KNL]
3525 Set the number of jiffies to delay each step of
3526 RCU grace-period initialization.
3528 rcutree.gp_preinit_delay= [KNL]
3529 Set the number of jiffies to delay each step of
3530 RCU grace-period pre-initialization, that is,
3531 the propagation of recent CPU-hotplug changes up
3532 the rcu_node combining tree.
3534 rcutree.rcu_fanout_exact= [KNL]
3535 Disable autobalancing of the rcu_node combining
3536 tree. This is used by rcutorture, and might
3537 possibly be useful for architectures having high
3538 cache-to-cache transfer latencies.
3540 rcutree.rcu_fanout_leaf= [KNL]
3541 Change the number of CPUs assigned to each
3542 leaf rcu_node structure. Useful for very
3543 large systems, which will choose the value 64,
3544 and for NUMA systems with large remote-access
3545 latencies, which will choose a value aligned
3546 with the appropriate hardware boundaries.
3548 rcutree.jiffies_till_sched_qs= [KNL]
3549 Set required age in jiffies for a
3550 given grace period before RCU starts
3551 soliciting quiescent-state help from
3552 rcu_note_context_switch().
3554 rcutree.jiffies_till_first_fqs= [KNL]
3555 Set delay from grace-period initialization to
3556 first attempt to force quiescent states.
3557 Units are jiffies, minimum value is zero,
3558 and maximum value is HZ.
3560 rcutree.jiffies_till_next_fqs= [KNL]
3561 Set delay between subsequent attempts to force
3562 quiescent states. Units are jiffies, minimum
3563 value is one, and maximum value is HZ.
3565 rcutree.kthread_prio= [KNL,BOOT]
3566 Set the SCHED_FIFO priority of the RCU per-CPU
3567 kthreads (rcuc/N). This value is also used for
3568 the priority of the RCU boost threads (rcub/N)
3569 and for the RCU grace-period kthreads (rcu_bh,
3570 rcu_preempt, and rcu_sched). If RCU_BOOST is
3571 set, valid values are 1-99 and the default is 1
3572 (the least-favored priority). Otherwise, when
3573 RCU_BOOST is not set, valid values are 0-99 and
3574 the default is zero (non-realtime operation).
3576 rcutree.rcu_nocb_leader_stride= [KNL]
3577 Set the number of NOCB kthread groups, which
3578 defaults to the square root of the number of
3579 CPUs. Larger numbers reduces the wakeup overhead
3580 on the per-CPU grace-period kthreads, but increases
3581 that same overhead on each group's leader.
3583 rcutree.qhimark= [KNL]
3584 Set threshold of queued RCU callbacks beyond which
3585 batch limiting is disabled.
3587 rcutree.qlowmark= [KNL]
3588 Set threshold of queued RCU callbacks below which
3589 batch limiting is re-enabled.
3591 rcutree.rcu_idle_gp_delay= [KNL]
3592 Set wakeup interval for idle CPUs that have
3593 RCU callbacks (RCU_FAST_NO_HZ=y).
3595 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3596 Set wakeup interval for idle CPUs that have
3597 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3598 Lazy RCU callbacks are those which RCU can
3599 prove do nothing more than free memory.
3601 rcutree.rcu_kick_kthreads= [KNL]
3602 Cause the grace-period kthread to get an extra
3603 wake_up() if it sleeps three times longer than
3604 it should at force-quiescent-state time.
3605 This wake_up() will be accompanied by a
3606 WARN_ONCE() splat and an ftrace_dump().
3608 rcuperf.gp_async= [KNL]
3609 Measure performance of asynchronous
3610 grace-period primitives such as call_rcu().
3612 rcuperf.gp_async_max= [KNL]
3613 Specify the maximum number of outstanding
3614 callbacks per writer thread. When a writer
3615 thread exceeds this limit, it invokes the
3616 corresponding flavor of rcu_barrier() to allow
3617 previously posted callbacks to drain.
3619 rcuperf.gp_exp= [KNL]
3620 Measure performance of expedited synchronous
3621 grace-period primitives.
3623 rcuperf.holdoff= [KNL]
3624 Set test-start holdoff period. The purpose of
3625 this parameter is to delay the start of the
3626 test until boot completes in order to avoid
3629 rcuperf.nreaders= [KNL]
3630 Set number of RCU readers. The value -1 selects
3631 N, where N is the number of CPUs. A value
3632 "n" less than -1 selects N-n+1, where N is again
3633 the number of CPUs. For example, -2 selects N
3634 (the number of CPUs), -3 selects N+1, and so on.
3635 A value of "n" less than or equal to -N selects
3638 rcuperf.nwriters= [KNL]
3639 Set number of RCU writers. The values operate
3640 the same as for rcuperf.nreaders.
3641 N, where N is the number of CPUs
3643 rcuperf.perf_type= [KNL]
3644 Specify the RCU implementation to test.
3646 rcuperf.shutdown= [KNL]
3647 Shut the system down after performance tests
3648 complete. This is useful for hands-off automated
3651 rcuperf.verbose= [KNL]
3652 Enable additional printk() statements.
3654 rcuperf.writer_holdoff= [KNL]
3655 Write-side holdoff between grace periods,
3656 in microseconds. The default of zero says
3659 rcutorture.cbflood_inter_holdoff= [KNL]
3660 Set holdoff time (jiffies) between successive
3661 callback-flood tests.
3663 rcutorture.cbflood_intra_holdoff= [KNL]
3664 Set holdoff time (jiffies) between successive
3665 bursts of callbacks within a given callback-flood
3668 rcutorture.cbflood_n_burst= [KNL]
3669 Set the number of bursts making up a given
3670 callback-flood test. Set this to zero to
3671 disable callback-flood testing.
3673 rcutorture.cbflood_n_per_burst= [KNL]
3674 Set the number of callbacks to be registered
3675 in a given burst of a callback-flood test.
3677 rcutorture.fqs_duration= [KNL]
3678 Set duration of force_quiescent_state bursts
3681 rcutorture.fqs_holdoff= [KNL]
3682 Set holdoff time within force_quiescent_state bursts
3685 rcutorture.fqs_stutter= [KNL]
3686 Set wait time between force_quiescent_state bursts
3689 rcutorture.gp_cond= [KNL]
3690 Use conditional/asynchronous update-side
3691 primitives, if available.
3693 rcutorture.gp_exp= [KNL]
3694 Use expedited update-side primitives, if available.
3696 rcutorture.gp_normal= [KNL]
3697 Use normal (non-expedited) asynchronous
3698 update-side primitives, if available.
3700 rcutorture.gp_sync= [KNL]
3701 Use normal (non-expedited) synchronous
3702 update-side primitives, if available. If all
3703 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3704 rcutorture.gp_normal=, and rcutorture.gp_sync=
3705 are zero, rcutorture acts as if is interpreted
3706 they are all non-zero.
3708 rcutorture.n_barrier_cbs= [KNL]
3709 Set callbacks/threads for rcu_barrier() testing.
3711 rcutorture.nfakewriters= [KNL]
3712 Set number of concurrent RCU writers. These just
3713 stress RCU, they don't participate in the actual
3714 test, hence the "fake".
3716 rcutorture.nreaders= [KNL]
3717 Set number of RCU readers. The value -1 selects
3718 N-1, where N is the number of CPUs. A value
3719 "n" less than -1 selects N-n-2, where N is again
3720 the number of CPUs. For example, -2 selects N
3721 (the number of CPUs), -3 selects N+1, and so on.
3723 rcutorture.object_debug= [KNL]
3724 Enable debug-object double-call_rcu() testing.
3726 rcutorture.onoff_holdoff= [KNL]
3727 Set time (s) after boot for CPU-hotplug testing.
3729 rcutorture.onoff_interval= [KNL]
3730 Set time (jiffies) between CPU-hotplug operations,
3731 or zero to disable CPU-hotplug testing.
3733 rcutorture.shuffle_interval= [KNL]
3734 Set task-shuffle interval (s). Shuffling tasks
3735 allows some CPUs to go into dyntick-idle mode
3736 during the rcutorture test.
3738 rcutorture.shutdown_secs= [KNL]
3739 Set time (s) after boot system shutdown. This
3740 is useful for hands-off automated testing.
3742 rcutorture.stall_cpu= [KNL]
3743 Duration of CPU stall (s) to test RCU CPU stall
3744 warnings, zero to disable.
3746 rcutorture.stall_cpu_holdoff= [KNL]
3747 Time to wait (s) after boot before inducing stall.
3749 rcutorture.stall_cpu_irqsoff= [KNL]
3750 Disable interrupts while stalling if set.
3752 rcutorture.stat_interval= [KNL]
3753 Time (s) between statistics printk()s.
3755 rcutorture.stutter= [KNL]
3756 Time (s) to stutter testing, for example, specifying
3757 five seconds causes the test to run for five seconds,
3758 wait for five seconds, and so on. This tests RCU's
3759 ability to transition abruptly to and from idle.
3761 rcutorture.test_boost= [KNL]
3762 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3763 "Maybe" means test if the RCU implementation
3764 under test support RCU priority boosting.
3766 rcutorture.test_boost_duration= [KNL]
3767 Duration (s) of each individual boost test.
3769 rcutorture.test_boost_interval= [KNL]
3770 Interval (s) between each boost test.
3772 rcutorture.test_no_idle_hz= [KNL]
3773 Test RCU's dyntick-idle handling. See also the
3774 rcutorture.shuffle_interval parameter.
3776 rcutorture.torture_type= [KNL]
3777 Specify the RCU implementation to test.
3779 rcutorture.verbose= [KNL]
3780 Enable additional printk() statements.
3782 rcupdate.rcu_cpu_stall_suppress= [KNL]
3783 Suppress RCU CPU stall warning messages.
3785 rcupdate.rcu_cpu_stall_timeout= [KNL]
3786 Set timeout for RCU CPU stall warning messages.
3788 rcupdate.rcu_expedited= [KNL]
3789 Use expedited grace-period primitives, for
3790 example, synchronize_rcu_expedited() instead
3791 of synchronize_rcu(). This reduces latency,
3792 but can increase CPU utilization, degrade
3793 real-time latency, and degrade energy efficiency.
3794 No effect on CONFIG_TINY_RCU kernels.
3796 rcupdate.rcu_normal= [KNL]
3797 Use only normal grace-period primitives,
3798 for example, synchronize_rcu() instead of
3799 synchronize_rcu_expedited(). This improves
3800 real-time latency, CPU utilization, and
3801 energy efficiency, but can expose users to
3802 increased grace-period latency. This parameter
3803 overrides rcupdate.rcu_expedited. No effect on
3804 CONFIG_TINY_RCU kernels.
3806 rcupdate.rcu_normal_after_boot= [KNL]
3807 Once boot has completed (that is, after
3808 rcu_end_inkernel_boot() has been invoked), use
3809 only normal grace-period primitives. No effect
3810 on CONFIG_TINY_RCU kernels.
3812 rcupdate.rcu_task_stall_timeout= [KNL]
3813 Set timeout in jiffies for RCU task stall warning
3814 messages. Disable with a value less than or equal
3817 rcupdate.rcu_self_test= [KNL]
3818 Run the RCU early boot self tests
3820 rcupdate.rcu_self_test_bh= [KNL]
3821 Run the RCU bh early boot self tests
3823 rcupdate.rcu_self_test_sched= [KNL]
3824 Run the RCU sched early boot self tests
3828 Run specified binary instead of /init from the ramdisk,
3829 used for early userspace startup. See initrd.
3832 Turn on/off individual RDT features. List is:
3833 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3835 E.g. to turn on cmt and turn off mba use:
3839 Format (x86 or x86_64):
3840 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3842 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3844 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3845 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3846 reboot_force is either force or not specified,
3847 reboot_cpu is s[mp]#### with #### being the processor
3848 to be used for rebooting.
3851 [KNL, SMP] Set scheduler's default relax_domain_level.
3852 See Documentation/cgroup-v1/cpusets.txt.
3854 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3855 Format: <base1>,<size1>[,<base2>,<size2>,...]
3856 Reserve I/O ports or memory so the kernel won't use
3857 them. If <base> is less than 0x10000, the region
3858 is assumed to be I/O ports; otherwise it is memory.
3860 reservetop= [X86-32]
3862 Reserves a hole at the top of the kernel virtual
3867 Set the amount of memory to reserve for BIOS at
3868 the bottom of the address space.
3870 reset_devices [KNL] Force drivers to reset the underlying device
3871 during initialization.
3874 Specify the partition device for software suspend
3876 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3878 resume_offset= [SWSUSP]
3879 Specify the offset from the beginning of the partition
3880 given by "resume=" at which the swap header is located,
3881 in <PAGE_SIZE> units (needed only for swap files).
3882 See Documentation/power/swsusp-and-swap-files.txt
3884 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3885 read the resume files
3887 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3888 Useful for devices that are detected asynchronously
3889 (e.g. USB and MMC devices).
3891 hibernate= [HIBERNATION]
3892 noresume Don't check if there's a hibernation image
3893 present during boot.
3894 nocompress Don't compress/decompress hibernation images.
3895 no Disable hibernation and resume.
3896 protect_image Turn on image protection during restoration
3897 (that will set all pages holding image data
3898 during restoration read-only).
3900 retain_initrd [RAM] Keep initrd memory after extraction
3902 rfkill.default_state=
3903 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3904 etc. communication is blocked by default.
3907 rfkill.master_switch_mode=
3908 0 The "airplane mode" button does nothing.
3909 1 The "airplane mode" button toggles between everything
3910 blocked and the previous configuration.
3911 2 The "airplane mode" button toggles between everything
3912 blocked and everything unblocked.
3914 rhash_entries= [KNL,NET]
3915 Set number of hash buckets for route cache
3918 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3921 ro [KNL] Mount root device read-only on boot
3924 on Mark read-only kernel memory as read-only (default).
3925 off Leave read-only kernel memory writable for debugging.
3928 Enable the uart passthrough on the designated usb port
3929 on Rockchip SoCs. When active, the signals of the
3930 debug-uart get routed to the D+ and D- pins of the usb
3931 port and the regular usb controller gets disabled.
3933 root= [KNL] Root filesystem
3934 See name_to_dev_t comment in init/do_mounts.c.
3936 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3937 mount the root filesystem
3939 rootflags= [KNL] Set root filesystem mount option string
3941 rootfstype= [KNL] Set root filesystem type
3943 rootwait [KNL] Wait (indefinitely) for root device to show up.
3944 Useful for devices that are detected asynchronously
3945 (e.g. USB and MMC devices).
3947 rproc_mem=nn[KMG][@address]
3948 [KNL,ARM,CMA] Remoteproc physical memory block.
3949 Memory area to be used by remote processor image,
3952 rw [KNL] Mount root device read-write on boot
3954 S [KNL] Run init in single mode
3956 s390_iommu= [HW,S390]
3957 Set s390 IOTLB flushing mode
3959 With strict flushing every unmap operation will result in
3960 an IOTLB flush. Default is lazy flushing before reuse,
3964 See drivers/net/irda/sa1100_ir.c.
3966 sbni= [NET] Granch SBNI12 leased line adapter
3968 sched_debug [KNL] Enables verbose scheduler debug messages.
3970 schedstats= [KNL,X86] Enable or disable scheduled statistics.
3971 Allowed values are enable and disable. This feature
3972 incurs a small amount of overhead in the scheduler
3973 but is useful for debugging and performance tuning.
3975 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3976 xtime_lock contention on larger systems, and/or RCU lock
3977 contention on all systems with CONFIG_MAXSMP set.
3978 Format: { "0" | "1" }
3979 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3981 Note: increases power consumption, thus should only be
3982 enabled if running jitter sensitive (HPC/RT) workloads.
3984 security= [SECURITY] Choose a security module to enable at boot.
3985 If this boot parameter is not specified, only the first
3986 security module asking for security registration will be
3987 loaded. An invalid security module name will be treated
3988 as if no module has been chosen.
3990 selinux= [SELINUX] Disable or enable SELinux at boot time.
3991 Format: { "0" | "1" }
3992 See security/selinux/Kconfig help text.
3995 Default value is set via kernel config option.
3996 If enabled at boot time, /selinux/disable can be used
3997 later to disable prior to initial policy load.
3999 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4000 Format: { "0" | "1" }
4001 See security/apparmor/Kconfig help text
4004 Default value is set via kernel config option.
4006 serialnumber [BUGS=X86-32]
4009 Maximal number of shapers.
4017 Disable merging of slabs with similar size. May be
4018 necessary if there is some reason to distinguish
4019 allocs to different slabs, especially in hardened
4020 environments where the risk of heap overflows and
4021 layout control by attackers can usually be
4022 frustrated by disabling merging. This will reduce
4023 most of the exposure of a heap attack to a single
4024 cache (risks via metadata attacks are mostly
4025 unchanged). Debug options disable merging on their
4027 For more information see Documentation/vm/slub.rst.
4029 slab_max_order= [MM, SLAB]
4030 Determines the maximum allowed order for slabs.
4031 A high setting may cause OOMs due to memory
4032 fragmentation. Defaults to 1 for systems with
4033 more than 32MB of RAM, 0 otherwise.
4035 slub_debug[=options[,slabs]] [MM, SLUB]
4036 Enabling slub_debug allows one to determine the
4037 culprit if slab objects become corrupted. Enabling
4038 slub_debug can create guard zones around objects and
4039 may poison objects when not in use. Also tracks the
4040 last alloc / free. For more information see
4041 Documentation/vm/slub.rst.
4043 slub_memcg_sysfs= [MM, SLUB]
4044 Determines whether to enable sysfs directories for
4045 memory cgroup sub-caches. 1 to enable, 0 to disable.
4046 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4047 Enabling this can lead to a very high number of debug
4048 directories and files being created under
4051 slub_max_order= [MM, SLUB]
4052 Determines the maximum allowed order for slabs.
4053 A high setting may cause OOMs due to memory
4054 fragmentation. For more information see
4055 Documentation/vm/slub.rst.
4057 slub_min_objects= [MM, SLUB]
4058 The minimum number of objects per slab. SLUB will
4059 increase the slab order up to slub_max_order to
4060 generate a sufficiently large slab able to contain
4061 the number of objects indicated. The higher the number
4062 of objects the smaller the overhead of tracking slabs
4063 and the less frequently locks need to be acquired.
4064 For more information see Documentation/vm/slub.rst.
4066 slub_min_order= [MM, SLUB]
4067 Determines the minimum page order for slabs. Must be
4068 lower than slub_max_order.
4069 For more information see Documentation/vm/slub.rst.
4071 slub_nomerge [MM, SLUB]
4072 Same with slab_nomerge. This is supported for legacy.
4073 See slab_nomerge for more information.
4076 Format: <io1>[,<io2>[,...,<io8>]]
4078 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4079 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4080 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4081 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4082 smsc-ircc2.ircc_irq= [HW] IRQ line
4083 smsc-ircc2.ircc_dma= [HW] DMA channel
4084 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4085 0: Toshiba Satellite 1800 (GP data pin select)
4086 1: Fast pin select (default)
4089 smt [KNL,S390] Set the maximum number of threads (logical
4090 CPUs) to use per physical CPU on systems capable of
4091 symmetric multithreading (SMT). Will be capped to the
4092 actual hardware limit.
4094 Default: -1 (no limit)
4097 [KNL] Should the soft-lockup detector generate panics.
4100 A nonzero value instructs the soft-lockup detector
4101 to panic the machine when a soft-lockup occurs. This
4102 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4103 which is the respective build-time switch to that
4106 softlockup_all_cpu_backtrace=
4107 [KNL] Should the soft-lockup detector generate
4108 backtraces on all cpus.
4111 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4112 See Documentation/laptops/sonypi.txt
4114 spectre_v2= [X86] Control mitigation of Spectre variant 2
4115 (indirect branch speculation) vulnerability.
4117 on - unconditionally enable
4118 off - unconditionally disable
4119 auto - kernel detects whether your CPU model is
4122 Selecting 'on' will, and 'auto' may, choose a
4123 mitigation method at run time according to the
4124 CPU, the available microcode, the setting of the
4125 CONFIG_RETPOLINE configuration option, and the
4126 compiler with which the kernel was built.
4128 Specific mitigations can also be selected manually:
4130 retpoline - replace indirect branches
4131 retpoline,generic - google's original retpoline
4132 retpoline,amd - AMD-specific minimal thunk
4134 Not specifying this option is equivalent to
4137 spec_store_bypass_disable=
4138 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4139 (Speculative Store Bypass vulnerability)
4141 Certain CPUs are vulnerable to an exploit against a
4142 a common industry wide performance optimization known
4143 as "Speculative Store Bypass" in which recent stores
4144 to the same memory location may not be observed by
4145 later loads during speculative execution. The idea
4146 is that such stores are unlikely and that they can
4147 be detected prior to instruction retirement at the
4148 end of a particular speculation execution window.
4150 In vulnerable processors, the speculatively forwarded
4151 store can be used in a cache side channel attack, for
4152 example to read memory to which the attacker does not
4153 directly have access (e.g. inside sandboxed code).
4155 This parameter controls whether the Speculative Store
4156 Bypass optimization is used.
4158 On x86 the options are:
4160 on - Unconditionally disable Speculative Store Bypass
4161 off - Unconditionally enable Speculative Store Bypass
4162 auto - Kernel detects whether the CPU model contains an
4163 implementation of Speculative Store Bypass and
4164 picks the most appropriate mitigation. If the
4165 CPU is not vulnerable, "off" is selected. If the
4166 CPU is vulnerable the default mitigation is
4167 architecture and Kconfig dependent. See below.
4168 prctl - Control Speculative Store Bypass per thread
4169 via prctl. Speculative Store Bypass is enabled
4170 for a process by default. The state of the control
4171 is inherited on fork.
4172 seccomp - Same as "prctl" above, but all seccomp threads
4173 will disable SSB unless they explicitly opt out.
4175 Default mitigations:
4176 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4178 On powerpc the options are:
4180 on,auto - On Power8 and Power9 insert a store-forwarding
4181 barrier on kernel entry and exit. On Power7
4182 perform a software flush on kernel entry and
4186 Not specifying this option is equivalent to
4187 spec_store_bypass_disable=auto.
4189 spia_io_base= [HW,MTD]
4194 srcutree.counter_wrap_check [KNL]
4195 Specifies how frequently to check for
4196 grace-period sequence counter wrap for the
4197 srcu_data structure's ->srcu_gp_seq_needed field.
4198 The greater the number of bits set in this kernel
4199 parameter, the less frequently counter wrap will
4200 be checked for. Note that the bottom two bits
4203 srcutree.exp_holdoff [KNL]
4204 Specifies how many nanoseconds must elapse
4205 since the end of the last SRCU grace period for
4206 a given srcu_struct until the next normal SRCU
4207 grace period will be considered for automatic
4208 expediting. Set to zero to disable automatic
4212 Speculative Store Bypass Disable control
4214 On CPUs that are vulnerable to the Speculative
4215 Store Bypass vulnerability and offer a
4216 firmware based mitigation, this parameter
4217 indicates how the mitigation should be used:
4219 force-on: Unconditionally enable mitigation for
4220 for both kernel and userspace
4221 force-off: Unconditionally disable mitigation for
4222 for both kernel and userspace
4223 kernel: Always enable mitigation in the
4224 kernel, and offer a prctl interface
4225 to allow userspace to register its
4226 interest in being mitigated too.
4228 stack_guard_gap= [MM]
4229 override the default stack gap protection. The value
4230 is in page units and it defines how many pages prior
4231 to (for stacks growing down) resp. after (for stacks
4232 growing up) the main stack are reserved for no other
4233 mapping. Default value is 256 pages.
4236 Enabled the stack tracer on boot up.
4238 stacktrace_filter=[function-list]
4239 [FTRACE] Limit the functions that the stack tracer
4240 will trace at boot up. function-list is a comma separated
4241 list of functions. This list can be changed at run
4242 time by the stack_trace_filter file in the debugfs
4243 tracing directory. Note, this enables stack tracing
4244 and the stacktrace above is not needed.
4248 Set the STI (builtin display/keyboard on the HP-PARISC
4249 machines) console (graphic card) which should be used
4250 as the initial boot-console.
4251 See also comment in drivers/video/console/sticore.c.
4254 See comment in drivers/video/console/sticore.c.
4257 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4259 sunrpc.min_resvport=
4260 sunrpc.max_resvport=
4262 SunRPC servers often require that client requests
4263 originate from a privileged port (i.e. a port in the
4264 range 0 < portnr < 1024).
4265 An administrator who wishes to reserve some of these
4266 ports for other uses may adjust the range that the
4267 kernel's sunrpc client considers to be privileged
4268 using these two parameters to set the minimum and
4269 maximum port values.
4271 sunrpc.svc_rpc_per_connection_limit=
4273 Limit the number of requests that the server will
4274 process in parallel from a single connection.
4275 The default value is 0 (no limit).
4279 Control how the NFS server code allocates CPUs to
4280 service thread pools. Depending on how many NICs
4281 you have and where their interrupts are bound, this
4282 option will affect which CPUs will do NFS serving.
4283 Note: this parameter cannot be changed while the
4284 NFS server is running.
4286 auto the server chooses an appropriate mode
4287 automatically using heuristics
4288 global a single global pool contains all CPUs
4289 percpu one pool for each CPU
4290 pernode one pool for each NUMA node (equivalent
4291 to global on non-NUMA machines)
4293 sunrpc.tcp_slot_table_entries=
4294 sunrpc.udp_slot_table_entries=
4296 Sets the upper limit on the number of simultaneous
4297 RPC calls that can be sent from the client to a
4298 server. Increasing these values may allow you to
4299 improve throughput, but will also increase the
4300 amount of memory reserved for use by the client.
4302 suspend.pm_test_delay=
4304 Sets the number of seconds to remain in a suspend test
4305 mode before resuming the system (see
4306 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4307 is set. Default value is 5.
4310 [KNL] Enable accounting of swap in memory resource
4311 controller if no parameter or 1 is given or disable
4312 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4314 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4315 Format: { <int> | force | noforce }
4316 <int> -- Number of I/O TLB slabs
4317 force -- force using of bounce buffers even if they
4318 wouldn't be automatically used by the kernel
4319 noforce -- Never use bounce buffers (for debugging)
4323 sysfs.deprecated=0|1 [KNL]
4324 Enable/disable old style sysfs layout for old udev
4325 on older distributions. When this option is enabled
4326 very new udev will not work anymore. When this option
4327 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4328 in older udev will not work anymore.
4329 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4330 the kernel configuration.
4332 sysrq_always_enabled
4334 Ignore sysrq setting - this boot parameter will
4335 neutralize any effect of /proc/sys/kernel/sysrq.
4336 Useful for debugging.
4338 tcpmhash_entries= [KNL,NET]
4339 Set the number of tcp_metrics_hash slots.
4340 Default value is 8192 or 16384 depending on total
4341 ram pages. This is used to specify the TCP metrics
4342 cache size. See Documentation/networking/ip-sysctl.txt
4343 "tcp_no_metrics_save" section for more details.
4347 test_suspend= [SUSPEND][,N]
4348 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4349 standby suspend) or "freeze" (for suspend type freeze)
4350 as the system sleep state during system startup with
4351 the optional capability to repeat N number of times.
4352 The system is woken from this state using a
4353 wakeup-capable RTC alarm.
4355 thash_entries= [KNL,NET]
4356 Set number of hash buckets for TCP connection
4358 thermal.act= [HW,ACPI]
4359 -1: disable all active trip points in all thermal zones
4360 <degrees C>: override all lowest active trip points
4362 thermal.crt= [HW,ACPI]
4363 -1: disable all critical trip points in all thermal zones
4364 <degrees C>: override all critical trip points
4366 thermal.nocrt= [HW,ACPI]
4367 Set to disable actions on ACPI thermal zone
4368 critical and hot trip points.
4370 thermal.off= [HW,ACPI]
4371 1: disable ACPI thermal control
4373 thermal.psv= [HW,ACPI]
4374 -1: disable all passive trip points
4375 <degrees C>: override all passive trip points to this
4378 thermal.tzp= [HW,ACPI]
4379 Specify global default ACPI thermal zone polling rate
4380 <deci-seconds>: poll all this frequency
4381 0: no polling (default)
4384 Force threading of all interrupt handlers except those
4385 marked explicitly IRQF_NO_THREAD.
4388 Enable the Transcendent memory driver if built-in.
4390 tmem.cleancache=0|1 [KNL, XEN]
4391 Default is on (1). Disable the usage of the cleancache
4392 API to send anonymous pages to the hypervisor.
4394 tmem.frontswap=0|1 [KNL, XEN]
4395 Default is on (1). Disable the usage of the frontswap
4396 API to send swap pages to the hypervisor. If disabled
4397 the selfballooning and selfshrinking are force disabled.
4399 tmem.selfballooning=0|1 [KNL, XEN]
4400 Default is on (1). Disable the driving of swap pages
4403 tmem.selfshrinking=0|1 [KNL, XEN]
4404 Default is on (1). Partial swapoff that immediately
4405 transfers pages from Xen hypervisor back to the
4406 kernel based on different criteria.
4410 Specify if the kernel should make use of the cpu
4411 topology information if the hardware supports this.
4412 The scheduler will make use of this information and
4413 e.g. base its process migration decisions on it.
4416 topology_updates= [KNL, PPC, NUMA]
4418 Specify if the kernel should ignore (off)
4419 topology updates sent by the hypervisor to this
4424 tpm_suspend_pcr=[HW,TPM]
4425 Format: integer pcr id
4426 Specify that at suspend time, the tpm driver
4427 should extend the specified pcr with zeros,
4428 as a workaround for some chips which fail to
4429 flush the last written pcr on TPM_SaveState.
4430 This will guarantee that all the other pcrs
4433 trace_buf_size=nn[KMG]
4434 [FTRACE] will set tracing buffer size on each cpu.
4436 trace_event=[event-list]
4437 [FTRACE] Set and start specified trace events in order
4438 to facilitate early boot debugging. The event-list is a
4439 comma separated list of trace events to enable. See
4440 also Documentation/trace/events.rst
4442 trace_options=[option-list]
4443 [FTRACE] Enable or disable tracer options at boot.
4444 The option-list is a comma delimited list of options
4445 that can be enabled or disabled just as if you were
4446 to echo the option name into
4448 /sys/kernel/debug/tracing/trace_options
4450 For example, to enable stacktrace option (to dump the
4451 stack trace of each event), add to the command line:
4453 trace_options=stacktrace
4455 See also Documentation/trace/ftrace.rst "trace options"
4459 Have the tracepoints sent to printk as well as the
4460 tracing ring buffer. This is useful for early boot up
4461 where the system hangs or reboots and does not give the
4462 option for reading the tracing buffer or performing a
4463 ftrace_dump_on_oops.
4465 To turn off having tracepoints sent to printk,
4466 echo 0 > /proc/sys/kernel/tracepoint_printk
4467 Note, echoing 1 into this file without the
4468 tracepoint_printk kernel cmdline option has no effect.
4472 Having tracepoints sent to printk() and activating high
4473 frequency tracepoints such as irq or sched, can cause
4474 the system to live lock.
4477 [FTRACE] enable this option to disable tracing when a
4478 warning is hit. This turns off "tracing_on". Tracing can
4479 be enabled again by echoing '1' into the "tracing_on"
4480 file located in /sys/kernel/debug/tracing/
4482 This option is useful, as it disables the trace before
4483 the WARNING dump is called, which prevents the trace to
4484 be filled with content caused by the warning output.
4486 This option can also be set at run time via the sysctl
4487 option: kernel/traceoff_on_warning
4489 transparent_hugepage=
4491 Format: [always|madvise|never]
4492 Can be used to control the default behavior of the system
4493 with respect to transparent hugepages.
4494 See Documentation/admin-guide/mm/transhuge.rst
4497 tsc= Disable clocksource stability checks for TSC.
4499 [x86] reliable: mark tsc clocksource as reliable, this
4500 disables clocksource verification at runtime, as well
4501 as the stability checks done at bootup. Used to enable
4502 high-resolution timer mode on older hardware, and in
4503 virtualized environment.
4504 [x86] noirqtime: Do not use TSC to do irq accounting.
4505 Used to run time disable IRQ_TIME_ACCOUNTING on any
4506 platforms where RDTSC is slow and this accounting
4508 [x86] unstable: mark the TSC clocksource as unstable, this
4509 marks the TSC unconditionally unstable at bootup and
4510 avoids any further wobbles once the TSC watchdog notices.
4512 turbografx.map[2|3]= [HW,JOY]
4513 TurboGraFX parallel port interface
4515 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4516 See also Documentation/input/devices/joystick-parport.rst
4518 udbg-immortal [PPC] When debugging early kernel crashes that
4519 happen after console_init() and before a proper
4520 console driver takes over, this boot options might
4521 help "seeing" what's going on.
4523 uhash_entries= [KNL,NET]
4524 Set number of hash buckets for UDP/UDP-Lite connections
4527 [USB] Ignore overcurrent events (default N).
4528 Some badly-designed motherboards generate lots of
4529 bogus events, for ports that aren't wired to
4530 anything. Set this parameter to avoid log spamming.
4531 Note that genuine overcurrent events won't be
4535 [X86] Cause panic on unknown NMI.
4537 usbcore.authorized_default=
4538 [USB] Default USB device authorization:
4539 (default -1 = authorized except for wireless USB,
4540 0 = not authorized, 1 = authorized)
4542 usbcore.autosuspend=
4543 [USB] The autosuspend time delay (in seconds) used
4544 for newly-detected USB devices (default 2). This
4545 is the time required before an idle device will be
4546 autosuspended. Devices for which the delay is set
4547 to a negative value won't be autosuspended at all.
4549 usbcore.usbfs_snoop=
4550 [USB] Set to log all usbfs traffic (default 0 = off).
4552 usbcore.usbfs_snoop_max=
4553 [USB] Maximum number of bytes to snoop in each URB
4556 usbcore.blinkenlights=
4557 [USB] Set to cycle leds on hubs (default 0 = off).
4559 usbcore.old_scheme_first=
4560 [USB] Start with the old device initialization
4561 scheme (default 0 = off).
4563 usbcore.usbfs_memory_mb=
4564 [USB] Memory limit (in MB) for buffers allocated by
4565 usbfs (default = 16, 0 = max = 2047).
4567 usbcore.use_both_schemes=
4568 [USB] Try the other device initialization scheme
4569 if the first one fails (default 1 = enabled).
4571 usbcore.initial_descriptor_timeout=
4572 [USB] Specifies timeout for the initial 64-byte
4573 USB_REQ_GET_DESCRIPTOR request in milliseconds
4574 (default 5000 = 5.0 seconds).
4576 usbcore.nousb [USB] Disable the USB subsystem
4579 [USB] A list of quirk entries to augment the built-in
4580 usb core quirk list. List entries are separated by
4581 commas. Each entry has the form
4582 VendorID:ProductID:Flags. The IDs are 4-digit hex
4583 numbers and Flags is a set of letters. Each letter
4584 will change the built-in quirk; setting it if it is
4585 clear and clearing it if it is set. The letters have
4586 the following meanings:
4587 a = USB_QUIRK_STRING_FETCH_255 (string
4588 descriptors must not be fetched using
4590 b = USB_QUIRK_RESET_RESUME (device can't resume
4591 correctly so reset it instead);
4592 c = USB_QUIRK_NO_SET_INTF (device can't handle
4593 Set-Interface requests);
4594 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4595 handle its Configuration or Interface
4597 e = USB_QUIRK_RESET (device can't be reset
4598 (e.g morph devices), don't use reset);
4599 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4600 more interface descriptions than the
4601 bNumInterfaces count, and can't handle
4602 talking to these interfaces);
4603 g = USB_QUIRK_DELAY_INIT (device needs a pause
4604 during initialization, after we read
4605 the device descriptor);
4606 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4607 high speed and super speed interrupt
4608 endpoints, the USB 2.0 and USB 3.0 spec
4609 require the interval in microframes (1
4610 microframe = 125 microseconds) to be
4611 calculated as interval = 2 ^
4613 Devices with this quirk report their
4614 bInterval as the result of this
4615 calculation instead of the exponent
4616 variable used in the calculation);
4617 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4618 handle device_qualifier descriptor
4620 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4621 generates spurious wakeup, ignore
4622 remote wakeup capability);
4623 k = USB_QUIRK_NO_LPM (device can't handle Link
4625 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4626 (Device reports its bInterval as linear
4627 frames instead of the USB 2.0
4629 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4630 to be disconnected before suspend to
4631 prevent spurious wakeup);
4632 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4633 pause after every control message);
4634 Example: quirks=0781:5580:bk,0a5c:5834:gij
4637 [USBHID] The interval which mice are to be polled at.
4640 [USBHID] The interval which joysticks are to be polled at.
4643 [USBHID] The interval which keyboards are to be polled at.
4645 usb-storage.delay_use=
4646 [UMS] The delay in seconds before a new device is
4647 scanned for Logical Units (default 1).
4650 [UMS] A list of quirks entries to supplement or
4651 override the built-in unusual_devs list. List
4652 entries are separated by commas. Each entry has
4653 the form VID:PID:Flags where VID and PID are Vendor
4654 and Product ID values (4-digit hex numbers) and
4655 Flags is a set of characters, each corresponding
4656 to a common usb-storage quirk flag as follows:
4657 a = SANE_SENSE (collect more than 18 bytes
4659 b = BAD_SENSE (don't collect more than 18
4660 bytes of sense data);
4661 c = FIX_CAPACITY (decrease the reported
4662 device capacity by one sector);
4663 d = NO_READ_DISC_INFO (don't use
4664 READ_DISC_INFO command);
4665 e = NO_READ_CAPACITY_16 (don't use
4666 READ_CAPACITY_16 command);
4667 f = NO_REPORT_OPCODES (don't use report opcodes
4669 g = MAX_SECTORS_240 (don't transfer more than
4670 240 sectors at a time, uas only);
4671 h = CAPACITY_HEURISTICS (decrease the
4672 reported device capacity by one
4673 sector if the number is odd);
4674 i = IGNORE_DEVICE (don't bind to this
4676 j = NO_REPORT_LUNS (don't use report luns
4678 l = NOT_LOCKABLE (don't try to lock and
4679 unlock ejectable media);
4680 m = MAX_SECTORS_64 (don't transfer more
4681 than 64 sectors = 32 KB at a time);
4682 n = INITIAL_READ10 (force a retry of the
4683 initial READ(10) command);
4684 o = CAPACITY_OK (accept the capacity
4685 reported by the device);
4686 p = WRITE_CACHE (the device cache is ON
4688 r = IGNORE_RESIDUE (the device reports
4689 bogus residue values);
4690 s = SINGLE_LUN (the device has only one
4692 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4693 commands, uas only);
4694 u = IGNORE_UAS (don't bind to the uas driver);
4695 w = NO_WP_DETECT (don't test whether the
4696 medium is write-protected).
4697 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4698 even if the device claims no cache)
4699 Example: quirks=0419:aaf5:rl,0421:0433:rc
4701 user_debug= [KNL,ARM]
4703 See arch/arm/Kconfig.debug help text.
4704 1 - undefined instruction events
4706 4 - invalid data aborts
4709 Example: user_debug=31
4712 [X86] Flags controlling user PTE allocations.
4714 nohigh = do not allocate PTE pages in
4715 HIGHMEM regardless of setting
4719 On X86_32, this is an alias for vdso32=. Otherwise:
4721 vdso=1: enable VDSO (the default)
4722 vdso=0: disable VDSO mapping
4724 vdso32= [X86] Control the 32-bit vDSO
4725 vdso32=1: enable 32-bit VDSO
4726 vdso32=0 or vdso32=2: disable 32-bit VDSO
4728 See the help text for CONFIG_COMPAT_VDSO for more
4729 details. If CONFIG_COMPAT_VDSO is set, the default is
4730 vdso32=0; otherwise, the default is vdso32=1.
4732 For compatibility with older kernels, vdso32=2 is an
4735 Try vdso32=0 if you encounter an error that says:
4736 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4739 vector=percpu: enable percpu vector domain
4741 video= [FB] Frame buffer configuration
4742 See Documentation/fb/modedb.txt.
4744 video.brightness_switch_enabled= [0,1]
4745 If set to 1, on receiving an ACPI notify event
4746 generated by hotkey, video driver will adjust brightness
4747 level and then send out the event to user space through
4748 the allocated input device; If set to 0, video driver
4749 will only send out the event without touching backlight
4754 [VMMIO] Memory mapped virtio (platform) device.
4756 <size>@<baseaddr>:<irq>[:<id>]
4758 <size> := size (can use standard suffixes
4760 <baseaddr> := physical base address
4761 <irq> := interrupt number (as passed to
4763 <id> := (optional) platform device id
4765 virtio_mmio.device=1K@0x100b0000:48:7
4767 Can be used multiple times for multiple devices.
4769 vga= [BOOT,X86-32] Select a particular video mode
4770 See Documentation/x86/boot.txt and
4771 Documentation/svga.txt.
4772 Use vga=ask for menu.
4773 This is actually a boot loader parameter; the value is
4774 passed to the kernel using a special protocol.
4776 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4777 size of <nn>. This can be used to increase the
4778 minimum size (128MB on x86). It can also be used to
4779 decrease the size and leave more room for directly
4782 vmcp_cma=nn[MG] [KNL,S390]
4783 Sets the memory size reserved for contiguous memory
4784 allocations for the vmcp device driver.
4786 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4789 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4792 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4796 Controls the behavior of vsyscalls (i.e. calls to
4797 fixed addresses of 0xffffffffff600x00 from legacy
4798 code). Most statically-linked binaries and older
4799 versions of glibc use these calls. Because these
4800 functions are at fixed addresses, they make nice
4801 targets for exploits that can control RIP.
4803 emulate [default] Vsyscalls turn into traps and are
4804 emulated reasonably safely.
4806 native Vsyscalls are native syscall instructions.
4807 This is a little bit faster than trapping
4808 and makes a few dynamic recompilers work
4809 better than they would in emulation mode.
4810 It also makes exploits much easier to write.
4812 none Vsyscalls don't work at all. This makes
4813 them quite hard to use for exploits but
4814 might break your system.
4816 vt.color= [VT] Default text color.
4817 Format: 0xYX, X = foreground, Y = background.
4818 Default: 0x07 = light gray on black.
4820 vt.cur_default= [VT] Default cursor shape.
4821 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4822 the parameters of the <Esc>[?A;B;Cc escape sequence;
4823 see VGA-softcursor.txt. Default: 2 = underline.
4825 vt.default_blu= [VT]
4826 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4827 Change the default blue palette of the console.
4828 This is a 16-member array composed of values
4831 vt.default_grn= [VT]
4832 Format: <green0>,<green1>,<green2>,...,<green15>
4833 Change the default green palette of the console.
4834 This is a 16-member array composed of values
4837 vt.default_red= [VT]
4838 Format: <red0>,<red1>,<red2>,...,<red15>
4839 Change the default red palette of the console.
4840 This is a 16-member array composed of values
4846 Set system-wide default UTF-8 mode for all tty's.
4847 Default is 1, i.e. UTF-8 mode is enabled for all
4848 newly opened terminals.
4850 vt.global_cursor_default=
4853 Set system-wide default for whether a cursor
4854 is shown on new VTs. Default is -1,
4855 i.e. cursors will be created by default unless
4856 overridden by individual drivers. 0 will hide
4857 cursors, 1 will display them.
4859 vt.italic= [VT] Default color for italic text; 0-15.
4862 vt.underline= [VT] Default color for underlined text; 0-15.
4865 watchdog timers [HW,WDT] For information on watchdog timers,
4866 see Documentation/watchdog/watchdog-parameters.txt
4867 or other driver-specific files in the
4868 Documentation/watchdog/ directory.
4870 workqueue.watchdog_thresh=
4871 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4872 warn stall conditions and dump internal state to
4873 help debugging. 0 disables workqueue stall
4874 detection; otherwise, it's the stall threshold
4875 duration in seconds. The default value is 30 and
4876 it can be updated at runtime by writing to the
4877 corresponding sysfs file.
4879 workqueue.disable_numa
4880 By default, all work items queued to unbound
4881 workqueues are affine to the NUMA nodes they're
4882 issued on, which results in better behavior in
4883 general. If NUMA affinity needs to be disabled for
4884 whatever reason, this option can be used. Note
4885 that this also can be controlled per-workqueue for
4886 workqueues visible under /sys/bus/workqueue/.
4888 workqueue.power_efficient
4889 Per-cpu workqueues are generally preferred because
4890 they show better performance thanks to cache
4891 locality; unfortunately, per-cpu workqueues tend to
4892 be more power hungry than unbound workqueues.
4894 Enabling this makes the per-cpu workqueues which
4895 were observed to contribute significantly to power
4896 consumption unbound, leading to measurably lower
4897 power usage at the cost of small performance
4900 The default value of this parameter is determined by
4901 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4903 workqueue.debug_force_rr_cpu
4904 Workqueue used to implicitly guarantee that work
4905 items queued without explicit CPU specified are put
4906 on the local CPU. This guarantee is no longer true
4907 and while local CPU is still preferred work items
4908 may be put on foreign CPUs. This debug option
4909 forces round-robin CPU selection to flush out
4910 usages which depend on the now broken guarantee.
4911 When enabled, memory and cache locality will be
4914 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4915 default x2apic cluster mode on platforms
4918 x86_intel_mid_timer= [X86-32,APBT]
4919 Choose timer option for x86 Intel MID platform.
4920 Two valid options are apbt timer only and lapic timer
4921 plus one apbt timer for broadcast timer.
4922 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4924 xen_512gb_limit [KNL,X86-64,XEN]
4925 Restricts the kernel running paravirtualized under Xen
4926 to use only up to 512 GB of RAM. The reason to do so is
4927 crash analysis tools and Xen tools for doing domain
4928 save/restore/migration must be enabled to handle larger
4931 xen_emul_unplug= [HW,X86,XEN]
4932 Unplug Xen emulated devices
4933 Format: [unplug0,][unplug1]
4934 ide-disks -- unplug primary master IDE devices
4935 aux-ide-disks -- unplug non-primary-master IDE devices
4936 nics -- unplug network devices
4937 all -- unplug all emulated devices (NICs and IDE disks)
4938 unnecessary -- unplugging emulated devices is
4939 unnecessary even if the host did not respond to
4941 never -- do not unplug even if version check succeeds
4943 xen_nopvspin [X86,XEN]
4944 Disables the ticketlock slowpath using Xen PV
4948 Disables the PV optimizations forcing the HVM guest to
4949 run as generic HVM guest with no PV drivers.
4951 xirc2ps_cs= [NET,PCMCIA]
4953 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
4955 xhci-hcd.quirks [USB,KNL]
4956 A hex value specifying bitmask with supplemental xhci
4957 host controller quirks. Meaning of each bit can be
4958 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob