1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
5 force -- enable ACPI if default was off
6 on -- enable ACPI but allow fallback to DT [arm64]
7 off -- disable ACPI if default was on
8 noirq -- do not use ACPI for IRQ routing
9 strict -- Be less tolerant of platforms that are not
10 strictly ACPI specification compliant.
11 rsdt -- prefer RSDT over (default) XSDT
12 copy_dsdt -- copy DSDT to memory
13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
27 If set to vendor, prefer vendor specific driver
28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
29 of the ACPI video.ko driver.
31 acpi_force_32bit_fadt_addr
32 force FADT to use 32 bit addresses rather than the
33 64 bit X_* addresses. Some firmware have broken 64
34 bit addresses for force ACPI ignore these and use
35 the older legacy 32 bit addresses.
37 acpica_no_return_repair [HW, ACPI]
38 Disable AML predefined validation mechanism
39 This mechanism can repair the evaluation result to make
40 the return objects more ACPI specification compliant.
41 This option is useful for developers to identify the
42 root cause of an AML interpreter issue when the issue
43 has something to do with the repair mechanism.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
49 debug output. Bits in debug_layer correspond to a
50 _COMPONENT in an ACPI source file, e.g.,
51 #define _COMPONENT ACPI_PCI_COMPONENT
52 Bits in debug_level correspond to a level in
53 ACPI_DEBUG_PRINT statements, e.g.,
54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
55 The debug_level mask defaults to "info". See
56 Documentation/acpi/debug.txt for more information about
57 debug layers and levels.
59 Enable processor driver info messages:
60 acpi.debug_layer=0x20000000
61 Enable PCI/PCI interrupt routing info messages:
62 acpi.debug_layer=0x400000
63 Enable AML "Debug" output, i.e., stores to the Debug
64 object while interpreting AML:
65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
66 Enable all messages related to ACPI hardware:
67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
69 Some values produce so much output that the system is
70 unusable. The "log_buf_len" parameter may be useful
71 if you need to capture more output.
73 acpi_enforce_resources= [ACPI]
75 Check for resource conflicts between native drivers
76 and ACPI OperationRegions (SystemIO and SystemMemory
77 only). IO ports and memory declared in ACPI might be
78 used by the ACPI subsystem in arbitrary AML code and
79 can interfere with legacy drivers.
80 strict (default): access to resources claimed by ACPI
81 is denied; legacy drivers trying to access reserved
82 resources will fail to bind to device using them.
83 lax: access to resources claimed by ACPI is allowed;
84 legacy drivers trying to access reserved resources
85 will bind successfully but a warning message is logged.
86 no: ACPI OperationRegions are not marked as reserved,
87 no further checks are performed.
89 acpi_force_table_verification [HW,ACPI]
90 Enable table checksum verification during early stage.
91 By default, this is disabled due to x86 early mapping
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
109 acpi_mask_gpe= [HW,ACPI]
110 Due to the existence of _Lxx/_Exx, some GPEs triggered
111 by unsupported hardware/firmware features can result in
112 GPE floodings that cannot be automatically disabled by
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/driver-api/clk.rst.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
645 [KNL] Change console messages format
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
728 [KNL] Disable crypto self-tests
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
752 [KNL] Enable printing [hashed] pointers early in the
753 boot sequence. If enabled, we use a weak hash instead
754 of siphash to hash pointers. Use this option if you are
755 seeing instances of '(___ptrval___)') and need to see a
756 value (hashed pointer) instead. Cryptographically
757 insecure, please do not use on production kernels.
760 [KNL] verbose self-tests
762 Print debugging info while doing the locking API
764 We default to 0 (no extra messages), setting it to
765 1 will print _a lot_ more information - normally
766 only useful to kernel developers.
768 debug_objects [KNL] Enable object debugging
771 [KNL] Disable object debugging
773 debug_guardpage_minorder=
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter allows control of the order of pages that will
776 be intentionally kept free (and hence protected) by the
777 buddy allocator. Bigger value increase the probability
778 of catching random memory corruption, but reduce the
779 amount of memory for normal system use. The maximum
780 possible value is MAX_ORDER/2. Setting this parameter
781 to 1 or 2 should be enough to identify most random
782 memory corruption problems caused by bugs in kernel or
783 driver code when a CPU writes to (or reads from) a
784 random memory location. Note that there exists a class
785 of memory corruptions problems caused by buggy H/W or
786 F/W or by drivers badly programing DMA (basically when
787 memory is written at bus level and the CPU MMU is
788 bypassed) which are not detectable by
789 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
790 tracking down these problems.
793 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
794 parameter enables the feature at boot time. In
795 default, it is disabled. We can avoid allocating huge
796 chunk of memory for debug pagealloc if we don't enable
797 it at boot time and the system will work mostly same
798 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
799 on: enable the feature
801 debugpat [X86] Enable PAT debugging
803 decnet.addr= [HW,NET]
804 Format: <area>[,<node>]
805 See also Documentation/networking/decnet.txt.
808 [same as hugepagesz=] The size of the default
809 HugeTLB page size. This is the size represented by
810 the legacy /proc/ hugepages APIs, used for SHM, and
811 default size when mounting hugetlbfs filesystems.
812 Defaults to the default architecture's huge page size
815 deferred_probe_timeout=
816 [KNL] Debugging option to set a timeout in seconds for
817 deferred probe to give up waiting on dependencies to
818 probe. Only specific dependencies (subsystems or
819 drivers) that have opted in will be ignored. A timeout of 0
820 will timeout at the end of initcalls. This option will also
821 dump out devices still on the deferred probe list after
825 Set number of hash buckets for dentry cache.
827 disable_1tb_segments [PPC]
828 Disables the use of 1TB hash page table segments. This
829 causes the kernel to fall back to 256MB segments which
830 can be useful when debugging issues that require an SLB
834 See Documentation/networking/ipv6.txt.
837 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
838 hardening is enabled for this boot. Hardened
839 usercopy checking is used to protect the kernel
840 from reading or writing beyond known memory
841 allocation boundaries as a proactive defense
842 against bounds-checking flaws in the kernel's
843 copy_to_user()/copy_from_user() interface.
844 on Perform hardened usercopy checks (default).
845 off Disable hardened usercopy checks.
848 Disable RADIX MMU mode on POWER9
850 disable_cpu_apicid= [X86,APIC,SMP]
852 The number of initial APIC ID for the
853 corresponding CPU to be disabled at boot,
854 mostly used for the kdump 2nd kernel to
855 disable BSP to wake up multiple CPUs without
856 causing system reset or hang due to sending
859 disable_counter_freezing [HW]
860 Disable Intel PMU counter freezing feature.
861 The feature only exists starting from
862 Arch Perfmon v4 (Skylake and newer).
864 disable_ddw [PPC/PSERIES]
865 Disable Dynamic DMA Window support. Use this if
866 to workaround buggy firmware.
869 See Documentation/networking/ipv6.txt.
871 disable_mtrr_cleanup [X86]
872 The kernel tries to adjust MTRR layout from continuous
873 to discrete, to make X server driver able to add WB
874 entry later. This parameter disables that.
876 disable_mtrr_trim [X86, Intel and AMD only]
877 By default the kernel will trim any uncacheable
878 memory out of your available memory pool based on
879 MTRR settings. This parameter disables that behavior,
880 possibly causing your machine to run very slowly.
882 disable_timer_pin_1 [X86]
883 Disable PIN 1 of APIC timer
884 Can be useful to work around chipset bugs.
886 dis_ucode_ldr [X86] Disable the microcode loader.
888 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
889 this option disables the debugging code at boot.
891 dma_debug_entries=<number>
892 This option allows to tune the number of preallocated
893 entries for DMA-API debugging code. One entry is
894 required per DMA-API allocation. Use this if the
895 DMA-API debugging code disables itself because the
896 architectural default is too low.
898 dma_debug_driver=<driver_name>
899 With this option the DMA-API debugging driver
900 filter feature can be enabled at boot time. Just
901 pass the driver to filter for as the parameter.
902 The filter can be disabled or changed to another
903 driver later using sysfs.
905 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
906 Broken monitors, graphic adapters, KVMs and EDIDless
907 panels may send no or incorrect EDID data sets.
908 This parameter allows to specify an EDID data sets
909 in the /lib/firmware directory that are used instead.
910 Generic built-in EDID data sets are used, if one of
911 edid/1024x768.bin, edid/1280x1024.bin,
912 edid/1680x1050.bin, or edid/1920x1080.bin is given
913 and no file with the same name exists. Details and
914 instructions how to build your own EDID data are
915 available in Documentation/EDID/HOWTO.txt. An EDID
916 data set will only be used for a particular connector,
917 if its name and a colon are prepended to the EDID
918 name. Each connector may use a unique EDID data
919 set by separating the files with a comma. An EDID
920 data set with no connector name will be used for
921 any connectors not explicitly specified.
926 Format: {"off" | "known"}
927 Control how the dt_cpu_ftrs device-tree binding is
928 used for CPU feature discovery and setup (if it
930 off: Do not use it, fall back to legacy cpu table.
931 known: Do not pass through unknown features to guests
932 or userspace, only those that the kernel is aware of.
934 dump_apple_properties [X86]
935 Dump name and content of EFI device properties on
936 x86 Macs. Useful for driver authors to determine
937 what data is available or for reverse-engineering.
939 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
940 module.dyndbg[="val"]
941 Enable debug messages at boot time. See
942 Documentation/admin-guide/dynamic-debug-howto.rst
945 nompx [X86] Disables Intel Memory Protection Extensions.
946 See Documentation/x86/intel_mpx.txt for more
947 information about the feature.
949 nopku [X86] Disable Memory Protection Keys CPU feature found
952 module.async_probe [KNL]
953 Enable asynchronous probe on this module.
955 early_ioremap_debug [KNL]
956 Enable debug messages in early_ioremap support. This
957 is useful for tracking down temporary early mappings
958 which are not unmapped.
960 earlycon= [KNL] Output early console device and options.
962 [ARM64] The early console is determined by the
963 stdout-path property in device tree's chosen node,
964 or determined by the ACPI SPCR table.
966 [X86] When used with no options the early console is
967 determined by the ACPI SPCR table.
969 cdns,<addr>[,options]
970 Start an early, polled-mode console on a Cadence
971 (xuartps) serial port at the specified address. Only
972 supported option is baud rate. If baud rate is not
973 specified, the serial port must already be setup and
976 uart[8250],io,<addr>[,options]
977 uart[8250],mmio,<addr>[,options]
978 uart[8250],mmio32,<addr>[,options]
979 uart[8250],mmio32be,<addr>[,options]
980 uart[8250],0x<addr>[,options]
981 Start an early, polled-mode console on the 8250/16550
982 UART at the specified I/O port or MMIO address.
983 MMIO inter-register address stride is either 8-bit
984 (mmio) or 32-bit (mmio32 or mmio32be).
985 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
986 to be equivalent to 'mmio'. 'options' are specified
987 in the same format described for "console=ttyS<n>"; if
988 unspecified, the h/w is not initialized.
992 Start an early, polled-mode console on a pl011 serial
993 port at the specified address. The pl011 serial port
994 must already be setup and configured. Options are not
995 yet supported. If 'mmio32' is specified, then only
996 the driver will use only 32-bit accessors to read/write
997 the device registers.
1000 Start an early, polled-mode console on a meson serial
1001 port at the specified address. The serial port must
1002 already be setup and configured. Options are not yet
1006 Start an early, polled-mode console on an msm serial
1007 port at the specified address. The serial port
1008 must already be setup and configured. Options are not
1011 msm_serial_dm,<addr>
1012 Start an early, polled-mode console on an msm serial
1013 dm port at the specified address. The serial port
1014 must already be setup and configured. Options are not
1018 Start an early, polled-mode console on a serial port
1019 of an Actions Semi SoC, such as S500 or S900, at the
1020 specified address. The serial port must already be
1021 setup and configured. Options are not yet supported.
1023 smh Use ARM semihosting calls for early console.
1031 Use early console provided by serial driver available
1032 on Samsung SoCs, requires selecting proper type and
1033 a correct base address of the selected UART port. The
1034 serial port must already be setup and configured.
1035 Options are not yet supported.
1038 Start an early, polled-mode console on a lantiq serial
1039 (lqasc) port at the specified address. The serial port
1040 must already be setup and configured. Options are not
1045 Use early console provided by Freescale LP UART driver
1046 found on Freescale Vybrid and QorIQ LS1021A processors.
1047 A valid base address must be provided, and the serial
1048 port must already be setup and configured.
1051 Start an early, polled-mode console on the
1052 Armada 3700 serial port at the specified
1053 address. The serial port must already be setup
1054 and configured. Options are not yet supported.
1057 Start an early, polled-mode console on a Qualcomm
1058 Generic Interface (GENI) based serial port at the
1059 specified address. The serial port must already be
1060 setup and configured. Options are not yet supported.
1062 earlyprintk= [X86,SH,ARM,M68k,S390]
1067 earlyprintk=serial[,ttySn[,baudrate]]
1068 earlyprintk=serial[,0x...[,baudrate]]
1069 earlyprintk=ttySn[,baudrate]
1070 earlyprintk=dbgp[debugController#]
1071 earlyprintk=pciserial,bus:device.function[,baudrate]
1072 earlyprintk=xdbc[xhciController#]
1074 earlyprintk is useful when the kernel crashes before
1075 the normal console is initialized. It is not enabled by
1076 default because it has some cosmetic problems.
1078 Append ",keep" to not disable it when the real console
1081 Only one of vga, efi, serial, or usb debug port can
1084 Currently only ttyS0 and ttyS1 may be specified by
1085 name. Other I/O ports may be explicitly specified
1086 on some architectures (x86 and arm at least) by
1087 replacing ttySn with an I/O port address, like this:
1088 earlyprintk=serial,0x1008,115200
1089 You can find the port for a given device in
1090 /proc/tty/driver/serial:
1091 2: uart:ST16650V2 port:00001008 irq:18 ...
1093 Interaction with the standard serial driver is not
1096 The VGA and EFI output is eventually overwritten by
1099 The xen output can only be used by Xen PV guests.
1101 The sclp output can only be used on s390.
1103 edac_report= [HW,EDAC] Control how to report EDAC event
1104 Format: {"on" | "off" | "force"}
1105 on: enable EDAC to report H/W event. May be overridden
1106 by other higher priority error reporting module.
1107 off: disable H/W event reporting through EDAC.
1108 force: enforce the use of EDAC to report H/W event.
1111 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1114 This is designed to be used in conjunction with
1115 the boot argument: earlyprintk=vga
1118 Format: {"off" | "on" | "skip[mbr]"}
1121 Format: { "old_map", "nochunk", "noruntime", "debug" }
1122 old_map [X86-64]: switch to the old ioremap-based EFI
1123 runtime services mapping. 32-bit still uses this one by
1125 nochunk: disable reading files in "chunks" in the EFI
1126 boot stub, as chunking can cause problems with some
1127 firmware implementations.
1128 noruntime : disable EFI runtime services support
1129 debug: enable misc debug output
1131 efi_no_storage_paranoia [EFI; X86]
1132 Using this parameter you can use more than 50% of
1133 your efi variable storage. Use this parameter only if
1134 you are really sure that your UEFI does sane gc and
1135 fulfills the spec otherwise your board may brick.
1137 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1138 Add arbitrary attribute to specific memory range by
1139 updating original EFI memory map.
1140 Region of memory which aa attribute is added to is
1142 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1143 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1144 attribute is added to range 0x100000000-0x180000000 and
1145 0x10a0000000-0x1120000000.
1147 Using this parameter you can do debugging of EFI memmap
1148 related feature. For example, you can do debugging of
1149 Address Range Mirroring feature even if your box
1152 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1153 that is to be dynamically loaded by Linux. If there are
1154 multiple variables with the same name but with different
1155 vendor GUIDs, all of them will be loaded. See
1156 Documentation/acpi/ssdt-overlays.txt for details.
1159 eisa_irq_edge= [PARISC,HW]
1160 See header of drivers/parisc/eisa.c.
1163 See comment before function elanfreq_setup() in
1164 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1167 Format: {"cfq" | "deadline" | "noop"}
1168 See Documentation/block/cfq-iosched.txt and
1169 Documentation/block/deadline-iosched.txt for details.
1171 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1172 Specifies physical address of start of kernel core
1173 image elf header and optionally the size. Generally
1174 kexec loader will pass this option to capture kernel.
1175 See Documentation/kdump/kdump.txt for details.
1177 enable_mtrr_cleanup [X86]
1178 The kernel tries to adjust MTRR layout from continuous
1179 to discrete, to make X server driver able to add WB
1180 entry later. This parameter enables that.
1182 enable_timer_pin_1 [X86]
1183 Enable PIN 1 of APIC timer
1184 Can be useful to work around chipset bugs
1185 (in particular on some ATI chipsets).
1186 The kernel tries to set a reasonable default.
1188 enforcing [SELINUX] Set initial enforcing status.
1190 See security/selinux/Kconfig help text.
1191 0 -- permissive (log only, no denials).
1192 1 -- enforcing (deny and log).
1194 Value can be changed at runtime via /selinux/enforce.
1197 Disable Error Record Serialization Table (ERST)
1200 ether= [HW,NET] Ethernet cards parameters
1201 This option is obsoleted by the "netdev=" option, which
1202 has equivalent usage. See its documentation for details.
1206 Permit 'security.evm' to be updated regardless of
1207 current integrity status.
1211 fail_make_request=[KNL]
1212 General fault injection mechanism.
1213 Format: <interval>,<probability>,<space>,<times>
1214 See also Documentation/fault-injection/.
1217 See Documentation/blockdev/floppy.txt.
1219 force_pal_cache_flush
1220 [IA-64] Avoid check_sal_cache_flush which may hang on
1221 buggy SAL_CACHE_FLUSH implementations. Using this
1222 parameter will force ia64_sal_cache_flush to call
1223 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1226 Forcefully enable Physical Address Extension (PAE).
1227 Many Pentium M systems disable PAE but may have a
1228 functionally usable PAE implementation.
1229 Warning: use of this parameter will taint the kernel
1230 and may cause unknown problems.
1233 [FTRACE] will set and start the specified tracer
1234 as early as possible in order to facilitate early
1237 ftrace_dump_on_oops[=orig_cpu]
1238 [FTRACE] will dump the trace buffers on oops.
1239 If no parameter is passed, ftrace will dump
1240 buffers of all CPUs, but if you pass orig_cpu, it will
1241 dump only the buffer of the CPU that triggered the
1244 ftrace_filter=[function-list]
1245 [FTRACE] Limit the functions traced by the function
1246 tracer at boot up. function-list is a comma separated
1247 list of functions. This list can be changed at run
1248 time by the set_ftrace_filter file in the debugfs
1251 ftrace_notrace=[function-list]
1252 [FTRACE] Do not trace the functions specified in
1253 function-list. This list can be changed at run time
1254 by the set_ftrace_notrace file in the debugfs
1257 ftrace_graph_filter=[function-list]
1258 [FTRACE] Limit the top level callers functions traced
1259 by the function graph tracer at boot up.
1260 function-list is a comma separated list of functions
1261 that can be changed at run time by the
1262 set_graph_function file in the debugfs tracing directory.
1264 ftrace_graph_notrace=[function-list]
1265 [FTRACE] Do not trace from the functions specified in
1266 function-list. This list is a comma separated list of
1267 functions that can be changed at run time by the
1268 set_graph_notrace file in the debugfs tracing directory.
1270 ftrace_graph_max_depth=<uint>
1271 [FTRACE] Used with the function graph tracer. This is
1272 the max depth it will trace into a function. This value
1273 can be changed at run time by the max_graph_depth file
1274 in the tracefs tracing directory. default: 0 (no limit)
1277 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1278 support via parallel port (up to 5 devices per port)
1279 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1280 See also Documentation/input/devices/joystick-parport.rst
1284 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1288 gcov_persist= [GCOV] When non-zero (default), profiling data for
1289 kernel modules is saved and remains accessible via
1290 debugfs, even when the module is unloaded/reloaded.
1291 When zero, profiling data is discarded and associated
1292 debugfs files are removed at module unload time.
1294 goldfish [X86] Enable the goldfish android emulator platform.
1295 Don't use this when you are not running on the
1298 gpt [EFI] Forces disk with valid GPT signature but
1299 invalid Protective MBR to be treated as GPT. If the
1300 primary GPT is corrupted, it enables the backup/alternate
1301 GPT to be used instead.
1303 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1304 the "Enable 0" bit of the configuration register.
1307 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1308 the "Enable 0" bit of the configuration register.
1311 grcan.select= [HW] Select which physical interface to use.
1314 grcan.txsize= [HW] Sets the size of the tx buffer.
1315 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1317 grcan.rxsize= [HW] Sets the size of the rx buffer.
1318 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1321 gpio-mockup.gpio_mockup_ranges
1322 [HW] Sets the ranges of gpiochip of for this device.
1323 Format: <start1>,<end1>,<start2>,<end2>...
1325 hardlockup_all_cpu_backtrace=
1326 [KNL] Should the hard-lockup detector generate
1327 backtraces on all cpus.
1330 hashdist= [KNL,NUMA] Large hashes allocated during boot
1331 are distributed across NUMA nodes. Defaults on
1332 for 64-bit NUMA, off otherwise.
1333 Format: 0 | 1 (for off | on)
1335 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1337 hd= [EIDE] (E)IDE hard drive subsystem geometry
1338 Format: <cyl>,<head>,<sect>
1341 Disable Hardware Error Source Table (HEST) support;
1342 corresponding firmware-first mode error processing
1343 logic will be disabled.
1345 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1346 size of <nn>. This works even on boxes that have no
1347 highmem otherwise. This also works to reduce highmem
1348 size on bigger boxes.
1350 highres= [KNL] Enable/disable high resolution timer mode.
1351 Valid parameters: "on", "off"
1355 See Documentation/isdn/README.HiSax.
1359 hpet= [X86-32,HPET] option to control HPET usage
1360 Format: { enable (default) | disable | force |
1362 disable: disable HPET and use PIT instead
1363 force: allow force enabled of undocumented chips (ICH4,
1365 verbose: show contents of HPET registers during setup
1367 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1368 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1370 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1371 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1372 On x86-64 and powerpc, this option can be specified
1373 multiple times interleaved with hugepages= to reserve
1374 huge pages of different sizes. Valid pages sizes on
1375 x86-64 are 2M (when the CPU supports "pse") and 1G
1376 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1379 [KNL] Should the hung task detector generate panics.
1382 A nonzero value instructs the kernel to panic when a
1383 hung task is detected. The default value is controlled
1384 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1385 option. The value selected by this boot parameter can
1386 be changed later by the kernel.hung_task_panic sysctl.
1388 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1389 terminal devices. Valid values: 0..8
1390 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1391 If specified, z/VM IUCV HVC accepts connections
1392 from listed z/VM user IDs only.
1394 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1395 which allow the hypervisor to 'idle' the
1396 guest on lock contention.
1399 Do not unregister boot console at start. This is only
1400 useful for debugging when something happens in the window
1401 between unregistering the boot console and initializing
1404 i2c_bus= [HW] Override the default board specific I2C bus speed
1405 or register an additional I2C bus that is not
1406 registered from board initialization code.
1410 i8042.debug [HW] Toggle i8042 debug mode
1411 i8042.unmask_kbd_data
1412 [HW] Enable printing of interrupt data from the KBD port
1413 (disabled by default, and as a pre-condition
1414 requires that i8042.debug=1 be enabled)
1415 i8042.direct [HW] Put keyboard port into non-translated mode
1416 i8042.dumbkbd [HW] Pretend that controller can only read data from
1417 keyboard and cannot control its state
1418 (Don't attempt to blink the leds)
1419 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1420 i8042.nokbd [HW] Don't check/create keyboard port
1421 i8042.noloop [HW] Disable the AUX Loopback command while probing
1423 i8042.nomux [HW] Don't check presence of an active multiplexing
1425 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1427 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1428 i8042.reset [HW] Reset the controller during init, cleanup and
1429 suspend-to-ram transitions, only during s2r
1430 transitions, or never reset
1431 Format: { 1 | Y | y | 0 | N | n }
1432 1, Y, y: always reset controller
1433 0, N, n: don't ever reset controller
1434 Default: only on s2r transitions on x86; most other
1435 architectures force reset to be always executed
1436 i8042.unlock [HW] Unlock (ignore) the keylock
1437 i8042.kbdreset [HW] Reset device connected to KBD port
1441 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1442 indicates that the driver is running on unsupported
1444 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1445 does not match list of supported models.
1447 [HW] Report power status in /proc/i8k
1448 (disabled by default)
1449 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1452 i915.invert_brightness=
1453 [DRM] Invert the sense of the variable that is used to
1454 set the brightness of the panel backlight. Normally a
1455 brightness value of 0 indicates backlight switched off,
1456 and the maximum of the brightness value sets the backlight
1457 to maximum brightness. If this parameter is set to 0
1458 (default) and the machine requires it, or this parameter
1459 is set to 1, a brightness value of 0 sets the backlight
1460 to maximum brightness, and the maximum of the brightness
1461 value switches the backlight off.
1462 -1 -- never invert brightness
1463 0 -- machine default
1464 1 -- force brightness inversion
1467 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1469 ide-core.nodma= [HW] (E)IDE subsystem
1470 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1471 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1472 .cdrom .chs .ignore_cable are additional options
1473 See Documentation/ide/ide.txt.
1475 ide-generic.probe-mask= [HW] (E)IDE subsystem
1477 Probe mask for legacy ISA IDE ports. Depending on
1478 platform up to 6 ports are supported, enabled by
1479 setting corresponding bits in the mask to 1. The
1480 default value is 0x0, which has a special meaning.
1481 On systems that have PCI, it triggers scanning the
1482 PCI bus for the first and the second port, which
1483 are then probed. On systems without PCI the value
1484 of 0x0 enables probing the two first ports as if it
1487 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1488 Claim all unknown PCI IDE storage controllers.
1491 Format: idle=poll, idle=halt, idle=nomwait
1492 Poll forces a polling idle loop that can slightly
1493 improve the performance of waking up a idle CPU, but
1494 will use a lot of power and make the system run hot.
1496 idle=halt: Halt is forced to be used for CPU idle.
1497 In such case C2/C3 won't be used again.
1498 idle=nomwait: Disable mwait for CPU C-states
1500 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1501 Format: { strict | legacy | 2008 | relaxed }
1504 Choose which programs will be accepted for execution
1505 based on the IEEE 754 NaN encoding(s) supported by
1506 the FPU and the NaN encoding requested with the value
1507 of an ELF file header flag individually set by each
1508 binary. Hardware implementations are permitted to
1509 support either or both of the legacy and the 2008 NaN
1512 Available settings are as follows:
1513 strict accept binaries that request a NaN encoding
1514 supported by the FPU
1515 legacy only accept legacy-NaN binaries, if supported
1517 2008 only accept 2008-NaN binaries, if supported
1519 relaxed accept any binaries regardless of whether
1520 supported by the FPU
1522 The FPU emulator is always able to support both NaN
1523 encodings, so if no FPU hardware is present or it has
1524 been disabled with 'nofpu', then the settings of
1525 'legacy' and '2008' strap the emulator accordingly,
1526 'relaxed' straps the emulator for both legacy-NaN and
1527 2008-NaN, whereas 'strict' enables legacy-NaN only on
1528 legacy processors and both NaN encodings on MIPS32 or
1531 The setting for ABS.fmt/NEG.fmt instruction execution
1532 mode generally follows that for the NaN encoding,
1533 except where unsupported by hardware.
1535 ignore_loglevel [KNL]
1536 Ignore loglevel setting - this will print /all/
1537 kernel messages to the console. Useful for debugging.
1538 We also add it as printk module parameter, so users
1539 could change it dynamically, usually by
1540 /sys/module/printk/parameters/ignore_loglevel.
1543 Ignore RLIMIT_DATA setting for data mappings,
1544 print warning at first misuse. Can be changed via
1545 /sys/module/kernel/parameters/ignore_rlimit_data.
1547 ihash_entries= [KNL]
1548 Set number of hash buckets for inode cache.
1550 ima_appraise= [IMA] appraise integrity measurements
1551 Format: { "off" | "enforce" | "fix" | "log" }
1554 ima_appraise_tcb [IMA]
1555 The builtin appraise policy appraises all files
1558 ima_canonical_fmt [IMA]
1559 Use the canonical format for the binary runtime
1560 measurements, instead of host native format.
1563 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1567 The list of supported hash algorithms is defined
1568 in crypto/hash_info.h.
1571 The builtin policies to load during IMA setup.
1572 Format: "tcb | appraise_tcb | secure_boot |
1575 The "tcb" policy measures all programs exec'd, files
1576 mmap'd for exec, and all files opened with the read
1577 mode bit set by either the effective uid (euid=0) or
1580 The "appraise_tcb" policy appraises the integrity of
1581 all files owned by root. (This is the equivalent
1582 of ima_appraise_tcb.)
1584 The "secure_boot" policy appraises the integrity
1585 of files (eg. kexec kernel image, kernel modules,
1586 firmware, policy, etc) based on file signatures.
1588 The "fail_securely" policy forces file signature
1589 verification failure also on privileged mounted
1590 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1593 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1594 Load a policy which meets the needs of the Trusted
1595 Computing Base. This means IMA will measure all
1596 programs exec'd, files mmap'd for exec, and all files
1597 opened for read by uid=0.
1600 Select one of defined IMA measurements template formats.
1601 Formats: { "ima" | "ima-ng" | "ima-sig" }
1605 [IMA] Define a custom template format.
1606 Format: { "field1|...|fieldN" }
1608 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1609 Format: <min_file_size>
1610 Set the minimal file size for using asynchronous hash.
1611 If left unspecified, ahash usage is disabled.
1613 ahash performance varies for different data sizes on
1614 different crypto accelerators. This option can be used
1615 to achieve the best performance for a particular HW.
1617 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1619 Set hashing buffer size. Default: 4k.
1621 ahash performance varies for different chunk sizes on
1622 different crypto accelerators. This option can be used
1623 to achieve best performance for particular HW.
1627 Run specified binary instead of /sbin/init as init
1630 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1631 for working out where the kernel is dying during
1634 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1635 initcall functions. Useful for debugging built-in
1636 modules and initcalls.
1638 initrd= [BOOT] Specify the location of the initial ramdisk
1640 init_pkru= [x86] Specify the default memory protection keys rights
1641 register contents for all processes. 0x55555554 by
1642 default (disallow access to all but pkey 0). Can
1643 override in debugfs after boot.
1645 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1648 int_pln_enable [x86] Enable power limit notification interrupt
1650 integrity_audit=[IMA]
1651 Format: { "0" | "1" }
1652 0 -- basic integrity auditing messages. (Default)
1653 1 -- additional integrity auditing messages.
1655 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1657 Enable intel iommu driver.
1659 Disable intel iommu driver.
1660 igfx_off [Default Off]
1661 By default, gfx is mapped as normal device. If a gfx
1662 device has a dedicated DMAR unit, the DMAR unit is
1663 bypassed by not enabling DMAR with this option. In
1664 this case, gfx device will use physical address for
1667 With this option iommu will not optimize to look
1668 for io virtual address below 32-bit forcing dual
1669 address cycle on pci bus for cards supporting greater
1670 than 32-bit addressing. The default is to look
1671 for translation below 32-bit and if not available
1672 then look in the higher range.
1673 strict [Default Off]
1674 With this option on every unmap_single operation will
1675 result in a hardware IOTLB flush operation as opposed
1676 to batching them for performance.
1677 sp_off [Default Off]
1678 By default, super page will be supported if Intel IOMMU
1679 has the capability. With this option, super page will
1681 ecs_off [Default Off]
1682 By default, extended context tables will be supported if
1683 the hardware advertises that it has support both for the
1684 extended tables themselves, and also PASID support. With
1685 this option set, extended tables will not be used even
1686 on hardware which claims to support them.
1687 tboot_noforce [Default Off]
1688 Do not force the Intel IOMMU enabled under tboot.
1689 By default, tboot will force Intel IOMMU on, which
1690 could harm performance of some high-throughput
1691 devices like 40GBit network cards, even if identity
1693 Note that using this option lowers the security
1694 provided by tboot because it makes the system
1695 vulnerable to DMA attacks.
1697 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1698 0 disables intel_idle and fall back on acpi_idle.
1699 1 to 9 specify maximum depth of C-state.
1703 Do not enable intel_pstate as the default
1704 scaling driver for the supported processors
1706 Use intel_pstate as a scaling driver, but configure it
1707 to work with generic cpufreq governors (instead of
1708 enabling its internal governor). This mode cannot be
1709 used along with the hardware-managed P-states (HWP)
1712 Enable intel_pstate on systems that prohibit it by default
1713 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1714 instead of acpi-cpufreq may disable platform features, such
1715 as thermal controls and power capping, that rely on ACPI
1716 P-States information being indicated to OSPM and therefore
1717 should be used with caution. This option does not work with
1718 processors that aren't supported by the intel_pstate driver
1719 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1721 Do not enable hardware P state control (HWP)
1724 Only load intel_pstate on systems which support
1725 hardware P state control (HWP) if available.
1727 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1728 Description Table, specifies preferred power management
1729 profile as "Enterprise Server" or "Performance Server",
1730 then this feature is turned on by default.
1732 Allow per-logical-CPU P-State performance control limits using
1733 cpufreq sysfs interface
1735 intremap= [X86-64, Intel-IOMMU]
1736 on enable Interrupt Remapping (default)
1737 off disable Interrupt Remapping
1738 nosid disable Source ID checking
1740 BIOS x2APIC opt-out request will be ignored
1741 nopost disable Interrupt Posting
1743 iomem= Disable strict checking of access to MMIO memory
1744 strict regions from userspace.
1759 nobypass [PPC/POWERNV]
1760 Disable IOMMU bypass, using IOMMU for PCI devices.
1763 [ARM64] Configure DMA to bypass the IOMMU by default.
1764 Format: { "0" | "1" }
1765 0 - Use IOMMU translation for DMA.
1766 1 - Bypass the IOMMU for DMA.
1767 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1769 io7= [HW] IO7 for Marvel based alpha systems
1770 See comment before marvel_specify_io7 in
1771 arch/alpha/kernel/core_marvel.c.
1773 io_delay= [X86] I/O delay method
1775 Standard port 0x80 based delay
1777 Alternate port 0xed based delay (needed on some systems)
1779 Simple two microseconds delay
1784 See Documentation/filesystems/nfs/nfsroot.txt.
1786 irqaffinity= [SMP] Set the default irq affinity mask
1787 The argument is a cpu list, as described above.
1789 irqchip.gicv2_force_probe=
1792 Force the kernel to look for the second 4kB page
1793 of a GICv2 controller even if the memory range
1794 exposed by the device tree is too small.
1796 irqchip.gicv3_nolpi=
1798 Force the kernel to ignore the availability of
1799 LPIs (and by consequence ITSs). Intended for system
1800 that use the kernel as a bootloader, and thus want
1801 to let secondary kernels in charge of setting up
1805 When an interrupt is not handled search all handlers
1806 for it. Intended to get systems with badly broken
1810 When an interrupt is not handled search all handlers
1811 for it. Also check all handlers each timer
1812 interrupt. Intended to get systems with badly broken
1816 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1818 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1819 [Deprecated - use cpusets instead]
1820 Format: [flag-list,]<cpu-list>
1822 Specify one or more CPUs to isolate from disturbances
1823 specified in the flag list (default: domain):
1826 Disable the tick when a single task runs.
1828 A residual 1Hz tick is offloaded to workqueues, which you
1829 need to affine to housekeeping through the global
1830 workqueue's affinity configured via the
1831 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1832 by using the 'domain' flag described below.
1834 NOTE: by default the global workqueue runs on all CPUs,
1835 so to protect individual CPUs the 'cpumask' file has to
1836 be configured manually after bootup.
1839 Isolate from the general SMP balancing and scheduling
1840 algorithms. Note that performing domain isolation this way
1841 is irreversible: it's not possible to bring back a CPU to
1842 the domains once isolated through isolcpus. It's strongly
1843 advised to use cpusets instead to disable scheduler load
1844 balancing through the "cpuset.sched_load_balance" file.
1845 It offers a much more flexible interface where CPUs can
1846 move in and out of an isolated set anytime.
1848 You can move a process onto or off an "isolated" CPU via
1849 the CPU affinity syscalls or cpuset.
1850 <cpu number> begins at 0 and the maximum value is
1851 "number of CPUs in system - 1".
1853 The format of <cpu-list> is described above.
1859 ivrs_ioapic [HW,X86_64]
1860 Provide an override to the IOAPIC-ID<->DEVICE-ID
1861 mapping provided in the IVRS ACPI table. For
1862 example, to map IOAPIC-ID decimal 10 to
1863 PCI device 00:14.0 write the parameter as:
1864 ivrs_ioapic[10]=00:14.0
1866 ivrs_hpet [HW,X86_64]
1867 Provide an override to the HPET-ID<->DEVICE-ID
1868 mapping provided in the IVRS ACPI table. For
1869 example, to map HPET-ID decimal 0 to
1870 PCI device 00:14.0 write the parameter as:
1871 ivrs_hpet[0]=00:14.0
1873 ivrs_acpihid [HW,X86_64]
1874 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1875 mapping provided in the IVRS ACPI table. For
1876 example, to map UART-HID:UID AMD0020:0 to
1877 PCI device 00:14.5 write the parameter as:
1878 ivrs_acpihid[00:14.5]=AMD0020:0
1880 js= [HW,JOY] Analog joystick
1881 See Documentation/input/joydev/joystick.rst.
1884 When CONFIG_RANDOMIZE_BASE is set, this disables
1885 kernel and module base offset ASLR (Address Space
1886 Layout Randomization).
1889 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1890 report on every invalid memory access. Without this
1891 parameter KASAN will print report only for the first
1896 kernelcore= [KNL,X86,IA-64,PPC]
1897 Format: nn[KMGTPE] | nn% | "mirror"
1898 This parameter specifies the amount of memory usable by
1899 the kernel for non-movable allocations. The requested
1900 amount is spread evenly throughout all nodes in the
1901 system as ZONE_NORMAL. The remaining memory is used for
1902 movable memory in its own zone, ZONE_MOVABLE. In the
1903 event, a node is too small to have both ZONE_NORMAL and
1904 ZONE_MOVABLE, kernelcore memory will take priority and
1905 other nodes will have a larger ZONE_MOVABLE.
1907 ZONE_MOVABLE is used for the allocation of pages that
1908 may be reclaimed or moved by the page migration
1909 subsystem. Note that allocations like PTEs-from-HighMem
1910 still use the HighMem zone if it exists, and the Normal
1911 zone if it does not.
1913 It is possible to specify the exact amount of memory in
1914 the form of "nn[KMGTPE]", a percentage of total system
1915 memory in the form of "nn%", or "mirror". If "mirror"
1916 option is specified, mirrored (reliable) memory is used
1917 for non-movable allocations and remaining memory is used
1918 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1919 are exclusive, so you cannot specify multiple forms.
1921 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1922 Format: <Controller#>[,poll interval]
1923 The controller # is the number of the ehci usb debug
1924 port as it is probed via PCI. The poll interval is
1925 optional and is the number seconds in between
1926 each poll cycle to the debug port in case you need
1927 the functionality for interrupting the kernel with
1928 gdb or control-c on the dbgp connection. When
1929 not using this parameter you use sysrq-g to break into
1930 the kernel debugger.
1932 kgdboc= [KGDB,HW] kgdb over consoles.
1933 Requires a tty driver that supports console polling,
1934 or a supported polling keyboard driver (non-usb).
1935 Serial only format: <serial_device>[,baud]
1936 keyboard only format: kbd
1937 keyboard and serial format: kbd,<serial_device>[,baud]
1938 Optional Kernel mode setting:
1939 kms, kbd format: kms,kbd
1940 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1942 kgdbwait [KGDB] Stop kernel execution and enter the
1943 kernel debugger at the earliest opportunity.
1945 kmac= [MIPS] korina ethernet MAC address.
1946 Configure the RouterBoard 532 series on-chip
1947 Ethernet adapter MAC address.
1949 kmemleak= [KNL] Boot-time kmemleak enable/disable
1950 Valid arguments: on, off
1952 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1955 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1956 Default is 0 (don't ignore, but inject #GP)
1958 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1959 Default is false (don't support).
1961 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1965 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1966 Default is 1 (enabled)
1968 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1970 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1972 kvm-arm.vgic_v3_group0_trap=
1973 [KVM,ARM] Trap guest accesses to GICv3 group-0
1976 kvm-arm.vgic_v3_group1_trap=
1977 [KVM,ARM] Trap guest accesses to GICv3 group-1
1980 kvm-arm.vgic_v3_common_trap=
1981 [KVM,ARM] Trap guest accesses to GICv3 common
1984 kvm-arm.vgic_v4_enable=
1985 [KVM,ARM] Allow use of GICv4 for direct injection of
1988 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1989 (virtualized MMU) support on capable Intel chips.
1990 Default is 1 (enabled)
1992 kvm-intel.emulate_invalid_guest_state=
1993 [KVM,Intel] Enable emulation of invalid guest states
1994 Default is 0 (disabled)
1996 kvm-intel.flexpriority=
1997 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1998 Default is 1 (enabled)
2001 [KVM,Intel] Enable VMX nesting (nVMX).
2002 Default is 0 (disabled)
2004 kvm-intel.unrestricted_guest=
2005 [KVM,Intel] Disable unrestricted guest feature
2006 (virtualized real and unpaged mode) on capable
2007 Intel chips. Default is 1 (enabled)
2009 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2012 Valid arguments: never, cond, always
2014 always: L1D cache flush on every VMENTER.
2015 cond: Flush L1D on VMENTER only when the code between
2016 VMEXIT and VMENTER can leak host memory.
2017 never: Disables the mitigation
2019 Default is cond (do L1 cache flush in specific instances)
2021 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2022 feature (tagged TLBs) on capable Intel chips.
2023 Default is 1 (enabled)
2025 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2028 The kernel PTE inversion protection is unconditionally
2029 enabled and cannot be disabled.
2032 Provides all available mitigations for the
2033 L1TF vulnerability. Disables SMT and
2034 enables all mitigations in the
2035 hypervisors, i.e. unconditional L1D flush.
2037 SMT control and L1D flush control via the
2038 sysfs interface is still possible after
2039 boot. Hypervisors will issue a warning
2040 when the first VM is started in a
2041 potentially insecure configuration,
2042 i.e. SMT enabled or L1D flush disabled.
2045 Same as 'full', but disables SMT and L1D
2046 flush runtime control. Implies the
2047 'nosmt=force' command line option.
2048 (i.e. sysfs control of SMT is disabled.)
2051 Leaves SMT enabled and enables the default
2052 hypervisor mitigation, i.e. conditional
2055 SMT control and L1D flush control via the
2056 sysfs interface is still possible after
2057 boot. Hypervisors will issue a warning
2058 when the first VM is started in a
2059 potentially insecure configuration,
2060 i.e. SMT enabled or L1D flush disabled.
2064 Disables SMT and enables the default
2065 hypervisor mitigation.
2067 SMT control and L1D flush control via the
2068 sysfs interface is still possible after
2069 boot. Hypervisors will issue a warning
2070 when the first VM is started in a
2071 potentially insecure configuration,
2072 i.e. SMT enabled or L1D flush disabled.
2075 Same as 'flush', but hypervisors will not
2076 warn when a VM is started in a potentially
2077 insecure configuration.
2080 Disables hypervisor mitigations and doesn't
2085 For details see: Documentation/admin-guide/l1tf.rst
2091 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2094 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2095 value for LAPIC timer one-shot implementation. Default
2096 back to the programmable timer unit in the LAPIC.
2098 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2101 libata.dma= [LIBATA] DMA control
2102 libata.dma=0 Disable all PATA and SATA DMA
2103 libata.dma=1 PATA and SATA Disk DMA only
2104 libata.dma=2 ATAPI (CDROM) DMA only
2105 libata.dma=4 Compact Flash DMA only
2106 Combinations also work, so libata.dma=3 enables DMA
2107 for disks and CDROMs, but not CFs.
2109 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2110 libata.ignore_hpa=0 keep BIOS limits (default)
2111 libata.ignore_hpa=1 ignore limits, using full disk
2113 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2117 libata.force= [LIBATA] Force configurations. The format is comma
2118 separated list of "[ID:]VAL" where ID is
2119 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2120 matching port, link or device. Basically, it matches
2121 the ATA ID string printed on console by libata. If
2122 the whole ID part is omitted, the last PORT and DEVICE
2123 values are used. If ID hasn't been specified yet, the
2124 configuration applies to all ports, links and devices.
2126 If only DEVICE is omitted, the parameter applies to
2127 the port and all links and devices behind it. DEVICE
2128 number of 0 either selects the first device or the
2129 first fan-out link behind PMP device. It does not
2130 select the host link. DEVICE number of 15 selects the
2131 host link and device attached to it.
2133 The VAL specifies the configuration to force. As long
2134 as there's no ambiguity shortcut notation is allowed.
2135 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2136 The following configurations can be forced.
2138 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2139 Any ID with matching PORT is used.
2141 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2143 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2144 udma[/][16,25,33,44,66,100,133] notation is also
2147 * [no]ncq: Turn on or off NCQ.
2149 * [no]ncqtrim: Turn off queued DSM TRIM.
2151 * nohrst, nosrst, norst: suppress hard, soft
2154 * rstonce: only attempt one reset during
2155 hot-unplug link recovery
2157 * dump_id: dump IDENTIFY data.
2159 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2161 * disable: Disable this device.
2163 If there are multiple matching configurations changing
2164 the same attribute, the last one is used.
2166 memblock=debug [KNL] Enable memblock debug messages.
2168 load_ramdisk= [RAM] List of ramdisks to load from floppy
2169 See Documentation/blockdev/ramdisk.txt.
2171 lockd.nlm_grace_period=P [NFS] Assign grace period.
2174 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2177 lockd.nlm_timeout=T [NFS] Assign timeout value.
2180 lockd.nlm_udpport=M [NFS] Assign UDP port.
2183 locktorture.nreaders_stress= [KNL]
2184 Set the number of locking read-acquisition kthreads.
2185 Defaults to being automatically set based on the
2186 number of online CPUs.
2188 locktorture.nwriters_stress= [KNL]
2189 Set the number of locking write-acquisition kthreads.
2191 locktorture.onoff_holdoff= [KNL]
2192 Set time (s) after boot for CPU-hotplug testing.
2194 locktorture.onoff_interval= [KNL]
2195 Set time (s) between CPU-hotplug operations, or
2196 zero to disable CPU-hotplug testing.
2198 locktorture.shuffle_interval= [KNL]
2199 Set task-shuffle interval (jiffies). Shuffling
2200 tasks allows some CPUs to go into dyntick-idle
2201 mode during the locktorture test.
2203 locktorture.shutdown_secs= [KNL]
2204 Set time (s) after boot system shutdown. This
2205 is useful for hands-off automated testing.
2207 locktorture.stat_interval= [KNL]
2208 Time (s) between statistics printk()s.
2210 locktorture.stutter= [KNL]
2211 Time (s) to stutter testing, for example,
2212 specifying five seconds causes the test to run for
2213 five seconds, wait for five seconds, and so on.
2214 This tests the locking primitive's ability to
2215 transition abruptly to and from idle.
2217 locktorture.torture_type= [KNL]
2218 Specify the locking implementation to test.
2220 locktorture.verbose= [KNL]
2221 Enable additional printk() statements.
2223 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2226 loglevel= All Kernel Messages with a loglevel smaller than the
2227 console loglevel will be printed to the console. It can
2228 also be changed with klogd or other programs. The
2229 loglevels are defined as follows:
2231 0 (KERN_EMERG) system is unusable
2232 1 (KERN_ALERT) action must be taken immediately
2233 2 (KERN_CRIT) critical conditions
2234 3 (KERN_ERR) error conditions
2235 4 (KERN_WARNING) warning conditions
2236 5 (KERN_NOTICE) normal but significant condition
2237 6 (KERN_INFO) informational
2238 7 (KERN_DEBUG) debug-level messages
2240 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2241 in bytes. n must be a power of two and greater
2242 than the minimal size. The minimal size is defined
2243 by LOG_BUF_SHIFT kernel config parameter. There is
2244 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2245 that allows to increase the default size depending on
2246 the number of CPUs. See init/Kconfig for more details.
2248 logo.nologo [FB] Disables display of the built-in Linux logo.
2249 This may be used to provide more screen space for
2250 kernel log messages and is useful when debugging
2251 kernel boot problems.
2253 lp=0 [LP] Specify parallel ports to use, e.g,
2254 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2255 lp=reset first parallel port). 'lp=0' disables the
2256 lp=auto printer driver. 'lp=reset' (which can be
2257 specified in addition to the ports) causes
2258 attached printers to be reset. Using
2259 lp=port1,port2,... specifies the parallel ports
2260 to associate lp devices with, starting with
2261 lp0. A port specification may be 'none' to skip
2262 that lp device, or a parport name such as
2263 'parport0'. Specifying 'lp=auto' instead of a
2264 port specification list means that device IDs
2265 from each port should be examined, to see if
2266 an IEEE 1284-compliant printer is attached; if
2267 so, the driver will manage that printer.
2268 See also header of drivers/char/lp.c.
2271 Sets loops_per_jiffy to given constant, thus avoiding
2272 time-consuming boot-time autodetection (up to 250 ms per
2273 CPU). 0 enables autodetection (default). To determine
2274 the correct value for your kernel, boot with normal
2275 autodetection and see what value is printed. Note that
2276 on SMP systems the preset will be applied to all CPUs,
2277 which is likely to cause problems if your CPUs need
2278 significantly divergent settings. An incorrect value
2279 will cause delays in the kernel to be wrong, leading to
2280 unpredictable I/O errors and other breakage. Although
2281 unlikely, in the extreme case this might damage your
2285 Format: <io>,<irq>,<dma>
2287 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2289 machvec= [IA-64] Force the use of a particular machine-vector
2290 (machvec) in a generic kernel.
2291 Example: machvec=hpzx1_swiotlb
2293 machtype= [Loongson] Share the same kernel image file between different
2295 Example: machtype=lemote-yeeloong-2f-7inch
2297 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2298 than or equal to this physical address is ignored.
2300 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2301 will bring up during bootup. maxcpus=n : n >= 0 limits
2302 the kernel to bring up 'n' processors. Surely after
2303 bootup you can bring up the other plugged cpu by executing
2304 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2305 only takes effect during system bootup.
2306 While n=0 is a special case, it is equivalent to "nosmp",
2307 which also disables the IO APIC.
2309 max_loop= [LOOP] The number of loop block devices that get
2310 (loop.max_loop) unconditionally pre-created at init time. The default
2311 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2312 of statically allocating a predefined number, loop
2313 devices can be requested on-demand with the
2314 /dev/loop-control interface.
2316 mce [X86-32] Machine Check Exception
2318 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2320 md= [HW] RAID subsystems devices and level
2321 See Documentation/admin-guide/md.rst.
2324 Format: <first>,<last>
2325 Specifies range of consoles to be captured by the MDA.
2327 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2328 Amount of memory to be used when the kernel is not able
2329 to see the whole system memory or for test.
2330 [X86] Work as limiting max address. Use together
2331 with memmap= to avoid physical address space collisions.
2332 Without memmap= PCI devices could be placed at addresses
2333 belonging to unused RAM.
2335 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2339 [KNL,SH] Allow user to override the default size for
2340 per-device physically contiguous DMA buffers.
2342 memhp_default_state=online/offline
2343 [KNL] Set the initial state for the memory hotplug
2344 onlining policy. If not specified, the default value is
2345 set according to the
2346 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2348 See Documentation/memory-hotplug.txt.
2350 memmap=exactmap [KNL,X86] Enable setting of an exact
2351 E820 memory map, as specified by the user.
2352 Such memmap=exactmap lines can be constructed based on
2353 BIOS output or other requirements. See the memmap=nn@ss
2356 memmap=nn[KMG]@ss[KMG]
2357 [KNL] Force usage of a specific region of memory.
2358 Region of memory to be used is from ss to ss+nn.
2359 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2360 which limits max address to nn[KMG].
2361 Multiple different regions can be specified,
2364 memmap=100M@2G,100M#3G,1G!1024G
2366 memmap=nn[KMG]#ss[KMG]
2367 [KNL,ACPI] Mark specific memory as ACPI data.
2368 Region of memory to be marked is from ss to ss+nn.
2370 memmap=nn[KMG]$ss[KMG]
2371 [KNL,ACPI] Mark specific memory as reserved.
2372 Region of memory to be reserved is from ss to ss+nn.
2373 Example: Exclude memory from 0x18690000-0x1869ffff
2374 memmap=64K$0x18690000
2376 memmap=0x10000$0x18690000
2377 Some bootloaders may need an escape character before '$',
2378 like Grub2, otherwise '$' and the following number
2381 memmap=nn[KMG]!ss[KMG]
2382 [KNL,X86] Mark specific memory as protected.
2383 Region of memory to be used, from ss to ss+nn.
2384 The memory region may be marked as e820 type 12 (0xc)
2385 and is NVDIMM or ADR memory.
2387 memmap=<size>%<offset>-<oldtype>+<newtype>
2388 [KNL,ACPI] Convert memory within the specified region
2389 from <oldtype> to <newtype>. If "-<oldtype>" is left
2390 out, the whole region will be marked as <newtype>,
2391 even if previously unavailable. If "+<newtype>" is left
2392 out, matching memory will be removed. Types are
2393 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2394 3 = ACPI, 12 = PRAM.
2396 memory_corruption_check=0/1 [X86]
2397 Some BIOSes seem to corrupt the first 64k of
2398 memory when doing things like suspend/resume.
2399 Setting this option will scan the memory
2400 looking for corruption. Enabling this will
2401 both detect corruption and prevent the kernel
2402 from using the memory being corrupted.
2403 However, its intended as a diagnostic tool; if
2404 repeatable BIOS-originated corruption always
2405 affects the same memory, you can use memmap=
2406 to prevent the kernel from using that memory.
2408 memory_corruption_check_size=size [X86]
2409 By default it checks for corruption in the low
2410 64k, making this memory unavailable for normal
2411 use. Use this parameter to scan for
2412 corruption in more or less memory.
2414 memory_corruption_check_period=seconds [X86]
2415 By default it checks for corruption every 60
2416 seconds. Use this parameter to check at some
2417 other rate. 0 disables periodic checking.
2419 memtest= [KNL,X86,ARM] Enable memtest
2421 default : 0 <disable>
2422 Specifies the number of memtest passes to be
2423 performed. Each pass selects another test
2424 pattern from a given set of patterns. Memtest
2425 fills the memory with this pattern, validates
2426 memory contents and reserves bad memory
2427 regions that are detected.
2429 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2430 Valid arguments: on, off
2431 Default (depends on kernel configuration option):
2432 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2433 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2434 mem_encrypt=on: Activate SME
2435 mem_encrypt=off: Do not activate SME
2437 Refer to Documentation/x86/amd-memory-encryption.txt
2438 for details on when memory encryption can be activated.
2440 mem_sleep_default= [SUSPEND] Default system suspend mode:
2441 s2idle - Suspend-To-Idle
2442 shallow - Power-On Suspend or equivalent (if supported)
2443 deep - Suspend-To-RAM or equivalent (if supported)
2444 See Documentation/admin-guide/pm/sleep-states.rst.
2446 meye.*= [HW] Set MotionEye Camera parameters
2447 See Documentation/media/v4l-drivers/meye.rst.
2449 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2450 Multi-Function General Purpose Timers on AMD Geode
2453 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2454 the BIOS has incorrectly applied a workaround. TinyBIOS
2455 version 0.98 is known to be affected, 0.99 fixes the
2456 problem by letting the user disable the workaround.
2460 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2461 physical address is ignored.
2463 mini2440= [ARM,HW,KNL]
2464 Format:[0..2][b][c][t]
2466 MINI2440 configuration specification:
2467 0 - The attached screen is the 3.5" TFT
2468 1 - The attached screen is the 7" TFT
2469 2 - The VGA Shield is attached (1024x768)
2470 Leaving out the screen size parameter will not load
2471 the TFT driver, and the framebuffer will be left
2473 b - Enable backlight. The TFT backlight pin will be
2474 linked to the kernel VESA blanking code and a GPIO
2475 LED. This parameter is not necessary when using the
2477 c - Enable the s3c camera interface.
2478 t - Reserved for enabling touchscreen support. The
2479 touchscreen support is not enabled in the mainstream
2480 kernel as of 2.6.30, a preliminary port can be found
2481 in the "bleeding edge" mini2440 support kernel at
2482 http://repo.or.cz/w/linux-2.6/mini2440.git
2485 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2486 parameter allows control of the logging verbosity for
2487 the additional memory initialisation checks. A value
2488 of 0 disables mminit logging and a level of 4 will
2489 log everything. Information is printed at KERN_DEBUG
2490 so loglevel=8 may also need to be specified.
2493 [KNL] When CONFIG_MODULE_SIG is set, this means that
2494 modules without (valid) signatures will fail to load.
2495 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2496 is always true, so this option does nothing.
2498 module_blacklist= [KNL] Do not load a comma-separated list of
2499 modules. Useful for debugging problem modules.
2502 [MOUSE] Maximum time between finger touching and
2503 leaving touchpad surface for touch to be considered
2504 a tap and be reported as a left button click (for
2505 touchpads working in absolute mode only).
2507 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2508 reporting absolute coordinates, such as tablets
2509 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2510 reporting absolute coordinates, such as tablets
2512 movablecore= [KNL,X86,IA-64,PPC]
2513 Format: nn[KMGTPE] | nn%
2514 This parameter is the complement to kernelcore=, it
2515 specifies the amount of memory used for migratable
2516 allocations. If both kernelcore and movablecore is
2517 specified, then kernelcore will be at *least* the
2518 specified value but may be more. If movablecore on its
2519 own is specified, the administrator must be careful
2520 that the amount of memory usable for all allocations
2523 movable_node [KNL] Boot-time switch to make hotplugable memory
2524 NUMA nodes to be movable. This means that the memory
2525 of such nodes will be usable only for movable
2526 allocations which rules out almost all kernel
2527 allocations. Use with caution!
2529 MTD_Partition= [MTD]
2530 Format: <name>,<region-number>,<size>,<offset>
2532 MTD_Region= [MTD] Format:
2533 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2536 See drivers/mtd/cmdlinepart.c.
2538 multitce=off [PPC] This parameter disables the use of the pSeries
2539 firmware feature for updating multiple TCE entries
2542 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2544 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2546 boundary - index of last SLC block on Flex-OneNAND.
2547 The remaining blocks are configured as MLC blocks.
2548 lock - Configure if Flex-OneNAND boundary should be locked.
2549 Once locked, the boundary cannot be changed.
2550 1 indicates lock status, 0 indicates unlock status.
2553 ARM/S3C2412 JIVE boot control
2555 See arch/arm/mach-s3c2412/mach-jive.c
2557 mtouchusb.raw_coordinates=
2558 [HW] Make the MicroTouch USB driver use raw coordinates
2559 ('y', default) or cooked coordinates ('n')
2561 mtrr_chunk_size=nn[KMG] [X86]
2562 used for mtrr cleanup. It is largest continuous chunk
2563 that could hold holes aka. UC entries.
2565 mtrr_gran_size=nn[KMG] [X86]
2566 Used for mtrr cleanup. It is granularity of mtrr block.
2568 Large value could prevent small alignment from
2571 mtrr_spare_reg_nr=n [X86]
2573 Range: 0,7 : spare reg number
2575 Used for mtrr cleanup. It is spare mtrr entries number.
2576 Set to 2 or more if your graphical card needs more.
2578 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2580 netdev= [NET] Network devices parameters
2581 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2582 Note that mem_start is often overloaded to mean
2583 something different and driver-specific.
2584 This usage is only documented in each driver source
2588 [NETFILTER] Enable connection tracking flow accounting
2589 0 to disable accounting
2590 1 to enable accounting
2593 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2594 See Documentation/filesystems/nfs/nfsroot.txt.
2596 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2597 See Documentation/filesystems/nfs/nfsroot.txt.
2599 nfsrootdebug [NFS] enable nfsroot debugging messages.
2600 See Documentation/filesystems/nfs/nfsroot.txt.
2602 nfs.callback_nr_threads=
2603 [NFSv4] set the total number of threads that the
2604 NFS client will assign to service NFSv4 callback
2607 nfs.callback_tcpport=
2608 [NFS] set the TCP port on which the NFSv4 callback
2609 channel should listen.
2612 [NFS] sets the pathname to the program which is used
2613 to update the NFS client cache entries.
2615 nfs.cache_getent_timeout=
2616 [NFS] sets the timeout after which an attempt to
2617 update a cache entry is deemed to have failed.
2619 nfs.idmap_cache_timeout=
2620 [NFS] set the maximum lifetime for idmapper cache
2624 [NFS] enable 64-bit inode numbers.
2625 If zero, the NFS client will fake up a 32-bit inode
2626 number for the readdir() and stat() syscalls instead
2627 of returning the full 64-bit number.
2628 The default is to return 64-bit inode numbers.
2630 nfs.max_session_cb_slots=
2631 [NFSv4.1] Sets the maximum number of session
2632 slots the client will assign to the callback
2633 channel. This determines the maximum number of
2634 callbacks the client will process in parallel for
2635 a particular server.
2637 nfs.max_session_slots=
2638 [NFSv4.1] Sets the maximum number of session slots
2639 the client will attempt to negotiate with the server.
2640 This limits the number of simultaneous RPC requests
2641 that the client can send to the NFSv4.1 server.
2642 Note that there is little point in setting this
2643 value higher than the max_tcp_slot_table_limit.
2645 nfs.nfs4_disable_idmapping=
2646 [NFSv4] When set to the default of '1', this option
2647 ensures that both the RPC level authentication
2648 scheme and the NFS level operations agree to use
2649 numeric uids/gids if the mount is using the
2650 'sec=sys' security flavour. In effect it is
2651 disabling idmapping, which can make migration from
2652 legacy NFSv2/v3 systems to NFSv4 easier.
2653 Servers that do not support this mode of operation
2654 will be autodetected by the client, and it will fall
2655 back to using the idmapper.
2656 To turn off this behaviour, set the value to '0'.
2658 [NFS4] Specify an additional fixed unique ident-
2659 ification string that NFSv4 clients can insert into
2660 their nfs_client_id4 string. This is typically a
2661 UUID that is generated at system install time.
2663 nfs.send_implementation_id =
2664 [NFSv4.1] Send client implementation identification
2665 information in exchange_id requests.
2666 If zero, no implementation identification information
2668 The default is to send the implementation identification
2671 nfs.recover_lost_locks =
2672 [NFSv4] Attempt to recover locks that were lost due
2673 to a lease timeout on the server. Please note that
2674 doing this risks data corruption, since there are
2675 no guarantees that the file will remain unchanged
2676 after the locks are lost.
2677 If you want to enable the kernel legacy behaviour of
2678 attempting to recover these locks, then set this
2680 The default parameter value of '0' causes the kernel
2681 not to attempt recovery of lost locks.
2683 nfs4.layoutstats_timer =
2684 [NFSv4.2] Change the rate at which the kernel sends
2685 layoutstats to the pNFS metadata server.
2687 Setting this to value to 0 causes the kernel to use
2688 whatever value is the default set by the layout
2689 driver. A non-zero value sets the minimum interval
2690 in seconds between layoutstats transmissions.
2692 nfsd.nfs4_disable_idmapping=
2693 [NFSv4] When set to the default of '1', the NFSv4
2694 server will return only numeric uids and gids to
2695 clients using auth_sys, and will accept numeric uids
2696 and gids from such clients. This is intended to ease
2697 migration from NFSv2/v3.
2699 nmi_debug= [KNL,SH] Specify one or more actions to take
2700 when a NMI is triggered.
2701 Format: [state][,regs][,debounce][,die]
2703 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2704 Format: [panic,][nopanic,][num]
2706 0 - turn hardlockup detector in nmi_watchdog off
2707 1 - turn hardlockup detector in nmi_watchdog on
2708 When panic is specified, panic when an NMI watchdog
2709 timeout occurs (or 'nopanic' to override the opposite
2710 default). To disable both hard and soft lockup detectors,
2711 please see 'nowatchdog'.
2712 This is useful when you use a panic=... timeout and
2713 need the box quickly up again.
2715 These settings can be accessed at runtime via
2716 the nmi_watchdog and hardlockup_panic sysctls.
2718 netpoll.carrier_timeout=
2719 [NET] Specifies amount of time (in seconds) that
2720 netpoll should wait for a carrier. By default netpoll
2723 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2724 emulation library even if a 387 maths coprocessor
2727 no5lvl [X86-64] Disable 5-level paging mode. Forces
2728 kernel to use 4-level paging instead.
2731 [HW] Never suspend the console
2732 Disable suspending of consoles during suspend and
2733 hibernate operations. Once disabled, debugging
2734 messages can reach various consoles while the rest
2735 of the system is being put to sleep (ie, while
2736 debugging driver suspend/resume hooks). This may
2737 not work reliably with all consoles, but is known
2738 to work with serial and VGA consoles.
2739 To facilitate more flexible debugging, we also add
2740 console_suspend, a printk module parameter to control
2741 it. Users could use console_suspend (usually
2742 /sys/module/printk/parameters/console_suspend) to
2743 turn on/off it dynamically.
2745 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2746 caches in the slab allocator. Saves per-node memory,
2747 but will impact performance.
2751 noaltinstr [S390] Disables alternative instructions patching
2752 (CPU alternatives feature).
2754 noapic [SMP,APIC] Tells the kernel to not make use of any
2755 IOAPICs that may be present in the system.
2757 noautogroup Disable scheduler automatic task group creation.
2759 nobats [PPC] Do not use BATs for mapping kernel lowmem
2760 on "Classic" PPC cores.
2764 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2766 nodelayacct [KNL] Disable per-task delay accounting
2768 nodsp [SH] Disable hardware DSP at boot time.
2770 noefi Disable EFI runtime services support.
2775 On X86-32 available only on PAE configured kernels.
2776 noexec=on: enable non-executable mappings (default)
2777 noexec=off: disable non-executable mappings
2780 Disable SMAP (Supervisor Mode Access Prevention)
2781 even if it is supported by processor.
2784 Disable SMEP (Supervisor Mode Execution Prevention)
2785 even if it is supported by processor.
2788 This affects only 32-bit executables.
2789 noexec32=on: enable non-executable mappings (default)
2790 read doesn't imply executable mappings
2791 noexec32=off: disable non-executable mappings
2792 read implies executable mappings
2794 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2796 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2797 register save and restore. The kernel will only save
2798 legacy floating-point registers on task switch.
2800 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2802 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2803 Equivalent to smt=1.
2805 [KNL,x86] Disable symmetric multithreading (SMT).
2806 nosmt=force: Force disable SMT, cannot be undone
2807 via the sysfs control file.
2809 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2810 check bypass). With this option data leaks are possible
2813 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2814 (indirect branch prediction) vulnerability. System may
2815 allow data leaks with this option, which is equivalent
2818 nospec_store_bypass_disable
2819 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2821 noxsave [BUGS=X86] Disables x86 extended register state save
2822 and restore using xsave. The kernel will fallback to
2823 enabling legacy floating-point and sse state.
2825 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2826 register states. The kernel will fall back to use
2827 xsave to save the states. By using this parameter,
2828 performance of saving the states is degraded because
2829 xsave doesn't support modified optimization while
2830 xsaveopt supports it on xsaveopt enabled systems.
2832 noxsaves [X86] Disables xsaves and xrstors used in saving and
2833 restoring x86 extended register state in compacted
2834 form of xsave area. The kernel will fall back to use
2835 xsaveopt and xrstor to save and restore the states
2836 in standard form of xsave area. By using this
2837 parameter, xsave area per process might occupy more
2838 memory on xsaves enabled systems.
2840 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2841 wfi(ARM) instruction doesn't work correctly and not to
2842 use it. This is also useful when using JTAG debugger.
2844 no_file_caps Tells the kernel not to honor file capabilities. The
2845 only way then for a file to be executed with privilege
2846 is to be setuid root or executed by root.
2848 nohalt [IA-64] Tells the kernel not to use the power saving
2849 function PAL_HALT_LIGHT when idle. This increases
2850 power-consumption. On the positive side, it reduces
2851 interrupt wake-up latency, which may improve performance
2852 in certain environments such as networked servers or
2855 nohibernate [HIBERNATION] Disable hibernation and resume.
2857 nohz= [KNL] Boottime enable/disable dynamic ticks
2858 Valid arguments: on, off
2861 nohz_full= [KNL,BOOT,SMP,ISOL]
2862 The argument is a cpu list, as described above.
2863 In kernels built with CONFIG_NO_HZ_FULL=y, set
2864 the specified list of CPUs whose tick will be stopped
2865 whenever possible. The boot CPU will be forced outside
2866 the range to maintain the timekeeping. Any CPUs
2867 in this list will have their RCU callbacks offloaded,
2868 just as if they had also been called out in the
2869 rcu_nocbs= boot parameter.
2871 noiotrap [SH] Disables trapped I/O port accesses.
2873 noirqdebug [X86-32] Disables the code which attempts to detect and
2874 disable unhandled interrupt sources.
2876 no_timer_check [X86,APIC] Disables the code which tests for
2877 broken timer IRQ sources.
2879 noisapnp [ISAPNP] Disables ISA PnP code.
2881 noinitrd [RAM] Tells the kernel not to load any configured
2884 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2886 [Deprecated - use intremap=off]
2890 noinvpcid [X86] Disable the INVPCID cpu feature.
2892 nojitter [IA-64] Disables jitter checking for ITC timers.
2894 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2896 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2900 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2901 clock and use the default one.
2903 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2904 steal time is computed, but won't influence scheduler
2907 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2909 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2911 noltlbs [PPC] Do not use large page/tlb entries for kernel
2912 lowmem mapping on PPC40x and PPC8xx
2914 nomca [IA-64] Disable machine check abort handling
2916 nomce [X86-32] Disable Machine Check Exception
2918 nomfgpt [X86-32] Disable Multi-Function General Purpose
2919 Timer usage (for AMD Geode machines).
2921 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2922 shutdown the other cpus. Instead use the REBOOT_VECTOR
2925 nomodule Disable module load
2927 nopat [X86] Disable PAT (page attribute table extension of
2928 pagetables) support.
2930 nopcid [X86-64] Disable the PCID cpu feature.
2932 norandmaps Don't use address space randomization. Equivalent to
2933 echo 0 > /proc/sys/kernel/randomize_va_space
2935 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2936 with UP alternatives
2938 nordrand [X86] Disable kernel use of the RDRAND and
2939 RDSEED instructions even if they are supported
2940 by the processor. RDRAND and RDSEED are still
2941 available to user space applications.
2943 noresume [SWSUSP] Disables resume and restores original swap
2946 no-scroll [VGA] Disables scrollback.
2947 This is required for the Braillex ib80-piezo Braille
2948 reader made by F.H. Papenmeier (Germany).
2952 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2954 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2955 and disable the IO APIC. legacy for "maxcpus=0".
2957 nosoftlockup [KNL] Disable the soft-lockup detector.
2959 nosync [HW,M68K] Disables sync negotiation for all devices.
2961 nowatchdog [KNL] Disable both lockup detectors, i.e.
2962 soft-lockup and NMI watchdog (hard-lockup).
2966 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2968 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2969 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2970 Some features depend on CPU0. Known dependencies are:
2971 1. Resume from suspend/hibernate depends on CPU0.
2972 Suspend/hibernate will fail if CPU0 is offline and you
2973 need to online CPU0 before suspend/hibernate.
2974 2. PIC interrupts also depend on CPU0. CPU0 can't be
2975 removed if a PIC interrupt is detected.
2976 It's said poweroff/reboot may depend on CPU0 on some
2977 machines although I haven't seen such issues so far
2978 after CPU0 is offline on a few tested machines.
2979 If the dependencies are under your control, you can
2980 turn on cpu0_hotplug.
2982 nps_mtm_hs_ctr= [KNL,ARC]
2983 This parameter sets the maximum duration, in
2984 cycles, each HW thread of the CTOP can run
2985 without interruptions, before HW switches it.
2986 The actual maximum duration is 16 times this
2988 Format: integer between 1 and 255
2991 nptcg= [IA-64] Override max number of concurrent global TLB
2992 purges which is reported from either PAL_VM_SUMMARY or
2995 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2996 could support. nr_cpus=n : n >= 1 limits the kernel to
2997 support 'n' processors. It could be larger than the
2998 number of already plugged CPU during bootup, later in
2999 runtime you can physically add extra cpu until it reaches
3000 n. So during boot up some boot time memory for per-cpu
3001 variables need be pre-allocated for later physical cpu
3004 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3006 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3007 Allowed values are enable and disable
3009 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3010 'node', 'default' can be specified
3011 This can be set from sysctl after boot.
3012 See Documentation/sysctl/vm.txt for details.
3014 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3015 See Documentation/debugging-via-ohci1394.txt for more
3018 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3019 Rather than timing out after 20 ms if an EC
3020 command is not properly ACKed, override the length
3021 of the timeout. We have interrupts disabled while
3022 waiting for the ACK, so if this is set too high
3023 interrupts *may* be lost!
3025 omap_mux= [OMAP] Override bootloader pin multiplexing.
3026 Format: <mux_mode0.mode_name=value>...
3027 For example, to override I2C bus2:
3028 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3030 oprofile.timer= [HW]
3031 Use timer interrupt instead of performance counters
3033 oprofile.cpu_type= Force an oprofile cpu type
3034 This might be useful if you have an older oprofile
3035 userland or if you want common events.
3036 Format: { arch_perfmon }
3037 arch_perfmon: [X86] Force use of architectural
3038 perfmon on Intel CPUs instead of the
3039 CPU specific event set.
3040 timer: [X86] Force use of architectural NMI
3041 timer mode (see also oprofile.timer
3042 for generic hr timer mode)
3044 oops=panic Always panic on oopses. Default is to just kill the
3045 process, but there is a small probability of
3046 deadlocking the machine.
3047 This will also cause panics on machine check exceptions.
3048 Useful together with panic=30 to trigger a reboot.
3050 page_owner= [KNL] Boot-time page_owner enabling option.
3051 Storage of the information about who allocated
3052 each page is disabled in default. With this switch,
3054 on: enable the feature
3056 page_poison= [KNL] Boot-time parameter changing the state of
3057 poisoning on the buddy allocator, available with
3058 CONFIG_PAGE_POISONING=y.
3059 off: turn off poisoning (default)
3060 on: turn on poisoning
3062 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3063 timeout > 0: seconds before rebooting
3064 timeout = 0: wait forever
3065 timeout < 0: reboot immediately
3068 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3071 crash_kexec_post_notifiers
3072 Run kdump after running panic-notifiers and dumping
3073 kmsg. This only for the users who doubt kdump always
3074 succeeds in any situation.
3075 Note that this also increases risks of kdump failure,
3076 because some panic notifiers can make the crashed
3077 kernel more unstable.
3079 parkbd.port= [HW] Parallel port number the keyboard adapter is
3080 connected to, default is 0.
3082 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3083 0 for XT, 1 for AT (default is AT).
3086 parport= [HW,PPT] Specify parallel ports. 0 disables.
3087 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3088 Use 'auto' to force the driver to use any
3089 IRQ/DMA settings detected (the default is to
3090 ignore detected IRQ/DMA settings because of
3091 possible conflicts). You can specify the base
3092 address, IRQ, and DMA settings; IRQ and DMA
3093 should be numbers, or 'auto' (for using detected
3094 settings on that particular port), or 'nofifo'
3095 (to avoid using a FIFO even if it is detected).
3096 Parallel ports are assigned in the order they
3097 are specified on the command line, starting
3100 parport_init_mode= [HW,PPT]
3101 Configure VIA parallel port to operate in
3102 a specific mode. This is necessary on Pegasos
3103 computer where firmware has no options for setting
3104 up parallel port mode and sets it to spp.
3105 Currently this function knows 686a and 8231 chips.
3106 Format: [spp|ps2|epp|ecp|ecpepp]
3109 Halt all CPUs after the first oops has been printed for
3110 the specified number of seconds. This is to be used if
3111 your oopses keep scrolling off the screen.
3116 See header of drivers/block/paride/pcd.c.
3117 See also Documentation/blockdev/paride.txt.
3119 pci=option[,option...] [PCI] various PCI subsystem options.
3121 Some options herein operate on a specific device
3122 or a set of devices (<pci_dev>). These are
3123 specified in one of the following formats:
3125 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3126 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3128 Note: the first format specifies a PCI
3129 bus/device/function address which may change
3130 if new hardware is inserted, if motherboard
3131 firmware changes, or due to changes caused
3132 by other kernel parameters. If the
3133 domain is left unspecified, it is
3134 taken to be zero. Optionally, a path
3135 to a device through multiple device/function
3136 addresses can be specified after the base
3137 address (this is more robust against
3138 renumbering issues). The second format
3139 selects devices using IDs from the
3140 configuration space which may match multiple
3141 devices in the system.
3143 earlydump dump PCI config space before the kernel
3145 off [X86] don't probe for the PCI bus
3146 bios [X86-32] force use of PCI BIOS, don't access
3147 the hardware directly. Use this if your machine
3148 has a non-standard PCI host bridge.
3149 nobios [X86-32] disallow use of PCI BIOS, only direct
3150 hardware access methods are allowed. Use this
3151 if you experience crashes upon bootup and you
3152 suspect they are caused by the BIOS.
3153 conf1 [X86] Force use of PCI Configuration Access
3154 Mechanism 1 (config address in IO port 0xCF8,
3155 data in IO port 0xCFC, both 32-bit).
3156 conf2 [X86] Force use of PCI Configuration Access
3157 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3158 the function, IO port 0xCFA, also 8-bit, sets
3159 bus number. The config space is then accessed
3160 through ports 0xC000-0xCFFF).
3161 See http://wiki.osdev.org/PCI for more info
3162 on the configuration access mechanisms.
3163 noaer [PCIE] If the PCIEAER kernel config parameter is
3164 enabled, this kernel boot option can be used to
3165 disable the use of PCIE advanced error reporting.
3166 nodomains [PCI] Disable support for multiple PCI
3167 root domains (aka PCI segments, in ACPI-speak).
3168 nommconf [X86] Disable use of MMCONFIG for PCI
3170 check_enable_amd_mmconf [X86] check for and enable
3171 properly configured MMIO access to PCI
3172 config space on AMD family 10h CPU
3173 nomsi [MSI] If the PCI_MSI kernel config parameter is
3174 enabled, this kernel boot option can be used to
3175 disable the use of MSI interrupts system-wide.
3176 noioapicquirk [APIC] Disable all boot interrupt quirks.
3177 Safety option to keep boot IRQs enabled. This
3178 should never be necessary.
3179 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3180 primary IO-APIC for bridges that cannot disable
3181 boot IRQs. This fixes a source of spurious IRQs
3182 when the system masks IRQs.
3183 noioapicreroute [APIC] Disable workaround that uses the
3184 boot IRQ equivalent of an IRQ that connects to
3185 a chipset where boot IRQs cannot be disabled.
3186 The opposite of ioapicreroute.
3187 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3188 routing table. These calls are known to be buggy
3189 on several machines and they hang the machine
3190 when used, but on other computers it's the only
3191 way to get the interrupt routing table. Try
3192 this option if the kernel is unable to allocate
3193 IRQs or discover secondary PCI buses on your
3195 rom [X86] Assign address space to expansion ROMs.
3196 Use with caution as certain devices share
3197 address decoders between ROMs and other
3199 norom [X86] Do not assign address space to
3200 expansion ROMs that do not already have
3201 BIOS assigned address ranges.
3202 nobar [X86] Do not assign address space to the
3203 BARs that weren't assigned by the BIOS.
3204 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3205 assigned automatically to PCI devices. You can
3206 make the kernel exclude IRQs of your ISA cards
3208 pirqaddr=0xAAAAA [X86] Specify the physical address
3209 of the PIRQ table (normally generated
3210 by the BIOS) if it is outside the
3211 F0000h-100000h range.
3212 lastbus=N [X86] Scan all buses thru bus #N. Can be
3213 useful if the kernel is unable to find your
3214 secondary buses and you want to tell it
3215 explicitly which ones they are.
3216 assign-busses [X86] Always assign all PCI bus
3217 numbers ourselves, overriding
3218 whatever the firmware may have done.
3219 usepirqmask [X86] Honor the possible IRQ mask stored
3220 in the BIOS $PIR table. This is needed on
3221 some systems with broken BIOSes, notably
3222 some HP Pavilion N5400 and Omnibook XE3
3223 notebooks. This will have no effect if ACPI
3224 IRQ routing is enabled.
3225 noacpi [X86] Do not use ACPI for IRQ routing
3226 or for PCI scanning.
3227 use_crs [X86] Use PCI host bridge window information
3228 from ACPI. On BIOSes from 2008 or later, this
3229 is enabled by default. If you need to use this,
3230 please report a bug.
3231 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3232 If you need to use this, please report a bug.
3233 routeirq Do IRQ routing for all PCI devices.
3234 This is normally done in pci_enable_device(),
3235 so this option is a temporary workaround
3236 for broken drivers that don't call it.
3237 skip_isa_align [X86] do not align io start addr, so can
3238 handle more pci cards
3239 noearly [X86] Don't do any early type 1 scanning.
3240 This might help on some broken boards which
3241 machine check when some devices' config space
3242 is read. But various workarounds are disabled
3243 and some IOMMU drivers will not work.
3244 bfsort Sort PCI devices into breadth-first order.
3245 This sorting is done to get a device
3246 order compatible with older (<= 2.4) kernels.
3247 nobfsort Don't sort PCI devices into breadth-first order.
3248 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3249 tuning and use the BIOS-configured MPS defaults.
3250 pcie_bus_safe Set every device's MPS to the largest value
3251 supported by all devices below the root complex.
3252 pcie_bus_perf Set device MPS to the largest allowable MPS
3253 based on its parent bus. Also set MRRS (Max
3254 Read Request Size) to the largest supported
3255 value (no larger than the MPS that the device
3256 or bus can support) for best performance.
3257 pcie_bus_peer2peer Set every device's MPS to 128B, which
3258 every device is guaranteed to support. This
3259 configuration allows peer-to-peer DMA between
3260 any pair of devices, possibly at the cost of
3261 reduced performance. This also guarantees
3262 that hot-added devices will work.
3263 cbiosize=nn[KMG] The fixed amount of bus space which is
3264 reserved for the CardBus bridge's IO window.
3265 The default value is 256 bytes.
3266 cbmemsize=nn[KMG] The fixed amount of bus space which is
3267 reserved for the CardBus bridge's memory
3268 window. The default value is 64 megabytes.
3271 [<order of align>@]<pci_dev>[; ...]
3272 Specifies alignment and device to reassign
3273 aligned memory resources. How to
3274 specify the device is described above.
3275 If <order of align> is not specified,
3276 PAGE_SIZE is used as alignment.
3277 PCI-PCI bridge can be specified, if resource
3278 windows need to be expanded.
3279 To specify the alignment for several
3280 instances of a device, the PCI vendor,
3281 device, subvendor, and subdevice may be
3282 specified, e.g., 4096@pci:8086:9c22:103c:198f
3283 ecrc= Enable/disable PCIe ECRC (transaction layer
3284 end-to-end CRC checking).
3285 bios: Use BIOS/firmware settings. This is the
3289 hpiosize=nn[KMG] The fixed amount of bus space which is
3290 reserved for hotplug bridge's IO window.
3291 Default size is 256 bytes.
3292 hpmemsize=nn[KMG] The fixed amount of bus space which is
3293 reserved for hotplug bridge's memory window.
3294 Default size is 2 megabytes.
3295 hpbussize=nn The minimum amount of additional bus numbers
3296 reserved for buses below a hotplug bridge.
3298 realloc= Enable/disable reallocating PCI bridge resources
3299 if allocations done by BIOS are too small to
3300 accommodate resources required by all child
3302 off: Turn realloc off
3304 realloc same as realloc=on
3305 noari do not use PCIe ARI.
3306 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3307 do not use PCIe ATS (and IOMMU device IOTLB).
3308 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3309 only look for one device below a PCIe downstream
3311 big_root_window Try to add a big 64bit memory window to the PCIe
3312 root complex on AMD CPUs. Some GFX hardware
3313 can resize a BAR to allow access to all VRAM.
3314 Adding the window is slightly risky (it may
3315 conflict with unreported devices), so this
3317 disable_acs_redir=<pci_dev>[; ...]
3318 Specify one or more PCI devices (in the format
3319 specified above) separated by semicolons.
3320 Each device specified will have the PCI ACS
3321 redirect capabilities forced off which will
3322 allow P2P traffic between devices through
3323 bridges without forcing it upstream. Note:
3324 this removes isolation between devices and
3325 may put more devices in an IOMMU group.
3327 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3330 force Enable ASPM even on devices that claim not to support it.
3331 WARNING: Forcing ASPM on may cause system lockups.
3333 pcie_ports= [PCIE] PCIe port services handling:
3334 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3335 even if the platform doesn't give the OS permission to
3336 use them. This may cause conflicts if the platform
3337 also tries to use these services.
3338 compat Disable native PCIe services (PME, AER, DPC, PCIe
3341 pcie_port_pm= [PCIE] PCIe port power management handling:
3342 off Disable power management of all PCIe ports
3343 force Forcibly enable power management of all PCIe ports
3345 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3346 nomsi Do not use MSI for native PCIe PME signaling (this makes
3347 all PCIe root ports use INTx for all services).
3349 pcmv= [HW,PCMCIA] BadgePAD 4
3353 Keep all power-domains already enabled by bootloader on,
3354 even if no driver has claimed them. This is useful
3355 for debug and development, but should not be
3356 needed on a platform with proper driver support.
3359 See Documentation/blockdev/paride.txt.
3361 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3364 See arch/parisc/kernel/pdc_chassis.c
3366 percpu_alloc= Select which percpu first chunk allocator to use.
3367 Currently supported values are "embed" and "page".
3368 Archs may support subset or none of the selections.
3369 See comments in mm/percpu.c for details on each
3370 allocator. This parameter is primarily for debugging
3371 and performance comparison.
3374 See Documentation/blockdev/paride.txt.
3377 See Documentation/blockdev/paride.txt.
3379 pirq= [SMP,APIC] Manual mp-table setup
3380 See Documentation/x86/i386/IO-APIC.txt.
3382 plip= [PPT,NET] Parallel port network link
3383 Format: { parport<nr> | timid | 0 }
3384 See also Documentation/admin-guide/parport.rst.
3386 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3387 Override pmtimer IOPort with a hex value.
3391 Enable PNP debug messages (depends on the
3392 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3393 via /sys/module/pnp/parameters/debug. We always show
3394 current resource usage; turning this on also shows
3395 possible settings and some assignment information.
3401 { on | off | curr | res | no-curr | no-res }
3404 [ISAPNP] Exclude IRQs for the autoconfiguration
3407 [ISAPNP] Exclude DMAs for the autoconfiguration
3409 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3410 Ranges are in pairs (I/O port base and size).
3413 [ISAPNP] Exclude memory regions for the
3415 Ranges are in pairs (memory base and size).
3417 ports= [IP_VS_FTP] IPVS ftp helper module
3419 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3421 Format: <port>,<port>....
3423 powersave=off [PPC] This option disables power saving features.
3424 It specifically disables cpuidle and sets the
3425 platform machine description specific power_save
3426 function to NULL. On Idle the CPU just reduces
3429 ppc_strict_facility_enable
3430 [PPC] This option catches any kernel floating point,
3431 Altivec, VSX and SPE outside of regions specifically
3432 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3433 There is some performance impact when enabling this.
3437 Disable Hardware Transactional Memory
3439 print-fatal-signals=
3440 [KNL] debug: print fatal signals
3442 If enabled, warn about various signal handling
3443 related application anomalies: too many signals,
3444 too many POSIX.1 timers, fatal signals causing a
3447 If you hit the warning due to signal overflow,
3448 you might want to try "ulimit -i unlimited".
3452 printk.always_kmsg_dump=
3453 Trigger kmsg_dump for cases other than kernel oops or
3455 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3458 printk.devkmsg={on,off,ratelimit}
3459 Control writing to /dev/kmsg.
3460 on - unlimited logging to /dev/kmsg from userspace
3461 off - logging to /dev/kmsg disabled
3462 ratelimit - ratelimit the logging
3465 printk.time= Show timing data prefixed to each printk message line
3466 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3468 processor.max_cstate= [HW,ACPI]
3469 Limit processor to maximum C-state
3470 max_cstate=9 overrides any DMI blacklist limit.
3472 processor.nocst [HW,ACPI]
3473 Ignore the _CST method to determine C-states,
3474 instead using the legacy FADT method
3476 profile= [KNL] Enable kernel profiling via /proc/profile
3477 Format: [<profiletype>,]<number>
3478 Param: <profiletype>: "schedule", "sleep", or "kvm"
3479 [defaults to kernel profiling]
3480 Param: "schedule" - profile schedule points.
3481 Param: "sleep" - profile D-state sleeping (millisecs).
3482 Requires CONFIG_SCHEDSTATS
3483 Param: "kvm" - profile VM exits.
3484 Param: <number> - step/bucket size as a power of 2 for
3485 statistical time based profiling.
3487 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3489 See Documentation/blockdev/ramdisk.txt.
3491 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3492 probe for; one of (bare|imps|exps|lifebook|any).
3493 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3495 psmouse.resetafter= [HW,MOUSE]
3496 Try to reset the device after so many bad packets
3499 [HW,MOUSE] Set desired mouse resolution, in dpi.
3500 psmouse.smartscroll=
3501 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3502 0 = disabled, 1 = enabled (default).
3504 pstore.backend= Specify the name of the pstore backend to use
3507 See Documentation/blockdev/paride.txt.
3509 pti= [X86_64] Control Page Table Isolation of user and
3510 kernel address spaces. Disabling this feature
3511 removes hardening, but improves performance of
3512 system calls and interrupts.
3514 on - unconditionally enable
3515 off - unconditionally disable
3516 auto - kernel detects whether your CPU model is
3517 vulnerable to issues that PTI mitigates
3519 Not specifying this option is equivalent to pti=auto.
3522 Equivalent to pti=off
3525 [KNL] Number of legacy pty's. Overwrites compiled-in
3528 quiet [KNL] Disable most log messages
3533 See Documentation/admin-guide/md.rst.
3535 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3536 See Documentation/blockdev/ramdisk.txt.
3538 random.trust_cpu={on,off}
3539 [KNL] Enable or disable trusting the use of the
3540 CPU's random number generator (if available) to
3541 fully seed the kernel's CRNG. Default is controlled
3542 by CONFIG_RANDOM_TRUST_CPU.
3544 ras=option[,option,...] [KNL] RAS-specific options
3547 Disable the Correctable Errors Collector,
3548 see CONFIG_RAS_CEC help text.
3551 The argument is a cpu list, as described above.
3553 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3554 the specified list of CPUs to be no-callback CPUs.
3555 Invocation of these CPUs' RCU callbacks will be
3556 offloaded to "rcuox/N" kthreads created for that
3557 purpose, where "x" is "p" for RCU-preempt, and
3558 "s" for RCU-sched, and "N" is the CPU number.
3559 This reduces OS jitter on the offloaded CPUs,
3560 which can be useful for HPC and real-time
3561 workloads. It can also improve energy efficiency
3562 for asymmetric multiprocessors.
3565 Rather than requiring that offloaded CPUs
3566 (specified by rcu_nocbs= above) explicitly
3567 awaken the corresponding "rcuoN" kthreads,
3568 make these kthreads poll for callbacks.
3569 This improves the real-time response for the
3570 offloaded CPUs by relieving them of the need to
3571 wake up the corresponding kthread, but degrades
3572 energy efficiency by requiring that the kthreads
3573 periodically wake up to do the polling.
3575 rcutree.blimit= [KNL]
3576 Set maximum number of finished RCU callbacks to
3577 process in one batch.
3579 rcutree.dump_tree= [KNL]
3580 Dump the structure of the rcu_node combining tree
3581 out at early boot. This is used for diagnostic
3582 purposes, to verify correct tree setup.
3584 rcutree.gp_cleanup_delay= [KNL]
3585 Set the number of jiffies to delay each step of
3586 RCU grace-period cleanup.
3588 rcutree.gp_init_delay= [KNL]
3589 Set the number of jiffies to delay each step of
3590 RCU grace-period initialization.
3592 rcutree.gp_preinit_delay= [KNL]
3593 Set the number of jiffies to delay each step of
3594 RCU grace-period pre-initialization, that is,
3595 the propagation of recent CPU-hotplug changes up
3596 the rcu_node combining tree.
3598 rcutree.rcu_fanout_exact= [KNL]
3599 Disable autobalancing of the rcu_node combining
3600 tree. This is used by rcutorture, and might
3601 possibly be useful for architectures having high
3602 cache-to-cache transfer latencies.
3604 rcutree.rcu_fanout_leaf= [KNL]
3605 Change the number of CPUs assigned to each
3606 leaf rcu_node structure. Useful for very
3607 large systems, which will choose the value 64,
3608 and for NUMA systems with large remote-access
3609 latencies, which will choose a value aligned
3610 with the appropriate hardware boundaries.
3612 rcutree.jiffies_till_sched_qs= [KNL]
3613 Set required age in jiffies for a
3614 given grace period before RCU starts
3615 soliciting quiescent-state help from
3616 rcu_note_context_switch(). If not specified, the
3617 kernel will calculate a value based on the most
3618 recent settings of rcutree.jiffies_till_first_fqs
3619 and rcutree.jiffies_till_next_fqs.
3620 This calculated value may be viewed in
3621 rcutree.jiffies_to_sched_qs. Any attempt to
3622 set rcutree.jiffies_to_sched_qs will be
3623 cheerfully overwritten.
3625 rcutree.jiffies_till_first_fqs= [KNL]
3626 Set delay from grace-period initialization to
3627 first attempt to force quiescent states.
3628 Units are jiffies, minimum value is zero,
3629 and maximum value is HZ.
3631 rcutree.jiffies_till_next_fqs= [KNL]
3632 Set delay between subsequent attempts to force
3633 quiescent states. Units are jiffies, minimum
3634 value is one, and maximum value is HZ.
3636 rcutree.kthread_prio= [KNL,BOOT]
3637 Set the SCHED_FIFO priority of the RCU per-CPU
3638 kthreads (rcuc/N). This value is also used for
3639 the priority of the RCU boost threads (rcub/N)
3640 and for the RCU grace-period kthreads (rcu_bh,
3641 rcu_preempt, and rcu_sched). If RCU_BOOST is
3642 set, valid values are 1-99 and the default is 1
3643 (the least-favored priority). Otherwise, when
3644 RCU_BOOST is not set, valid values are 0-99 and
3645 the default is zero (non-realtime operation).
3647 rcutree.rcu_nocb_leader_stride= [KNL]
3648 Set the number of NOCB kthread groups, which
3649 defaults to the square root of the number of
3650 CPUs. Larger numbers reduces the wakeup overhead
3651 on the per-CPU grace-period kthreads, but increases
3652 that same overhead on each group's leader.
3654 rcutree.qhimark= [KNL]
3655 Set threshold of queued RCU callbacks beyond which
3656 batch limiting is disabled.
3658 rcutree.qlowmark= [KNL]
3659 Set threshold of queued RCU callbacks below which
3660 batch limiting is re-enabled.
3662 rcutree.rcu_idle_gp_delay= [KNL]
3663 Set wakeup interval for idle CPUs that have
3664 RCU callbacks (RCU_FAST_NO_HZ=y).
3666 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3667 Set wakeup interval for idle CPUs that have
3668 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3669 Lazy RCU callbacks are those which RCU can
3670 prove do nothing more than free memory.
3672 rcutree.rcu_kick_kthreads= [KNL]
3673 Cause the grace-period kthread to get an extra
3674 wake_up() if it sleeps three times longer than
3675 it should at force-quiescent-state time.
3676 This wake_up() will be accompanied by a
3677 WARN_ONCE() splat and an ftrace_dump().
3679 rcuperf.gp_async= [KNL]
3680 Measure performance of asynchronous
3681 grace-period primitives such as call_rcu().
3683 rcuperf.gp_async_max= [KNL]
3684 Specify the maximum number of outstanding
3685 callbacks per writer thread. When a writer
3686 thread exceeds this limit, it invokes the
3687 corresponding flavor of rcu_barrier() to allow
3688 previously posted callbacks to drain.
3690 rcuperf.gp_exp= [KNL]
3691 Measure performance of expedited synchronous
3692 grace-period primitives.
3694 rcuperf.holdoff= [KNL]
3695 Set test-start holdoff period. The purpose of
3696 this parameter is to delay the start of the
3697 test until boot completes in order to avoid
3700 rcuperf.nreaders= [KNL]
3701 Set number of RCU readers. The value -1 selects
3702 N, where N is the number of CPUs. A value
3703 "n" less than -1 selects N-n+1, where N is again
3704 the number of CPUs. For example, -2 selects N
3705 (the number of CPUs), -3 selects N+1, and so on.
3706 A value of "n" less than or equal to -N selects
3709 rcuperf.nwriters= [KNL]
3710 Set number of RCU writers. The values operate
3711 the same as for rcuperf.nreaders.
3712 N, where N is the number of CPUs
3714 rcuperf.perf_type= [KNL]
3715 Specify the RCU implementation to test.
3717 rcuperf.shutdown= [KNL]
3718 Shut the system down after performance tests
3719 complete. This is useful for hands-off automated
3722 rcuperf.verbose= [KNL]
3723 Enable additional printk() statements.
3725 rcuperf.writer_holdoff= [KNL]
3726 Write-side holdoff between grace periods,
3727 in microseconds. The default of zero says
3730 rcutorture.cbflood_inter_holdoff= [KNL]
3731 Set holdoff time (jiffies) between successive
3732 callback-flood tests.
3734 rcutorture.cbflood_intra_holdoff= [KNL]
3735 Set holdoff time (jiffies) between successive
3736 bursts of callbacks within a given callback-flood
3739 rcutorture.cbflood_n_burst= [KNL]
3740 Set the number of bursts making up a given
3741 callback-flood test. Set this to zero to
3742 disable callback-flood testing.
3744 rcutorture.cbflood_n_per_burst= [KNL]
3745 Set the number of callbacks to be registered
3746 in a given burst of a callback-flood test.
3748 rcutorture.fqs_duration= [KNL]
3749 Set duration of force_quiescent_state bursts
3752 rcutorture.fqs_holdoff= [KNL]
3753 Set holdoff time within force_quiescent_state bursts
3756 rcutorture.fqs_stutter= [KNL]
3757 Set wait time between force_quiescent_state bursts
3760 rcutorture.gp_cond= [KNL]
3761 Use conditional/asynchronous update-side
3762 primitives, if available.
3764 rcutorture.gp_exp= [KNL]
3765 Use expedited update-side primitives, if available.
3767 rcutorture.gp_normal= [KNL]
3768 Use normal (non-expedited) asynchronous
3769 update-side primitives, if available.
3771 rcutorture.gp_sync= [KNL]
3772 Use normal (non-expedited) synchronous
3773 update-side primitives, if available. If all
3774 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3775 rcutorture.gp_normal=, and rcutorture.gp_sync=
3776 are zero, rcutorture acts as if is interpreted
3777 they are all non-zero.
3779 rcutorture.n_barrier_cbs= [KNL]
3780 Set callbacks/threads for rcu_barrier() testing.
3782 rcutorture.nfakewriters= [KNL]
3783 Set number of concurrent RCU writers. These just
3784 stress RCU, they don't participate in the actual
3785 test, hence the "fake".
3787 rcutorture.nreaders= [KNL]
3788 Set number of RCU readers. The value -1 selects
3789 N-1, where N is the number of CPUs. A value
3790 "n" less than -1 selects N-n-2, where N is again
3791 the number of CPUs. For example, -2 selects N
3792 (the number of CPUs), -3 selects N+1, and so on.
3794 rcutorture.object_debug= [KNL]
3795 Enable debug-object double-call_rcu() testing.
3797 rcutorture.onoff_holdoff= [KNL]
3798 Set time (s) after boot for CPU-hotplug testing.
3800 rcutorture.onoff_interval= [KNL]
3801 Set time (jiffies) between CPU-hotplug operations,
3802 or zero to disable CPU-hotplug testing.
3804 rcutorture.shuffle_interval= [KNL]
3805 Set task-shuffle interval (s). Shuffling tasks
3806 allows some CPUs to go into dyntick-idle mode
3807 during the rcutorture test.
3809 rcutorture.shutdown_secs= [KNL]
3810 Set time (s) after boot system shutdown. This
3811 is useful for hands-off automated testing.
3813 rcutorture.stall_cpu= [KNL]
3814 Duration of CPU stall (s) to test RCU CPU stall
3815 warnings, zero to disable.
3817 rcutorture.stall_cpu_holdoff= [KNL]
3818 Time to wait (s) after boot before inducing stall.
3820 rcutorture.stall_cpu_irqsoff= [KNL]
3821 Disable interrupts while stalling if set.
3823 rcutorture.stat_interval= [KNL]
3824 Time (s) between statistics printk()s.
3826 rcutorture.stutter= [KNL]
3827 Time (s) to stutter testing, for example, specifying
3828 five seconds causes the test to run for five seconds,
3829 wait for five seconds, and so on. This tests RCU's
3830 ability to transition abruptly to and from idle.
3832 rcutorture.test_boost= [KNL]
3833 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3834 "Maybe" means test if the RCU implementation
3835 under test support RCU priority boosting.
3837 rcutorture.test_boost_duration= [KNL]
3838 Duration (s) of each individual boost test.
3840 rcutorture.test_boost_interval= [KNL]
3841 Interval (s) between each boost test.
3843 rcutorture.test_no_idle_hz= [KNL]
3844 Test RCU's dyntick-idle handling. See also the
3845 rcutorture.shuffle_interval parameter.
3847 rcutorture.torture_type= [KNL]
3848 Specify the RCU implementation to test.
3850 rcutorture.verbose= [KNL]
3851 Enable additional printk() statements.
3853 rcupdate.rcu_cpu_stall_suppress= [KNL]
3854 Suppress RCU CPU stall warning messages.
3856 rcupdate.rcu_cpu_stall_timeout= [KNL]
3857 Set timeout for RCU CPU stall warning messages.
3859 rcupdate.rcu_expedited= [KNL]
3860 Use expedited grace-period primitives, for
3861 example, synchronize_rcu_expedited() instead
3862 of synchronize_rcu(). This reduces latency,
3863 but can increase CPU utilization, degrade
3864 real-time latency, and degrade energy efficiency.
3865 No effect on CONFIG_TINY_RCU kernels.
3867 rcupdate.rcu_normal= [KNL]
3868 Use only normal grace-period primitives,
3869 for example, synchronize_rcu() instead of
3870 synchronize_rcu_expedited(). This improves
3871 real-time latency, CPU utilization, and
3872 energy efficiency, but can expose users to
3873 increased grace-period latency. This parameter
3874 overrides rcupdate.rcu_expedited. No effect on
3875 CONFIG_TINY_RCU kernels.
3877 rcupdate.rcu_normal_after_boot= [KNL]
3878 Once boot has completed (that is, after
3879 rcu_end_inkernel_boot() has been invoked), use
3880 only normal grace-period primitives. No effect
3881 on CONFIG_TINY_RCU kernels.
3883 rcupdate.rcu_task_stall_timeout= [KNL]
3884 Set timeout in jiffies for RCU task stall warning
3885 messages. Disable with a value less than or equal
3888 rcupdate.rcu_self_test= [KNL]
3889 Run the RCU early boot self tests
3893 Run specified binary instead of /init from the ramdisk,
3894 used for early userspace startup. See initrd.
3897 Turn on/off individual RDT features. List is:
3898 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3900 E.g. to turn on cmt and turn off mba use:
3904 Format (x86 or x86_64):
3905 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3907 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3909 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3910 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3911 reboot_force is either force or not specified,
3912 reboot_cpu is s[mp]#### with #### being the processor
3913 to be used for rebooting.
3916 [KNL, SMP] Set scheduler's default relax_domain_level.
3917 See Documentation/cgroup-v1/cpusets.txt.
3919 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3920 Format: <base1>,<size1>[,<base2>,<size2>,...]
3921 Reserve I/O ports or memory so the kernel won't use
3922 them. If <base> is less than 0x10000, the region
3923 is assumed to be I/O ports; otherwise it is memory.
3925 reservetop= [X86-32]
3927 Reserves a hole at the top of the kernel virtual
3932 Set the amount of memory to reserve for BIOS at
3933 the bottom of the address space.
3935 reset_devices [KNL] Force drivers to reset the underlying device
3936 during initialization.
3939 Specify the partition device for software suspend
3941 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3943 resume_offset= [SWSUSP]
3944 Specify the offset from the beginning of the partition
3945 given by "resume=" at which the swap header is located,
3946 in <PAGE_SIZE> units (needed only for swap files).
3947 See Documentation/power/swsusp-and-swap-files.txt
3949 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3950 read the resume files
3952 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3953 Useful for devices that are detected asynchronously
3954 (e.g. USB and MMC devices).
3956 hibernate= [HIBERNATION]
3957 noresume Don't check if there's a hibernation image
3958 present during boot.
3959 nocompress Don't compress/decompress hibernation images.
3960 no Disable hibernation and resume.
3961 protect_image Turn on image protection during restoration
3962 (that will set all pages holding image data
3963 during restoration read-only).
3965 retain_initrd [RAM] Keep initrd memory after extraction
3967 rfkill.default_state=
3968 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3969 etc. communication is blocked by default.
3972 rfkill.master_switch_mode=
3973 0 The "airplane mode" button does nothing.
3974 1 The "airplane mode" button toggles between everything
3975 blocked and the previous configuration.
3976 2 The "airplane mode" button toggles between everything
3977 blocked and everything unblocked.
3979 rhash_entries= [KNL,NET]
3980 Set number of hash buckets for route cache
3983 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
3986 ro [KNL] Mount root device read-only on boot
3989 on Mark read-only kernel memory as read-only (default).
3990 off Leave read-only kernel memory writable for debugging.
3993 Enable the uart passthrough on the designated usb port
3994 on Rockchip SoCs. When active, the signals of the
3995 debug-uart get routed to the D+ and D- pins of the usb
3996 port and the regular usb controller gets disabled.
3998 root= [KNL] Root filesystem
3999 See name_to_dev_t comment in init/do_mounts.c.
4001 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4002 mount the root filesystem
4004 rootflags= [KNL] Set root filesystem mount option string
4006 rootfstype= [KNL] Set root filesystem type
4008 rootwait [KNL] Wait (indefinitely) for root device to show up.
4009 Useful for devices that are detected asynchronously
4010 (e.g. USB and MMC devices).
4012 rproc_mem=nn[KMG][@address]
4013 [KNL,ARM,CMA] Remoteproc physical memory block.
4014 Memory area to be used by remote processor image,
4017 rw [KNL] Mount root device read-write on boot
4019 S [KNL] Run init in single mode
4021 s390_iommu= [HW,S390]
4022 Set s390 IOTLB flushing mode
4024 With strict flushing every unmap operation will result in
4025 an IOTLB flush. Default is lazy flushing before reuse,
4029 See drivers/net/irda/sa1100_ir.c.
4031 sbni= [NET] Granch SBNI12 leased line adapter
4033 sched_debug [KNL] Enables verbose scheduler debug messages.
4035 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4036 Allowed values are enable and disable. This feature
4037 incurs a small amount of overhead in the scheduler
4038 but is useful for debugging and performance tuning.
4040 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4041 xtime_lock contention on larger systems, and/or RCU lock
4042 contention on all systems with CONFIG_MAXSMP set.
4043 Format: { "0" | "1" }
4044 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4046 Note: increases power consumption, thus should only be
4047 enabled if running jitter sensitive (HPC/RT) workloads.
4049 security= [SECURITY] Choose a security module to enable at boot.
4050 If this boot parameter is not specified, only the first
4051 security module asking for security registration will be
4052 loaded. An invalid security module name will be treated
4053 as if no module has been chosen.
4055 selinux= [SELINUX] Disable or enable SELinux at boot time.
4056 Format: { "0" | "1" }
4057 See security/selinux/Kconfig help text.
4060 Default value is set via kernel config option.
4061 If enabled at boot time, /selinux/disable can be used
4062 later to disable prior to initial policy load.
4064 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4065 Format: { "0" | "1" }
4066 See security/apparmor/Kconfig help text
4069 Default value is set via kernel config option.
4071 serialnumber [BUGS=X86-32]
4074 Maximal number of shapers.
4082 Disable merging of slabs with similar size. May be
4083 necessary if there is some reason to distinguish
4084 allocs to different slabs, especially in hardened
4085 environments where the risk of heap overflows and
4086 layout control by attackers can usually be
4087 frustrated by disabling merging. This will reduce
4088 most of the exposure of a heap attack to a single
4089 cache (risks via metadata attacks are mostly
4090 unchanged). Debug options disable merging on their
4092 For more information see Documentation/vm/slub.rst.
4094 slab_max_order= [MM, SLAB]
4095 Determines the maximum allowed order for slabs.
4096 A high setting may cause OOMs due to memory
4097 fragmentation. Defaults to 1 for systems with
4098 more than 32MB of RAM, 0 otherwise.
4100 slub_debug[=options[,slabs]] [MM, SLUB]
4101 Enabling slub_debug allows one to determine the
4102 culprit if slab objects become corrupted. Enabling
4103 slub_debug can create guard zones around objects and
4104 may poison objects when not in use. Also tracks the
4105 last alloc / free. For more information see
4106 Documentation/vm/slub.rst.
4108 slub_memcg_sysfs= [MM, SLUB]
4109 Determines whether to enable sysfs directories for
4110 memory cgroup sub-caches. 1 to enable, 0 to disable.
4111 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4112 Enabling this can lead to a very high number of debug
4113 directories and files being created under
4116 slub_max_order= [MM, SLUB]
4117 Determines the maximum allowed order for slabs.
4118 A high setting may cause OOMs due to memory
4119 fragmentation. For more information see
4120 Documentation/vm/slub.rst.
4122 slub_min_objects= [MM, SLUB]
4123 The minimum number of objects per slab. SLUB will
4124 increase the slab order up to slub_max_order to
4125 generate a sufficiently large slab able to contain
4126 the number of objects indicated. The higher the number
4127 of objects the smaller the overhead of tracking slabs
4128 and the less frequently locks need to be acquired.
4129 For more information see Documentation/vm/slub.rst.
4131 slub_min_order= [MM, SLUB]
4132 Determines the minimum page order for slabs. Must be
4133 lower than slub_max_order.
4134 For more information see Documentation/vm/slub.rst.
4136 slub_nomerge [MM, SLUB]
4137 Same with slab_nomerge. This is supported for legacy.
4138 See slab_nomerge for more information.
4141 Format: <io1>[,<io2>[,...,<io8>]]
4143 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4144 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4145 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4146 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4147 smsc-ircc2.ircc_irq= [HW] IRQ line
4148 smsc-ircc2.ircc_dma= [HW] DMA channel
4149 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4150 0: Toshiba Satellite 1800 (GP data pin select)
4151 1: Fast pin select (default)
4154 smt [KNL,S390] Set the maximum number of threads (logical
4155 CPUs) to use per physical CPU on systems capable of
4156 symmetric multithreading (SMT). Will be capped to the
4157 actual hardware limit.
4159 Default: -1 (no limit)
4162 [KNL] Should the soft-lockup detector generate panics.
4165 A nonzero value instructs the soft-lockup detector
4166 to panic the machine when a soft-lockup occurs. This
4167 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4168 which is the respective build-time switch to that
4171 softlockup_all_cpu_backtrace=
4172 [KNL] Should the soft-lockup detector generate
4173 backtraces on all cpus.
4176 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4177 See Documentation/laptops/sonypi.txt
4179 spectre_v2= [X86] Control mitigation of Spectre variant 2
4180 (indirect branch speculation) vulnerability.
4182 on - unconditionally enable
4183 off - unconditionally disable
4184 auto - kernel detects whether your CPU model is
4187 Selecting 'on' will, and 'auto' may, choose a
4188 mitigation method at run time according to the
4189 CPU, the available microcode, the setting of the
4190 CONFIG_RETPOLINE configuration option, and the
4191 compiler with which the kernel was built.
4193 Specific mitigations can also be selected manually:
4195 retpoline - replace indirect branches
4196 retpoline,generic - google's original retpoline
4197 retpoline,amd - AMD-specific minimal thunk
4199 Not specifying this option is equivalent to
4202 spec_store_bypass_disable=
4203 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4204 (Speculative Store Bypass vulnerability)
4206 Certain CPUs are vulnerable to an exploit against a
4207 a common industry wide performance optimization known
4208 as "Speculative Store Bypass" in which recent stores
4209 to the same memory location may not be observed by
4210 later loads during speculative execution. The idea
4211 is that such stores are unlikely and that they can
4212 be detected prior to instruction retirement at the
4213 end of a particular speculation execution window.
4215 In vulnerable processors, the speculatively forwarded
4216 store can be used in a cache side channel attack, for
4217 example to read memory to which the attacker does not
4218 directly have access (e.g. inside sandboxed code).
4220 This parameter controls whether the Speculative Store
4221 Bypass optimization is used.
4223 On x86 the options are:
4225 on - Unconditionally disable Speculative Store Bypass
4226 off - Unconditionally enable Speculative Store Bypass
4227 auto - Kernel detects whether the CPU model contains an
4228 implementation of Speculative Store Bypass and
4229 picks the most appropriate mitigation. If the
4230 CPU is not vulnerable, "off" is selected. If the
4231 CPU is vulnerable the default mitigation is
4232 architecture and Kconfig dependent. See below.
4233 prctl - Control Speculative Store Bypass per thread
4234 via prctl. Speculative Store Bypass is enabled
4235 for a process by default. The state of the control
4236 is inherited on fork.
4237 seccomp - Same as "prctl" above, but all seccomp threads
4238 will disable SSB unless they explicitly opt out.
4240 Default mitigations:
4241 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4243 On powerpc the options are:
4245 on,auto - On Power8 and Power9 insert a store-forwarding
4246 barrier on kernel entry and exit. On Power7
4247 perform a software flush on kernel entry and
4251 Not specifying this option is equivalent to
4252 spec_store_bypass_disable=auto.
4254 spia_io_base= [HW,MTD]
4259 srcutree.counter_wrap_check [KNL]
4260 Specifies how frequently to check for
4261 grace-period sequence counter wrap for the
4262 srcu_data structure's ->srcu_gp_seq_needed field.
4263 The greater the number of bits set in this kernel
4264 parameter, the less frequently counter wrap will
4265 be checked for. Note that the bottom two bits
4268 srcutree.exp_holdoff [KNL]
4269 Specifies how many nanoseconds must elapse
4270 since the end of the last SRCU grace period for
4271 a given srcu_struct until the next normal SRCU
4272 grace period will be considered for automatic
4273 expediting. Set to zero to disable automatic
4277 Speculative Store Bypass Disable control
4279 On CPUs that are vulnerable to the Speculative
4280 Store Bypass vulnerability and offer a
4281 firmware based mitigation, this parameter
4282 indicates how the mitigation should be used:
4284 force-on: Unconditionally enable mitigation for
4285 for both kernel and userspace
4286 force-off: Unconditionally disable mitigation for
4287 for both kernel and userspace
4288 kernel: Always enable mitigation in the
4289 kernel, and offer a prctl interface
4290 to allow userspace to register its
4291 interest in being mitigated too.
4293 stack_guard_gap= [MM]
4294 override the default stack gap protection. The value
4295 is in page units and it defines how many pages prior
4296 to (for stacks growing down) resp. after (for stacks
4297 growing up) the main stack are reserved for no other
4298 mapping. Default value is 256 pages.
4301 Enabled the stack tracer on boot up.
4303 stacktrace_filter=[function-list]
4304 [FTRACE] Limit the functions that the stack tracer
4305 will trace at boot up. function-list is a comma separated
4306 list of functions. This list can be changed at run
4307 time by the stack_trace_filter file in the debugfs
4308 tracing directory. Note, this enables stack tracing
4309 and the stacktrace above is not needed.
4313 Set the STI (builtin display/keyboard on the HP-PARISC
4314 machines) console (graphic card) which should be used
4315 as the initial boot-console.
4316 See also comment in drivers/video/console/sticore.c.
4319 See comment in drivers/video/console/sticore.c.
4322 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4324 sunrpc.min_resvport=
4325 sunrpc.max_resvport=
4327 SunRPC servers often require that client requests
4328 originate from a privileged port (i.e. a port in the
4329 range 0 < portnr < 1024).
4330 An administrator who wishes to reserve some of these
4331 ports for other uses may adjust the range that the
4332 kernel's sunrpc client considers to be privileged
4333 using these two parameters to set the minimum and
4334 maximum port values.
4336 sunrpc.svc_rpc_per_connection_limit=
4338 Limit the number of requests that the server will
4339 process in parallel from a single connection.
4340 The default value is 0 (no limit).
4344 Control how the NFS server code allocates CPUs to
4345 service thread pools. Depending on how many NICs
4346 you have and where their interrupts are bound, this
4347 option will affect which CPUs will do NFS serving.
4348 Note: this parameter cannot be changed while the
4349 NFS server is running.
4351 auto the server chooses an appropriate mode
4352 automatically using heuristics
4353 global a single global pool contains all CPUs
4354 percpu one pool for each CPU
4355 pernode one pool for each NUMA node (equivalent
4356 to global on non-NUMA machines)
4358 sunrpc.tcp_slot_table_entries=
4359 sunrpc.udp_slot_table_entries=
4361 Sets the upper limit on the number of simultaneous
4362 RPC calls that can be sent from the client to a
4363 server. Increasing these values may allow you to
4364 improve throughput, but will also increase the
4365 amount of memory reserved for use by the client.
4367 suspend.pm_test_delay=
4369 Sets the number of seconds to remain in a suspend test
4370 mode before resuming the system (see
4371 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4372 is set. Default value is 5.
4375 [KNL] Enable accounting of swap in memory resource
4376 controller if no parameter or 1 is given or disable
4377 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4379 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4380 Format: { <int> | force | noforce }
4381 <int> -- Number of I/O TLB slabs
4382 force -- force using of bounce buffers even if they
4383 wouldn't be automatically used by the kernel
4384 noforce -- Never use bounce buffers (for debugging)
4388 sysfs.deprecated=0|1 [KNL]
4389 Enable/disable old style sysfs layout for old udev
4390 on older distributions. When this option is enabled
4391 very new udev will not work anymore. When this option
4392 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4393 in older udev will not work anymore.
4394 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4395 the kernel configuration.
4397 sysrq_always_enabled
4399 Ignore sysrq setting - this boot parameter will
4400 neutralize any effect of /proc/sys/kernel/sysrq.
4401 Useful for debugging.
4403 tcpmhash_entries= [KNL,NET]
4404 Set the number of tcp_metrics_hash slots.
4405 Default value is 8192 or 16384 depending on total
4406 ram pages. This is used to specify the TCP metrics
4407 cache size. See Documentation/networking/ip-sysctl.txt
4408 "tcp_no_metrics_save" section for more details.
4412 test_suspend= [SUSPEND][,N]
4413 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4414 standby suspend) or "freeze" (for suspend type freeze)
4415 as the system sleep state during system startup with
4416 the optional capability to repeat N number of times.
4417 The system is woken from this state using a
4418 wakeup-capable RTC alarm.
4420 thash_entries= [KNL,NET]
4421 Set number of hash buckets for TCP connection
4423 thermal.act= [HW,ACPI]
4424 -1: disable all active trip points in all thermal zones
4425 <degrees C>: override all lowest active trip points
4427 thermal.crt= [HW,ACPI]
4428 -1: disable all critical trip points in all thermal zones
4429 <degrees C>: override all critical trip points
4431 thermal.nocrt= [HW,ACPI]
4432 Set to disable actions on ACPI thermal zone
4433 critical and hot trip points.
4435 thermal.off= [HW,ACPI]
4436 1: disable ACPI thermal control
4438 thermal.psv= [HW,ACPI]
4439 -1: disable all passive trip points
4440 <degrees C>: override all passive trip points to this
4443 thermal.tzp= [HW,ACPI]
4444 Specify global default ACPI thermal zone polling rate
4445 <deci-seconds>: poll all this frequency
4446 0: no polling (default)
4449 Force threading of all interrupt handlers except those
4450 marked explicitly IRQF_NO_THREAD.
4453 Enable the Transcendent memory driver if built-in.
4455 tmem.cleancache=0|1 [KNL, XEN]
4456 Default is on (1). Disable the usage of the cleancache
4457 API to send anonymous pages to the hypervisor.
4459 tmem.frontswap=0|1 [KNL, XEN]
4460 Default is on (1). Disable the usage of the frontswap
4461 API to send swap pages to the hypervisor. If disabled
4462 the selfballooning and selfshrinking are force disabled.
4464 tmem.selfballooning=0|1 [KNL, XEN]
4465 Default is on (1). Disable the driving of swap pages
4468 tmem.selfshrinking=0|1 [KNL, XEN]
4469 Default is on (1). Partial swapoff that immediately
4470 transfers pages from Xen hypervisor back to the
4471 kernel based on different criteria.
4475 Specify if the kernel should make use of the cpu
4476 topology information if the hardware supports this.
4477 The scheduler will make use of this information and
4478 e.g. base its process migration decisions on it.
4481 topology_updates= [KNL, PPC, NUMA]
4483 Specify if the kernel should ignore (off)
4484 topology updates sent by the hypervisor to this
4489 tpm_suspend_pcr=[HW,TPM]
4490 Format: integer pcr id
4491 Specify that at suspend time, the tpm driver
4492 should extend the specified pcr with zeros,
4493 as a workaround for some chips which fail to
4494 flush the last written pcr on TPM_SaveState.
4495 This will guarantee that all the other pcrs
4498 trace_buf_size=nn[KMG]
4499 [FTRACE] will set tracing buffer size on each cpu.
4501 trace_event=[event-list]
4502 [FTRACE] Set and start specified trace events in order
4503 to facilitate early boot debugging. The event-list is a
4504 comma separated list of trace events to enable. See
4505 also Documentation/trace/events.rst
4507 trace_options=[option-list]
4508 [FTRACE] Enable or disable tracer options at boot.
4509 The option-list is a comma delimited list of options
4510 that can be enabled or disabled just as if you were
4511 to echo the option name into
4513 /sys/kernel/debug/tracing/trace_options
4515 For example, to enable stacktrace option (to dump the
4516 stack trace of each event), add to the command line:
4518 trace_options=stacktrace
4520 See also Documentation/trace/ftrace.rst "trace options"
4524 Have the tracepoints sent to printk as well as the
4525 tracing ring buffer. This is useful for early boot up
4526 where the system hangs or reboots and does not give the
4527 option for reading the tracing buffer or performing a
4528 ftrace_dump_on_oops.
4530 To turn off having tracepoints sent to printk,
4531 echo 0 > /proc/sys/kernel/tracepoint_printk
4532 Note, echoing 1 into this file without the
4533 tracepoint_printk kernel cmdline option has no effect.
4537 Having tracepoints sent to printk() and activating high
4538 frequency tracepoints such as irq or sched, can cause
4539 the system to live lock.
4542 [FTRACE] enable this option to disable tracing when a
4543 warning is hit. This turns off "tracing_on". Tracing can
4544 be enabled again by echoing '1' into the "tracing_on"
4545 file located in /sys/kernel/debug/tracing/
4547 This option is useful, as it disables the trace before
4548 the WARNING dump is called, which prevents the trace to
4549 be filled with content caused by the warning output.
4551 This option can also be set at run time via the sysctl
4552 option: kernel/traceoff_on_warning
4554 transparent_hugepage=
4556 Format: [always|madvise|never]
4557 Can be used to control the default behavior of the system
4558 with respect to transparent hugepages.
4559 See Documentation/admin-guide/mm/transhuge.rst
4562 tsc= Disable clocksource stability checks for TSC.
4564 [x86] reliable: mark tsc clocksource as reliable, this
4565 disables clocksource verification at runtime, as well
4566 as the stability checks done at bootup. Used to enable
4567 high-resolution timer mode on older hardware, and in
4568 virtualized environment.
4569 [x86] noirqtime: Do not use TSC to do irq accounting.
4570 Used to run time disable IRQ_TIME_ACCOUNTING on any
4571 platforms where RDTSC is slow and this accounting
4573 [x86] unstable: mark the TSC clocksource as unstable, this
4574 marks the TSC unconditionally unstable at bootup and
4575 avoids any further wobbles once the TSC watchdog notices.
4577 turbografx.map[2|3]= [HW,JOY]
4578 TurboGraFX parallel port interface
4580 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4581 See also Documentation/input/devices/joystick-parport.rst
4583 udbg-immortal [PPC] When debugging early kernel crashes that
4584 happen after console_init() and before a proper
4585 console driver takes over, this boot options might
4586 help "seeing" what's going on.
4588 uhash_entries= [KNL,NET]
4589 Set number of hash buckets for UDP/UDP-Lite connections
4592 [USB] Ignore overcurrent events (default N).
4593 Some badly-designed motherboards generate lots of
4594 bogus events, for ports that aren't wired to
4595 anything. Set this parameter to avoid log spamming.
4596 Note that genuine overcurrent events won't be
4600 [X86] Cause panic on unknown NMI.
4602 usbcore.authorized_default=
4603 [USB] Default USB device authorization:
4604 (default -1 = authorized except for wireless USB,
4605 0 = not authorized, 1 = authorized)
4607 usbcore.autosuspend=
4608 [USB] The autosuspend time delay (in seconds) used
4609 for newly-detected USB devices (default 2). This
4610 is the time required before an idle device will be
4611 autosuspended. Devices for which the delay is set
4612 to a negative value won't be autosuspended at all.
4614 usbcore.usbfs_snoop=
4615 [USB] Set to log all usbfs traffic (default 0 = off).
4617 usbcore.usbfs_snoop_max=
4618 [USB] Maximum number of bytes to snoop in each URB
4621 usbcore.blinkenlights=
4622 [USB] Set to cycle leds on hubs (default 0 = off).
4624 usbcore.old_scheme_first=
4625 [USB] Start with the old device initialization
4626 scheme (default 0 = off).
4628 usbcore.usbfs_memory_mb=
4629 [USB] Memory limit (in MB) for buffers allocated by
4630 usbfs (default = 16, 0 = max = 2047).
4632 usbcore.use_both_schemes=
4633 [USB] Try the other device initialization scheme
4634 if the first one fails (default 1 = enabled).
4636 usbcore.initial_descriptor_timeout=
4637 [USB] Specifies timeout for the initial 64-byte
4638 USB_REQ_GET_DESCRIPTOR request in milliseconds
4639 (default 5000 = 5.0 seconds).
4641 usbcore.nousb [USB] Disable the USB subsystem
4644 [USB] A list of quirk entries to augment the built-in
4645 usb core quirk list. List entries are separated by
4646 commas. Each entry has the form
4647 VendorID:ProductID:Flags. The IDs are 4-digit hex
4648 numbers and Flags is a set of letters. Each letter
4649 will change the built-in quirk; setting it if it is
4650 clear and clearing it if it is set. The letters have
4651 the following meanings:
4652 a = USB_QUIRK_STRING_FETCH_255 (string
4653 descriptors must not be fetched using
4655 b = USB_QUIRK_RESET_RESUME (device can't resume
4656 correctly so reset it instead);
4657 c = USB_QUIRK_NO_SET_INTF (device can't handle
4658 Set-Interface requests);
4659 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4660 handle its Configuration or Interface
4662 e = USB_QUIRK_RESET (device can't be reset
4663 (e.g morph devices), don't use reset);
4664 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4665 more interface descriptions than the
4666 bNumInterfaces count, and can't handle
4667 talking to these interfaces);
4668 g = USB_QUIRK_DELAY_INIT (device needs a pause
4669 during initialization, after we read
4670 the device descriptor);
4671 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4672 high speed and super speed interrupt
4673 endpoints, the USB 2.0 and USB 3.0 spec
4674 require the interval in microframes (1
4675 microframe = 125 microseconds) to be
4676 calculated as interval = 2 ^
4678 Devices with this quirk report their
4679 bInterval as the result of this
4680 calculation instead of the exponent
4681 variable used in the calculation);
4682 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4683 handle device_qualifier descriptor
4685 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4686 generates spurious wakeup, ignore
4687 remote wakeup capability);
4688 k = USB_QUIRK_NO_LPM (device can't handle Link
4690 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4691 (Device reports its bInterval as linear
4692 frames instead of the USB 2.0
4694 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4695 to be disconnected before suspend to
4696 prevent spurious wakeup);
4697 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4698 pause after every control message);
4699 Example: quirks=0781:5580:bk,0a5c:5834:gij
4702 [USBHID] The interval which mice are to be polled at.
4705 [USBHID] The interval which joysticks are to be polled at.
4708 [USBHID] The interval which keyboards are to be polled at.
4710 usb-storage.delay_use=
4711 [UMS] The delay in seconds before a new device is
4712 scanned for Logical Units (default 1).
4715 [UMS] A list of quirks entries to supplement or
4716 override the built-in unusual_devs list. List
4717 entries are separated by commas. Each entry has
4718 the form VID:PID:Flags where VID and PID are Vendor
4719 and Product ID values (4-digit hex numbers) and
4720 Flags is a set of characters, each corresponding
4721 to a common usb-storage quirk flag as follows:
4722 a = SANE_SENSE (collect more than 18 bytes
4724 b = BAD_SENSE (don't collect more than 18
4725 bytes of sense data);
4726 c = FIX_CAPACITY (decrease the reported
4727 device capacity by one sector);
4728 d = NO_READ_DISC_INFO (don't use
4729 READ_DISC_INFO command);
4730 e = NO_READ_CAPACITY_16 (don't use
4731 READ_CAPACITY_16 command);
4732 f = NO_REPORT_OPCODES (don't use report opcodes
4734 g = MAX_SECTORS_240 (don't transfer more than
4735 240 sectors at a time, uas only);
4736 h = CAPACITY_HEURISTICS (decrease the
4737 reported device capacity by one
4738 sector if the number is odd);
4739 i = IGNORE_DEVICE (don't bind to this
4741 j = NO_REPORT_LUNS (don't use report luns
4743 l = NOT_LOCKABLE (don't try to lock and
4744 unlock ejectable media);
4745 m = MAX_SECTORS_64 (don't transfer more
4746 than 64 sectors = 32 KB at a time);
4747 n = INITIAL_READ10 (force a retry of the
4748 initial READ(10) command);
4749 o = CAPACITY_OK (accept the capacity
4750 reported by the device);
4751 p = WRITE_CACHE (the device cache is ON
4753 r = IGNORE_RESIDUE (the device reports
4754 bogus residue values);
4755 s = SINGLE_LUN (the device has only one
4757 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4758 commands, uas only);
4759 u = IGNORE_UAS (don't bind to the uas driver);
4760 w = NO_WP_DETECT (don't test whether the
4761 medium is write-protected).
4762 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4763 even if the device claims no cache)
4764 Example: quirks=0419:aaf5:rl,0421:0433:rc
4766 user_debug= [KNL,ARM]
4768 See arch/arm/Kconfig.debug help text.
4769 1 - undefined instruction events
4771 4 - invalid data aborts
4774 Example: user_debug=31
4777 [X86] Flags controlling user PTE allocations.
4779 nohigh = do not allocate PTE pages in
4780 HIGHMEM regardless of setting
4784 On X86_32, this is an alias for vdso32=. Otherwise:
4786 vdso=1: enable VDSO (the default)
4787 vdso=0: disable VDSO mapping
4789 vdso32= [X86] Control the 32-bit vDSO
4790 vdso32=1: enable 32-bit VDSO
4791 vdso32=0 or vdso32=2: disable 32-bit VDSO
4793 See the help text for CONFIG_COMPAT_VDSO for more
4794 details. If CONFIG_COMPAT_VDSO is set, the default is
4795 vdso32=0; otherwise, the default is vdso32=1.
4797 For compatibility with older kernels, vdso32=2 is an
4800 Try vdso32=0 if you encounter an error that says:
4801 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4804 vector=percpu: enable percpu vector domain
4806 video= [FB] Frame buffer configuration
4807 See Documentation/fb/modedb.txt.
4809 video.brightness_switch_enabled= [0,1]
4810 If set to 1, on receiving an ACPI notify event
4811 generated by hotkey, video driver will adjust brightness
4812 level and then send out the event to user space through
4813 the allocated input device; If set to 0, video driver
4814 will only send out the event without touching backlight
4819 [VMMIO] Memory mapped virtio (platform) device.
4821 <size>@<baseaddr>:<irq>[:<id>]
4823 <size> := size (can use standard suffixes
4825 <baseaddr> := physical base address
4826 <irq> := interrupt number (as passed to
4828 <id> := (optional) platform device id
4830 virtio_mmio.device=1K@0x100b0000:48:7
4832 Can be used multiple times for multiple devices.
4834 vga= [BOOT,X86-32] Select a particular video mode
4835 See Documentation/x86/boot.txt and
4836 Documentation/svga.txt.
4837 Use vga=ask for menu.
4838 This is actually a boot loader parameter; the value is
4839 passed to the kernel using a special protocol.
4841 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4842 size of <nn>. This can be used to increase the
4843 minimum size (128MB on x86). It can also be used to
4844 decrease the size and leave more room for directly
4847 vmcp_cma=nn[MG] [KNL,S390]
4848 Sets the memory size reserved for contiguous memory
4849 allocations for the vmcp device driver.
4851 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4854 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4857 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4861 Controls the behavior of vsyscalls (i.e. calls to
4862 fixed addresses of 0xffffffffff600x00 from legacy
4863 code). Most statically-linked binaries and older
4864 versions of glibc use these calls. Because these
4865 functions are at fixed addresses, they make nice
4866 targets for exploits that can control RIP.
4868 emulate [default] Vsyscalls turn into traps and are
4869 emulated reasonably safely.
4871 native Vsyscalls are native syscall instructions.
4872 This is a little bit faster than trapping
4873 and makes a few dynamic recompilers work
4874 better than they would in emulation mode.
4875 It also makes exploits much easier to write.
4877 none Vsyscalls don't work at all. This makes
4878 them quite hard to use for exploits but
4879 might break your system.
4881 vt.color= [VT] Default text color.
4882 Format: 0xYX, X = foreground, Y = background.
4883 Default: 0x07 = light gray on black.
4885 vt.cur_default= [VT] Default cursor shape.
4886 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4887 the parameters of the <Esc>[?A;B;Cc escape sequence;
4888 see VGA-softcursor.txt. Default: 2 = underline.
4890 vt.default_blu= [VT]
4891 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4892 Change the default blue palette of the console.
4893 This is a 16-member array composed of values
4896 vt.default_grn= [VT]
4897 Format: <green0>,<green1>,<green2>,...,<green15>
4898 Change the default green palette of the console.
4899 This is a 16-member array composed of values
4902 vt.default_red= [VT]
4903 Format: <red0>,<red1>,<red2>,...,<red15>
4904 Change the default red palette of the console.
4905 This is a 16-member array composed of values
4911 Set system-wide default UTF-8 mode for all tty's.
4912 Default is 1, i.e. UTF-8 mode is enabled for all
4913 newly opened terminals.
4915 vt.global_cursor_default=
4918 Set system-wide default for whether a cursor
4919 is shown on new VTs. Default is -1,
4920 i.e. cursors will be created by default unless
4921 overridden by individual drivers. 0 will hide
4922 cursors, 1 will display them.
4924 vt.italic= [VT] Default color for italic text; 0-15.
4927 vt.underline= [VT] Default color for underlined text; 0-15.
4930 watchdog timers [HW,WDT] For information on watchdog timers,
4931 see Documentation/watchdog/watchdog-parameters.txt
4932 or other driver-specific files in the
4933 Documentation/watchdog/ directory.
4935 workqueue.watchdog_thresh=
4936 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4937 warn stall conditions and dump internal state to
4938 help debugging. 0 disables workqueue stall
4939 detection; otherwise, it's the stall threshold
4940 duration in seconds. The default value is 30 and
4941 it can be updated at runtime by writing to the
4942 corresponding sysfs file.
4944 workqueue.disable_numa
4945 By default, all work items queued to unbound
4946 workqueues are affine to the NUMA nodes they're
4947 issued on, which results in better behavior in
4948 general. If NUMA affinity needs to be disabled for
4949 whatever reason, this option can be used. Note
4950 that this also can be controlled per-workqueue for
4951 workqueues visible under /sys/bus/workqueue/.
4953 workqueue.power_efficient
4954 Per-cpu workqueues are generally preferred because
4955 they show better performance thanks to cache
4956 locality; unfortunately, per-cpu workqueues tend to
4957 be more power hungry than unbound workqueues.
4959 Enabling this makes the per-cpu workqueues which
4960 were observed to contribute significantly to power
4961 consumption unbound, leading to measurably lower
4962 power usage at the cost of small performance
4965 The default value of this parameter is determined by
4966 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4968 workqueue.debug_force_rr_cpu
4969 Workqueue used to implicitly guarantee that work
4970 items queued without explicit CPU specified are put
4971 on the local CPU. This guarantee is no longer true
4972 and while local CPU is still preferred work items
4973 may be put on foreign CPUs. This debug option
4974 forces round-robin CPU selection to flush out
4975 usages which depend on the now broken guarantee.
4976 When enabled, memory and cache locality will be
4979 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4980 default x2apic cluster mode on platforms
4983 x86_intel_mid_timer= [X86-32,APBT]
4984 Choose timer option for x86 Intel MID platform.
4985 Two valid options are apbt timer only and lapic timer
4986 plus one apbt timer for broadcast timer.
4987 x86_intel_mid_timer=apbt_only | lapic_and_apbt
4989 xen_512gb_limit [KNL,X86-64,XEN]
4990 Restricts the kernel running paravirtualized under Xen
4991 to use only up to 512 GB of RAM. The reason to do so is
4992 crash analysis tools and Xen tools for doing domain
4993 save/restore/migration must be enabled to handle larger
4996 xen_emul_unplug= [HW,X86,XEN]
4997 Unplug Xen emulated devices
4998 Format: [unplug0,][unplug1]
4999 ide-disks -- unplug primary master IDE devices
5000 aux-ide-disks -- unplug non-primary-master IDE devices
5001 nics -- unplug network devices
5002 all -- unplug all emulated devices (NICs and IDE disks)
5003 unnecessary -- unplugging emulated devices is
5004 unnecessary even if the host did not respond to
5006 never -- do not unplug even if version check succeeds
5008 xen_nopvspin [X86,XEN]
5009 Disables the ticketlock slowpath using Xen PV
5013 Disables the PV optimizations forcing the HVM guest to
5014 run as generic HVM guest with no PV drivers.
5016 xen_scrub_pages= [XEN]
5017 Boolean option to control scrubbing pages before giving them back
5018 to Xen, for use by other domains. Can be also changed at runtime
5019 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5020 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5022 xirc2ps_cs= [NET,PCMCIA]
5024 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5026 xhci-hcd.quirks [USB,KNL]
5027 A hex value specifying bitmask with supplemental xhci
5028 host controller quirks. Meaning of each bit can be
5029 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob