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diff --git a/Documentation/admin-guide/kernel-parameters.rst b/Documentation/admin-guide/kernel-parameters.rst new file mode 100644 index 000000000000..b0804273b6e3 --- /dev/null +++ b/Documentation/admin-guide/kernel-parameters.rst @@ -0,0 +1,4577 @@ +Kernel Parameters +~~~~~~~~~~~~~~~~~ + +The following is a consolidated list of the kernel parameters as +implemented by the __setup(), core_param() and module_param() macros +and sorted into English Dictionary order (defined as ignoring all +punctuation and sorting digits before letters in a case insensitive +manner), and with descriptions where known. + +The kernel parses parameters from the kernel command line up to "--"; +if it doesn't recognize a parameter and it doesn't contain a '.', the +parameter gets passed to init: parameters with '=' go into init's +environment, others are passed as command line arguments to init. +Everything after "--" is passed as an argument to init. + +Module parameters can be specified in two ways: via the kernel command +line with a module name prefix, or via modprobe, e.g.:: + + (kernel command line) usbcore.blinkenlights=1 + (modprobe command line) modprobe usbcore blinkenlights=1 + +Parameters for modules which are built into the kernel need to be +specified on the kernel command line. modprobe looks through the +kernel command line (/proc/cmdline) and collects module parameters +when it loads a module, so the kernel command line can be used for +loadable modules too. + +Hyphens (dashes) and underscores are equivalent in parameter names, so:: + + log_buf_len=1M print-fatal-signals=1 + +can also be entered as:: + + log-buf-len=1M print_fatal_signals=1 + +Double-quotes can be used to protect spaces in values, e.g.:: + + param="spaces in here" + +cpu lists: +---------- + +Some kernel parameters take a list of CPUs as a value, e.g. isolcpus, +nohz_full, irqaffinity, rcu_nocbs. The format of this list is: + + <cpu number>,...,<cpu number> + +or + + <cpu number>-<cpu number> + (must be a positive range in ascending order) + +or a mixture + +<cpu number>,...,<cpu number>-<cpu number> + +Note that for the special case of a range one can split the range into equal +sized groups and for each group use some amount from the beginning of that +group: + + <cpu number>-cpu number>:<used size>/<group size> + +For example one can add to the command line following parameter: + + isolcpus=1,2,10-20,100-2000:2/25 + +where the final item represents CPUs 100,101,125,126,150,151,... + + + +This document may not be entirely up to date and comprehensive. The command +"modinfo -p ${modulename}" shows a current list of all parameters of a loadable +module. Loadable modules, after being loaded into the running kernel, also +reveal their parameters in /sys/module/${modulename}/parameters/. Some of these +parameters may be changed at runtime by the command +``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``. + +The parameters listed below are only valid if certain kernel build options were +enabled and if respective hardware is present. The text in square brackets at +the beginning of each description states the restrictions within which a +parameter is applicable:: + + ACPI ACPI support is enabled. + AGP AGP (Accelerated Graphics Port) is enabled. + ALSA ALSA sound support is enabled. + APIC APIC support is enabled. + APM Advanced Power Management support is enabled. + ARM ARM architecture is enabled. + AVR32 AVR32 architecture is enabled. + AX25 Appropriate AX.25 support is enabled. + BLACKFIN Blackfin architecture is enabled. + CLK Common clock infrastructure is enabled. + CMA Contiguous Memory Area support is enabled. + DRM Direct Rendering Management support is enabled. + DYNAMIC_DEBUG Build in debug messages and enable them at runtime + EDD BIOS Enhanced Disk Drive Services (EDD) is enabled + EFI EFI Partitioning (GPT) is enabled + EIDE EIDE/ATAPI support is enabled. + EVM Extended Verification Module + FB The frame buffer device is enabled. + FTRACE Function tracing enabled. + GCOV GCOV profiling is enabled. + HW Appropriate hardware is enabled. + IA-64 IA-64 architecture is enabled. + IMA Integrity measurement architecture is enabled. + IOSCHED More than one I/O scheduler is enabled. + IP_PNP IP DHCP, BOOTP, or RARP is enabled. + IPV6 IPv6 support is enabled. + ISAPNP ISA PnP code is enabled. + ISDN Appropriate ISDN support is enabled. + JOY Appropriate joystick support is enabled. + KGDB Kernel debugger support is enabled. + KVM Kernel Virtual Machine support is enabled. + LIBATA Libata driver is enabled + LP Printer support is enabled. + LOOP Loopback device support is enabled. + M68k M68k architecture is enabled. + These options have more detailed description inside of + Documentation/m68k/kernel-options.txt. + MDA MDA console support is enabled. + MIPS MIPS architecture is enabled. + MOUSE Appropriate mouse support is enabled. + MSI Message Signaled Interrupts (PCI). + MTD MTD (Memory Technology Device) support is enabled. + NET Appropriate network support is enabled. + NUMA NUMA support is enabled. + NFS Appropriate NFS support is enabled. + OSS OSS sound support is enabled. + PV_OPS A paravirtualized kernel is enabled. + PARIDE The ParIDE (parallel port IDE) subsystem is enabled. + PARISC The PA-RISC architecture is enabled. + PCI PCI bus support is enabled. + PCIE PCI Express support is enabled. + PCMCIA The PCMCIA subsystem is enabled. + PNP Plug & Play support is enabled. + PPC PowerPC architecture is enabled. + PPT Parallel port support is enabled. + PS2 Appropriate PS/2 support is enabled. + RAM RAM disk support is enabled. + S390 S390 architecture is enabled. + SCSI Appropriate SCSI support is enabled. + A lot of drivers have their options described inside + the Documentation/scsi/ sub-directory. + SECURITY Different security models are enabled. + SELINUX SELinux support is enabled. + APPARMOR AppArmor support is enabled. + SERIAL Serial support is enabled. + SH SuperH architecture is enabled. + SMP The kernel is an SMP kernel. + SPARC Sparc architecture is enabled. + SWSUSP Software suspend (hibernation) is enabled. + SUSPEND System suspend states are enabled. + TPM TPM drivers are enabled. + TS Appropriate touchscreen support is enabled. + UMS USB Mass Storage support is enabled. + USB USB support is enabled. + USBHID USB Human Interface Device support is enabled. + V4L Video For Linux support is enabled. + VMMIO Driver for memory mapped virtio devices is enabled. + VGA The VGA console has been enabled. + VT Virtual terminal support is enabled. + WDT Watchdog support is enabled. + XT IBM PC/XT MFM hard disk support is enabled. + X86-32 X86-32, aka i386 architecture is enabled. + X86-64 X86-64 architecture is enabled. + More X86-64 boot options can be found in + Documentation/x86/x86_64/boot-options.txt . + X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) + X86_UV SGI UV support is enabled. + XEN Xen support is enabled + +In addition, the following text indicates that the option:: + + BUGS= Relates to possible processor bugs on the said processor. + KNL Is a kernel start-up parameter. + BOOT Is a boot loader parameter. + +Parameters denoted with BOOT are actually interpreted by the boot +loader, and have no meaning to the kernel directly. +Do not modify the syntax of boot loader parameters without extreme +need or coordination with <Documentation/x86/boot.txt>. + +There are also arch-specific kernel-parameters not documented here. +See for example <Documentation/x86/x86_64/boot-options.txt>. + +Note that ALL kernel parameters listed below are CASE SENSITIVE, and that +a trailing = on the name of any parameter states that that parameter will +be entered as an environment variable, whereas its absence indicates that +it will appear as a kernel argument readable via /proc/cmdline by programs +running once the system is up. + +The number of kernel parameters is not limited, but the length of the +complete command line (parameters including spaces etc.) is limited to +a fixed number of characters. This limit depends on the architecture +and is between 256 and 4096 characters. It is defined in the file +./include/asm/setup.h as COMMAND_LINE_SIZE. + +Finally, the [KMG] suffix is commonly described after a number of kernel +parameter values. These 'K', 'M', and 'G' letters represent the _binary_ +multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30 +bytes respectively. Such letter suffixes can also be entirely omitted:: + + + acpi= [HW,ACPI,X86,ARM64] + Advanced Configuration and Power Interface + Format: { force | on | off | strict | noirq | rsdt | + copy_dsdt } + force -- enable ACPI if default was off + on -- enable ACPI but allow fallback to DT [arm64] + off -- disable ACPI if default was on + noirq -- do not use ACPI for IRQ routing + strict -- Be less tolerant of platforms that are not + strictly ACPI specification compliant. + rsdt -- prefer RSDT over (default) XSDT + copy_dsdt -- copy DSDT to memory + For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" + are available + + See also Documentation/power/runtime_pm.txt, pci=noacpi + + acpi_apic_instance= [ACPI, IOAPIC] + Format: <int> + 2: use 2nd APIC table, if available + 1,0: use 1st APIC table + default: 0 + + acpi_backlight= [HW,ACPI] + acpi_backlight=vendor + acpi_backlight=video + If set to vendor, prefer vendor specific driver + (e.g. thinkpad_acpi, sony_acpi, etc.) instead + of the ACPI video.ko driver. + + acpi_force_32bit_fadt_addr + force FADT to use 32 bit addresses rather than the + 64 bit X_* addresses. Some firmware have broken 64 + bit addresses for force ACPI ignore these and use + the older legacy 32 bit addresses. + + acpica_no_return_repair [HW, ACPI] + Disable AML predefined validation mechanism + This mechanism can repair the evaluation result to make + the return objects more ACPI specification compliant. + This option is useful for developers to identify the + root cause of an AML interpreter issue when the issue + has something to do with the repair mechanism. + + acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] + acpi.debug_level= [HW,ACPI,ACPI_DEBUG] + Format: <int> + CONFIG_ACPI_DEBUG must be enabled to produce any ACPI + debug output. Bits in debug_layer correspond to a + _COMPONENT in an ACPI source file, e.g., + #define _COMPONENT ACPI_PCI_COMPONENT + Bits in debug_level correspond to a level in + ACPI_DEBUG_PRINT statements, e.g., + ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... + The debug_level mask defaults to "info". See + Documentation/acpi/debug.txt for more information about + debug layers and levels. + + Enable processor driver info messages: + acpi.debug_layer=0x20000000 + Enable PCI/PCI interrupt routing info messages: + acpi.debug_layer=0x400000 + Enable AML "Debug" output, i.e., stores to the Debug + object while interpreting AML: + acpi.debug_layer=0xffffffff acpi.debug_level=0x2 + Enable all messages related to ACPI hardware: + acpi.debug_layer=0x2 acpi.debug_level=0xffffffff + + Some values produce so much output that the system is + unusable. The "log_buf_len" parameter may be useful + if you need to capture more output. + + acpi_enforce_resources= [ACPI] + { strict | lax | no } + Check for resource conflicts between native drivers + and ACPI OperationRegions (SystemIO and SystemMemory + only). IO ports and memory declared in ACPI might be + used by the ACPI subsystem in arbitrary AML code and + can interfere with legacy drivers. + strict (default): access to resources claimed by ACPI + is denied; legacy drivers trying to access reserved + resources will fail to bind to device using them. + lax: access to resources claimed by ACPI is allowed; + legacy drivers trying to access reserved resources + will bind successfully but a warning message is logged. + no: ACPI OperationRegions are not marked as reserved, + no further checks are performed. + + acpi_force_table_verification [HW,ACPI] + Enable table checksum verification during early stage. + By default, this is disabled due to x86 early mapping + size limitation. + + acpi_irq_balance [HW,ACPI] + ACPI will balance active IRQs + default in APIC mode + + acpi_irq_nobalance [HW,ACPI] + ACPI will not move active IRQs (default) + default in PIC mode + + acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA + Format: <irq>,<irq>... + + acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for + use by PCI + Format: <irq>,<irq>... + + acpi_no_auto_serialize [HW,ACPI] + Disable auto-serialization of AML methods + AML control methods that contain the opcodes to create + named objects will be marked as "Serialized" by the + auto-serialization feature. + This feature is enabled by default. + This option allows to turn off the feature. + + acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump + kernels. + + acpi_no_static_ssdt [HW,ACPI] + Disable installation of static SSDTs at early boot time + By default, SSDTs contained in the RSDT/XSDT will be + installed automatically and they will appear under + /sys/firmware/acpi/tables. + This option turns off this feature. + Note that specifying this option does not affect + dynamic table installation which will install SSDT + tables to /sys/firmware/acpi/tables/dynamic. + + acpi_rsdp= [ACPI,EFI,KEXEC] + Pass the RSDP address to the kernel, mostly used + on machines running EFI runtime service to boot the + second kernel for kdump. + + acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS + Format: To spoof as Windows 98: ="Microsoft Windows" + + acpi_rev_override [ACPI] Override the _REV object to return 5 (instead + of 2 which is mandated by ACPI 6) as the supported ACPI + specification revision (when using this switch, it may + be necessary to carry out a cold reboot _twice_ in a + row to make it take effect on the platform firmware). + + acpi_osi= [HW,ACPI] Modify list of supported OS interface strings + acpi_osi="string1" # add string1 + acpi_osi="!string2" # remove string2 + acpi_osi=!* # remove all strings + acpi_osi=! # disable all built-in OS vendor + strings + acpi_osi=!! # enable all built-in OS vendor + strings + acpi_osi= # disable all strings + + 'acpi_osi=!' can be used in combination with single or + multiple 'acpi_osi="string1"' to support specific OS + vendor string(s). Note that such command can only + affect the default state of the OS vendor strings, thus + it cannot affect the default state of the feature group + strings and the current state of the OS vendor strings, + specifying it multiple times through kernel command line + is meaningless. This command is useful when one do not + care about the state of the feature group strings which + should be controlled by the OSPM. + Examples: + 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent + to 'acpi_osi="Windows 2000" acpi_osi=!', they all + can make '_OSI("Windows 2000")' TRUE. + + 'acpi_osi=' cannot be used in combination with other + 'acpi_osi=' command lines, the _OSI method will not + exist in the ACPI namespace. NOTE that such command can + only affect the _OSI support state, thus specifying it + multiple times through kernel command line is also + meaningless. + Examples: + 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' + FALSE. + + 'acpi_osi=!*' can be used in combination with single or + multiple 'acpi_osi="string1"' to support specific + string(s). Note that such command can affect the + current state of both the OS vendor strings and the + feature group strings, thus specifying it multiple times + through kernel command line is meaningful. But it may + still not able to affect the final state of a string if + there are quirks related to this string. This command + is useful when one want to control the state of the + feature group strings to debug BIOS issues related to + the OSPM features. + Examples: + 1. 'acpi_osi="Module Device" acpi_osi=!*' can make + '_OSI("Module Device")' FALSE. + 2. 'acpi_osi=!* acpi_osi="Module Device"' can make + '_OSI("Module Device")' TRUE. + 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is + equivalent to + 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' + and + 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', + they all will make '_OSI("Windows 2000")' TRUE. + + acpi_pm_good [X86] + Override the pmtimer bug detection: force the kernel + to assume that this machine's pmtimer latches its value + and always returns good values. + + acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode + Format: { level | edge | high | low } + + acpi_skip_timer_override [HW,ACPI] + Recognize and ignore IRQ0/pin2 Interrupt Override. + For broken nForce2 BIOS resulting in XT-PIC timer. + + acpi_sleep= [HW,ACPI] Sleep options + Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, + old_ordering, nonvs, sci_force_enable } + See Documentation/power/video.txt for information on + s3_bios and s3_mode. + s3_beep is for debugging; it makes the PC's speaker beep + as soon as the kernel's real-mode entry point is called. + s4_nohwsig prevents ACPI hardware signature from being + used during resume from hibernation. + old_ordering causes the ACPI 1.0 ordering of the _PTS + control method, with respect to putting devices into + low power states, to be enforced (the ACPI 2.0 ordering + of _PTS is used by default). + nonvs prevents the kernel from saving/restoring the + ACPI NVS memory during suspend/hibernation and resume. + sci_force_enable causes the kernel to set SCI_EN directly + on resume from S1/S3 (which is against the ACPI spec, + but some broken systems don't work without it). + + acpi_use_timer_override [HW,ACPI] + Use timer override. For some broken Nvidia NF5 boards + that require a timer override, but don't have HPET + + add_efi_memmap [EFI; X86] Include EFI memory map in + kernel's map of available physical RAM. + + agp= [AGP] + { off | try_unsupported } + off: disable AGP support + try_unsupported: try to drive unsupported chipsets + (may crash computer or cause data corruption) + + ALSA [HW,ALSA] + See Documentation/sound/alsa/alsa-parameters.txt + + alignment= [KNL,ARM] + Allow the default userspace alignment fault handler + behaviour to be specified. Bit 0 enables warnings, + bit 1 enables fixups, and bit 2 sends a segfault. + + align_va_addr= [X86-64] + Align virtual addresses by clearing slice [14:12] when + allocating a VMA at process creation time. This option + gives you up to 3% performance improvement on AMD F15h + machines (where it is enabled by default) for a + CPU-intensive style benchmark, and it can vary highly in + a microbenchmark depending on workload and compiler. + + 32: only for 32-bit processes + 64: only for 64-bit processes + on: enable for both 32- and 64-bit processes + off: disable for both 32- and 64-bit processes + + alloc_snapshot [FTRACE] + Allocate the ftrace snapshot buffer on boot up when the + main buffer is allocated. This is handy if debugging + and you need to use tracing_snapshot() on boot up, and + do not want to use tracing_snapshot_alloc() as it needs + to be done where GFP_KERNEL allocations are allowed. + + amd_iommu= [HW,X86-64] + Pass parameters to the AMD IOMMU driver in the system. + Possible values are: + fullflush - enable flushing of IO/TLB entries when + they are unmapped. Otherwise they are + flushed before they will be reused, which + is a lot of faster + off - do not initialize any AMD IOMMU found in + the system + force_isolation - Force device isolation for all + devices. The IOMMU driver is not + allowed anymore to lift isolation + requirements as needed. This option + does not override iommu=pt + + amd_iommu_dump= [HW,X86-64] + Enable AMD IOMMU driver option to dump the ACPI table + for AMD IOMMU. With this option enabled, AMD IOMMU + driver will print ACPI tables for AMD IOMMU during + IOMMU initialization. + + amd_iommu_intr= [HW,X86-64] + Specifies one of the following AMD IOMMU interrupt + remapping modes: + legacy - Use legacy interrupt remapping mode. + vapic - Use virtual APIC mode, which allows IOMMU + to inject interrupts directly into guest. + This mode requires kvm-amd.avic=1. + (Default when IOMMU HW support is present.) + + amijoy.map= [HW,JOY] Amiga joystick support + Map of devices attached to JOY0DAT and JOY1DAT + Format: <a>,<b> + See also Documentation/input/joystick.txt + + analog.map= [HW,JOY] Analog joystick and gamepad support + Specifies type or capabilities of an analog joystick + connected to one of 16 gameports + Format: <type1>,<type2>,..<type16> + + apc= [HW,SPARC] + Power management functions (SPARCstation-4/5 + deriv.) + Format: noidle + Disable APC CPU standby support. SPARCstation-Fox does + not play well with APC CPU idle - disable it if you have + APC and your system crashes randomly. + + apic= [APIC,X86-32] Advanced Programmable Interrupt Controller + Change the output verbosity whilst booting + Format: { quiet (default) | verbose | debug } + Change the amount of debugging information output + when initialising the APIC and IO-APIC components. + + apic_extnmi= [APIC,X86] External NMI delivery setting + Format: { bsp (default) | all | none } + bsp: External NMI is delivered only to CPU 0 + all: External NMIs are broadcast to all CPUs as a + backup of CPU 0 + none: External NMI is masked for all CPUs. This is + useful so that a dump capture kernel won't be + shot down by NMI + + autoconf= [IPV6] + See Documentation/networking/ipv6.txt. + + show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller + Limit apic dumping. The parameter defines the maximal + number of local apics being dumped. Also it is possible + to set it to "all" by meaning -- no limit here. + Format: { 1 (default) | 2 | ... | all }. + The parameter valid if only apic=debug or + apic=verbose is specified. + Example: apic=debug show_lapic=all + + apm= [APM] Advanced Power Management + See header of arch/x86/kernel/apm_32.c. + + arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards + Format: <io>,<irq>,<nodeID> + + ataflop= [HW,M68k] + + atarimouse= [HW,MOUSE] Atari Mouse + + atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, + EzKey and similar keyboards + + atkbd.reset= [HW] Reset keyboard during initialization + + atkbd.set= [HW] Select keyboard code set + Format: <int> (2 = AT (default), 3 = PS/2) + + atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar + keyboards + + atkbd.softraw= [HW] Choose between synthetic and real raw mode + Format: <bool> (0 = real, 1 = synthetic (default)) + + atkbd.softrepeat= [HW] + Use software keyboard repeat + + audit= [KNL] Enable the audit sub-system + Format: { "0" | "1" } (0 = disabled, 1 = enabled) + 0 - kernel audit is disabled and can not be enabled + until the next reboot + unset - kernel audit is initialized but disabled and + will be fully enabled by the userspace auditd. + 1 - kernel audit is initialized and partially enabled, + storing at most audit_backlog_limit messages in + RAM until it is fully enabled by the userspace + auditd. + Default: unset + + audit_backlog_limit= [KNL] Set the audit queue size limit. + Format: <int> (must be >=0) + Default: 64 + + bau= [X86_UV] Enable the BAU on SGI UV. The default + behavior is to disable the BAU (i.e. bau=0). + Format: { "0" | "1" } + 0 - Disable the BAU. + 1 - Enable the BAU. + unset - Disable the BAU. + + baycom_epp= [HW,AX25] + Format: <io>,<mode> + + baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem + Format: <io>,<mode> + See header of drivers/net/hamradio/baycom_par.c. + + baycom_ser_fdx= [HW,AX25] + BayCom Serial Port AX.25 Modem (Full Duplex Mode) + Format: <io>,<irq>,<mode>[,<baud>] + See header of drivers/net/hamradio/baycom_ser_fdx.c. + + baycom_ser_hdx= [HW,AX25] + BayCom Serial Port AX.25 Modem (Half Duplex Mode) + Format: <io>,<irq>,<mode> + See header of drivers/net/hamradio/baycom_ser_hdx.c. + + blkdevparts= Manual partition parsing of block device(s) for + embedded devices based on command line input. + See Documentation/block/cmdline-partition.txt + + boot_delay= Milliseconds to delay each printk during boot. + Values larger than 10 seconds (10000) are changed to + no delay (0). + Format: integer + + bootmem_debug [KNL] Enable bootmem allocator debug messages. + + bert_disable [ACPI] + Disable BERT OS support on buggy BIOSes. + + bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) + bttv.radio= Most important insmod options are available as + kernel args too. + bttv.pll= See Documentation/video4linux/bttv/Insmod-options + bttv.tuner= + + bulk_remove=off [PPC] This parameter disables the use of the pSeries + firmware feature for flushing multiple hpte entries + at a time. + + c101= [NET] Moxa C101 synchronous serial card + + cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. + Sometimes CPU hardware bugs make them report the cache + size incorrectly. The kernel will attempt work arounds + to fix known problems, but for some CPUs it is not + possible to determine what the correct size should be. + This option provides an override for these situations. + + ca_keys= [KEYS] This parameter identifies a specific key(s) on + the system trusted keyring to be used for certificate + trust validation. + format: { id:<keyid> | builtin } + + cca= [MIPS] Override the kernel pages' cache coherency + algorithm. Accepted values range from 0 to 7 + inclusive. See arch/mips/include/asm/pgtable-bits.h + for platform specific values (SB1, Loongson3 and + others). + + ccw_timeout_log [S390] + See Documentation/s390/CommonIO for details. + + cgroup_disable= [KNL] Disable a particular controller + Format: {name of the controller(s) to disable} + The effects of cgroup_disable=foo are: + - foo isn't auto-mounted if you mount all cgroups in + a single hierarchy + - foo isn't visible as an individually mountable + subsystem + {Currently only "memory" controller deal with this and + cut the overhead, others just disable the usage. So + only cgroup_disable=memory is actually worthy} + + cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1 + Format: { controller[,controller...] | "all" } + Like cgroup_disable, but only applies to cgroup v1; + the blacklisted controllers remain available in cgroup2. + + cgroup.memory= [KNL] Pass options to the cgroup memory controller. + Format: <string> + nosocket -- Disable socket memory accounting. + nokmem -- Disable kernel memory accounting. + + checkreqprot [SELINUX] Set initial checkreqprot flag value. + Format: { "0" | "1" } + See security/selinux/Kconfig help text. + 0 -- check protection applied by kernel (includes + any implied execute protection). + 1 -- check protection requested by application. + Default value is set via a kernel config option. + Value can be changed at runtime via + /selinux/checkreqprot. + + cio_ignore= [S390] + See Documentation/s390/CommonIO for details. + clk_ignore_unused + [CLK] + Prevents the clock framework from automatically gating + clocks that have not been explicitly enabled by a Linux + device driver but are enabled in hardware at reset or + by the bootloader/firmware. Note that this does not + force such clocks to be always-on nor does it reserve + those clocks in any way. This parameter is useful for + debug and development, but should not be needed on a + platform with proper driver support. For more + information, see Documentation/clk.txt. + + clock= [BUGS=X86-32, HW] gettimeofday clocksource override. + [Deprecated] + Forces specified clocksource (if available) to be used + when calculating gettimeofday(). If specified + clocksource is not available, it defaults to PIT. + Format: { pit | tsc | cyclone | pmtmr } + + clocksource= Override the default clocksource + Format: <string> + Override the default clocksource and use the clocksource + with the name specified. + Some clocksource names to choose from, depending on + the platform: + [all] jiffies (this is the base, fallback clocksource) + [ACPI] acpi_pm + [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, + pxa_timer,timer3,32k_counter,timer0_1 + [AVR32] avr32 + [X86-32] pit,hpet,tsc; + scx200_hrt on Geode; cyclone on IBM x440 + [MIPS] MIPS + [PARISC] cr16 + [S390] tod + [SH] SuperH + [SPARC64] tick + [X86-64] hpet,tsc + + clocksource.arm_arch_timer.evtstrm= + [ARM,ARM64] + Format: <bool> + Enable/disable the eventstream feature of the ARM + architected timer so that code using WFE-based polling + loops can be debugged more effectively on production + systems. + + clocksource.arm_arch_timer.fsl-a008585= + [ARM64] + Format: <bool> + Enable/disable the workaround of Freescale/NXP + erratum A-008585. This can be useful for KVM + guests, if the guest device tree doesn't show the + erratum. If unspecified, the workaround is + enabled based on the device tree. + + clearcpuid=BITNUM [X86] + Disable CPUID feature X for the kernel. See + arch/x86/include/asm/cpufeatures.h for the valid bit + numbers. Note the Linux specific bits are not necessarily + stable over kernel options, but the vendor specific + ones should be. + Also note that user programs calling CPUID directly + or using the feature without checking anything + will still see it. This just prevents it from + being used by the kernel or shown in /proc/cpuinfo. + Also note the kernel might malfunction if you disable + some critical bits. + + cma=nn[MG]@[start[MG][-end[MG]]] + [ARM,X86,KNL] + Sets the size of kernel global memory area for + contiguous memory allocations and optionally the + placement constraint by the physical address range of + memory allocations. A value of 0 disables CMA + altogether. For more information, see + include/linux/dma-contiguous.h + + cmo_free_hint= [PPC] Format: { yes | no } + Specify whether pages are marked as being inactive + when they are freed. This is used in CMO environments + to determine OS memory pressure for page stealing by + a hypervisor. + Default: yes + + coherent_pool=nn[KMG] [ARM,KNL] + Sets the size of memory pool for coherent, atomic dma + allocations, by default set to 256K. + + code_bytes [X86] How many bytes of object code to print + in an oops report. + Range: 0 - 8192 + Default: 64 + + com20020= [HW,NET] ARCnet - COM20020 chipset + Format: + <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] + + com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) + Format: <io>[,<irq>] + + com90xx= [HW,NET] + ARCnet - COM90xx chipset (memory-mapped buffers) + Format: <io>[,<irq>[,<memstart>]] + + condev= [HW,S390] console device + conmode= + + console= [KNL] Output console device and options. + + tty<n> Use the virtual console device <n>. + + ttyS<n>[,options] + ttyUSB0[,options] + Use the specified serial port. The options are of + the form "bbbbpnf", where "bbbb" is the baud rate, + "p" is parity ("n", "o", or "e"), "n" is number of + bits, and "f" is flow control ("r" for RTS or + omit it). Default is "9600n8". + + See Documentation/serial-console.txt for more + information. See + Documentation/networking/netconsole.txt for an + alternative. + + uart[8250],io,<addr>[,options] + uart[8250],mmio,<addr>[,options] + uart[8250],mmio16,<addr>[,options] + uart[8250],mmio32,<addr>[,options] + uart[8250],0x<addr>[,options] + Start an early, polled-mode console on the 8250/16550 + UART at the specified I/O port or MMIO address, + switching to the matching ttyS device later. + MMIO inter-register address stride is either 8-bit + (mmio), 16-bit (mmio16), or 32-bit (mmio32). + If none of [io|mmio|mmio16|mmio32], <addr> is assumed + to be equivalent to 'mmio'. 'options' are specified in + the same format described for ttyS above; if unspecified, + the h/w is not re-initialized. + + hvc<n> Use the hypervisor console device <n>. This is for + both Xen and PowerPC hypervisors. + + If the device connected to the port is not a TTY but a braille + device, prepend "brl," before the device type, for instance + console=brl,ttyS0 + For now, only VisioBraille is supported. + + consoleblank= [KNL] The console blank (screen saver) timeout in + seconds. Defaults to 10*60 = 10mins. A value of 0 + disables the blank timer. + + coredump_filter= + [KNL] Change the default value for + /proc/<pid>/coredump_filter. + See also Documentation/filesystems/proc.txt. + + cpuidle.off=1 [CPU_IDLE] + disable the cpuidle sub-system + + cpu_init_udelay=N + [X86] Delay for N microsec between assert and de-assert + of APIC INIT to start processors. This delay occurs + on every CPU online, such as boot, and resume from suspend. + Default: 10000 + + cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver + Format: + <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] + + crashkernel=size[KMG][@offset[KMG]] + [KNL] Using kexec, Linux can switch to a 'crash kernel' + upon panic. This parameter reserves the physical + memory region [offset, offset + size] for that kernel + image. If '@offset' is omitted, then a suitable offset + is selected automatically. Check + Documentation/kdump/kdump.txt for further details. + + crashkernel=range1:size1[,range2:size2,...][@offset] + [KNL] Same as above, but depends on the memory + in the running system. The syntax of range is + start-[end] where start and end are both + a memory unit (amount[KMG]). See also + Documentation/kdump/kdump.txt for an example. + + crashkernel=size[KMG],high + [KNL, x86_64] range could be above 4G. Allow kernel + to allocate physical memory region from top, so could + be above 4G if system have more than 4G ram installed. + Otherwise memory region will be allocated below 4G, if + available. + It will be ignored if crashkernel=X is specified. + crashkernel=size[KMG],low + [KNL, x86_64] range under 4G. When crashkernel=X,high + is passed, kernel could allocate physical memory region + above 4G, that cause second kernel crash on system + that require some amount of low memory, e.g. swiotlb + requires at least 64M+32K low memory, also enough extra + low memory is needed to make sure DMA buffers for 32-bit + devices won't run out. Kernel would try to allocate at + at least 256M below 4G automatically. + This one let user to specify own low range under 4G + for second kernel instead. + 0: to disable low allocation. + It will be ignored when crashkernel=X,high is not used + or memory reserved is below 4G. + + cryptomgr.notests + [KNL] Disable crypto self-tests + + cs89x0_dma= [HW,NET] + Format: <dma> + + cs89x0_media= [HW,NET] + Format: { rj45 | aui | bnc } + + dasd= [HW,NET] + See header of drivers/s390/block/dasd_devmap.c. + + db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port + (one device per port) + Format: <port#>,<type> + See also Documentation/input/joystick-parport.txt + + ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot + time. See Documentation/dynamic-debug-howto.txt for + details. Deprecated, see dyndbg. + + debug [KNL] Enable kernel debugging (events log level). + + debug_locks_verbose= + [KNL] verbose self-tests + Format=<0|1> + Print debugging info while doing the locking API + self-tests. + We default to 0 (no extra messages), setting it to + 1 will print _a lot_ more information - normally + only useful to kernel developers. + + debug_objects [KNL] Enable object debugging + + no_debug_objects + [KNL] Disable object debugging + + debug_guardpage_minorder= + [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this + parameter allows control of the order of pages that will + be intentionally kept free (and hence protected) by the + buddy allocator. Bigger value increase the probability + of catching random memory corruption, but reduce the + amount of memory for normal system use. The maximum + possible value is MAX_ORDER/2. Setting this parameter + to 1 or 2 should be enough to identify most random + memory corruption problems caused by bugs in kernel or + driver code when a CPU writes to (or reads from) a + random memory location. Note that there exists a class + of memory corruptions problems caused by buggy H/W or + F/W or by drivers badly programing DMA (basically when + memory is written at bus level and the CPU MMU is + bypassed) which are not detectable by + CONFIG_DEBUG_PAGEALLOC, hence this option will not help + tracking down these problems. + + debug_pagealloc= + [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this + parameter enables the feature at boot time. In + default, it is disabled. We can avoid allocating huge + chunk of memory for debug pagealloc if we don't enable + it at boot time and the system will work mostly same + with the kernel built without CONFIG_DEBUG_PAGEALLOC. + on: enable the feature + + debugpat [X86] Enable PAT debugging + + decnet.addr= [HW,NET] + Format |