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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 000000000..959f73a32 --- /dev/null +++ b/Documentation/admin-guide/kernel-parameters.rst @@ -0,0 +1,224 @@ +.. _kernelparameters: + +The kernel's command-line parameters +==================================== + +The following is a consolidated list of the kernel parameters as implemented +by the __setup(), early_param(), 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,... + +The value "N" can be used to represent the numerically last CPU on the system, +i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system. + +Keep in mind that "N" is dynamic, so if system changes cause the bitmap width +to change, such as less cores in the CPU list, then N and any ranges using N +will also change. Use the same on a small 4 core system, and "16-N" becomes +"16-3" and now the same boot input will be flagged as invalid (start > end). + +The special case-tolerant group name "all" has a meaning of selecting all CPUs, +so that "nohz_full=all" is the equivalent of "nohz_full=0-N". + +The semantics of "N" and "all" is supported on a level of bitmaps and holds for +all users of bitmap_parse(). + +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. + APPARMOR AppArmor support is enabled. + ARM ARM architecture is enabled. + ARM64 ARM64 architecture is enabled. + AX25 Appropriate AX.25 support 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 + EVM Extended Verification Module + FB The frame buffer device is enabled. + FTRACE Function tracing enabled. + GCOV GCOV profiling is enabled. + HIBERNATION HIBERNATION is enabled. + HW Appropriate hardware is enabled. + HYPER_V HYPERV support is enabled. + IA-64 IA-64 architecture is enabled. + IMA Integrity measurement architecture 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. + ISOL CPU Isolation 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.rst. + 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. + OF Devicetree 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. + RISCV RISCV architecture is enabled. + RDT Intel Resource Director Technology. + 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. + 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. + 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. + 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.rst. + 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 + XTENSA xtensa architecture 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.rst>. + +There are also arch-specific kernel-parameters not documented here. +See for example <Documentation/x86/x86_64/boot-options.rst>. + +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/uapi/asm-generic/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', equaling 2^10, 2^20, and 2^30 +bytes respectively. Such letter suffixes can also be entirely omitted: + +.. include:: kernel-parameters.txt + :literal: + +Todo +---- + + Add more DRM drivers. |