0001 .. _kernelparameters:
0002
0003 The kernel's command-line parameters
0004 ====================================
0005
0006 The following is a consolidated list of the kernel parameters as implemented
0007 by the __setup(), early_param(), core_param() and module_param() macros
0008 and sorted into English Dictionary order (defined as ignoring all
0009 punctuation and sorting digits before letters in a case insensitive
0010 manner), and with descriptions where known.
0011
0012 The kernel parses parameters from the kernel command line up to "``--``";
0013 if it doesn't recognize a parameter and it doesn't contain a '.', the
0014 parameter gets passed to init: parameters with '=' go into init's
0015 environment, others are passed as command line arguments to init.
0016 Everything after "``--``" is passed as an argument to init.
0017
0018 Module parameters can be specified in two ways: via the kernel command
0019 line with a module name prefix, or via modprobe, e.g.::
0020
0021 (kernel command line) usbcore.blinkenlights=1
0022 (modprobe command line) modprobe usbcore blinkenlights=1
0023
0024 Parameters for modules which are built into the kernel need to be
0025 specified on the kernel command line. modprobe looks through the
0026 kernel command line (/proc/cmdline) and collects module parameters
0027 when it loads a module, so the kernel command line can be used for
0028 loadable modules too.
0029
0030 Hyphens (dashes) and underscores are equivalent in parameter names, so::
0031
0032 log_buf_len=1M print-fatal-signals=1
0033
0034 can also be entered as::
0035
0036 log-buf-len=1M print_fatal_signals=1
0037
0038 Double-quotes can be used to protect spaces in values, e.g.::
0039
0040 param="spaces in here"
0041
0042 cpu lists:
0043 ----------
0044
0045 Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
0046 nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
0047
0048 <cpu number>,...,<cpu number>
0049
0050 or
0051
0052 <cpu number>-<cpu number>
0053 (must be a positive range in ascending order)
0054
0055 or a mixture
0056
0057 <cpu number>,...,<cpu number>-<cpu number>
0058
0059 Note that for the special case of a range one can split the range into equal
0060 sized groups and for each group use some amount from the beginning of that
0061 group:
0062
0063 <cpu number>-<cpu number>:<used size>/<group size>
0064
0065 For example one can add to the command line following parameter:
0066
0067 isolcpus=1,2,10-20,100-2000:2/25
0068
0069 where the final item represents CPUs 100,101,125,126,150,151,...
0070
0071 The value "N" can be used to represent the numerically last CPU on the system,
0072 i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
0073
0074 Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
0075 to change, such as less cores in the CPU list, then N and any ranges using N
0076 will also change. Use the same on a small 4 core system, and "16-N" becomes
0077 "16-3" and now the same boot input will be flagged as invalid (start > end).
0078
0079 The special case-tolerant group name "all" has a meaning of selecting all CPUs,
0080 so that "nohz_full=all" is the equivalent of "nohz_full=0-N".
0081
0082 The semantics of "N" and "all" is supported on a level of bitmaps and holds for
0083 all users of bitmap_parse().
0084
0085 This document may not be entirely up to date and comprehensive. The command
0086 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
0087 module. Loadable modules, after being loaded into the running kernel, also
0088 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
0089 parameters may be changed at runtime by the command
0090 ``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
0091
0092 The parameters listed below are only valid if certain kernel build options were
0093 enabled and if respective hardware is present. The text in square brackets at
0094 the beginning of each description states the restrictions within which a
0095 parameter is applicable::
0096
0097 ACPI ACPI support is enabled.
0098 AGP AGP (Accelerated Graphics Port) is enabled.
0099 ALSA ALSA sound support is enabled.
0100 APIC APIC support is enabled.
0101 APM Advanced Power Management support is enabled.
0102 APPARMOR AppArmor support is enabled.
0103 ARM ARM architecture is enabled.
0104 ARM64 ARM64 architecture is enabled.
0105 AX25 Appropriate AX.25 support is enabled.
0106 CLK Common clock infrastructure is enabled.
0107 CMA Contiguous Memory Area support is enabled.
0108 DRM Direct Rendering Management support is enabled.
0109 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
0110 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
0111 EFI EFI Partitioning (GPT) is enabled
0112 EVM Extended Verification Module
0113 FB The frame buffer device is enabled.
0114 FTRACE Function tracing enabled.
0115 GCOV GCOV profiling is enabled.
0116 HIBERNATION HIBERNATION is enabled.
0117 HW Appropriate hardware is enabled.
0118 HYPER_V HYPERV support is enabled.
0119 IA-64 IA-64 architecture is enabled.
0120 IMA Integrity measurement architecture is enabled.
0121 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
0122 IPV6 IPv6 support is enabled.
0123 ISAPNP ISA PnP code is enabled.
0124 ISDN Appropriate ISDN support is enabled.
0125 ISOL CPU Isolation is enabled.
0126 JOY Appropriate joystick support is enabled.
0127 KGDB Kernel debugger support is enabled.
0128 KVM Kernel Virtual Machine support is enabled.
0129 LIBATA Libata driver is enabled
0130 LP Printer support is enabled.
0131 LOOP Loopback device support is enabled.
0132 M68k M68k architecture is enabled.
0133 These options have more detailed description inside of
0134 Documentation/m68k/kernel-options.rst.
0135 MDA MDA console support is enabled.
0136 MIPS MIPS architecture is enabled.
0137 MOUSE Appropriate mouse support is enabled.
0138 MSI Message Signaled Interrupts (PCI).
0139 MTD MTD (Memory Technology Device) support is enabled.
0140 NET Appropriate network support is enabled.
0141 NUMA NUMA support is enabled.
0142 NFS Appropriate NFS support is enabled.
0143 OF Devicetree is enabled.
0144 PV_OPS A paravirtualized kernel is enabled.
0145 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
0146 PARISC The PA-RISC architecture is enabled.
0147 PCI PCI bus support is enabled.
0148 PCIE PCI Express support is enabled.
0149 PCMCIA The PCMCIA subsystem is enabled.
0150 PNP Plug & Play support is enabled.
0151 PPC PowerPC architecture is enabled.
0152 PPT Parallel port support is enabled.
0153 PS2 Appropriate PS/2 support is enabled.
0154 RAM RAM disk support is enabled.
0155 RISCV RISCV architecture is enabled.
0156 RDT Intel Resource Director Technology.
0157 S390 S390 architecture is enabled.
0158 SCSI Appropriate SCSI support is enabled.
0159 A lot of drivers have their options described inside
0160 the Documentation/scsi/ sub-directory.
0161 SECURITY Different security models are enabled.
0162 SELINUX SELinux support is enabled.
0163 SERIAL Serial support is enabled.
0164 SH SuperH architecture is enabled.
0165 SMP The kernel is an SMP kernel.
0166 SPARC Sparc architecture is enabled.
0167 SWSUSP Software suspend (hibernation) is enabled.
0168 SUSPEND System suspend states are enabled.
0169 TPM TPM drivers are enabled.
0170 UMS USB Mass Storage support is enabled.
0171 USB USB support is enabled.
0172 USBHID USB Human Interface Device support is enabled.
0173 V4L Video For Linux support is enabled.
0174 VMMIO Driver for memory mapped virtio devices is enabled.
0175 VGA The VGA console has been enabled.
0176 VT Virtual terminal support is enabled.
0177 WDT Watchdog support is enabled.
0178 X86-32 X86-32, aka i386 architecture is enabled.
0179 X86-64 X86-64 architecture is enabled.
0180 More X86-64 boot options can be found in
0181 Documentation/x86/x86_64/boot-options.rst.
0182 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
0183 X86_UV SGI UV support is enabled.
0184 XEN Xen support is enabled
0185 XTENSA xtensa architecture is enabled.
0186
0187 In addition, the following text indicates that the option::
0188
0189 BUGS= Relates to possible processor bugs on the said processor.
0190 KNL Is a kernel start-up parameter.
0191 BOOT Is a boot loader parameter.
0192
0193 Parameters denoted with BOOT are actually interpreted by the boot
0194 loader, and have no meaning to the kernel directly.
0195 Do not modify the syntax of boot loader parameters without extreme
0196 need or coordination with <Documentation/x86/boot.rst>.
0197
0198 There are also arch-specific kernel-parameters not documented here.
0199 See for example <Documentation/x86/x86_64/boot-options.rst>.
0200
0201 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
0202 a trailing = on the name of any parameter states that that parameter will
0203 be entered as an environment variable, whereas its absence indicates that
0204 it will appear as a kernel argument readable via /proc/cmdline by programs
0205 running once the system is up.
0206
0207 The number of kernel parameters is not limited, but the length of the
0208 complete command line (parameters including spaces etc.) is limited to
0209 a fixed number of characters. This limit depends on the architecture
0210 and is between 256 and 4096 characters. It is defined in the file
0211 ./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.
0212
0213 Finally, the [KMG] suffix is commonly described after a number of kernel
0214 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
0215 multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
0216 bytes respectively. Such letter suffixes can also be entirely omitted:
0217
0218 .. include:: kernel-parameters.txt
0219 :literal:
0220
0221 Todo
0222 ----
0223
0224 Add more DRM drivers.
