1.. SPDX-License-Identifier: GPL-2.0 2 3.. _kernelparameters: 4 5The kernel's command-line parameters 6==================================== 7 8The following is a consolidated list of the kernel parameters as implemented 9by the __setup(), early_param(), core_param() and module_param() macros 10and sorted into English Dictionary order (defined as ignoring all 11punctuation and sorting digits before letters in a case insensitive 12manner), and with descriptions where known. 13 14The kernel parses parameters from the kernel command line up to "``--``"; 15if it doesn't recognize a parameter and it doesn't contain a '.', the 16parameter gets passed to init: parameters with '=' go into init's 17environment, others are passed as command line arguments to init. 18Everything after "``--``" is passed as an argument to init. 19 20Module parameters can be specified in two ways: via the kernel command 21line with a module name prefix, or via modprobe, e.g.:: 22 23 (kernel command line) usbcore.blinkenlights=1 24 (modprobe command line) modprobe usbcore blinkenlights=1 25 26Parameters for modules which are built into the kernel need to be 27specified on the kernel command line. modprobe looks through the 28kernel command line (/proc/cmdline) and collects module parameters 29when it loads a module, so the kernel command line can be used for 30loadable modules too. 31 32This document may not be entirely up to date and comprehensive. The command 33"modinfo -p ${modulename}" shows a current list of all parameters of a loadable 34module. Loadable modules, after being loaded into the running kernel, also 35reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 36parameters may be changed at runtime by the command 37``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``. 38 39Special handling 40---------------- 41 42Hyphens (dashes) and underscores are equivalent in parameter names, so:: 43 44 log_buf_len=1M print-fatal-signals=1 45 46can also be entered as:: 47 48 log-buf-len=1M print_fatal_signals=1 49 50Double-quotes can be used to protect spaces in values, e.g.:: 51 52 param="spaces in here" 53 54cpu lists 55~~~~~~~~~ 56 57Some kernel parameters take a list of CPUs as a value, e.g. isolcpus, 58nohz_full, irqaffinity, rcu_nocbs. The format of this list is: 59 60 <cpu number>,...,<cpu number> 61 62or 63 64 <cpu number>-<cpu number> 65 (must be a positive range in ascending order) 66 67or a mixture 68 69<cpu number>,...,<cpu number>-<cpu number> 70 71Note that for the special case of a range one can split the range into equal 72sized groups and for each group use some amount from the beginning of that 73group: 74 75 <cpu number>-<cpu number>:<used size>/<group size> 76 77For example one can add to the command line following parameter: 78 79 isolcpus=1,2,10-20,100-2000:2/25 80 81where the final item represents CPUs 100,101,125,126,150,151,... 82 83The value "N" can be used to represent the numerically last CPU on the system, 84i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system. 85 86Keep in mind that "N" is dynamic, so if system changes cause the bitmap width 87to change, such as less cores in the CPU list, then N and any ranges using N 88will also change. Use the same on a small 4 core system, and "16-N" becomes 89"16-3" and now the same boot input will be flagged as invalid (start > end). 90 91The special case-tolerant group name "all" has a meaning of selecting all CPUs, 92so that "nohz_full=all" is the equivalent of "nohz_full=0-N". 93 94The semantics of "N" and "all" is supported on a level of bitmaps and holds for 95all users of bitmap_parselist(). 96 97Metric suffixes 98~~~~~~~~~~~~~~~ 99 100The [KMG] suffix is commonly described after a number of kernel 101parameter values. 'K', 'M', 'G', 'T', 'P', and 'E' suffixes are allowed. 102These letters represent the _binary_ multipliers 'Kilo', 'Mega', 'Giga', 103'Tera', 'Peta', and 'Exa', equaling 2^10, 2^20, 2^30, 2^40, 2^50, and 1042^60 bytes respectively. Such letter suffixes can also be entirely omitted. 105 106Kernel Build Options 107-------------------- 108 109The parameters listed below are only valid if certain kernel build options 110were enabled and if respective hardware is present. This list should be kept 111in alphabetical order. The text in square brackets at the beginning 112of each description states the restrictions within which a parameter 113is applicable:: 114 115 ACPI ACPI support is enabled. 116 AGP AGP (Accelerated Graphics Port) is enabled. 117 ALSA ALSA sound support is enabled. 118 APIC APIC support is enabled. 119 APM Advanced Power Management support is enabled. 120 APPARMOR AppArmor support is enabled. 121 ARM ARM architecture is enabled. 122 ARM64 ARM64 architecture is enabled. 123 AX25 Appropriate AX.25 support is enabled. 124 CLK Common clock infrastructure is enabled. 125 CMA Contiguous Memory Area support is enabled. 126 DRM Direct Rendering Management support is enabled. 127 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 128 EARLY Parameter processed too early to be embedded in initrd. 129 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 130 EFI EFI Partitioning (GPT) is enabled 131 EVM Extended Verification Module 132 FB The frame buffer device is enabled. 133 FTRACE Function tracing enabled. 134 GCOV GCOV profiling is enabled. 135 HIBERNATION HIBERNATION is enabled. 136 HW Appropriate hardware is enabled. 137 HYPER_V HYPERV support is enabled. 138 IMA Integrity measurement architecture is enabled. 139 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 140 IPV6 IPv6 support is enabled. 141 ISAPNP ISA PnP code is enabled. 142 ISDN Appropriate ISDN support is enabled. 143 ISOL CPU Isolation is enabled. 144 JOY Appropriate joystick support is enabled. 145 KGDB Kernel debugger support is enabled. 146 KVM Kernel Virtual Machine support is enabled. 147 LIBATA Libata driver is enabled 148 LOONGARCH LoongArch architecture is enabled. 149 LOOP Loopback device support is enabled. 150 LP Printer support is enabled. 151 M68k M68k architecture is enabled. 152 These options have more detailed description inside of 153 Documentation/arch/m68k/kernel-options.rst. 154 MDA MDA console support is enabled. 155 MIPS MIPS architecture is enabled. 156 MOUSE Appropriate mouse support is enabled. 157 MSI Message Signaled Interrupts (PCI). 158 MTD MTD (Memory Technology Device) support is enabled. 159 NET Appropriate network support is enabled. 160 NFS Appropriate NFS support is enabled. 161 NUMA NUMA support is enabled. 162 OF Devicetree is enabled. 163 PARISC The PA-RISC architecture is enabled. 164 PCI PCI bus support is enabled. 165 PCIE PCI Express support is enabled. 166 PCMCIA The PCMCIA subsystem is enabled. 167 PNP Plug & Play support is enabled. 168 PPC PowerPC architecture is enabled. 169 PPT Parallel port support is enabled. 170 PS2 Appropriate PS/2 support is enabled. 171 PV_OPS A paravirtualized kernel is enabled. 172 RAM RAM disk support is enabled. 173 RDT Intel Resource Director Technology. 174 RISCV RISCV architecture is enabled. 175 S390 S390 architecture is enabled. 176 SCSI Appropriate SCSI support is enabled. 177 A lot of drivers have their options described inside 178 the Documentation/scsi/ sub-directory. 179 SDW SoundWire support is enabled. 180 SECURITY Different security models are enabled. 181 SELINUX SELinux support is enabled. 182 SERIAL Serial support is enabled. 183 SH SuperH architecture is enabled. 184 SMP The kernel is an SMP kernel. 185 SPARC Sparc architecture is enabled. 186 SUSPEND System suspend states are enabled. 187 SWSUSP Software suspend (hibernation) is enabled. 188 TPM TPM drivers are enabled. 189 UMS USB Mass Storage support is enabled. 190 USB USB support is enabled. 191 USBHID USB Human Interface Device support is enabled. 192 V4L Video For Linux support is enabled. 193 VGA The VGA console has been enabled. 194 VMMIO Driver for memory mapped virtio devices is enabled. 195 VT Virtual terminal support is enabled. 196 WDT Watchdog support is enabled. 197 X86-32 X86-32, aka i386 architecture is enabled. 198 X86-64 X86-64 architecture is enabled. 199 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 200 X86_UV SGI UV support is enabled. 201 XEN Xen support is enabled 202 XTENSA xtensa architecture is enabled. 203 204In addition, the following text indicates that the option:: 205 206 BOOT Is a boot loader parameter. 207 BUGS= Relates to possible processor bugs on the said processor. 208 KNL Is a kernel start-up parameter. 209 210Parameters denoted with BOOT are actually interpreted by the boot 211loader, and have no meaning to the kernel directly. 212Do not modify the syntax of boot loader parameters without extreme 213need or coordination with <Documentation/arch/x86/boot.rst>. 214 215There are also arch-specific kernel-parameters not documented here. 216 217Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 218a trailing = on the name of any parameter states that the parameter will 219be entered as an environment variable, whereas its absence indicates that 220it will appear as a kernel argument readable via /proc/cmdline by programs 221running once the system is up. 222 223The number of kernel parameters is not limited, but the length of the 224complete command line (parameters including spaces etc.) is limited to 225a fixed number of characters. This limit depends on the architecture 226and is between 256 and 4096 characters. It is defined in the file 227./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE. 228 229.. include:: kernel-parameters.txt 230 :literal: 231