1.. _kernelparameters: 2 3The kernel's command-line parameters 4==================================== 5 6The following is a consolidated list of the kernel parameters as implemented 7by the __setup(), early_param(), core_param() and module_param() macros 8and sorted into English Dictionary order (defined as ignoring all 9punctuation and sorting digits before letters in a case insensitive 10manner), and with descriptions where known. 11 12The kernel parses parameters from the kernel command line up to "``--``"; 13if it doesn't recognize a parameter and it doesn't contain a '.', the 14parameter gets passed to init: parameters with '=' go into init's 15environment, others are passed as command line arguments to init. 16Everything after "``--``" is passed as an argument to init. 17 18Module parameters can be specified in two ways: via the kernel command 19line with a module name prefix, or via modprobe, e.g.:: 20 21 (kernel command line) usbcore.blinkenlights=1 22 (modprobe command line) modprobe usbcore blinkenlights=1 23 24Parameters for modules which are built into the kernel need to be 25specified on the kernel command line. modprobe looks through the 26kernel command line (/proc/cmdline) and collects module parameters 27when it loads a module, so the kernel command line can be used for 28loadable modules too. 29 30Hyphens (dashes) and underscores are equivalent in parameter names, so:: 31 32 log_buf_len=1M print-fatal-signals=1 33 34can also be entered as:: 35 36 log-buf-len=1M print_fatal_signals=1 37 38Double-quotes can be used to protect spaces in values, e.g.:: 39 40 param="spaces in here" 41 42cpu lists: 43---------- 44 45Some kernel parameters take a list of CPUs as a value, e.g. isolcpus, 46nohz_full, irqaffinity, rcu_nocbs. The format of this list is: 47 48 <cpu number>,...,<cpu number> 49 50or 51 52 <cpu number>-<cpu number> 53 (must be a positive range in ascending order) 54 55or a mixture 56 57<cpu number>,...,<cpu number>-<cpu number> 58 59Note that for the special case of a range one can split the range into equal 60sized groups and for each group use some amount from the beginning of that 61group: 62 63 <cpu number>-<cpu number>:<used size>/<group size> 64 65For example one can add to the command line following parameter: 66 67 isolcpus=1,2,10-20,100-2000:2/25 68 69where the final item represents CPUs 100,101,125,126,150,151,... 70 71 72 73This document may not be entirely up to date and comprehensive. The command 74"modinfo -p ${modulename}" shows a current list of all parameters of a loadable 75module. Loadable modules, after being loaded into the running kernel, also 76reveal their parameters in /sys/module/${modulename}/parameters/. Some of these 77parameters may be changed at runtime by the command 78``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``. 79 80The parameters listed below are only valid if certain kernel build options were 81enabled and if respective hardware is present. The text in square brackets at 82the beginning of each description states the restrictions within which a 83parameter is applicable:: 84 85 ACPI ACPI support is enabled. 86 AGP AGP (Accelerated Graphics Port) is enabled. 87 ALSA ALSA sound support is enabled. 88 APIC APIC support is enabled. 89 APM Advanced Power Management support is enabled. 90 ARM ARM architecture is enabled. 91 ARM64 ARM64 architecture is enabled. 92 AX25 Appropriate AX.25 support is enabled. 93 CLK Common clock infrastructure is enabled. 94 CMA Contiguous Memory Area support is enabled. 95 DRM Direct Rendering Management support is enabled. 96 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 97 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 98 EFI EFI Partitioning (GPT) is enabled 99 EIDE EIDE/ATAPI support is enabled. 100 EVM Extended Verification Module 101 FB The frame buffer device is enabled. 102 FTRACE Function tracing enabled. 103 GCOV GCOV profiling is enabled. 104 HW Appropriate hardware is enabled. 105 IA-64 IA-64 architecture is enabled. 106 IMA Integrity measurement architecture is enabled. 107 IOSCHED More than one I/O scheduler is enabled. 108 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 109 IPV6 IPv6 support is enabled. 110 ISAPNP ISA PnP code is enabled. 111 ISDN Appropriate ISDN support is enabled. 112 ISOL CPU Isolation is enabled. 113 JOY Appropriate joystick support is enabled. 114 KGDB Kernel debugger support is enabled. 115 KVM Kernel Virtual Machine support is enabled. 116 LIBATA Libata driver is enabled 117 LP Printer support is enabled. 118 LOOP Loopback device support is enabled. 119 M68k M68k architecture is enabled. 120 These options have more detailed description inside of 121 Documentation/m68k/kernel-options.rst. 122 MDA MDA console support is enabled. 123 MIPS MIPS architecture is enabled. 124 MOUSE Appropriate mouse support is enabled. 125 MSI Message Signaled Interrupts (PCI). 126 MTD MTD (Memory Technology Device) support is enabled. 127 NET Appropriate network support is enabled. 128 NUMA NUMA support is enabled. 129 NFS Appropriate NFS support is enabled. 130 OF Devicetree is enabled. 131 OSS OSS sound support is enabled. 132 PV_OPS A paravirtualized kernel is enabled. 133 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 134 PARISC The PA-RISC architecture is enabled. 135 PCI PCI bus support is enabled. 136 PCIE PCI Express support is enabled. 137 PCMCIA The PCMCIA subsystem is enabled. 138 PNP Plug & Play support is enabled. 139 PPC PowerPC architecture is enabled. 140 PPT Parallel port support is enabled. 141 PS2 Appropriate PS/2 support is enabled. 142 RAM RAM disk support is enabled. 143 RDT Intel Resource Director Technology. 144 S390 S390 architecture is enabled. 145 SCSI Appropriate SCSI support is enabled. 146 A lot of drivers have their options described inside 147 the Documentation/scsi/ sub-directory. 148 SECURITY Different security models are enabled. 149 SELINUX SELinux support is enabled. 150 APPARMOR AppArmor support is enabled. 151 SERIAL Serial support is enabled. 152 SH SuperH architecture is enabled. 153 SMP The kernel is an SMP kernel. 154 SPARC Sparc architecture is enabled. 155 SWSUSP Software suspend (hibernation) is enabled. 156 SUSPEND System suspend states are enabled. 157 TPM TPM drivers are enabled. 158 TS Appropriate touchscreen support is enabled. 159 UMS USB Mass Storage support is enabled. 160 USB USB support is enabled. 161 USBHID USB Human Interface Device support is enabled. 162 V4L Video For Linux support is enabled. 163 VMMIO Driver for memory mapped virtio devices is enabled. 164 VGA The VGA console has been enabled. 165 VT Virtual terminal support is enabled. 166 WDT Watchdog support is enabled. 167 XT IBM PC/XT MFM hard disk support is enabled. 168 X86-32 X86-32, aka i386 architecture is enabled. 169 X86-64 X86-64 architecture is enabled. 170 More X86-64 boot options can be found in 171 Documentation/x86/x86_64/boot-options.rst. 172 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 173 X86_UV SGI UV support is enabled. 174 XEN Xen support is enabled 175 XTENSA xtensa architecture is enabled. 176 177In addition, the following text indicates that the option:: 178 179 BUGS= Relates to possible processor bugs on the said processor. 180 KNL Is a kernel start-up parameter. 181 BOOT Is a boot loader parameter. 182 183Parameters denoted with BOOT are actually interpreted by the boot 184loader, and have no meaning to the kernel directly. 185Do not modify the syntax of boot loader parameters without extreme 186need or coordination with <Documentation/x86/boot.rst>. 187 188There are also arch-specific kernel-parameters not documented here. 189See for example <Documentation/x86/x86_64/boot-options.rst>. 190 191Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 192a trailing = on the name of any parameter states that that parameter will 193be entered as an environment variable, whereas its absence indicates that 194it will appear as a kernel argument readable via /proc/cmdline by programs 195running once the system is up. 196 197The number of kernel parameters is not limited, but the length of the 198complete command line (parameters including spaces etc.) is limited to 199a fixed number of characters. This limit depends on the architecture 200and is between 256 and 4096 characters. It is defined in the file 201./include/asm/setup.h as COMMAND_LINE_SIZE. 202 203Finally, the [KMG] suffix is commonly described after a number of kernel 204parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 205multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30 206bytes respectively. Such letter suffixes can also be entirely omitted: 207 208.. include:: kernel-parameters.txt 209 :literal: 210 211Todo 212---- 213 214 Add more DRM drivers. 215