1.. _kernelparameters: 2 3The kernel's command-line parameters 4==================================== 5 6The following is a consolidated list of the kernel parameters as 7implemented by the __setup(), 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 AX25 Appropriate AX.25 support is enabled. 92 CLK Common clock infrastructure is enabled. 93 CMA Contiguous Memory Area support is enabled. 94 DRM Direct Rendering Management support is enabled. 95 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 96 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 97 EFI EFI Partitioning (GPT) is enabled 98 EIDE EIDE/ATAPI support is enabled. 99 EVM Extended Verification Module 100 FB The frame buffer device is enabled. 101 FTRACE Function tracing enabled. 102 GCOV GCOV profiling is enabled. 103 HW Appropriate hardware is enabled. 104 IA-64 IA-64 architecture is enabled. 105 IMA Integrity measurement architecture is enabled. 106 IOSCHED More than one I/O scheduler is enabled. 107 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 108 IPV6 IPv6 support is enabled. 109 ISAPNP ISA PnP code is enabled. 110 ISDN Appropriate ISDN support is enabled. 111 ISOL CPU Isolation is enabled. 112 JOY Appropriate joystick support is enabled. 113 KGDB Kernel debugger support is enabled. 114 KVM Kernel Virtual Machine support is enabled. 115 LIBATA Libata driver is enabled 116 LP Printer support is enabled. 117 LOOP Loopback device support is enabled. 118 M68k M68k architecture is enabled. 119 These options have more detailed description inside of 120 Documentation/m68k/kernel-options.txt. 121 MDA MDA console support is enabled. 122 MIPS MIPS architecture is enabled. 123 MOUSE Appropriate mouse support is enabled. 124 MSI Message Signaled Interrupts (PCI). 125 MTD MTD (Memory Technology Device) support is enabled. 126 NET Appropriate network support is enabled. 127 NUMA NUMA support is enabled. 128 NFS Appropriate NFS support is enabled. 129 OSS OSS sound support is enabled. 130 PV_OPS A paravirtualized kernel is enabled. 131 PARIDE The ParIDE (parallel port IDE) subsystem is enabled. 132 PARISC The PA-RISC architecture is enabled. 133 PCI PCI bus support is enabled. 134 PCIE PCI Express support is enabled. 135 PCMCIA The PCMCIA subsystem is enabled. 136 PNP Plug & Play support is enabled. 137 PPC PowerPC architecture is enabled. 138 PPT Parallel port support is enabled. 139 PS2 Appropriate PS/2 support is enabled. 140 RAM RAM disk support is enabled. 141 RDT Intel Resource Director Technology. 142 S390 S390 architecture is enabled. 143 SCSI Appropriate SCSI support is enabled. 144 A lot of drivers have their options described inside 145 the Documentation/scsi/ sub-directory. 146 SECURITY Different security models are enabled. 147 SELINUX SELinux support is enabled. 148 APPARMOR AppArmor support is enabled. 149 SERIAL Serial support is enabled. 150 SH SuperH architecture is enabled. 151 SMP The kernel is an SMP kernel. 152 SPARC Sparc architecture is enabled. 153 SWSUSP Software suspend (hibernation) is enabled. 154 SUSPEND System suspend states are enabled. 155 TPM TPM drivers are enabled. 156 TS Appropriate touchscreen support is enabled. 157 UMS USB Mass Storage support is enabled. 158 USB USB support is enabled. 159 USBHID USB Human Interface Device support is enabled. 160 V4L Video For Linux support is enabled. 161 VMMIO Driver for memory mapped virtio devices is enabled. 162 VGA The VGA console has been enabled. 163 VT Virtual terminal support is enabled. 164 WDT Watchdog support is enabled. 165 XT IBM PC/XT MFM hard disk support is enabled. 166 X86-32 X86-32, aka i386 architecture is enabled. 167 X86-64 X86-64 architecture is enabled. 168 More X86-64 boot options can be found in 169 Documentation/x86/x86_64/boot-options.txt . 170 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 171 X86_UV SGI UV support is enabled. 172 XEN Xen support is enabled 173 174In addition, the following text indicates that the option:: 175 176 BUGS= Relates to possible processor bugs on the said processor. 177 KNL Is a kernel start-up parameter. 178 BOOT Is a boot loader parameter. 179 180Parameters denoted with BOOT are actually interpreted by the boot 181loader, and have no meaning to the kernel directly. 182Do not modify the syntax of boot loader parameters without extreme 183need or coordination with <Documentation/x86/boot.txt>. 184 185There are also arch-specific kernel-parameters not documented here. 186See for example <Documentation/x86/x86_64/boot-options.txt>. 187 188Note that ALL kernel parameters listed below are CASE SENSITIVE, and that 189a trailing = on the name of any parameter states that that parameter will 190be entered as an environment variable, whereas its absence indicates that 191it will appear as a kernel argument readable via /proc/cmdline by programs 192running once the system is up. 193 194The number of kernel parameters is not limited, but the length of the 195complete command line (parameters including spaces etc.) is limited to 196a fixed number of characters. This limit depends on the architecture 197and is between 256 and 4096 characters. It is defined in the file 198./include/asm/setup.h as COMMAND_LINE_SIZE. 199 200Finally, the [KMG] suffix is commonly described after a number of kernel 201parameter values. These 'K', 'M', and 'G' letters represent the _binary_ 202multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30 203bytes respectively. Such letter suffixes can also be entirely omitted: 204 205.. include:: kernel-parameters.txt 206 :literal: 207 208Todo 209---- 210 211 Add more DRM drivers. 212