3 The kernel's command-line parameters
4 ====================================
6 The following is a consolidated list of the kernel parameters as implemented
7 by the __setup(), early_param(), core_param() and module_param() macros
8 and sorted into English Dictionary order (defined as ignoring all
9 punctuation and sorting digits before letters in a case insensitive
10 manner), and with descriptions where known.
12 The kernel parses parameters from the kernel command line up to "``--``";
13 if it doesn't recognize a parameter and it doesn't contain a '.', the
14 parameter gets passed to init: parameters with '=' go into init's
15 environment, others are passed as command line arguments to init.
16 Everything after "``--``" is passed as an argument to init.
18 Module parameters can be specified in two ways: via the kernel command
19 line with a module name prefix, or via modprobe, e.g.::
21 (kernel command line) usbcore.blinkenlights=1
22 (modprobe command line) modprobe usbcore blinkenlights=1
24 Parameters for modules which are built into the kernel need to be
25 specified on the kernel command line. modprobe looks through the
26 kernel command line (/proc/cmdline) and collects module parameters
27 when it loads a module, so the kernel command line can be used for
30 Hyphens (dashes) and underscores are equivalent in parameter names, so::
32 log_buf_len=1M print-fatal-signals=1
34 can also be entered as::
36 log-buf-len=1M print_fatal_signals=1
38 Double-quotes can be used to protect spaces in values, e.g.::
40 param="spaces in here"
45 Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
46 nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
48 <cpu number>,...,<cpu number>
52 <cpu number>-<cpu number>
53 (must be a positive range in ascending order)
57 <cpu number>,...,<cpu number>-<cpu number>
59 Note that for the special case of a range one can split the range into equal
60 sized groups and for each group use some amount from the beginning of that
63 <cpu number>-cpu number>:<used size>/<group size>
65 For example one can add to the command line following parameter:
67 isolcpus=1,2,10-20,100-2000:2/25
69 where the final item represents CPUs 100,101,125,126,150,151,...
73 This document may not be entirely up to date and comprehensive. The command
74 "modinfo -p ${modulename}" shows a current list of all parameters of a loadable
75 module. Loadable modules, after being loaded into the running kernel, also
76 reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
77 parameters may be changed at runtime by the command
78 ``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
80 The parameters listed below are only valid if certain kernel build options were
81 enabled and if respective hardware is present. The text in square brackets at
82 the beginning of each description states the restrictions within which a
83 parameter is applicable::
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.
177 In addition, the following text indicates that the option::
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.
183 Parameters denoted with BOOT are actually interpreted by the boot
184 loader, and have no meaning to the kernel directly.
185 Do not modify the syntax of boot loader parameters without extreme
186 need or coordination with <Documentation/x86/boot.rst>.
188 There are also arch-specific kernel-parameters not documented here.
189 See for example <Documentation/x86/x86_64/boot-options.rst>.
191 Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
192 a trailing = on the name of any parameter states that that parameter will
193 be entered as an environment variable, whereas its absence indicates that
194 it will appear as a kernel argument readable via /proc/cmdline by programs
195 running once the system is up.
197 The number of kernel parameters is not limited, but the length of the
198 complete command line (parameters including spaces etc.) is limited to
199 a fixed number of characters. This limit depends on the architecture
200 and is between 256 and 4096 characters. It is defined in the file
201 ./include/asm/setup.h as COMMAND_LINE_SIZE.
203 Finally, the [KMG] suffix is commonly described after a number of kernel
204 parameter values. These 'K', 'M', and 'G' letters represent the _binary_
205 multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
206 bytes respectively. Such letter suffixes can also be entirely omitted:
208 .. include:: kernel-parameters.txt
214 Add more DRM drivers.