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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
71The value "N" can be used to represent the numerically last CPU on the system,
72i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
73
74Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
75to change, such as less cores in the CPU list, then N and any ranges using N
76will also change. Use the same on a small 4 core system, and "16-N" becomes
77"16-3" and now the same boot input will be flagged as invalid (start > end).
78
79The special case-tolerant group name "all" has a meaning of selecting all CPUs,
80so that "nohz_full=all" is the equivalent of "nohz_full=0-N".
81
82The semantics of "N" and "all" is supported on a level of bitmaps and holds for
83all users of bitmap_parse().
84
85This document may not be entirely up to date and comprehensive. The command
86"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
87module. Loadable modules, after being loaded into the running kernel, also
88reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
89parameters may be changed at runtime by the command
90``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
91
92The parameters listed below are only valid if certain kernel build options were
93enabled and if respective hardware is present. The text in square brackets at
94the beginning of each description states the restrictions within which a
95parameter is applicable::
96
97 ACPI ACPI support is enabled.
98 AGP AGP (Accelerated Graphics Port) is enabled.
99 ALSA ALSA sound support is enabled.
100 APIC APIC support is enabled.
101 APM Advanced Power Management support is enabled.
102 ARM ARM architecture is enabled.
103 ARM64 ARM64 architecture is enabled.
104 AX25 Appropriate AX.25 support is enabled.
105 CLK Common clock infrastructure is enabled.
106 CMA Contiguous Memory Area support is enabled.
107 DRM Direct Rendering Management support is enabled.
108 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
109 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
110 EFI EFI Partitioning (GPT) is enabled
111 EIDE EIDE/ATAPI support is enabled.
112 EVM Extended Verification Module
113 FB The frame buffer device is enabled.
114 FTRACE Function tracing enabled.
115 GCOV GCOV profiling is enabled.
116 HW Appropriate hardware is enabled.
117 IA-64 IA-64 architecture is enabled.
118 IMA Integrity measurement architecture is enabled.
119 IOSCHED More than one I/O scheduler is enabled.
120 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
121 IPV6 IPv6 support is enabled.
122 ISAPNP ISA PnP code is enabled.
123 ISDN Appropriate ISDN support is enabled.
124 ISOL CPU Isolation is enabled.
125 JOY Appropriate joystick support is enabled.
126 KGDB Kernel debugger support is enabled.
127 KVM Kernel Virtual Machine support is enabled.
128 LIBATA Libata driver is enabled
129 LP Printer support is enabled.
130 LOOP Loopback device support is enabled.
131 M68k M68k architecture is enabled.
132 These options have more detailed description inside of
133 Documentation/m68k/kernel-options.rst.
134 MDA MDA console support is enabled.
135 MIPS MIPS architecture is enabled.
136 MOUSE Appropriate mouse support is enabled.
137 MSI Message Signaled Interrupts (PCI).
138 MTD MTD (Memory Technology Device) support is enabled.
139 NET Appropriate network support is enabled.
140 NUMA NUMA support is enabled.
141 NFS Appropriate NFS support is enabled.
142 OF Devicetree is enabled.
143 OSS OSS sound support is enabled.
144 PV_OPS A paravirtualized kernel is enabled.
145 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
146 PARISC The PA-RISC architecture is enabled.
147 PCI PCI bus support is enabled.
148 PCIE PCI Express support is enabled.
149 PCMCIA The PCMCIA subsystem is enabled.
150 PNP Plug & Play support is enabled.
151 PPC PowerPC architecture is enabled.
152 PPT Parallel port support is enabled.
153 PS2 Appropriate PS/2 support is enabled.
154 RAM RAM disk support is enabled.
155 RISCV RISCV architecture is enabled.
156 RDT Intel Resource Director Technology.
157 S390 S390 architecture is enabled.
158 SCSI Appropriate SCSI support is enabled.
159 A lot of drivers have their options described inside
160 the Documentation/scsi/ sub-directory.
161 SECURITY Different security models are enabled.
162 SELINUX SELinux support is enabled.
163 APPARMOR AppArmor support is enabled.
164 SERIAL Serial support is enabled.
165 SH SuperH architecture is enabled.
166 SMP The kernel is an SMP kernel.
167 SPARC Sparc architecture is enabled.
168 SWSUSP Software suspend (hibernation) is enabled.
169 SUSPEND System suspend states are enabled.
170 TPM TPM drivers are enabled.
171 TS Appropriate touchscreen support is enabled.
172 UMS USB Mass Storage support is enabled.
173 USB USB support is enabled.
174 USBHID USB Human Interface Device support is enabled.
175 V4L Video For Linux support is enabled.
176 VMMIO Driver for memory mapped virtio devices is enabled.
177 VGA The VGA console has been enabled.
178 VT Virtual terminal support is enabled.
179 WDT Watchdog support is enabled.
180 XT IBM PC/XT MFM hard disk support is enabled.
181 X86-32 X86-32, aka i386 architecture is enabled.
182 X86-64 X86-64 architecture is enabled.
183 More X86-64 boot options can be found in
184 Documentation/x86/x86_64/boot-options.rst.
185 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
186 X86_UV SGI UV support is enabled.
187 XEN Xen support is enabled
188 XTENSA xtensa architecture is enabled.
189
190In addition, the following text indicates that the option::
191
192 BUGS= Relates to possible processor bugs on the said processor.
193 KNL Is a kernel start-up parameter.
194 BOOT Is a boot loader parameter.
195
196Parameters denoted with BOOT are actually interpreted by the boot
197loader, and have no meaning to the kernel directly.
198Do not modify the syntax of boot loader parameters without extreme
199need or coordination with <Documentation/x86/boot.rst>.
200
201There are also arch-specific kernel-parameters not documented here.
202See for example <Documentation/x86/x86_64/boot-options.rst>.
203
204Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
205a trailing = on the name of any parameter states that that parameter will
206be entered as an environment variable, whereas its absence indicates that
207it will appear as a kernel argument readable via /proc/cmdline by programs
208running once the system is up.
209
210The number of kernel parameters is not limited, but the length of the
211complete command line (parameters including spaces etc.) is limited to
212a fixed number of characters. This limit depends on the architecture
213and is between 256 and 4096 characters. It is defined in the file
214./include/asm/setup.h as COMMAND_LINE_SIZE.
215
216Finally, the [KMG] suffix is commonly described after a number of kernel
217parameter values. These 'K', 'M', and 'G' letters represent the _binary_
218multipliers 'Kilo', 'Mega', and 'Giga', equaling 2^10, 2^20, and 2^30
219bytes respectively. Such letter suffixes can also be entirely omitted:
220
221.. include:: kernel-parameters.txt
222 :literal:
223
224Todo
225----
226
227 Add more DRM drivers.
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
30This document may not be entirely up to date and comprehensive. The command
31"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
32module. Loadable modules, after being loaded into the running kernel, also
33reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
34parameters may be changed at runtime by the command
35``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
36
37Special handling
38----------------
39
40Hyphens (dashes) and underscores are equivalent in parameter names, so::
41
42 log_buf_len=1M print-fatal-signals=1
43
44can also be entered as::
45
46 log-buf-len=1M print_fatal_signals=1
47
48Double-quotes can be used to protect spaces in values, e.g.::
49
50 param="spaces in here"
51
52cpu lists
53~~~~~~~~~
54
55Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
56nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
57
58 <cpu number>,...,<cpu number>
59
60or
61
62 <cpu number>-<cpu number>
63 (must be a positive range in ascending order)
64
65or a mixture
66
67<cpu number>,...,<cpu number>-<cpu number>
68
69Note that for the special case of a range one can split the range into equal
70sized groups and for each group use some amount from the beginning of that
71group:
72
73 <cpu number>-<cpu number>:<used size>/<group size>
74
75For example one can add to the command line following parameter:
76
77 isolcpus=1,2,10-20,100-2000:2/25
78
79where the final item represents CPUs 100,101,125,126,150,151,...
80
81The value "N" can be used to represent the numerically last CPU on the system,
82i.e "foo_cpus=16-N" would be equivalent to "16-31" on a 32 core system.
83
84Keep in mind that "N" is dynamic, so if system changes cause the bitmap width
85to change, such as less cores in the CPU list, then N and any ranges using N
86will also change. Use the same on a small 4 core system, and "16-N" becomes
87"16-3" and now the same boot input will be flagged as invalid (start > end).
88
89The special case-tolerant group name "all" has a meaning of selecting all CPUs,
90so that "nohz_full=all" is the equivalent of "nohz_full=0-N".
91
92The semantics of "N" and "all" is supported on a level of bitmaps and holds for
93all users of bitmap_parselist().
94
95Metric suffixes
96~~~~~~~~~~~~~~~
97
98The [KMG] suffix is commonly described after a number of kernel
99parameter values. 'K', 'M', 'G', 'T', 'P', and 'E' suffixes are allowed.
100These letters represent the _binary_ multipliers 'Kilo', 'Mega', 'Giga',
101'Tera', 'Peta', and 'Exa', equaling 2^10, 2^20, 2^30, 2^40, 2^50, and
1022^60 bytes respectively. Such letter suffixes can also be entirely omitted.
103
104Kernel Build Options
105--------------------
106
107The parameters listed below are only valid if certain kernel build options
108were enabled and if respective hardware is present. This list should be kept
109in alphabetical order. The text in square brackets at the beginning
110of each description states the restrictions within which a parameter
111is applicable::
112
113 ACPI ACPI support is enabled.
114 AGP AGP (Accelerated Graphics Port) is enabled.
115 ALSA ALSA sound support is enabled.
116 APIC APIC support is enabled.
117 APM Advanced Power Management support is enabled.
118 APPARMOR AppArmor support is enabled.
119 ARM ARM architecture is enabled.
120 ARM64 ARM64 architecture is enabled.
121 AX25 Appropriate AX.25 support is enabled.
122 CLK Common clock infrastructure is enabled.
123 CMA Contiguous Memory Area support is enabled.
124 DRM Direct Rendering Management support is enabled.
125 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
126 EARLY Parameter processed too early to be embedded in initrd.
127 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
128 EFI EFI Partitioning (GPT) is enabled
129 EVM Extended Verification Module
130 FB The frame buffer device is enabled.
131 FTRACE Function tracing enabled.
132 GCOV GCOV profiling is enabled.
133 HIBERNATION HIBERNATION is enabled.
134 HW Appropriate hardware is enabled.
135 HYPER_V HYPERV support is enabled.
136 IMA Integrity measurement architecture is enabled.
137 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
138 IPV6 IPv6 support is enabled.
139 ISAPNP ISA PnP code is enabled.
140 ISDN Appropriate ISDN support is enabled.
141 ISOL CPU Isolation is enabled.
142 JOY Appropriate joystick support is enabled.
143 KGDB Kernel debugger support is enabled.
144 KVM Kernel Virtual Machine support is enabled.
145 LIBATA Libata driver is enabled
146 LOONGARCH LoongArch architecture is enabled.
147 LOOP Loopback device support is enabled.
148 LP Printer support is enabled.
149 M68k M68k architecture is enabled.
150 These options have more detailed description inside of
151 Documentation/arch/m68k/kernel-options.rst.
152 MDA MDA console support is enabled.
153 MIPS MIPS architecture is enabled.
154 MOUSE Appropriate mouse support is enabled.
155 MSI Message Signaled Interrupts (PCI).
156 MTD MTD (Memory Technology Device) support is enabled.
157 NET Appropriate network support is enabled.
158 NFS Appropriate NFS support is enabled.
159 NUMA NUMA support is enabled.
160 OF Devicetree is enabled.
161 PARISC The PA-RISC architecture is enabled.
162 PCI PCI bus support is enabled.
163 PCIE PCI Express support is enabled.
164 PCMCIA The PCMCIA subsystem is enabled.
165 PNP Plug & Play support is enabled.
166 PPC PowerPC architecture is enabled.
167 PPT Parallel port support is enabled.
168 PS2 Appropriate PS/2 support is enabled.
169 PV_OPS A paravirtualized kernel is enabled.
170 RAM RAM disk support is enabled.
171 RDT Intel Resource Director Technology.
172 RISCV RISCV architecture is enabled.
173 S390 S390 architecture is enabled.
174 SCSI Appropriate SCSI support is enabled.
175 A lot of drivers have their options described inside
176 the Documentation/scsi/ sub-directory.
177 SDW SoundWire support is enabled.
178 SECURITY Different security models are enabled.
179 SELINUX SELinux support is enabled.
180 SERIAL Serial support is enabled.
181 SH SuperH architecture is enabled.
182 SMP The kernel is an SMP kernel.
183 SPARC Sparc architecture is enabled.
184 SUSPEND System suspend states are enabled.
185 SWSUSP Software suspend (hibernation) is enabled.
186 TPM TPM drivers are enabled.
187 UMS USB Mass Storage support is enabled.
188 USB USB support is enabled.
189 USBHID USB Human Interface Device support is enabled.
190 V4L Video For Linux support is enabled.
191 VGA The VGA console has been enabled.
192 VMMIO Driver for memory mapped virtio devices is enabled.
193 VT Virtual terminal support is enabled.
194 WDT Watchdog support is enabled.
195 X86-32 X86-32, aka i386 architecture is enabled.
196 X86-64 X86-64 architecture is enabled.
197 More X86-64 boot options can be found in
198 Documentation/arch/x86/x86_64/boot-options.rst.
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.
216See for example <Documentation/arch/x86/x86_64/boot-options.rst>.
217
218Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
219a trailing = on the name of any parameter states that that parameter will
220be entered as an environment variable, whereas its absence indicates that
221it will appear as a kernel argument readable via /proc/cmdline by programs
222running once the system is up.
223
224The number of kernel parameters is not limited, but the length of the
225complete command line (parameters including spaces etc.) is limited to
226a fixed number of characters. This limit depends on the architecture
227and is between 256 and 4096 characters. It is defined in the file
228./include/uapi/asm-generic/setup.h as COMMAND_LINE_SIZE.
229
230.. include:: kernel-parameters.txt
231 :literal: