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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
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.
1The kernel's command-line parameters
2====================================
3
4The following is a consolidated list of the kernel parameters as
5implemented by the __setup(), core_param() and module_param() macros
6and sorted into English Dictionary order (defined as ignoring all
7punctuation and sorting digits before letters in a case insensitive
8manner), and with descriptions where known.
9
10The kernel parses parameters from the kernel command line up to "--";
11if it doesn't recognize a parameter and it doesn't contain a '.', the
12parameter gets passed to init: parameters with '=' go into init's
13environment, others are passed as command line arguments to init.
14Everything after "--" is passed as an argument to init.
15
16Module parameters can be specified in two ways: via the kernel command
17line with a module name prefix, or via modprobe, e.g.::
18
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
21
22Parameters for modules which are built into the kernel need to be
23specified on the kernel command line. modprobe looks through the
24kernel command line (/proc/cmdline) and collects module parameters
25when it loads a module, so the kernel command line can be used for
26loadable modules too.
27
28Hyphens (dashes) and underscores are equivalent in parameter names, so::
29
30 log_buf_len=1M print-fatal-signals=1
31
32can also be entered as::
33
34 log-buf-len=1M print_fatal_signals=1
35
36Double-quotes can be used to protect spaces in values, e.g.::
37
38 param="spaces in here"
39
40cpu lists:
41----------
42
43Some kernel parameters take a list of CPUs as a value, e.g. isolcpus,
44nohz_full, irqaffinity, rcu_nocbs. The format of this list is:
45
46 <cpu number>,...,<cpu number>
47
48or
49
50 <cpu number>-<cpu number>
51 (must be a positive range in ascending order)
52
53or a mixture
54
55<cpu number>,...,<cpu number>-<cpu number>
56
57Note that for the special case of a range one can split the range into equal
58sized groups and for each group use some amount from the beginning of that
59group:
60
61 <cpu number>-cpu number>:<used size>/<group size>
62
63For example one can add to the command line following parameter:
64
65 isolcpus=1,2,10-20,100-2000:2/25
66
67where the final item represents CPUs 100,101,125,126,150,151,...
68
69
70
71This document may not be entirely up to date and comprehensive. The command
72"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
73module. Loadable modules, after being loaded into the running kernel, also
74reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
75parameters may be changed at runtime by the command
76``echo -n ${value} > /sys/module/${modulename}/parameters/${parm}``.
77
78The parameters listed below are only valid if certain kernel build options were
79enabled and if respective hardware is present. The text in square brackets at
80the beginning of each description states the restrictions within which a
81parameter is applicable::
82
83 ACPI ACPI support is enabled.
84 AGP AGP (Accelerated Graphics Port) is enabled.
85 ALSA ALSA sound support is enabled.
86 APIC APIC support is enabled.
87 APM Advanced Power Management support is enabled.
88 ARM ARM architecture is enabled.
89 AVR32 AVR32 architecture is enabled.
90 AX25 Appropriate AX.25 support is enabled.
91 BLACKFIN Blackfin architecture 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 JOY Appropriate joystick support is enabled.
112 KGDB Kernel debugger support is enabled.
113 KVM Kernel Virtual Machine support is enabled.
114 LIBATA Libata driver is enabled
115 LP Printer support is enabled.
116 LOOP Loopback device support is enabled.
117 M68k M68k architecture is enabled.
118 These options have more detailed description inside of
119 Documentation/m68k/kernel-options.txt.
120 MDA MDA console support is enabled.
121 MIPS MIPS architecture is enabled.
122 MOUSE Appropriate mouse support is enabled.
123 MSI Message Signaled Interrupts (PCI).
124 MTD MTD (Memory Technology Device) support is enabled.
125 NET Appropriate network support is enabled.
126 NUMA NUMA support is enabled.
127 NFS Appropriate NFS support is enabled.
128 OSS OSS sound support is enabled.
129 PV_OPS A paravirtualized kernel is enabled.
130 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
131 PARISC The PA-RISC architecture is enabled.
132 PCI PCI bus support is enabled.
133 PCIE PCI Express support is enabled.
134 PCMCIA The PCMCIA subsystem is enabled.
135 PNP Plug & Play support is enabled.
136 PPC PowerPC architecture is enabled.
137 PPT Parallel port support is enabled.
138 PS2 Appropriate PS/2 support is enabled.
139 RAM RAM disk support is enabled.
140 S390 S390 architecture is enabled.
141 SCSI Appropriate SCSI support is enabled.
142 A lot of drivers have their options described inside
143 the Documentation/scsi/ sub-directory.
144 SECURITY Different security models are enabled.
145 SELINUX SELinux support is enabled.
146 APPARMOR AppArmor support is enabled.
147 SERIAL Serial support is enabled.
148 SH SuperH architecture is enabled.
149 SMP The kernel is an SMP kernel.
150 SPARC Sparc architecture is enabled.
151 SWSUSP Software suspend (hibernation) is enabled.
152 SUSPEND System suspend states are enabled.
153 TPM TPM drivers are enabled.
154 TS Appropriate touchscreen support is enabled.
155 UMS USB Mass Storage support is enabled.
156 USB USB support is enabled.
157 USBHID USB Human Interface Device support is enabled.
158 V4L Video For Linux support is enabled.
159 VMMIO Driver for memory mapped virtio devices is enabled.
160 VGA The VGA console has been enabled.
161 VT Virtual terminal support is enabled.
162 WDT Watchdog support is enabled.
163 XT IBM PC/XT MFM hard disk support is enabled.
164 X86-32 X86-32, aka i386 architecture is enabled.
165 X86-64 X86-64 architecture is enabled.
166 More X86-64 boot options can be found in
167 Documentation/x86/x86_64/boot-options.txt .
168 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
169 X86_UV SGI UV support is enabled.
170 XEN Xen support is enabled
171
172In addition, the following text indicates that the option::
173
174 BUGS= Relates to possible processor bugs on the said processor.
175 KNL Is a kernel start-up parameter.
176 BOOT Is a boot loader parameter.
177
178Parameters denoted with BOOT are actually interpreted by the boot
179loader, and have no meaning to the kernel directly.
180Do not modify the syntax of boot loader parameters without extreme
181need or coordination with <Documentation/x86/boot.txt>.
182
183There are also arch-specific kernel-parameters not documented here.
184See for example <Documentation/x86/x86_64/boot-options.txt>.
185
186Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
187a trailing = on the name of any parameter states that that parameter will
188be entered as an environment variable, whereas its absence indicates that
189it will appear as a kernel argument readable via /proc/cmdline by programs
190running once the system is up.
191
192The number of kernel parameters is not limited, but the length of the
193complete command line (parameters including spaces etc.) is limited to
194a fixed number of characters. This limit depends on the architecture
195and is between 256 and 4096 characters. It is defined in the file
196./include/asm/setup.h as COMMAND_LINE_SIZE.
197
198Finally, the [KMG] suffix is commonly described after a number of kernel
199parameter values. These 'K', 'M', and 'G' letters represent the _binary_
200multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
201bytes respectively. Such letter suffixes can also be entirely omitted:
202
203.. include:: kernel-parameters.txt
204 :literal:
205
206Todo
207----
208
209 Add more DRM drivers.