xref: /linux/Documentation/admin-guide/kernel-parameters.rst (revision ec63e2a4897075e427c121d863bd89c44578094f)
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