1 .\" Copyright (c) 2003 Joseph Koshy
3 .\" Redistribution and use in source and binary forms, with or without
4 .\" modification, are permitted provided that the following conditions
6 .\" 1. Redistributions of source code must retain the above copyright
7 .\" notice, this list of conditions and the following disclaimer.
8 .\" 2. Redistributions in binary form must reproduce the above copyright
9 .\" notice, this list of conditions and the following disclaimer in the
10 .\" documentation and/or other materials provided with the distribution.
12 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
13 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
14 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
15 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
16 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
17 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
18 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
19 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
20 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
21 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 .Nd kernel configuration file format
33 A kernel configuration file specifies the configuration of a
38 to create a build environment where a kernel may be built using
41 A kernel configuration file comprises a sequence of specification
44 A specification directive starts with a keyword at the beginning
45 of the line and is followed by additional parameters.
47 A specification directive may be terminated by a semicolon
50 Long input lines may be broken into shorter lines by starting the
51 second and subsequent lines with a white space character.
59 A double quote character
61 starts a quoted string.
62 All characters up to the next quote character form the value
66 character may be inserted into a quoted string by
70 Numbers are specified using
76 character starts a comment; all characters from the
78 character till the end of the current line are ignored.
80 Whitespace between tokens is ignored, except inside quoted strings.
81 Whitespace following a comment line is ignored.
82 .Ss Configuration Directives
83 Kernel configuration directives may appear in any order
84 in a kernel configuration file.
85 Directives are processed in order of appearance with subsequent
86 directive lines overriding the effect of prior ones.
88 The list of keywords and their meanings are as follows:
90 .Bl -tag -width indent -compact
91 .\" -------- CPU --------
93 Specify the CPU this kernel will run on.
94 There can be more than one
96 directive in a configuration file.
97 The allowed list of CPU names is architecture specific and is
99 .Pa sys/conf/options. Ns Aq Ar arch .
100 .\" -------- DEVICE --------
102 .It Ic device Ar name Op , Ar name Op ...
103 .It Ic devices Ar name Op , Ar name Op ...
104 Configures the specified devices
105 for inclusion into the kernel image.
106 Devices that are common to all architectures are
109 Devices that are specific to architecture
111 are defined in the file
112 .Pa sys/conf/files. Ns Aq Ar arch .
113 .\" -------- ENV --------
115 .It Ic env Ar filename
116 Specifies a filename containing a kernel environment definition.
117 The kernel normally uses an environment prepared for it at boot time
120 This directive makes the kernel ignore the boot environment and use
121 the compiled-in environment instead, unless the boot environment contains
122 .Va static_env.disabled=1 .
124 This directive is useful for setting kernel tunables in
125 embedded environments that do not start from
127 .\" -------- FILES --------
129 .It Ic files Ar filename
130 Specifies a file containing a list of files specific to that kernel
131 configuration file (a la
132 .Pa files. Ns Aq Ar arch ) .
133 .\" -------- HINTS --------
135 .It Ic hints Ar filename
136 Specifies a file to load a static device configuration specification
140 onwards, the kernel reads the system's device configuration at boot
142 .Xr device.hints 5 ) .
143 This directive configures the kernel to use the static device configuration
146 unless the boot environment contains
147 .Va static_hints.disabled=1 .
150 must conform to the syntax specified by
152 Multiple hints lines are allowed.
153 The resulting hints will be the files concatenated in the order of appearance.
154 .\" -------- IDENT --------
157 Set the kernel name to
161 directive is required.
162 .\" -------- INCLUDE --------
164 .It Ic include Ar filename
165 Read subsequent text from file
167 and return to the current file after
169 is successfully processed.
170 .\" -------- MACHINE --------
172 .It Ic machine Ar arch Op Ar cpuarch
173 Specifies the architecture of the machine the kernel is being
179 .Bl -tag -width ".Cm powerpc" -compact
181 The DEC Alpha architecture.
183 The ARM architecture.
185 The AMD x86-64 architecture.
187 The Intel x86 based PC architecture.
189 The MIPS architecture.
191 The IBM PowerPC architecture.
193 The Sun Sparc64 architecture.
198 is specified, it points
200 to the cpu architecture of the machine.
203 is not specified, it is assumed to be the same as
206 corresponds to MACHINE.
208 corresponds to MACHINE_ARCH.
210 A kernel configuration file may have only one
213 .\" -------- MAKEOPTION --------
215 .It Ic makeoption Ar options
216 .It Ic makeoptions Ar options
219 to the generated makefile.
223 argument is a comma separated list of one or more option
225 Each option specification has the form
227 .D1 Ar MakeVariableName Ns Op = Ns Ar Value
228 .D1 Ar MakeVariableName Ns += Ns Ar Value
230 and results in the appropriate
232 variable definition being inserted into the generated makefile.
233 If only the name of the
235 variable is specified,
237 is assumed to be the empty string.
240 .Bd -literal -offset indent -compact
241 makeoptions MYMAKEOPTION="foo"
242 makeoptions MYMAKEOPTION+="bar"
243 makeoptions MYNULLMAKEOPTION
245 .\" -------- MAXUSERS --------
247 .It Ic maxusers Ar number
248 This optional directive is used to configure the size
249 of some kernel data structures.
252 can be 0 (the default) or an integer greater than or equal to 2.
253 A value of 0 indicates that the kernel should configure
254 its data structures according to the size of available
256 If auto configuration is requested, the kernel will set
257 this tunable to a value between 32 and 384.
261 this tunable can also be set at boot time using
263 .\" -------- NOCPU --------
265 .It Ic nocpu Ar cputype
266 Remove the specified CPU
267 from the list of previously selected CPUs.
268 This directive can be used to cancel the effect of
270 directives in files included using
272 .\" -------- NODEVICE --------
274 .It Ic nodevice Ar name Op , Ar name Op ...
275 .It Ic nodevices Ar name Op , Ar name Op ...
276 Remove the specified devices
277 from the list of previously selected devices.
278 This directive can be used to cancel the effects of
282 directives in files included using
284 .\" -------- NOMAKEOPTION --------
286 .It Ic nomakeoption Ar name
287 .It Ic nomakeoptions Ar name
288 Removes previously defined
292 from the kernel build.
293 This directive can be used to cancel the effects of
295 directives in files included using
297 .\" -------- NOOPTION --------
299 .It Ic nooption Ar name Op , Ar name Op ...
300 .It Ic nooptions Ar name Op , Ar name Op ...
301 Remove the specified kernel options
302 from the list of previously defined options.
303 This directive can be used to cancel the effects of
307 directives in files included using
309 .\" -------- OPTIONS --------
311 .It Ic option Ar optionspec Op , Ar optionspec Op ...
312 .It Ic options Ar optionspec Op , Ar optionspec Op ...
313 Add compile time kernel options to the kernel build.
314 Each option specification has the form
316 .D1 Ar name Ns Op = Ns Ar value
320 is not specified, it is assumed to be
322 Options common to all architectures are specified in
324 .Pa sys/conf/options .
325 Options specific to architecture
327 are specified in the file
328 .Pa sys/conf/options. Ns Aq Ar arch .
329 .\" -------- PROFILE --------
331 .It Ic profile Ar number
332 Enables kernel profiling if
337 is 2 or greater, the kernel is configured for
338 high-resolution profiling.
339 Kernels can also be built for profiling using the
344 .Ss Obsolete Directives
345 The following kernel configuration directives are obsolete.
346 .Bl -tag -width indent
347 .\" -------- CONFIG --------
349 This directive was used to specify the device to be used for the root
353 onwards, this information is passed to a booting kernel by
357 .Bl -tag -width ".Pa sys/conf/Makefile. Ns Ar arch" -compact
358 .It Pa sys/compile/ Ns Ar NAME
359 Compile directory created from a kernel configuration.
360 .It Pa sys/conf/Makefile. Ns Ar arch
362 fragments for architecture
364 .It Pa sys/conf/files
365 Devices common to all architectures.
366 .It Pa sys/conf/files. Ns Ar arch
367 Devices for architecture
369 .It Pa sys/conf/options
370 Options common to all architectures.
371 .It Pa sys/conf/options. Ns Ar arch
372 Options for architecture
384 .%T "Building 4.4BSD Kernels with Config"
385 .%A "Samuel J. Leffler"
386 .%A "Michael J. Karels"
391 utility first appeared in
393 and was subsequently revised in
396 The kernel configuration mechanism changed further in
400 moving toward an architecture supporting dynamic kernel