1 .\" Copyright (c) 2003 Joseph Koshy
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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.
123 This directive is useful for setting kernel tunables in
124 embedded environments that do not start from
126 .\" -------- FILES --------
128 .It Ic files Ar filename
129 Specifies a file containing a list of files specific to that kernel
130 configuration file (a la
131 .Pa files. Ns Aq Ar arch ) .
132 .\" -------- HINTS --------
134 .It Ic hints Ar filename
135 Specifies a file to load a static device configuration specification
139 onwards, the kernel reads the system's device configuration at boot
141 .Xr device.hints 5 ) .
142 This directive configures the kernel to use the static device configuration
147 must conform to the syntax specified by
149 Multiple hints lines are allowed.
150 The resulting hints will be the files concatenated in the order of appearance.
151 .\" -------- IDENT --------
154 Set the kernel name to
158 directive is required.
159 .\" -------- INCLUDE --------
161 .It Ic include Ar filename
162 Read subsequent text from file
164 and return to the current file after
166 is successfully processed.
167 .\" -------- MACHINE --------
169 .It Ic machine Ar arch Op Ar cpuarch
170 Specifies the architecture of the machine the kernel is being
176 .Bl -tag -width ".Cm powerpc" -compact
178 The DEC Alpha architecture.
180 The ARM architecture.
182 The AMD x86-64 architecture.
184 The Intel x86 based PC architecture.
186 The Intel IA64 architecture.
188 The MIPS architecture.
190 The PC98 architecture.
192 The IBM PowerPC architecture.
194 The Sun Sparc64 architecture.
199 is specified, it points
201 to the cpu architecture of the machine.
204 architecture requires its cpu architecture
209 is not specified, it is assumed to be the same as
212 corresponds to MACHINE.
214 corresponds to MACHINE_ARCH.
216 A kernel configuration file may have only one
219 .\" -------- MAKEOPTION --------
221 .It Ic makeoption Ar options
222 .It Ic makeoptions Ar options
225 to the generated makefile.
229 argument is a comma separated list of one or more option
231 Each option specification has the form
233 .D1 Ar MakeVariableName Ns Op = Ns Ar Value
234 .D1 Ar MakeVariableName Ns += Ns Ar Value
236 and results in the appropriate
238 variable definition being inserted into the generated makefile.
239 If only the name of the
241 variable is specified,
243 is assumed to be the empty string.
246 .Bd -literal -offset indent -compact
247 makeoptions MYMAKEOPTION="foo"
248 makeoptions MYMAKEOPTION+="bar"
249 makeoptions MYNULLMAKEOPTION
251 .\" -------- MAXUSERS --------
253 .It Ic maxusers Ar number
254 This optional directive is used to configure the size
255 of some kernel data structures.
258 can be 0 (the default) or an integer greater than or equal to 2.
259 A value of 0 indicates that the kernel should configure
260 its data structures according to the size of available
262 If auto configuration is requested, the kernel will set
263 this tunable to a value between 32 and 384.
267 this tunable can also be set at boot time using
269 .\" -------- NOCPU --------
271 .It Ic nocpu Ar cputype
272 Remove the specified CPU
273 from the list of previously selected CPUs.
274 This directive can be used to cancel the effect of
276 directives in files included using
278 .\" -------- NODEVICE --------
280 .It Ic nodevice Ar name Op , Ar name Op ...
281 .It Ic nodevices Ar name Op , Ar name Op ...
282 Remove the specified devices
283 from the list of previously selected devices.
284 This directive can be used to cancel the effects of
288 directives in files included using
290 .\" -------- NOMAKEOPTION --------
292 .It Ic nomakeoption Ar name
293 .It Ic nomakeoptions Ar name
294 Removes previously defined
298 from the kernel build.
299 This directive can be used to cancel the effects of
301 directives in files included using
303 .\" -------- NOOPTION --------
305 .It Ic nooption Ar name Op , Ar name Op ...
306 .It Ic nooptions Ar name Op , Ar name Op ...
307 Remove the specified kernel options
308 from the list of previously defined options.
309 This directive can be used to cancel the effects of
313 directives in files included using
315 .\" -------- OPTIONS --------
317 .It Ic option Ar optionspec Op , Ar optionspec Op ...
318 .It Ic options Ar optionspec Op , Ar optionspec Op ...
319 Add compile time kernel options to the kernel build.
320 Each option specification has the form
322 .D1 Ar name Ns Op = Ns Ar value
326 is not specified, it is assumed to be
328 Options common to all architectures are specified in
330 .Pa sys/conf/options .
331 Options specific to architecture
333 are specified in the file
334 .Pa sys/conf/options. Ns Aq Ar arch .
335 .\" -------- PROFILE --------
337 .It Ic profile Ar number
338 Enables kernel profiling if
343 is 2 or greater, the kernel is configured for
344 high-resolution profiling.
345 Kernels can also be built for profiling using the
350 .Ss Obsolete Directives
351 The following kernel configuration directives are obsolete.
352 .Bl -tag -width indent
353 .\" -------- CONFIG --------
355 This directive was used to specify the device to be used for the root
359 onwards, this information is passed to a booting kernel by
363 .Bl -tag -width ".Pa sys/conf/Makefile. Ns Ar arch" -compact
364 .It Pa sys/compile/ Ns Ar NAME
365 Compile directory created from a kernel configuration.
366 .It Pa sys/conf/Makefile. Ns Ar arch
368 fragments for architecture
370 .It Pa sys/conf/files
371 Devices common to all architectures.
372 .It Pa sys/conf/files. Ns Ar arch
373 Devices for architecture
375 .It Pa sys/conf/options
376 Options common to all architectures.
377 .It Pa sys/conf/options. Ns Ar arch
378 Options for architecture
390 .%T "Building 4.4BSD Kernels with Config"
391 .%A "Samuel J. Leffler"
392 .%A "Michael J. Karels"
397 utility first appeared in
399 and was subsequently revised in
402 The kernel configuration mechanism changed further in
406 moving toward an architecture supporting dynamic kernel