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CONFIG(5)                 FreeBSD File Formats Manual                CONFIG(5)

     config -- kernel configuration file format

     A kernel configuration file specifies the configuration of a FreeBSD ker-
     nel.  It is processed by config(8) to create a build environment where a
     kernel may be built using make(1).

   Lexical Structure
     A kernel configuration file comprises a sequence of specification direc-

     A specification directive starts with a keyword at the beginning of the
     line and is followed by additional parameters.

     A specification directive may be terminated by a semicolon `;' or by a
     newline.  Long input lines may be broken into shorter lines by starting
     the second and subsequent lines with a white space character.

     Case is significant, ``machine'' and ``MACHINE'' are different tokens.

     A double quote character `"' starts a quoted string.  All characters up
     to the next quote character form the value of the quoted string.  A `"'
     character may be inserted into a quoted string by using the sequence

     Numbers are specified using C-style syntax.

     A `#' character starts a comment; all characters from the `#' character
     till the end of the current line are ignored.

     Whitespace between tokens is ignored, except inside quoted strings.
     Whitespace following a comment line is ignored.

   Configuration Directives
     Kernel configuration directives may appear in any order in a kernel con-
     figuration file.  Directives are processed in order of appearance with
     subsequent directive lines overriding the effect of prior ones.

     The list of keywords and their meanings are as follows:

     cpu cputype
             Specify the CPU this kernel will run on.  There can be more than
             one cpu directive in a configuration file.  The allowed list of
             CPU names is architecture specific and is defined in the file

     device name [, name [...]]

     devices name [, name [...]]
             Configures the specified devices for inclusion into the kernel
             image.  Devices that are common to all architectures are defined
             in the file sys/conf/files.  Devices that are specific to archi-
             tecture arch are defined in the file sys/conf/files.<arch>.

     env filename
             Specifies a filename containing a kernel environment definition.
             The kernel normally uses an environment prepared for it at boot
             time by loader(8).  This directive makes the kernel ignore the
             boot environment and use the compiled-in environment instead.

             This directive is useful for setting kernel tunables in embedded
             environments that do not start from loader(8).

     files filename
             Specifies a file containing a list of files specific to that ker-
             nel configuration file (a la files.<arch>).

     hints filename
             Specifies a file to load a static device configuration specifica-
             tion from.  From FreeBSD 5.0 onwards, the kernel reads the sys-
             tem's device configuration at boot time (see device.hints(5)).
             This directive configures the kernel to use the static device
             configuration listed in filename.  The file filename must conform
             to the syntax specified by device.hints(5).

     ident name
             Set the kernel name to name.  At least one ident directive is

     include filename
             Read subsequent text from file filename and return to the current
             file after filename is successfully processed.

     machine arch
             Specifies the architecture of the machine the kernel is being
             compiled for.  Legal values for arch include:

             alpha    The DEC Alpha architecture.
             amd64    The AMD x86-64 architecture.
             i386     The Intel x86 based PC architecture.
             ia64     The Intel IA64 architecture.
             pc98     The PC98 architecture.
             powerpc  The IBM PowerPC architecture.
             sparc64  The Sun Sparc64 architecture.

             A kernel configuration file may have only one machine directive.

     makeoptions options
             Add options to the generated makefile.

             The options argument is a comma separated list of one or more
             option specifications.  Each option specification has the form


             and results in the appropriate make(1) variable definition being
             inserted into the generated makefile.  If only the name of the
             make(1) variable is specified, value is assumed to be the empty

                   makeoptions MYMAKEOPTION="foobar"
                   makeoptions MYNULLMAKEOPTION

     maxusers number
             This optional directive is used to configure the size of some
             kernel data structures.  The parameter number can be 0 (the
             default) or an integer greater than or equal to 2.  A value of 0
             indicates that the kernel should configure its data structures
             according to the size of available physical memory.  If auto con-
             figuration is requested, the kernel will set this tunable to a
             value between 32 and 384.

             As explained in tuning(7), this tunable can also be set at boot
             time using loader(8).

     nodevice name [, name [...]]

     nodevices name [, name [...]]
             Remove the specified devices from the list of previously selected
             devices.  This directive can be used to cancel the effects of
             device or devices directives in files included using include.

     nomakeoption name
             Removes previously defined make(1) option name from the kernel
             build.  This directive can be used to cancel the effects of
             makeoption directives in files included using include.

     nooption name [, name [...]]

     nooptions name [, name [...]]
             Remove the specified kernel options from the list of previously
             defined options.  This directive can be used to cancel the
             effects of option or options directives in files included using

     option optionspec [, optionspec [...]]

     options optionspec [, optionspec [...]]
             Add compile time kernel options to the kernel build.  Each option
             specification has the form


             If value is not specified, it is assumed to be NULL.  Options
             common to all architectures are specified in the file
             sys/conf/options.  Options specific to architecture arch are
             specified in the file sys/conf/options.<arch>.

     profile number
             Enables kernel profiling if number is non-zero.  If number is 2
             or greater, the kernel is configured for high-resolution profil-
             ing.  Kernels can also be built for profiling using the -p option
             to config(8).

   Obsolete Directives
     The following kernel configuration directives are obsolete.

     config  This directive was used to specify the device to be used for the
             root file system.  From FreeBSD 4.0 onwards, this information is
             passed to a booting kernel by loader(8).

     sys/compile/NAME        Compile directory created from a kernel configu-
     sys/conf/Makefile.arch  Makefile fragments for architecture arch.
     sys/conf/files          Devices common to all architectures.
     sys/conf/files.arch     Devices for architecture arch.
     sys/conf/options        Options common to all architectures.
     sys/conf/options.arch   Options for architecture arch.

     kenv(1), make(1), device.hints(5), loader.conf(5), config(8), kldload(8),

     Samuel J. Leffler and Michael J. Karels, Building 4.4BSD Kernels with

     The config(8) utility first appeared in 4.1BSD, and was subsequently
     revised in 4.4BSD.

     The kernel configuration mechanism changed further in FreeBSD 4.0 and
     FreeBSD 5.0, moving toward an architecture supporting dynamic kernel con-

FreeBSD 6.2                      May 13, 2004                      FreeBSD 6.2


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