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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
     kernel.  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

     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
     configuration 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
             architecture 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,
             unless the boot environment contains static_env.disabled=1.

             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
             kernel configuration file (a la files.<arch>).

     hints filename
             Specifies a file to load a static device configuration
             specification from.  From FreeBSD 5.0 onwards, the kernel reads
             the system's device configuration at boot time (see
             device.hints(5)).  This directive configures the kernel to use
             the static device configuration listed in filename, unless the
             boot environment contains static_hints.disabled=1.  The file
             filename must conform to the syntax specified by device.hints(5).
             Multiple hints lines are allowed.  The resulting hints will be
             the files concatenated in the order of appearance.

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

             alpha        The DEC Alpha architecture.
             arm          The ARM architecture.
             amd64        The AMD x86-64 architecture.
             i386         The Intel x86 based PC architecture.
             mips         The MIPS architecture.
             pc98         The PC98 architecture.
             powerpc      The IBM PowerPC architecture.
             sparc64      The Sun Sparc64 architecture.

             If argument cpuarch is specified, it points config(8) to the cpu
             architecture of the machine.  Currently the pc98 architecture
             requires its cpu architecture to be set to i386.  When cpuarch is
             not specified, it is assumed to be the same as arch.  arch
             corresponds to MACHINE.  cpuarch corresponds to MACHINE_ARCH.

             A kernel configuration file may have only one machine directive.

     makeoption options
     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="foo"
                   makeoptions MYMAKEOPTION+="bar"
                   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
             configuration 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).

     nocpu cputype
             Remove the specified CPU from the list of previously selected
             CPUs.  This directive can be used to cancel the effect of cpu
             directives in files included using include.

     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
     nomakeoptions 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
             profiling.  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 configuration.
     sys/conf/Makefile.arch             Makefile fragments for architecture
     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

FreeBSD 11.1-RELEASE-p4        February 21, 2016       FreeBSD 11.1-RELEASE-p4
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