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     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

   Lexical Structure
     A kernel configuration file comprises a sequence of specification directives.

     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 sys/conf/options.arch⟩.

     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

     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 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.  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 required.

     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.
             ia64     The Intel IA64 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 string.

                   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

     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 include.

     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


     sys/compile/NAME        Compile directory created from a kernel configuration.
     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), loader(8)

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


     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 configuration.