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CONFIG(5)		    BSD 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).  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.
	     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 corre‐
	     sponds 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 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).

     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 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‐

BSD			       December 3, 2005				   BSD

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