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sysctl(8)

NAME

     sysctl -- get or set kernel state

SYNOPSIS

     sysctl [-bdehNnox] name[=value] ...
     sysctl [-bdehNnox] -a

DESCRIPTION

     The sysctl utility retrieves kernel state and allows processes with
     appropriate privilege to set kernel state.  The state to be retrieved or
     set is described using a ``Management Information Base'' (``MIB'') style
     name, described as a dotted set of components.

     The following options are available:

     -A      Equivalent to -o -a (for compatibility).

     -a      List all the currently available non-opaque values.  This option
	     is ignored if one or more variable names are specified on the
	     command line.

     -b      Force the value of the variable(s) to be output in raw, binary
	     format.  No names are printed and no terminating newlines are
	     output.  This is mostly useful with a single variable.

     -d      Print the description of the variable instead of its value.

     -e      Separate the name and the value of the variable(s) with `='.
	     This is useful for producing output which can be fed back to the
	     sysctl utility.  This option is ignored if either -N or -n is
	     specified, or a variable is being set.

     -h      Format output for human, rather than machine, readability.

     -N      Show only variable names, not their values.  This is particularly
	     useful with shells that offer programmable completion.  To enable
	     completion of variable names in zsh(1), use the following code:

		   listsysctls () { set -A reply $(sysctl -AN ${1%.*}) }
		   compctl -K listsysctls sysctl

	     To enable completion of variable names in tcsh(1), use:

		   complete sysctl 'n/*/`sysctl -Na`/'

     -n      Show only variable values, not their names.  This option is use-
	     ful for setting shell variables.  For instance, to save the page-
	     size in variable psize, use:

		   set psize=`sysctl -n hw.pagesize`

     -o      Show opaque variables (which are normally suppressed).  The for-
	     mat and length are printed, as well as a hex dump of the first
	     sixteen bytes of the value.

     -X      Equivalent to -x -a (for compatibility).


     Some of the variables which cannot be modified during normal system oper-
     ation can be initialized via loader(8) tunables.  This can for example be
     done by setting them in loader.conf(5).  Please refer to loader.conf(5)
     for more information on which tunables are available and how to set them.

     The string and integer information is summarized below.  For a detailed
     description of these variable see sysctl(3).

     The changeable column indicates whether a process with appropriate privi-
     lege can change the value.  String, integer, and devices values can be
     set using sysctl.	For device values, value can be specified as a charac-
     ter device special file name.  Special values off and none denote ``no
     device''.

     Name				      Type	    Changeable
     kern.ostype			      string	    no
     kern.osrelease			      string	    no
     kern.osrevision			      integer	    no
     kern.version			      string	    no
     kern.maxvnodes			      integer	    yes
     kern.maxproc			      integer	    no
     kern.maxprocperuid 		      integer	    yes
     kern.maxfiles			      integer	    yes
     kern.maxfilesperproc		      integer	    yes
     kern.argmax			      integer	    no
     kern.securelevel			      integer	    raise only
     kern.hostname			      string	    yes
     kern.hostid			      integer	    yes
     kern.clockrate			      struct	    no
     kern.posix1version 		      integer	    no
     kern.ngroups			      integer	    no
     kern.job_control			      integer	    no
     kern.saved_ids			      integer	    no
     kern.boottime			      struct	    no
     kern.domainname			      string	    yes
     kern.filedelay			      integer	    yes
     kern.dirdelay			      integer	    yes
     kern.metadelay			      integer	    yes
     kern.osreldate			      string	    no
     kern.bootfile			      string	    yes
     kern.corefile			      string	    yes
     kern.dumpdev			      dev_t	    yes
     kern.logsigexit			      integer	    yes
     security.bsd.suser_enabled 	      integer	    yes
     security.bsd.see_other_uids	      integer	    yes
     security.bsd.unprivileged_proc_debug     integer	    yes
     security.bsd.unprivileged_read_msgbuf    integer	    yes
     vm.loadavg 			      struct	    no
     hw.machine 			      string	    no
     hw.model				      string	    no
     hw.ncpu				      integer	    no
     hw.byteorder			      integer	    no
     hw.physmem 			      integer	    no
     hw.usermem 			      integer	    no
     hw.pagesize			      integer	    no
     hw.floatingpoint			      integer	    no
     hw.machine_arch			      string	    no
     user.bc_string_max 		      integer	    no
     user.coll_weights_max		      integer	    no
     user.expr_nest_max 		      integer	    no
     user.line_max			      integer	    no
     user.re_dup_max			      integer	    no
     user.posix2_version		      integer	    no
     user.posix2_c_bind 		      integer	    no
     user.posix2_c_dev			      integer	    no
     user.posix2_char_term		      integer	    no
     user.posix2_fort_dev		      integer	    no
     user.posix2_fort_run		      integer	    no
     user.posix2_localedef		      integer	    no
     user.posix2_sw_dev 		      integer	    no
     user.posix2_upe			      integer	    no
     user.stream_max			      integer	    no
     user.tzname_max			      integer	    no

EXAMPLES

     For example, to retrieve the maximum number of processes allowed in the
     system, one would use the following request:

	   sysctl kern.maxproc

     To set the maximum number of processes allowed per uid to 1000, one would
     use the following request:

	   sysctl kern.maxprocperuid=1000

     The device used for crash dumps can be specified using:

	   sysctl kern.dumpdev=/dev/somedev

     which is equivalent to

	   dumpon /dev/somedev

     Information about the system clock rate may be obtained with:

	   sysctl kern.clockrate

     Information about the load average history may be obtained with:

	   sysctl vm.loadavg

     More variables than these exist, and the best and likely only place to
     search for their deeper meaning is undoubtedly the source where they are
     defined.

FILES

     <sys/sysctl.h>	   definitions for top level identifiers, second level
			   kernel and hardware identifiers, and user level
			   identifiers
     <sys/socket.h>	   definitions for second level network identifiers
     <sys/gmon.h>	   definitions for third level profiling identifiers
     <vm/vm_param.h>	   definitions for second level virtual memory identi-
			   fiers
     <netinet/in.h>	   definitions for third level Internet identifiers
			   and fourth level IP identifiers

BUGS

     The sysctl utility presently exploits an undocumented interface to the
     kernel sysctl facility to traverse the sysctl tree and to retrieve format
     and name information.  This correct interface is being thought about for
     the time being.

HISTORY

     A sysctl utility first appeared in 4.4BSD.

     In FreeBSD 2.2, sysctl was significantly remodeled.

FreeBSD 5.4			March 10, 2002			   FreeBSD 5.4

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