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SYSCTL(8)		FreeBSD	System Manager's Manual		     SYSCTL(8)

     sysctl -- get or set kernel state

     sysctl [-bdehiNnoRTtqx] [-B bufsize] [-f filename]	name[=value] ...
     sysctl [-bdehNnoRTtqx] [-B	bufsize] -a

     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.

     -B	bufsize
	     Set the buffer size to read from the sysctl to bufsize.  This is
	     necessary for a sysctl that has variable length, and the probe
	     value of 0	is a valid length, such	as kern.arandom.

     -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.

     -f	filename
	     Specify a file which contains a pair of name and value in each
	     line.  sysctl reads and processes the specified file first	and
	     then processes the	name and value pairs in	the command line argu-

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

     -i	     Ignore unknown OIDs.  The purpose is to make use of sysctl	for
	     collecting	data from a variety of machines	(not all of which are
	     necessarily running exactly the same software) easier.

     -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) (ports/shells/zsh),	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.

     -q	     Suppress some warnings generated by sysctl	to standard error.

     -T	     Display only variables that are settable via loader

     -t	     Print the type of the variable.

     -W	     Display only writable variables that are not statistical.	Useful
	     for determining the set of	runtime	tunable	sysctls.

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

     -x	     As	-o, but	prints a hex dump of the entire	value instead of just
	     the first few bytes.

     The information available from sysctl consists of integers, strings, and
     opaque types.  The	sysctl utility only knows about	a couple of opaque
     types, and	will resort to hexdumps	for the	rest.  The opaque information
     is	much more useful if retrieved by special purpose programs such as
     ps(1), systat(1), and netstat(1).

     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	and integer values can be set using

     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.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
     hw.realmem				      integer	    no
     machdep.adjkerntz			      integer	    yes
     machdep.disable_rtc_set		      integer	    yes
     machdep.guessed_bootdev		      string	    no
     user.cs_path			      string	    no
     user.bc_base_max			      integer	    no
     user.bc_dim_max			      integer	    no
     user.bc_scale_max			      integer	    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

     <sys/sysctl.h>	   definitions for top level identifiers, second level
			   kernel and hardware identifiers, and	user level
     <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-
     <netinet/in.h>	   definitions for third level Internet	identifiers
			   and fourth level IP identifiers
     <netinet/icmp_var.h>  definitions for fourth level	ICMP identifiers
     <netinet/udp_var.h>   definitions for fourth level	UDP identifiers

     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

     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

     The -w option has been deprecated and is silently ignored.

     sysctl(3),	loader.conf(5),	sysctl.conf(5),	loader(8)

     A sysctl utility first appeared in	4.4BSD.

     In	FreeBSD	2.2, sysctl was	significantly remodeled.

     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.

FreeBSD	11.0		       December	10, 2015		  FreeBSD 11.0


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