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

NAME

     sysctl -- get or set kernel state

SYNOPSIS

     sysctl [-bdehiNnoRTqx] [-B bufsize] [-f filename] name[=value] ...
     sysctl [-bdehNnoRTqx] [-B bufsize] -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 com-
	     mand 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 argument.

     -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 nec-
	     essarily 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 useful for setting shell variables.  For instance, to save the pagesize
	     in variable psize, use:

		   set psize=`sysctl -n hw.pagesize`

     -o      Show opaque variables (which are normally suppressed).  The format 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 (CTLFLAG_TUN).

     -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 operation can be initialized via loader(8) tunables.  This can for exam-
     ple 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 privilege can change the value.  String and integer values can be set
     using sysctl.

     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

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 identifiers
     <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

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

     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.

COMPATIBILITY

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

SEE ALSO

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

HISTORY

     A sysctl utility first appeared in 4.4BSD.

     In FreeBSD 2.2, sysctl was significantly remodeled.

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.

BSD
								 February 12, 2015							       BSD