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FreeBSD 11.0 - man page for sysctl (freebsd section 8)

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

     sysctl -- get or set kernel state

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

     -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

     -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 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 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

     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 pro-
     grams such as ps(1), systat(1), and netstat(1).

     Some of the variables which cannot be modified during normal system operation can be ini-
     tialized 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 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

     <sys/sysctl.h>	   definitions for top level identifiers, second level kernel and hard-
			   ware 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
     <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

	   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.

     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 facil-
     ity 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

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