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FreeBSD man pages : sysctl (8)
SYSCTL(8)		FreeBSD System Manager's Manual 	     SYSCTL(8)

NAME

sysctl - get or set kernel state

SYNOPSIS

sysctl [-beNnox] name[=value] ... sysctl [-beNnox] -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. -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. -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, use the following code: listsysctls () { set -A reply $(sysctl -AN ${1%.*}) } compctl -K listsysctls sysctl -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). -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, devices (dev_t), 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, systat, and netstat. 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 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 machdep.console_device dev_t no machdep.adjkerntz integer yes machdep.disable_rtc_set integer yes 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

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 <netinet/icmp_var.h> definitions for fourth level ICMP identifiers <netinet/udp_var.h> definitions for fourth level UDP identifiers

COMPATIBILITY

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

SEE ALSO

sysctl(3), sysctl.conf(5)

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 4.8 March 10, 2002 FreeBSD 4.8