SYSCTL(8) BSD System Manager's Manual SYSCTL(8)NAMEsysctl — get or set kernel state
SYNOPSISsysctl [-bdeNnox] name[=value] ...
sysctl [-bdeNnox] -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.
-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 (udev_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.
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 udev_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 long no
hw.usermem integer no
hw.pagesize integer no
hw.floatingpoint integer no
hw.machine_arch string no
hw.sensors.<xname>.<type><numt> struct no
machdep.console_device udev_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
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
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.
COMPATIBILITY
The -w option has been deprecated and is silently ignored.
SEE ALSOsysctl(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 3, 2011 BSD
