SYSCTL(8) System Manager's Manual SYSCTL(8)
NAME
sysctl - get or set kernel state
SYNOPSIS
sysctl [ -n ] name ...
sysctl [ -n ] -w name=value ...
sysctl [ -n ] -aA
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 -a flag can
be used to list all the currently available string or integer values. The -A flag will list all the known MIB names including tables.
Those with string or integer values will be printed as with the -a flag; for the table values, the name of the utility to retrieve them is
given.
The -n flag specifies that the printing of the field name should be suppressed and that only its value should be output. This flag is use-
ful for setting shell variables. For example, to save the pagesize in variable psize, use:
set psize=`sysctl -n hw.pagesize`
If just a MIB style name is given, the corresponding value is retrieved. If a value is to be set, the -w flag must be specified and the
MIB name followed by an equal sign and the new value to be used.
The information available from sysctl consists of integers, strings, and tables. The tabular information can only be retrieved by special
purpose programs such as ps, systat, and netstat. The string and integer information is summaried 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.
Name Type Changeable
kern.ostype string no
kern.osrelease string no
kern.osrevision long no
kern.version string no
kern.maxinodes integer no
kern.maxproc integer no
kern.maxfiles integer no
kern.maxtext integer no
kern.argmax integer no
kern.securelevel integer raise only
kern.hostname string yes
kern.hostid long 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
vm.loadavg struct no
machdep.console_device dev_t no
net.inet.ip.forwarding integer yes
net.inet.ip.redirect integer yes
net.inet.ip.ttl integer yes
net.inet.icmp.maskrepl integer yes
net.inet.udp.checksum integer yes
hw.machine string no
hw.model string no
hw.ncpu integer no
hw.byteorder integer no
hw.physmem long no
hw.usermem long no
hw.pagesize integer 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
EXAMPLES
For example, to retrieve the maximum number of processes allowed in the system, one would use the follow request:
sysctl kern.maxproc
To set the hostname of the system to foo.bar.com, one would use the follow request:
sysctl -w kern.hostname=foo.bar.com
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
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
<sys/vmparam.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
SEE ALSO
sysctl(3)
HISTORY
sysctl first appeared in 4.4BSD.
4th Berkeley Distribution June 6, 1993 SYSCTL(8)