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 useful 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.acctthresh	int	yes
	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
	machdep.mscp.printf	integer	yes
	machdep.tmscp.cache	integer	yes
	machdep.tmscp.printf	integer	yes
	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

<machine/cpu.h>
    definitions for second and third level machine dependent 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.