sysctl.8   [plain text]


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.\"	@(#)sysctl.8	8.2 (Berkeley) 5/9/95
.\"
.Dd "May 9, 1995"
.Dt SYSCTL 8
.Os
.Sh NAME
.Nm sysctl
.Nd get or set kernel state
.Sh SYNOPSIS
.Nm sysctl
.Op Fl bn
.Ar name ...
.Nm sysctl
.Op Fl bn
.Fl w
.Ar name=value ...
.Nm sysctl
.Op Fl bn
.Fl a
.Nm sysctl
.Op Fl bn
.Fl A
.Nm sysctl
.Op Fl bn
.Fl X
.Sh DESCRIPTION
The
.Nm 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.
.Pp
The following options are available:
.Bl -tag -width indent
.\" ==========
.It Fl A
List all MIB variables including 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.
.\" ==========
.It Fl 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.
.\" ==========
.It Fl 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.
.\" ==========
.It Fl n
Show only variable values, not their names.
This option is useful for setting shell variables.
For instance, to save the pagesize in variable
.Va psize ,
use:
.Pp
.Dl "set psize=`sysctl -n hw.pagesize`"
.\" ==========
.It Fl w Ar name=value
Used to set values.  The MIB name (
.Ar name
) followed by an equal sign and the new value (
.Ar value
) to be used.
.\" ==========
.It Fl X
Same as 
.Fl A ,
but prints a hex dump of the entire value
instead of just the first few bytes.
.El
.Pp
If just a MIB style name is given,
the corresponding value is retrieved.
.Pp
The information available from
.Nm sysctl
consists of integers, strings, and tables.
The tabular information can only be retrieved by special
purpose programs such as
.Nm ps ,
.Nm systat ,
and
.Nm netstat .
The string and integer information is summarized below.
For a detailed description of these variable see
.Xr sysctl 3 .
The changeable column indicates whether a process with appropriate
privilege can change the value.
.Bl -column net.inet.ip.forwardingxxxxxx integerxxx
.It Sy Name	Type	Changeable
.It kern.ostype	string	no
.It kern.osrelease	string	no
.It kern.osrevision	integer	no
.It kern.version	string	no
.It kern.maxvnodes	integer	yes
.It kern.maxproc	integer	yes
.It kern.maxfiles	integer	yes
.It kern.argmax	integer	no
.It kern.securelevel	integer	raise only
.It kern.hostname	string	yes
.It kern.hostid	integer	yes
.It kern.clockrate	struct	no
.It kern.posix1version	integer	no
.It kern.ngroups	integer	no
.It kern.job_control	integer	no
.It kern.saved_ids	integer	no
.It kern.link_max	integer	no
.It kern.max_canon	integer	no
.It kern.max_input	integer	no
.It kern.name_max	integer	no
.It kern.path_max	integer	no
.It kern.pipe_buf	integer	no
.It kern.chown_restricted	integer	no
.It kern.no_trunc	integer	no
.It kern.vdisable	integer	no
.It kern.boottime	struct	no
.It vm.loadavg	struct	no
.It vm.swapusage	struct	no
.It machdep.console_device	dev_t	no
.It net.inet.ip.forwarding	integer	yes
.It net.inet.ip.redirect	integer	yes
.It net.inet.ip.ttl	integer	yes
.It net.inet.icmp.maskrepl	integer	yes
.It net.inet.udp.checksum	integer	yes
.It hw.machine	string	no
.It hw.model	string	no
.It hw.ncpu	integer	no
.It hw.byteorder	integer	no
.It hw.physmem	integer	no
.It hw.usermem	integer	no
.It hw.memsize	integer	no
.It hw.pagesize	integer	no
.It user.cs_path	string	no
.It user.bc_base_max	integer	no
.It user.bc_dim_max	integer	no
.It user.bc_scale_max	integer	no
.It user.bc_string_max	integer	no
.It user.coll_weights_max	integer	no
.It user.expr_nest_max	integer	no
.It user.line_max	integer	no
.It user.re_dup_max	integer	no
.It user.posix2_version	integer	no
.It user.posix2_c_bind	integer	no
.It user.posix2_c_dev	integer	no
.It user.posix2_char_term	integer	no
.It user.posix2_fort_dev	integer	no
.It user.posix2_fort_run	integer	no
.It user.posix2_localedef	integer	no
.It user.posix2_sw_dev	integer	no
.It user.posix2_upe	integer	no
.El
.Pp
The
.Nm sysctl
program can get or set debugging variables
that have been identified for its display.
This information can be obtained by using the command:
.Bd -literal -offset indent
sysctl debug
.Ed
.Pp
In addition,
.Nm sysctl
can extract information about the filesystems that have been compiled
into the running system.
This information can be obtained by using the command:
.Bd -literal -offset indent
sysctl vfs
.Ed
.Pp
By default, only filesystems that are actively being used are listed.
Use of the
.Fl A
flag lists all the filesystems compiled into the running kernel.
.Sh EXAMPLES
.Pp
For example, to retrieve the maximum number of processes allowed
in the system, one would use the request:
.Bd -literal -offset indent
sysctl kern.maxproc
.Ed
.Pp
To set the maximum number of processes allowed
in the system to 1000, one would use the request:
.Bd -literal -offset inden
sysctl -w kern.maxproc=1000
.Ed
.Pp
Information about the system clock rate may be obtained with:
.Bd -literal -offset indent
sysctl kern.clockrate
.Ed
.Pp
Information about the load average history may be obtained with:
.Bd -literal -offset indent
sysctl vm.loadavg
.Ed
.Pp
Information about the system's swap space usage may be obtained with:
.Bd -literal -offset indent
sysctl vm.swapusage
.Ed
.Sh FILES
.Bl -tag -width <netinet/icmpXvar.h> -compact
.It Pa <sys/sysctl.h>
definitions for top level identifiers, second level kernel and hardware
identifiers, and user level identifiers
.It Pa <sys/socket.h>
definitions for second level network identifiers
.It Pa <sys/gmon.h>
definitions for third level profiling identifiers
.It Pa <vm/vm_param.h>
definitions for second level virtual memory identifiers
.It Pa <netinet/in.h>
definitions for third level Internet identifiers and
fourth level IP identifiers
.It Pa <netinet/icmp_var.h>
definitions for fourth level ICMP identifiers
.It Pa <netinet/udp_var.h>
definitions for fourth level UDP identifiers
.El
.Sh SEE ALSO
.Xr sysctl 3
.Sh HISTORY
.Nm sysctl
first appeared in 4.4BSD.