.\" $OpenBSD: sysctl.8,v 1.211 2017/03/16 19:30:57 jmc Exp $ .\" $NetBSD: sysctl.8,v 1.4 1995/09/30 07:12:49 thorpej Exp $ .\" .\" Copyright (c) 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)sysctl.8 8.2 (Berkeley) 5/9/95 .\" .Dd $Mdocdate: March 16 2017 $ .Dt SYSCTL 8 .Os .Sh NAME .Nm sysctl .Nd get or set kernel state .Sh SYNOPSIS .Nm sysctl .Op Fl Aan .Nm sysctl .Op Fl n .Ar name ... .Nm sysctl .Op Fl nq .Ar name Ns = Ns Ar value ... .Sh DESCRIPTION The .Nm 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 .Dq Management Information Base .Pq MIB style name, described as a dotted set of components. .Pp When retrieving a variable, a subset of the MIB name may be specified to retrieve a list of variables in that subset. For example, to list all the machdep variables: .Pp .Dl $ sysctl machdep .Pp When setting a variable, the MIB name should be followed by an equal sign and the new value. .Pp The options are as follows: .Bl -tag -width xxx .It Fl A List all the known MIB names including tables. Those with string or integer values will be printed as with the .Fl a flag; for the table values, the name of the utility to retrieve them is given. .It Fl a List all the currently available string or integer values. This is the default, if no parameters are given to .Nm . .It Fl n Suppress printing of the field name, only output the field value. Useful for setting shell variables. For example, to set the psize shell variable to the pagesize of the hardware: .Pp .Dl # set psize=`sysctl -n hw.pagesize` .It Fl q Suppress all output when setting a variable. This option overrides the behaviour of .Fl n . .It Ar name Ns = Ns Ar value Attempt to set the specified variable .Ar name to .Ar value . .El .Pp The information available from .Nm consists of integers, strings, and tables. For a detailed description of the variables, see .Xr sysctl 3 . Tables can only be retrieved by special purpose programs such as .Xr ps 1 , .Xr systat 1 , and .Xr netstat 1 . .Pp .Nm can extract information about the filesystems that have been compiled into the running system. This information can be obtained by using the command: .Pp .Dl $ sysctl vfs.mounts .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 FILES .Bl -tag -width -compact .It In sys/sysctl.h definitions for top level identifiers and second level kernel and hardware identifiers .It In sys/socket.h definitions for second level network identifiers .It In sys/gmon.h definitions for third level profiling identifiers .It In uvm/uvm_param.h definitions for second level virtual memory identifiers .It In uvm/uvm_swap_encrypt.h definitions for third level virtual memory identifiers .It In netinet/in.h definitions for third level IPv4/v6 identifiers and fourth level IPv4/v6 identifiers .It In netinet/ip_divert.h definitions for fourth level divert identifiers .It In netinet/icmp_var.h definitions for fourth level ICMP identifiers .It In netinet6/icmp6.h definitions for fourth level ICMPv6 identifiers .It In netinet/tcp_var.h definitions for fourth level TCP identifiers .It In netinet/udp_var.h definitions for fourth level UDP identifiers .It In ddb/db_var.h definitions for second level ddb identifiers .It In sys/mount.h definitions for second level vfs identifiers .It In nfs/nfs.h definitions for third level NFS identifiers .It In miscfs/fuse/fusefs.h definitions for third level fusefs identifiers .It In ufs/ffs/ffs_extern.h definitions for third level FFS identifiers .It In machine/cpu.h definitions for second level CPU identifiers .El .Sh EXAMPLES To retrieve the maximum number of processes allowed in the system: .Pp .Dl $ sysctl kern.maxproc .Pp To set the maximum number of processes allowed in the system to 1000: .Pp .Dl # sysctl kern.maxproc=1000 .Pp To retrieve information about the system clock rate: .Pp .Dl $ sysctl kern.clockrate .Pp To retrieve information about the load average history: .Pp .Dl $ sysctl vm.loadavg .Pp To make the .Xr chown 2 system call use traditional .Bx semantics (don't clear setuid/setgid bits): .Pp .Dl # sysctl fs.posix.setuid=0 .Pp To set the list of reserved TCP ports that should not be allocated by the kernel dynamically: .Pp .Dl # sysctl net.inet.tcp.baddynamic=749,750,751,760,761,871 .Dl # sysctl net.inet.udp.baddynamic=749,750,751,760,761,871,1024-2048 .Pp This can be used to keep daemons from stealing a specific port that another program needs to function. List elements may be separated by commas and/or whitespace; a hyphen may be used to specify a range of ports. .Pp It is also possible to add or remove ports from the current list: .Bd -literal -offset indent # sysctl net.inet.tcp.baddynamic=+748,+6000-6999 # sysctl net.inet.tcp.baddynamic=-871 .Ed .Pp To set the amount of shared memory available in the system and the maximum number of shared memory segments: .Bd -literal -offset indent # sysctl kern.shminfo.shmmax=33554432 # sysctl kern.shminfo.shmseg=32 .Ed .Pp To place core dumps from .Xr issetugid 2 programs (in this example .Xr bgpd 8 ) into a safe place for debugging purposes: .Bd -literal -offset indent # mkdir -m 700 /var/crash/bgpd # sysctl kern.nosuidcoredump=3 .Ed .Sh SEE ALSO .Xr sysctl 3 , .Xr options 4 , .Xr sysctl.conf 5 .Sh HISTORY .Nm first appeared in .Bx 4.4 .