.\"
.\" Copyright (c) 2011-2024 Craig Small <csmall@dropbear.xyz>
.\" Copyright (c) 2013-2023 Jim Warner <james.warner@comcast.net>
.\" Copyright (c) 2011-2012 Sami Kerola <kerolasa@iki.fi>
.\" Copyright (c) 2004-2006 Albert Cahalan
.\" Copyright (c) 1999      George Staikos <staikos@0wned.org>
.\"
.\" This program is free software; you can redistribute it and/or modify
.\" it under the terms of the GNU General Public License as published by
.\" the Free Software Foundation; either version 2 of the License, or
.\" (at your option) any later version.
.\"
.\"
.TH SYSCTL 8 2024-07-19 procps-ng
.SH NAME
sysctl \- configure kernel parameters at runtime
.SH SYNOPSIS
.B sysctl
.RI [ option " .\|.\|.\&]"
.IR variable [\c
.BI = value\c
] .\|.\|.
.P
.B sysctl \-p
.IR file-or-regexp " .\|.\|."
.SH DESCRIPTION
.B sysctl
is used to modify kernel parameters at runtime.  The parameters available
are those listed under \fI/proc/sys/\fR.  Procfs is required for
.B sysctl
support in Linux.  You can use
.B sysctl
to both read and write sysctl data.
.SH PARAMETERS
.TP
.I variable
The name of a key to read from.  An example is kernel.ostype.  The '/'
separator is also accepted in place of a '.'.
.TP
.IR  variable = value
To set a key, use the form
.IR  variable = value
where
.I variable
is the key and
.I value
is the value to set it to.  If the value contains quotes or characters
which are parsed by the shell, you may need to enclose the value in double
quotes.
.TP
\fB\-n\fR, \fB\-\-values\fR
Use this option to disable printing of the key name when printing values.
.TP
\fB\-e\fR, \fB\-\-ignore\fR
Use this option to ignore errors about unknown keys.
.TP
\fB\-N\fR, \fB\-\-names\fR
Use this option to only print the names.  It may be useful with shells that
have programmable completion.
.TP
\fB\-q\fR, \fB\-\-quiet\fR
Use this option to not display the values set to stdout.
.TP
\fB\-w\fR, \fB\-\-write\fR
Force all arguments to be write arguments and print an error if
they cannot be parsed this way.
.TP
\fB\-p\fR[\fIFILE\fR], \fB\-\-load\fR[=\fIFILE\fR]
Load in \fBsysctl\fR settings from the file specified or \fI/etc/sysctl.conf\fR
if none given.  Specifying \- as filename means reading data from standard
input. Using this option will mean arguments to
.B sysctl
are files, which are read in the order they are specified.
The file argument may be specified as regular expression.
.TP
\fB\-a\fR, \fB\-\-all\fR
Display all values currently available except deprecated and verboten parameters.
.TP
\fB\-\-deprecated\fR
Include deprecated parameters to
.B \-\-all
values listing.
.TP
\fB\-b\fR, \fB\-\-binary\fR
Print value without new line.
.TP
\fB\-\-system\fR
Load settings from all system configuration files. See the
.B SYSTEM FILE PRECEDENCE
section below.
.TP
\fB\-r\fR, \fB\-\-pattern\fR \fIpattern\fR
Only apply settings that match
.IR pattern .
The
.I pattern
uses extended regular expression syntax.
.TP
\fB\-A\fR
Alias of \fB\-a\fR
.TP
\fB\-d\fR
Alias of \fB\-h\fR
.TP
\fB\-f\fR
Alias of \fB\-p\fR
.TP
\fB\-X\fR
Alias of \fB\-a\fR
.TP
\fB\-o\fR
Does nothing, exists for BSD compatibility.
.TP
\fB\-x\fR
Does nothing, exists for BSD compatibility.
.TP
\fB\-h\fR, \fB\-\-help\fR
Display help text and exit.
.TP
\fB\-V\fR, \fB\-\-version\fR
Display version information and exit.
.SH FILES
.TS
Li.
/proc/sys
/etc/sysctl.d/\fR*\fP.conf
/run/sysctl.d/\fR*\fP.conf
/usr/local/lib/sysctl.d/\fR*\fP.conf
/usr/lib/sysctl.d/\fR*\fP.conf
/lib/sysctl.d/\fR*\fP.conf
/etc/sysctl.conf
.TE
.SH NOTES
.SS System file precedence
When using the \fB\-\-system\fR option,
.B sysctl
will read files from directories in the following list in given
order from top to bottom. Once a file of a given filename is loaded, any
file of the same name in subsequent directories is ignored.
.P
.TS
Li.
/etc/sysctl.d/\fR*\fP.conf
/run/sysctl.d/\fR*\fP.conf
/usr/local/lib/sysctl.d/\fR*\fP.conf
/usr/lib/sysctl.d/\fR*\fP.conf
/lib/sysctl.d/\fR*\fP.conf
.TE
.P
All configuration files are sorted in lexicographic order, regardless of the
directory they reside in. Configuration files can either be completely
replaced (by having a new configuration file with the same name in a
directory of higher priority) or partially replaced (by having a configuration
file that is ordered later).
.P
The file \fI/etc/sysctl.conf\fR is read last which means it can replace/override any
parameters previously set in files in the listed directories.

.SS Deprecated parameters
The
.B base_reachable_time
and
.B retrans_time
are deprecated.  The
.B sysctl
command does not allow changing values of these
parameters.  Users who insist to use deprecated kernel interfaces should push values
to \fB/proc\fR file system by other means.  For example:
.PP
echo 256 > /proc/sys/net/ipv6/neigh/eth0/base_reachable_time

.SS Verboten parameters
Certain kernel parameters should not be read due to side-effects and will be
skipped by \fBsysctl\fR using the \fB\-\-all\fR option.
.TP
.B stat_refresh
This parameter returns no value but flushes per-cpu vm statistics.

.SH EXAMPLES
/sbin/sysctl \-a
.br
/sbin/sysctl \-n kernel.hostname
.br
/sbin/sysctl \-w kernel.domainname="example.com"
.br
/sbin/sysctl \-p/etc/sysctl.conf
.br
/sbin/sysctl \-a \-\-pattern forward
.br
/sbin/sysctl \-a \-\-pattern forward$
.br
/sbin/sysctl \-a \-\-pattern 'net.ipv4.conf.(eth|wlan)0.arp'
.br
/sbin/sysctl \-\-pattern '\[char94]net.ipv6' \-\-system
.SH SEE ALSO
.BR proc (5),
.BR sysctl.conf (5),
.BR regex (7)
.SH "REPORTING BUGS"
Please send bug reports to
.MT procps@freelists.org
.ME .