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You are here: manpages

SYSCTL

Section: System Administration (8)
Updated: Jan 2012
Index Return to Main Contents

NAME

sysctl - configure kernel parameters at runtime

SYNOPSIS

sysctl [options] [variable[=value]] [...]
sysctl -p [file or regexp] [...]

DESCRIPTION

sysctl is used to modify kernel parameters at runtime. The parameters available are those listed under /proc/sys/. Procfs is required for sysctl support in Linux. You can use sysctl to both read and write sysctl data.

PARAMETERS

variable: The name of a key to read from. An example is kernel.ostype. The '/' separator is also accepted in place of a '.'.
variable=value: To set a key, use the form variable=value where variable is the key and 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. This requires the -w parameter to use.
-n, --values: Use this option to disable printing of the key name when printing values.
-e, --ignore: Use this option to ignore errors about unknown keys.
-N, --names: Use this option to only print the names. It may be useful with shells that have programmable completion.
-q, --quiet: Use this option to not display the values set to stdout.
-w, --write: Use this option when you want to change a sysctl setting.
-p[FILE], --load[=FILE]: Load in sysctl settings from the file specified or /etc/sysctl.conf if none given. Specifying - as filename means reading data from standard input. Using this option will mean arguments to sysctl are files, which are read in the order they are specified. The file argument may be specified as regular expression.
-a, --all: Display all values currently available.
--deprecated: Include deprecated parameters to --all values listing.
-b, --binary: Print value without new line.
--system: Load settings from all system configuration files.
/run/sysctl.d/*.conf
/etc/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf
-r, --pattern pattern: Only apply settings that match pattern. The pattern uses extended regular expression syntax.
-A: Alias of -a
-d: Alias of -h
-f: Alias of -p
-X: Alias of -a
-o: Does nothing, exists for BSD compatibility.
-x: Does nothing, exists for BSD compatibility.
-h, --help: Display help text and exit.
-V, --version: Display version information and exit.

EXAMPLES

/usr/sbin/sysctl -a
/usr/sbin/sysctl -n kernel.hostname
/usr/sbin/sysctl -w kernel.domainname="example.com"
/usr/sbin/sysctl -p/etc/sysctl.conf
/usr/sbin/sysctl -a --pattern forward
/usr/sbin/sysctl -a --pattern forward$
/usr/sbin/sysctl -a --pattern 'net.ipv4.conf.(eth|wlan)0.arp'
/usr/sbin/sysctl --system --pattern '^net.ipv6'

DEPRECATED PARAMETERS

The base_reachable_time and retrans_time are deprecated. The sysctl command does not allow changing values of these parameters. Users who insist to use deprecated kernel interfaces should push values to /proc file system by other means. For example:

echo 256 > /proc/sys/net/ipv6/neigh/eth0/base_reachable_time