sysctl man page

sysctl — configure kernel parameters at runtime

TL;DR

sysctl -a

sysctl -w {{section.tunable}}={{value}}

sysctl fs.file-nr

sysctl fs.file-max

sysctl -p

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

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

Files

/proc/sys
/etc/sysctl.conf

See Also

sysctl.conf(5) regex(7)

Author

George Staikos

Reporting Bugs

Please send bug reports to procps@freelists.org

Referenced By

coredump.conf(5), dash(1), firehol-conf(5), flowtop(8), perfalloc(1), pmdaperfevent(1), proc(5), racoon.conf(5), setkey(8), sysctl.conf(5), sysctl.d(5), systemd-coredump(8), systemd-sysctl.service(8).

Jan 2012 procps-ng System Administration