Linux Commands Examples

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configure kernel parameters at runtime


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

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/sbin/sysctl -a
/sbin/sysctl -n kernel.hostname
/sbin/sysctl -w kernel.domainname=""
/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’


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.

deprecated parameters

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

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





The name of a key to read from. An example is kernel.ostype. The ’/’ separator is also accepted in place of a ’.’.


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 order they are specified. The file argument can may be specified as reqular expression.

-a, --all

Display all values currently available.


Include deprecated parameters to --all values listing.

-b, --binary

Print value without new line.


Load settings from all system configuration files.

--pattern pattern

Only apply settings that match pattern. The pattern uses extended regular expression syntax.


Alias of -a


Alias of -h


Alias of -p


Alias of -a


Does nothing in favour of BSD compatibility.


Does nothing in favour of BSD compatibility.

-h, --help

Display help text and exit.

-V, --version

Display version information and exit.

reporting bugs

Please send bug reports to procps[:at:]freelists[:dot:]org (procps[:at:]freelists[:dot:]org)

see also

sysctl.conf regex


George Staikos (staikos[:at:]0wned[:dot:]org)

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