sysctl - Man Page

• Show all available variables and their values: sysctl -a
• Set a changeable kernel state variable: sysctl -w section.tunable=value
• Get currently open file handlers: sysctl fs.file-nr
• Get limit for simultaneous open files: sysctl fs.file-max
• Apply changes from /etc/sysctl.conf: sysctl -p

tldr.sh

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

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.

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.

-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

Force all arguments to be write arguments and print an error if they cannot be parsed this way.

-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. See the System File Precedence section below.

-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.

When using the --system option, 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.

/etc/sysctl.d/*.conf
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf

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).

/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 --pattern '^net.ipv6' --system

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

/proc/sys
/etc/sysctl.d/*.conf
/run/sysctl.d/*.conf
/usr/local/lib/sysctl.d/*.conf
/usr/lib/sysctl.d/*.conf
/lib/sysctl.d/*.conf
/etc/sysctl.conf

proc(5), sysctl.conf(5), regex(7)

George Staikos

Please send bug reports to procps@freelists.org

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