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sysctl.conf - Man Page

sysctl preload/configuration file


sysctl.conf is a simple file containing sysctl values to be read in and set by sysctl. The syntax is simply as follows:

# comment
; comment

token = value

Note that blank lines are ignored, and whitespace before and after a token or value is ignored, although a value can contain whitespace within.  Lines which begin with a # or ; are considered comments and ignored.

If a line begins with a single -, any attempts to set the value that fail will be ignored.


As the /etc/sysctl.conf file is used to override default kernel parameter values, only a small number of parameters is predefined in the file. Use /sbin/sysctl -a or follow sysctl(8) to list all possible parameters. The description of individual parameters can be found in the kernel documentation.

Maximum supported line length of the value is 4096 characters due to a limitation of /proc entries in Linux kernel.


# sysctl.conf sample
  kernel.domainname = example.com
; this one has a space which will be written to the sysctl!
  kernel.modprobe = /sbin/mod probe



The paths where sysctl preload files usually exist.  See also sysctl option --system.

See Also



George Staikos

Reporting Bugs

Please send bug reports to procps@freelists.org

Referenced By

sysctl(8), sysctl.d(5), ufw(8), ufw-framework(8).

2021-09-15 procps-ng File Formats