09-09-2008
Kernel tuning with sysctl
09-09-2008 08:00 AM
The Linux kernel is flexible, and you can even modify the way it works on the fly by dynamically changing some of its parameters, thanks to the sysctl command. Sysctl provides an interface that allows you to examine and change several hundred kernel parameters in Linux or BSD. Changes take effect immediately, and there's even a way to make them persist after a reboot. By using sysctl judiciously, you can optimize your box without having to
recompile your kernel, and get the results immediately.
Source...
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SYSCTL(8) SYSCTL(8)
NAME
sysctl - configure kernel parameters at runtime
SYNOPSIS
sysctl [-n] [-e] variable ...
sysctl [-n] [-e] [-q] -w variable=value ...
sysctl [-n] [-e] [-q] -p <filename>
sysctl [-n] [-e] -a
sysctl [-n] [-e] -A
DESCRIPTION
sysctl is used to modify kernel parameters at runtime. The parameters available are those listed under /proc/sys/. Procfs is required for
sysctl(8) support in Linux. You can use sysctl(8) 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 param-
eter to use.
-n Use this option to disable printing of the key name when printing values.
-e Use this option to ignore errors about unknown keys.
-N Use this option to only print the names. It may be useful with shells that have programmable completion.
-q Use this option to not display the values set to stdout.
-w Use this option when you want to change a sysctl setting.
-p Load in sysctl settings from the file specified or /etc/sysctl.conf if none given. Specifying - as filename means reading data from
standard input.
-a Display all values currently available.
-A Display all values currently available in table form.
EXAMPLES
/sbin/sysctl -a
/sbin/sysctl -n kernel.hostname
/sbin/sysctl -w kernel.domainname="example.com"
/sbin/sysctl -p /etc/sysctl.conf
FILES
/proc/sys /etc/sysctl.conf
SEE ALSO
sysctl.conf(5)
BUGS
The -A parameter behaves just as -a does.
AUTHOR
George Staikos, <staikos@0wned.org>
21 Sep 1999 SYSCTL(8)