The sysctl command is used to view, set, and
automated kernel settings in the /proc/sys/
directory.
To get a quick overview of all settings configurable in the
/proc/sys/ directory, type the sysctl
-a command as root. This will create a large, comprehensive
list, a small portion of which looks something like this:
net.ipv4.route.min_delay = 2
kernel.sysrq = 0
kernel.sem = 250 32000 32 128 |
This is the same basic information you would see if you viewed each of
the files individually. The only difference is the file location. The
/proc/sys/net/ipv4/route/min_delay file is signified by
net.ipv4.route.min_delay, with the
directory slashes replaced by dots and the
proc.sys portion assumed.
The sysctl command can be use in place of
echo to assign values to writable files in the
/proc/sys/ directory. For instance instead of using
this command:
echo 1 > /proc/sys/kernel/sysrq |
You can use this sysctl command:
sysctl -w kernel.sysrq="1"
kernel.sysrq = 1 |
While quickly setting single values like this in
/proc/sys/ is helpful during testing, it does not
work as well on a production system, as all
/proc/sys/ special settings are lost when the
machine is rebooted. To preserve the settings that you like to make
permanently to your kernel, add them to the
/etc/sysctl.conf file.
Every time the system boots, the
/etc/rc.d/rc.sysinit script is executed by
init. This script contains a command to execute
sysctl using /etc/sysctl.conf as
the values to set. Therefore, any values added to
/etc/sysctl.conf will take effect after the
system boots.
