procfs

External resources

	Wikipedia

procfs (process filesystem) is a virtual filesystem to output and change system and process information. It's generated by the kernel and mounted at /proc. The information in the sysfs filesystem replaces more and more system information of procfs.

Installation

You need to activate the following kernel options:

Kernel configuration

File systems  --->
    Pseudo filesystems  --->
        <*> /proc file system support

Configuration

Change your fstab to mount procfs at boot time to /proc:

File/etc/fstab

proc           /proc             proc        defaults                0 0

Usage

See the Wikipedia article for the file's purpose.

• Use cat to read the information, e.g. output the version of the currently running kernel:

user $ cat /proc/version

• To set values at runtime - if possible - use echo, e.g. to enable the magic SysRq key::

root # echo 1 > /proc/sys/kernel.sysrq

sysctl

External resources

	Wikipedia

sysctl is a mechanism to modify certain kernel parameters at runtime. It is part of procfs and the files are located at /proc/sys/. /usr/src/linux/Documentation/sysctl/ contains documentation of most files.

sysctl work with keys, which can be assembled from the file path by removing the /proc/sys prefix and replace the backsplash with a point. So, e.g. /proc/sys/kernel/sysrq becomes kernel.sysrq.

You can modify at runtime the files like above, but the tool sysctl (part of sys-process/procps) do it in a more structured way:

• To enable the magic sysrq key:

root # sysctl kernel.sysrq=1

• To show all keys and their current values:

root # sysctl -a

To configure kernel parameters at boot, add them to a .conf file in /etc/sysctl.d/. The recommended location for local settings is /etc/sysctl.d/local.conf. The legacy file /etc/sysctl.conf is also supported. To enable the magic SysRq key at boot:

File/etc/sysctl.d/local.conf

kernel.sysrq=1

OpenRC

The service sysctl read the files at boot and execute the settings. The service is enabled by default.

systemd

systemd knows beside /etc/sysctl.d/ also /usr/lib/sysctl.d/ for package-provided config files.

The service systemd-sysctl is enabled by default.