Filesystem Hierarchy Standard

The Filesystem Hierarchy Standard (FHS) is a reference describing the conventions used for the layout of Unix-like systems.

Most of these directories exist in all Unix-like operating systems and are generally used in much the same way; however, the descriptions here are those used specifically for the FHS and are not considered authoritative for platforms other than Linux.

Recent interpretations include backronyms such as "Editable Text Configuration" or "Extended Tool Chest".

[12] Most Linux distributions follow the Filesystem Hierarchy Standard and declare it their own policy to maintain FHS compliance.

According to the FHS version 2.3, such data were stored in /var/run, but this was a problem in some cases because this directory is not always available at early boot.

For example, below are the changes Debian made in its 2013 Wheezy release:[25] /usr originally stood for "user".