Chapter 6. File Tree Organization

Table of Contents
6.1. Shareable/Unshareable, Static/Variable Data
6.2. The root Directory: /
6.3. /usr: The Big One
6.4. /var: Modifiable Data During Use
6.5. /etc: Configuration Files

Nowadays, a UNIX system is big, very big. This is especially true with GNU/Linux: the amount of software available would make it an unmanageable system if there weren't any guidelines for the location of files in the tree.

The acknowledged standard in this respect is the FHS (Filesystem Hierarchy Standard), which is at version 2.2 at the time of writing this manual. The document which describes the standard is available on the Internet in different formats on The Pathname web site. This chapter gives only a brief summary, but it should be enough to teach you in what directory to look for (or place) a given file.

6.1. Shareable/Unshareable, Static/Variable Data

Data on a UNIX system can be classified according to these two criteria. Their meaning is the following: shareable data can be common to several computers in a network, while unshareable can not. Static data must not be modified in normal use, while variable data can. As we explore the tree structure, we will classify the different directories into each of these categories.

Note that these classifications are only recommended. It is not mandatory follow them, but adopting these guidelines will greatly help you manage your system. Also, keep in mind that the static/variable distinction only applies to system usage, its configuration. If you install a program, you will obviously have to modify "normally" static directories, i.e.: /usr.


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