Filesystem Hierarchy Standard

2 The Filesystem

This standard assumes that the operating system underlying an FHS-compliant file system supports the same basic security features found in most UNIX filesystems.

It is possible to define two independent categories of files: shareable vs. unshareable and variable vs. static. There should be a simple and easily understandable mapping from directories to the type of data they contain: directories may be mount points for other filesystems with different characteristics from the filesystem on which they are mounted.

Shareable data is that which can be shared between several different hosts; unshareable is that which must be specific to a particular host. For example, user home directories are shareable data, but device lock files are not.

Static data includes binaries, libraries, documentation, and anything that does not change without system administrator intervention; variable data is anything else that does change without system administrator intervention.


The distinction between shareable and unshareable data is needed for several reasons:

The "shareable" distinction can be used to support, for example:

The "static" versus "variable" distinction affects the filesystem in two major ways:

Here is a summarizing chart. This chart is only an example for a common FHS-compliant system, other chart layouts are possible within FHS-compliance.

shareable unshareable
static /usr /etc
/opt /boot
variable /var/mail /var/run
/var/spool/news /var/lock

Table 2.1


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Translated by troff2html v1.5 on 29 March 2002 by Daniel Quinlan