To frame its recommendations, the FHS defines two categories of data use, each with two opposing subtypes:

Data sharing

This category defines the scope of data use in a networked environment:


Sharable data can be used by multiple host systems on a network. Sharable files contain general-purpose information, without ties to any specific host. Examples include user data files, executable program files, and system documentation.


Data is not sharable when linked to a specific host, such as a unique configuration file.

Data modification

This category specifies how data changes:


Data is considered variable when changed by natural, frequent processes. Examples include user files and system logfiles, such as /var/log/messages.


Static data is left alone for the most part, remaining the same from day to day or even year to year. Examples include binary programs such as ls and bash, which change only when the system administrator performs an upgrade.

Some directories in the Linux filesystem are intended to hold specific types of data. For example, the executable files in /usr are rarely changed, and thus could be defined as static because they are needed by all users on a network. Before disks were as large as they are today, the files commonly found in /usr were often mounted from remote servers to preserve local disk space. Thus, in addition to being static, /usr is said to be sharable. Keeping files organized with respect to these attributes can simplify ...

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