Red Hat Software is committed to the Linux File System Standard, a collaborative document that defines the names and locations of many files and directories. We will continue to track the standard to keep Red Hat compliant.
While compliance with the standard means many things, the two most important are compatibility with other compliant systems, and the ability to mount the /usr partition read-only. The /usr partition contains common executables and is not meant to be changed by users. Because of the, the /usr partition can be mounted from the CD-ROM or from another machine via read-only NFS. The current Linux Filesystem Standard (FSSTND) document is the authoritative reference to any FSSTND compliant filesystem, but the standard leaves many areas undefined or extensible. In this section we provide an overview of the standard and a description of the parts of the filesystem not covered by the standard.
The complete standard can be viewed at:
http://www.eg.bucknell.edu/~quinlan/fsstnd