The Filesystem Hierarchy Standard (FHS) was developed in early 1996 for all Unix-like systems. The FHS is maintained by the Free Standards Group, a non-profit organization consisting of major software and hardware vendors, such as HP, Red Hat, IBM and Dell. Still, the vast majority of the Linux distributions, including those developed by members of the Free Standards Group, do not follow this proposed standard 100%. In particular, paths specifically created by the FHS editors, such as /srv/, do not see widespread usage. Some Linux systems reject the FHS in favor of a different approach, as in GoboLinux. Since the FHS began as a Linux initiative, other UNIX and Unix-like operating systems generally completely ignore it in favor of their own systems, which sometimes vary wildly -- for example, Mac OS X uses names such as /Library/, /Applications/, and /Users/ in tandem with its traditional UNIX directory hierarchy.

In the FHS all files and directories appear under the root directory "/", even if they are stored on different physical devices. Note however that some of these directories may or may not be present on a Unix system depending on whether certain subsystems, such as the X Window System, are installed.
The majority of these directories exist in all UNIX 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.

Unix/Linux Filesystem Structure

Unix/Linux Filesystem Management Commands