Frequently Asked Question

What is the Filesystem Hierarchy Standard and why does it exist?

The Filesystem Hierarchy Standard (FHS) is a document, first published in 1994, currently at version 3.0 (2015), that specifies which top-level directories a Unix-like system should have and what each is for. It is maintained by the Linux Foundation and is followed, with minor deviations, by every mainstream distribution: Debian, Ubuntu, Fedora, Arch, openSUSE, Alpine. The point is portability: an administrator who learns the layout on one distribution can find their way around any other, and a software package built for one can install on another without surprises.

Before the FHS, every commercial Unix vendor had its own opinions, Solaris put things one place, AIX another, HP-UX a third, and writing portable software was painful. The standard captures decades of accumulated convention rather than inventing new rules, which is why the names are cryptic (/etc, /usr, /var) but the placement of any given file is usually predictable once you know the principles. Reading the FHS once is genuinely useful even if you remember only the broad strokes afterwards.