The /usr filesystem is often large, since all programs are installed there. All files in /usr usually come from a Linux distribution; locally installed programs and other stuff goes below /usr/local. This makes it possible to update the system from a new version of the distribution, or even a completely new distribution, without having to install all programs again. Some of the subdirectories of /usr are listed below (some of the less important directories have been dropped; see the FSSTND for more information).
