Sometimes, it is wasteful to mount all NFS volumes users might possibly want to access; either because of the sheer number of volumes to be mounted, or because of the time this would take at startup. A viable alternative to this is a so-called automounter. This is a daemon that automatically and transparently mounts any NFS volume as needed, and unmounts them after they have not been used for some time. One of the clever things about an automounter is that it is able to mount a certain volume from alternative places. For instance, you may keep copies of your X-programs and support files on two or three hosts, and have all other hosts mount them via NFS. Using an automounter, you may specify all three of them to be mounted on /usr/X386; the automounter will then try to mount any of these until one of the mount attempts succeeds.
The automounter commonly used with is called amd. It was originally written by Jan-Simon Pendry and has been ported to by Rick Sladkey. The current version is amd-5.3.
Explaining amd is beyond the scope of this chapter; for a good manual please refer to the sources; they contain a texinfo file with very detailed information.