An automounter is a Unix daemon which automatically mounts filesystems which are accessed via NFS when they are needed and unmounts them when they haven't been used for a while. This is handy because it makes the NFS-mounting of users' home directories (for example) completely transparent; when a user wants to access their home directory, the automounter automatically mounts it. Unmounting filesystems which haven't been used for a while is useful because it means that your workstation won't hang when an "uninteresting" file system becomes unavailable.

When lots of workstations need to automount the same set of filesystems (as is likely to happen with users' home directories), it is useful for the lists of filesystems and mount points, which are known as the automounter maps, to be managed by NIS so that they are the same on every workstation.

A public domain automounter called amd is available for every flavour of Unix, but most systems seem to use one called autofs instead.