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.

An automounter automatically mounts/unmounts file systems based on its configuration table; the table maps local mount points to specifications of remote mounts. A simple example:

  /home   ourserver:/export/home

Automounters may allow all kinds of interesting gadgetry within these tables: for example, autofs allows several forms of wildcards, it allows tables to include other tables, and it allows tables to be taken from flat files or NIS/NIS+, in any combination.

Automounters aren't actually limited to NFS mounts; at least the Solaris autofs can work with other types of file systems.

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