The automounter is a tool that automatically mounts NFS filesystems when they are referenced and unmounts them when they are no longer needed. It applies NIS management to NFS configuration files so that you can edit a single NIS map and have it affect client mount information throughout the network. Using the automounter, you don't have to keep /etc/vfstab files up-to-date by hand. Mount information, including the server's name, filesystem pathname on the server, local mount point and mount options, is contained in automounter maps, which are usually maintained in NIS maps.
Why would you want to bother with another administrative tool? What's wrong with putting all of the remote filesystem information in each hosts' /etc/vfstab file? There are many motivations for using the automounter:
/etc/vfstab files on every host become much less complex as the automounter handles the common entries in this file.
The automounter maps may be maintained using NIS, streamlining the administration of mount tables for all hosts in the network the same way NIS streamlines user account information.
Your exposure to hanging a process when an NFS server crashes is greatly reduced. The automounter unmounts all filesystems that are not in use, removing dependencies on fileservers that are not currently referenced by the client.
The automounter extends the basic NFS mount protocol to find the "nearest server" for replicated, read-only filesystems. The NFS server that is ...