Overview of AutoFS

AutoFS is a client-side service that supports automatic mounting and unmounting of file systems. This process is nearly transparent to the user.

AutoFS is implemented as a virtual file system (VFS). It supports automounting by instructing the user-space daemon, automountd, to mount and unmount the directories it manages. It automatically mounts the appropriate file systems when needed and unmounts them if they have been idle for the configured period of time (10 minutes is the default value).

AutoFS has been enhanced to provide the features of the SUN ONC+ version 2.3 AutoFS product. This version of AutoFS is known as Enhanced AutoFS. With the Enhanced AutoFS implementation, both performance and scalability are significantly improved.

How AutoFS Works

AutoFS consists of the following components:

The automount command - It installs AutoFS mount points and associates an automount map with each mount point. The AutoFS file system monitor attempts to access directories within it and notifies the automountd daemon. The daemon uses the map to locate a file system and then mounts this file system at the point of reference within the AutoFS file system. The automount map determines the location of all the AutoFS mount points.
NOTE: You need to execute the automount command whenever the master map or the direct maps are updated.
The AutoFS file system (kernel AutoFS) - A virtual file system that provides a directory structure for automatic mounting. It includes autofskd, a kernel-based process that periodically cleans up mounts.
The automountd daemon - A stateless daemon that accepts RPC requests from kernel AutoFS to perform mounts or umounts.

Figure 1-1 “Interaction Among AutoFS Components” illustrates the interaction among the components of AutoFS.

Figure 1-1 Interaction Among AutoFS Components

The automount command is invoked at the system startup. It reads the AutoFS master map to create the initial set of AutoFS mount points in the internal mount table, /etc/mnttab. The automounted file systems are not mounted automatically at startup. The automounted file systems are points under which file systems are mounted when users request access to them.

When AutoFS receives a request to mount a file system that is not mounted, it calls the automountd daemon, which actually mounts the requested file system. Once you mount the file system, further access does not require any action from the automountd daemon. AutoFS mounts file systems at the configured mount points. It does not maintain its own directory of mount points with symbolic links into it.

The automountd daemon is completely independent from the automount command. Because of this separation, it is possible to add, delete, or change the AutoFS map information without having to stop and restart the automountd daemon.

After system startup, when the AutoFS mount points are set up, you can modify the set of mount points by modifying AutoFS maps and running the automount command to read them and modify the mount table accordingly. You do not have to stop and restart AutoFS.

If an automounted file system has been idle for a configured period of time (the default is 10 minutes), AutoFS unmounts it.

For more information on AutoFS, see the following man pages: automount (1M) and automountd (1M).




	WARNING! File systems under the management of AutoFS must always be maintained through AutoFS utilities, `automountd` and `automount`. Manually mounting and unmounting AutoFS managed file systems can lead to disruptive or unpredictable results, including but not limited to the following: Commands hang or do not return expected results. Applications fail due to their dependencies on these mounted file systems.

Overview of AutoFS

Technical documentation

» Table of Contents

» Index

How AutoFS Works