AIX Version 4.3 Differences Guide

The automount command is called at system startup time from /etc/rc.tcpip. It
loads the autofs kernel extension if it is not already loaded and reads the master
map information from the file /etc/auto_master. The automount command then
passes the information it read from the master map to the autofs kernel
extension. It then starts the automountd daemon and terminates.
The autofs kernel extension reads the information passed to it from the
automount command and maintains an internal table of the autofs mounts. These
autofs mounts are not automatically mounted at startup time. They are points
under which file systems can be mounted in the future.
When a client attempts to access a file system that is not presently mounted, the
autofs kernel extension intercepts the request and gets the automountd to mount
the requested directory. The automountd daemon locates the directory, mounts it
within autofs, and replies. On receiving the reply, autofs allows the waiting
request to proceed. Subsequent references to the mount are redirected by the
autofs. No further participation is required by automountd.
With this implementation of automatic mounting, the automountd daemon is
completely independent from the automount command. Because of this
separation, it is possible to add, delete, or change map information without first
having to stop and start the automountd daemon process. Once the file system is
mounted, further access does not require any action from automountd.
7.14.2.2 AutoFS Maps
AutoFS uses files referred to as maps for administration of network files. The map
files contain information about filesystems and the names of the hosts on the
network where the filesystems reside. Maps can be available locally or through a
network name service like NIS. AutoFS uses three types of maps:
• Master maps
• Direct maps
• Indirect maps
7.14.2.3 Master Maps
The auto_master map associates a directory with a map. It is a master list
specifying all the maps that autofs should know about.
Each line in the master map /etc/auto_master has the following syntax:
mount-point map-name [ mount-options ]
Mount-point
mount-point is the full (absolute) path name of a directory. If the directory does
not exist, autofs creates it if possible. If the directory exists and is not empty,
mounting on it hides its contents. In this case, autofs issues a warning message.
Map-name
map-name is the map autofs uses to find directions to locations, or mount
information. If the name is preceded by a slash (/), autofs interprets the name as
a local file. Otherwise, autofs searches for the mount information using the
search specified in the name service switch configuration file.
188 AIX Version 4.3 Differences Guide