Autofs Mount Process

What the autofs service does when a mount request is triggered depends on how the automounter maps are configured. The mount process is generally the same for all mounts, but the final result changes with the mount point specified and the complexity of the maps. The mount process has also been changed with the Solaris 2.6 release, to include the creation of the trigger nodes.

A Simple Autofs Mount

To help explain the autofs mount process, assume that the following files are installed.

$ cat /etc/auto_master
# Master map for automounter
#
+auto_master
/net        -hosts        -nosuid,nobrowse
/home       auto_home     -nobrowse
/xfn        -xfn
/share      auto_share
$ cat /etc/auto_share
# share directory map for automounter
#
ws          gumbo:/export/share/ws

When the /share directory is accessed the autofs service creates a trigger node for /share/ws which can be seen in /etc/mnttab as an entry which resembles the following entry:

-hosts  /share/ws     autofs  nosuid,nobrowse,ignore,nest,dev=###

When the /share/ws directory is accessed the autofs service completes the process with these steps:

1. pings the server's mount service to see if it's alive.

2. mounts the requested file system under /share. Now /etc/mnttab file contains the following entries:

   -hosts /share/ws autofs nosuid,nobrowse,ignore,nest,dev=### gumbo:/export/share/ws /share/ws nfs nosuid,dev=#### #####

Hierarchical Mounting

When multiple layers are defined in the automounter files, the mount process becomes more complex. If the /etc/auto_shared file from the previous example is expanded to contain:

# share directory map for automounter
#
ws       /       gumbo:/export/share/ws
         /usr    gumbo:/export/share/ws/usr

The mount process is basically the same as the previous example when the /share/ws mount point is accessed. In addition, a trigger node to the next level (/usr) is created in the /share/ws file system so that the next level can be easily mounted if it is accessed.

In this example, /export/share/ws/usr must exist on the NFS server for the trigger node to be created.

Autofs Unmounting

The unmounting that occurs after a certain amount of idle time is from the bottom up (reverse order of mounting). If one of the directories at a higher level in the hierarchy is busy, only file systems below that directory are unmounted.