On-demand NFS mounting utility: autofs. Learn what is autofs, why, and when to use autofs and autofs configuration steps in the Linux server.

The first place to manage mount points on any Linux system is /etc/fstab file. These files mount all listed mount points at the system startup and made them available to the user. Although I explained mainly how autofs advantages us with NFS mount points, it also works well with native mount points.

NFS mount points are also part of it. Now, the issue is even if users don’t access NFS mount points they are still mounted by /etc/fstab and leech some system resources in the background continuously. Like NFS services need to check connectivity, permissions, etc details of these mount points in the background continuously. If these NFS mounts are considerably high in numbers then managing them through /etc/fstab will be a major drawback since you are allotting major system resource chunk to system portion which is not frequently used by users.

Why use AutoFS?

In such a scenario, AutoFS comes in picture. AutoFS is on-demand NFS mounting facility. In short, it mounts NFS mount points when a user tries to access them. Again once time hits timeout value (since last activity on that NFS mount), it will automatically un-mount that NFS mount saving system resources serving idle mount point.

It also reduces your system boot time since the mounting task is done after system boot and when the user demands it.

When use AutoFS?

• If your system is having a large number of mount points
• Many of them are not being used frequently
• The system is tight on resources and every single piece of system resource counts

AutoFS configuration steps

First, you need to install package autofs using yum or apt. The main configuration file for autofs is /etc/auto.master which is also called a mast map file. This file has autofs controlled mount points details. The master file follows below format :

mount_point map_file options

where –

• mount_point is a directory on which mounts should be mounted
• map_file (automounter map file) is a file containing a list of mount points and their file systems from which they should be mounted
• options are extra options to be applied on mount_point

Sample master map file looks like one below :

/my_auto_mount  /etc/auto.misc --timeout=60

In above sample, mount points defined under /etc/auto.misc files can be mounted on /my_auto_mount directory with timeout value 60 sec.

Parameter map_file (automounter map file) in the above master map file is also a configuration file which has below format :

mount_point options source_location

where –

• mount_point is a directory on which mounts should be mounted
• options are mounting options
• source_location is FS or NFS path from where the mount will be mounted

Sample automounter map file looks like one below :

linux          -ro,soft,intr           ftp.example.org:/pub/linux
data1         -fstype=ext3            :/dev/fd0

Users should be aware of the share path. Means, in our case, /my_auto_mount and Linux, data1 these paths should be known to users in order to access them.

In all both these configuration file collectively tells :

Whenever user tries to access mount point Linux or data1 –

1. autofs checks data1 source (/dev/fs0) with option (-fstype=ext3)
2. mounts data1 on /my_auto_mount/data1
3. Un-mounts /my_auto_mount/data1 when there is no activity on mount for 60 secs

Once you are done with configuring your required mounts you can start autofs service.  Reload its configurations :

# /etc/init.d/autofs reload
Reloading maps

That’s it! Configuration is done!

Testing AutoFS configuration

Once you reload configuration, check and you will notice autofs defined mount points are not mounted on systems (output of df -h).

Now cd into /my_auto_mount/data1 and you will be presented with a listing of the content of data1 from /dev/fd0!

Another way is to use watch utility in another session and keep watch on command mount. As you execute commands, you will see mount point is mounted on system and after timeout value it’s un-mounted!