Recently, I had the opportunity to learn how to configure NFS shares in Linux. During my exploration of NFS, I came across something that I thought was really interesting and I want to share with Enable Sysadmin readers. What caught my attention is autofs. Let's dig into what autofs is and how it works.
Autofs defined
Autofs is an automount daemon that manages mount points as needed. In short, it only mounts a given share when that share is being accessed and are unmounted after a defined period of inactivity. Automounting NFS shares in this way conserves bandwidth and offers better performance compared to static mounts controlled by /etc/fstab.
How does it work?
Like most things in Linux, autofs uses a configuration file as the framework for completing tasks. It consults a map file located at /etc/auto.master. The file defines various mount points. Each entry in this file has three fields that need to be set for the daemon to work correctly. These fields are:
- Mount point
- Location of map file
- Optional field (allows for the inclusion of options)
Practical example
Let's look at how to mount a directory on our machines. For this demonstration, let's mount directory /afstest on our remote machine client.example.com (172.25.1.4) to the mount point /test/nfs_share. To do this, add the following to the auto.master file:
/test /etc/auto.misc --timeout 30
Once that is completed, add the following to our map file /etc/auto.misc:
autofstest -rw,soft,intr,rsize=8192,wsize=8192 client.example.com:/afstest
Field one in the auto.misc file is the name of the subdirectory in /misc. The second field contains our mount options, such as read and write permissions and size restrictions. The third field is the location of the NFS export.
NOTE: These fields are different from the fields listed in the /etc/auto.master
Once we have all of our options set, we need to restart the autofs service. Use the following command:
# /sbin/service autofs restart
Once complete, verify the active mount points by using this command:
# /sbin/service autofs status
As with all configuration file changes, if the service is running when the change is made, you need to reload the file. You can do this by restarting the service altogether or just doing a soft reload:
# /sbin/service autofs reload
Wrap up
The autofs utility is a great way to supplement your NFS journey with some additional insight into this useful feature. There is so much more to learn around the things we use every day if we just take the time to dig for it. Hopefully, you found this quick exercise helpful.
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