How to Use autofs for Dynamic Mounting on Linux Servers

Static mount entries in /etc/fstab cause every remote share to be mounted at boot, which can waste network bandwidth and server resources when many mounts are unused.

The autofs daemon solves this by mounting a filesystem only when a user accesses its path, acting as an on‑demand automounter.

Install autofs on a RHEL/CentOS system:

# yum install autofs
Loaded plugins: langpacks, product-id, subscription-manager
... (installation output) ...
Complete!

Configure the master map /etc/auto.master using the format mount‑point sub‑map‑file . Sub‑map files must end with .misc and contain detailed mount definitions.

# vim /etc/auto.master
# Sample auto.master file
# key [ -mount-options ] location
/media   /etc/iso.misc
/misc    /etc/auto.misc
+dir:/etc/auto.master.d
+auto.master

Create a sub‑map file for the CD device, e.g., /etc/iso.misc:

iso   -fstype=iso9660,ro,nosuid,nodev :/dev/cdrom

Start and enable autofs so it runs at boot:

# systemctl start autofs
# systemctl enable autofs

After configuration, the CD is not mounted initially, but navigating to /media/iso triggers autofs to mount it automatically, allowing you to list its contents. The df -h output shows the CD device appearing under /media/iso only after access.

# df -h
Filesystem      Size Used Avail Use% Mounted on
/dev/mapper/rhel-root 18G 3.0G 15G 17% /
... (other filesystems) ...
/dev/cdrom       3.5G 3.5G   0 100% /media/iso

This demonstrates how autofs reduces unnecessary resource usage while providing seamless access to remote or removable filesystems.