Control Mounting and Unmounting of Filesystems Part 1 Mount on demand

In this lesson, you’ll learn how to optimize Linux system performance by mounting filesystems only when they’re accessed. This technique, known as on-demand mounting, reduces unnecessary network traffic—especially for remote filesystems like NFS—and keeps your server load light.

Why On-Demand Mounting?

Defers mounting until a path is accessed
Saves network bandwidth for NFS and CIFS shares
Automatically unmounts after inactivity
Simplifies management of rarely used mount points

Consider a rarely used directory such as /backups. With on-demand mounting, nothing is mounted at boot or during idle periods. As soon as an application or user reads or writes /backups, the OS mounts the remote share automatically:

The image illustrates a diagram of "On Demand Mounting," showing multiple "/backups/" folders connected to a central fileserver.

Prerequisites

A Linux distribution with dnf or yum (RHEL, CentOS, Fedora)
Root or sudo privileges
Basic knowledge of NFS or other network filesystems

1. Install and Enable AutoFS

The most common tool for on-demand mounts is autofs. Install and start the service:

sudo dnf install autofs
sudo systemctl enable --now autofs.service

Note

If you’re using a different package manager such as yum or apt, adjust the install command accordingly.

2. Set Up a Simple NFS Server

To demonstrate, we’ll configure a basic NFS export on the local machine.

Install NFS utilities:
```
sudo dnf install nfs-utils
```

Start and enable the NFS server:

sudo systemctl enable --now nfs-server.service

Add an export in /etc/exports:

sudo vim /etc/exports

/etc 127.0.0.1(ro)

Reload the server to apply changes:

sudo systemctl reload nfs-server.service

3. Configure AutoFS Maps

AutoFS uses a master map and one or more map files to define mounts.

3.1 /etc/auto.master

Open the master configuration:

sudo vim /etc/auto.master

Add at the end:

/shares  /etc/auto.shares  --timeout=300

/shares: Parent directory that AutoFS will create
/etc/auto.shares: Map file listing the mounts
--timeout=300: Unmount after 300 seconds of inactivity

3.2 /etc/auto.shares

Edit the map file to define individual mounts:

sudo vim /etc/auto.shares

# Mount definitions for /shares
mynetworkshare -fstype=auto    127.0.0.1:/etc
mynetworkshare -fstype=nfs4    127.0.0.1:/etc
mynetworkshare -fstype=auto,ro 127.0.0.1:/etc
myext4files    -fstype=auto    :/dev/vdb2

Mount Name	fstype Options	Source	Description
mynetworkshare	auto	127.0.0.1:/etc	Auto-detect filesystem
mynetworkshare	nfs4	127.0.0.1:/etc	Force NFSv4
mynetworkshare	auto,ro	127.0.0.1:/etc	Read-only mount
myext4files	auto	:/dev/vdb2	Local ext4 partition

Reload AutoFS:

sudo systemctl reload autofs.service

4. Test the On-Demand Mount

Verify that /shares is empty:

ls /shares
# (no output; nothing is mounted yet)

Access the share to trigger the mount:

ls /shares/mynetworkshare/
# mysharedfile1  mysharedfile2

After 5 minutes of inactivity, AutoFS will unmount the share automatically.

5. Direct Mount Points (No Common Parent)

If you prefer absolute mount paths instead of a shared parent:

Update /etc/auto.master:

sudo vim /etc/auto.master

Replace the /shares entry with:

/-  /etc/auto.shares  --timeout=400

Modify /etc/auto.shares:

sudo vim /etc/auto.shares

/mynetworkshare         -fstype=auto    127.0.0.1:/etc
/localfiles/myext4files -fstype=auto    :/dev/vdb2

Reload AutoFS:
```
sudo systemctl reload autofs.service
```

Now you can access directly:

ls /mynetworkshare/
ls /localfiles/myext4files/
# mysharedfile3  mysharedfile4

Next Steps

You’ve successfully configured on-demand mounting with AutoFS and NFS. In the next lesson, we’ll explore advanced unmounting controls and troubleshooting techniques.

Links and References

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