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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.

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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.

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Prerequisites

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

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

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2. Set Up a Simple NFS Server

To demonstrate, we’ll configure a basic NFS export on the local machine.
  1. Install NFS utilities: 
    sudo dnf install nfs-utils
  2. Start and enable the NFS server: 
    sudo systemctl enable --now nfs-server.service
  3. Add an export in /etc/exports: 
    sudo vim /etc/exports

    /etc 127.0.0.1(ro)
  4. Reload the server to apply changes: 
    sudo systemctl reload nfs-server.service

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3. Configure AutoFS Maps

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

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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

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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 Namefstype OptionsSourceDescription
mynetworkshareauto127.0.0.1:/etcAuto-detect filesystem
mynetworksharenfs4127.0.0.1:/etcForce NFSv4
mynetworkshareauto,ro127.0.0.1:/etcRead-only mount
myext4filesauto:/dev/vdb2Local ext4 partition
Reload AutoFS: 
sudo systemctl reload autofs.service

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4. Test the On-Demand Mount

  1. Verify that /shares is empty: 
    ls /shares
# (no output; nothing is mounted yet)
  2. Access the share to trigger the mount: 
    ls /shares/mynetworkshare/
# mysharedfile1  mysharedfile2
  3. After 5 minutes of inactivity, AutoFS will unmount the share automatically.

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5. Direct Mount Points (No Common Parent)

If you prefer absolute mount paths instead of a shared parent:
  1. Update /etc/auto.master: 
    sudo vim /etc/auto.master
    Replace the /shares entry with: 
    /-  /etc/auto.shares  --timeout=400
  2. Modify /etc/auto.shares: 
    sudo vim /etc/auto.shares

    /mynetworkshare         -fstype=auto    127.0.0.1:/etc
/localfiles/myext4files -fstype=auto    :/dev/vdb2
  3. Reload AutoFS: 
    sudo systemctl reload autofs.service
Now you can access directly: 
ls /mynetworkshare/
ls /localfiles/myext4files/
# mysharedfile3  mysharedfile4

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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.

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