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Autofs

Autofs mounts a filesystem on first access and unmounts it after a period of disuse, instead of keeping it mounted from boot. It suits home directories and shares that are used occasionally, and it avoids a boot-time hang on an absent NFS server.

Track: RHCSA · Interview weight: Low

Must-Know Facts

Fact Value Verify with
Package autofs on both families rpm -q autofs
Master map /etc/auto.master and /etc/auto.master.d/* cat /etc/auto.master
Mount point Master map ties a directory to a map file ls /etc/auto.master.d
Direct map Absolute paths, key /- man 5 autofs
Indirect map A base directory with keys as subdirectories the map file
On-demand Mounts on access, not at boot findmnt after ls
Idle timeout Unmounts after inactivity (default 300s) --timeout
Service Reload maps by restarting the service systemctl restart autofs

Master Map and a Map File

The master map connects a base directory to a map file. An indirect map lists keys that become subdirectories under that base, each with its mount options and source.

echo '/nfs  /etc/auto.nfs' | sudo tee /etc/auto.master.d/nfs.autofs
echo 'shared  -rw,soft  172.16.1.3:/srv/nfs/shared' | sudo tee /etc/auto.nfs
sudo systemctl restart autofs

This maps /nfs/shared to the NFS export, mounted only when something accesses it. Editing a map takes effect after systemctl restart autofs.

The base directory is managed by autofs, not the filesystem

Autofs owns /nfs and populates subdirectories on demand, so ls /nfs may look empty until a specific key like /nfs/shared is accessed. Do not create real directories under an autofs base; they are shadowed by the automounts.

Mount on Access

Nothing is mounted until the path is used. The first access to /nfs/shared triggers the mount, and findmnt then shows it.

findmnt /nfs/shared || echo "not mounted yet"
ls /nfs/shared                       # access triggers the mount
findmnt -no TARGET,SOURCE,FSTYPE /nfs/shared

Output:

not mounted yet
README
/nfs/shared 172.16.1.3:/srv/nfs/shared nfs4

Before access the path is not mounted; after ls it is a live NFSv4 mount. It unmounts again once idle past the timeout, freeing the connection.

Autofs avoids the boot-time NFS hang

A static NFS entry in /etc/fstab can stall boot if the server is down. Autofs only touches the server on access, so a missing server delays the first use, not the whole boot.

Common Errors

an autofs path shows empty until it is accessed

Cause: this is expected: autofs mounts on demand, so the mount appears only after the path is used.

Fix: access the full path (ls /nfs/shared), not the parent alone; the parent is managed by autofs and stays empty.

map changes have no effect

Cause: autofs caches maps and does not reload them automatically after an edit.

Fix: sudo systemctl restart autofs to re-read the master and map files.

Interview Checkpoints

L1: What problem does autofs solve over a static fstab mount?

Say first: it mounts on demand and unmounts when idle, so shares are only connected when used and an absent server does not hang boot.

Proof: the path is unmounted until accessed, then findmnt shows the mount.

Follow-up: what is the default idle timeout? (300 seconds.)

L1: What is the difference between a direct and an indirect map?

Say first: a direct map uses absolute paths under the key /-; an indirect map has a base directory whose keys become subdirectories.

Proof: the master map references /- for direct, a base path for indirect.

Follow-up: which suits per-user home directories? (an indirect map with a wildcard key.)

L2: Configure autofs to mount an NFS export on access.

Say first: add a master entry pointing at a map file, define the key, and restart the service.

Proof:

echo '/nfs /etc/auto.nfs' | sudo tee /etc/auto.master.d/nfs.autofs
echo 'shared -rw 172.16.1.3:/srv/nfs/shared' | sudo tee /etc/auto.nfs
sudo systemctl restart autofs

Follow-up: how do you confirm it works? (ls /nfs/shared, then findmnt.)

L2: You edited a map but the change is not applied. Fix it.

Say first: autofs caches maps, so restart the service to reload them.

Proof: sudo systemctl restart autofs; access the path again.

Follow-up: why not wait for it to reload? (maps are not re-read automatically.)

L3: A user reports their home directory is empty on login. How do you check if autofs is involved?

Say first: confirm the home path is an autofs mount and that accessing it triggers the mount rather than showing an empty directory.

Proof: check /etc/auto.master.d and the map; findmnt the home path after the user accesses a file in it.

Follow-up: what breaks this on a network share? (the NFS server being unreachable at first access.)

L2: How do you make autofs unmount an idle share sooner?

Say first: lower the timeout on the master entry.

Proof: add --timeout=60 to the master map line, then restart autofs.

Follow-up: why unmount at all? (to release the server connection and avoid stale mounts.)

Captured on Rocky Linux 10.2 on an iximiuz Labs FlexBox microVM, kernel 6.1.167, 2026-09.