System Administration

Linux Autofs (Automounter) Cheatsheet

Comprehensive Autofs guide covering automatic filesystem mounting, master maps, indirect/direct maps, NFS configuration, troubleshooting, and best practices for on-demand network filesystem mounting in Linux.

#autofs #automounter #nfs #filesystem #linux #mount #sysadmin
Sign In to Download

Free account required

i

What is Autofs?

Autofs (automounter) is a kernel-based filesystem that automatically mounts filesystems on-demand when accessed and unmounts them after a period of inactivity. It's ideal for NFS shares and network drives, reducing boot time and network traffic.

On-Demand
Mounts only when accessed
Auto-Unmount
Unmounts after timeout
Transparent
Works seamlessly for users

Table of Contents

1. How Autofs Works 2. Installation & Setup 3. Master Map Configuration 4. Map Types (Direct/Indirect) 5. Common Configuration Examples 6. Commands & Management 7. Troubleshooting 8. Best Practices

How Autofs Works

The Automount Process

1
User accesses directory within mount point

User attempts to access a directory managed by autofs (e.g., cd /mnt/nfs/server1) 

$ cd /mnt/nfs/server1
# Autofs detects access attempt
2
Autofs checks map file for configuration

Autofs daemon consults the map file (/etc/auto.nfs) to see if the directory maps to a remote filesystem 

# Checking /etc/auto.nfs
server1    -fstype=nfs,rw    192.168.1.100:/export/data
✓
Directory Found - Mount Filesystem

If entry exists in map file, autofs dynamically mounts the remote filesystem to the specified mount point 

# Mount performed automatically
mount -t nfs 192.168.1.100:/export/data /mnt/nfs/server1
# User can now access files transparently
✗
Directory Not Found - Access Denied

If no matching entry in map file, access is denied with "No such file or directory" error 

$ cd /mnt/nfs/nonexistent
bash: cd: /mnt/nfs/nonexistent: No such file or directory
3
After inactivity period - Automatic unmount

After timeout (default 5 minutes), autofs automatically unmounts the filesystem if not in use 

# After 5 minutes of inactivity
# Autofs automatically unmounts
umount /mnt/nfs/server1

Autofs vs /etc/fstab

Feature Autofs /etc/fstab
Mount Time On-demand (when accessed) At boot time
Auto Unmount Yes (after timeout) No (manual unmount)
Network Failure Doesn't block boot Can hang boot process
Resource Usage Minimal (mounts as needed) Always mounted
Use Case Network shares, optional mounts Critical system filesystems

Key Benefits of Autofs

  • Faster Boot Times: No waiting for network mounts during startup
  • Reduced Network Traffic: Only active mounts consume bandwidth
  • Resilience: System doesn't hang if remote server is down
  • Resource Efficiency: Filesystems unmount when not in use
  • Transparent Operation: Users access files as if locally mounted
  • Centralized Management: Single configuration file for all mounts

Installation & Setup

Install Autofs

Before installing autofs, ensure your VPS environment meets basic requirements. See our performance benchmarks to find optimal server configurations. 

# Debian/Ubuntu
$ sudo apt update
$ sudo apt install autofs

# RHEL/CentOS/Rocky/Alma
$ sudo dnf install autofs

# Arch Linux
$ sudo pacman -S autofs

Enable and Start Autofs Service

# Enable autofs to start at boot
$ sudo systemctl enable autofs

# Start autofs service
$ sudo systemctl start autofs

# Check service status
$ sudo systemctl status autofs

# Restart after configuration changes
$ sudo systemctl restart autofs

Main Configuration Files

/etc/auto.master Master configuration file (defines mount points and map files)
/etc/auto.* Map files (define what and how to mount) - learn more about Linux filesystem management
/etc/autofs.conf Global autofs daemon settings (optional)

Master Map Configuration (/etc/auto.master)

Master Map Syntax

# Format:
# mount-point    map-file    [options]

# Examples:
/mnt/nfs         /etc/auto.nfs       --timeout=60
/misc            /etc/auto.misc      --timeout=300
/-               /etc/auto.direct    --ghost

Mount Point: Base directory for autofs mounts
Map File: Configuration file defining individual mounts
Options: Timeout, ghost mode, etc.

Example: /etc/auto.master

# /etc/auto.master - Master autofs configuration

# Mount NFS shares at /mnt/nfs/*
/mnt/nfs    /etc/auto.nfs    --timeout=60

# Mount miscellaneous filesystems at /misc/*
/misc       /etc/auto.misc   --timeout=300

# Direct mounts (full path specified in map)
/-          /etc/auto.direct --ghost

# Mount home directories from NFS server
/home       /etc/auto.home   --timeout=120

# Include other master map files
+auto.master

Common Master Map Options

Option Description Example
--timeout=N Unmount after N seconds of inactivity --timeout=60
--ghost Show mount points even when not mounted --ghost
--verbose Enable verbose logging --verbose
--nobrowse Don't show directory until accessed --nobrowse

Map Types (Direct vs Indirect)

Indirect Maps (Most Common)

Indirect maps mount filesystems as subdirectories under a common parent directory. The mount point is relative to the parent specified in auto.master.

Example: /etc/auto.master

/mnt/nfs    /etc/auto.nfs    --timeout=60

Example: /etc/auto.nfs (Indirect Map)

# Key         Options                      Location
server1       -fstype=nfs,rw               192.168.1.100:/export/data
server2       -fstype=nfs,ro,soft          nfs.example.com:/share
backup        -fstype=nfs,rw,noatime       10.0.0.50:/backups

Access paths: /mnt/nfs/server1, /mnt/nfs/server2, /mnt/nfs/backup

Direct Maps (Full Path)

Direct maps specify the full mount path. Use "/-" in auto.master to enable direct mounts. Useful for mounting to specific paths outside a common parent.

Example: /etc/auto.master

/-    /etc/auto.direct    --ghost

Example: /etc/auto.direct (Direct Map)

# Full-path             Options                 Location
/opt/software           -fstype=nfs,ro          nfs-server:/software
/data/shared            -fstype=nfs,rw          192.168.1.200:/shared
/mnt/archive            -fstype=nfs,ro,soft     backup.local:/archives

Access paths: /opt/software, /data/shared, /mnt/archive (exact paths)

When to Use Each Type

Use Indirect Maps For:
  • Multiple similar mounts (NFS servers)
  • User home directories
  • Common mount point prefix
  • Scalable configurations
Use Direct Maps For:
  • Specific mount paths
  • System directories (/opt, /data)
  • Mixed filesystem locations
  • Integration with existing paths

Common Configuration Examples

NFS Shares (Most Common)

Configure NFS network shares for automatic mounting. Use our Port Scanner tool to verify NFS port 2049 is accessible. 

# /etc/auto.master
/mnt/nfs    /etc/auto.nfs    --timeout=60

# /etc/auto.nfs
# Basic NFS mount
data        -fstype=nfs,rw                    nfs-server.local:/data

# NFS with soft mount (recommended for non-critical data)
backup      -fstype=nfs,rw,soft,timeo=10      192.168.1.50:/backups

# NFS with specific version (NFSv4)
media       -fstype=nfs4,ro,noexec            media-server:/media

# Multiple NFS servers (failover)
shared      -fstype=nfs,rw,soft               nfs1:/shared,nfs2:/shared

CIFS/SMB Shares (Windows)

# /etc/auto.master
/mnt/windows    /etc/auto.smb    --timeout=120

# /etc/auto.smb
# Basic SMB mount with credentials
share1    -fstype=cifs,rw,username=user,password=pass    ://server/share1

# SMB with credentials file (more secure)
share2    -fstype=cifs,rw,credentials=/etc/.smbcreds     ://192.168.1.10/share2

# Guest access (no credentials)
public    -fstype=cifs,ro,guest                          ://fileserver/public

# /etc/.smbcreds (chmod 600)
# username=myuser
# password=mypassword
# domain=WORKGROUP

SSHFS (Secure File Transfer)

Mount remote filesystems securely via SSH. For security best practices, see our OpenSSH hardening guide. 

# /etc/auto.master
/mnt/ssh    /etc/auto.sshfs    --timeout=60

# /etc/auto.sshfs
# SSHFS with key-based authentication
remote1    -fstype=fuse,rw,allow_other,IdentityFile=/root/.ssh/id_rsa    :sshfs\#[email protected]\:/data

# SSHFS with compression
remote2    -fstype=fuse,rw,compression=yes    :sshfs\#[email protected]\:/backup

User Home Directories

# /etc/auto.master
/home    /etc/auto.home    --timeout=300

# /etc/auto.home
# Wildcard entry - mounts home directory for any user
*    -fstype=nfs,rw    nfs-server:/home/&

# Access:
# /home/john → mounts nfs-server:/home/john
# /home/jane → mounts nfs-server:/home/jane

CD-ROM / USB Auto-mounting

# /etc/auto.master
/misc    /etc/auto.misc    --timeout=5

# /etc/auto.misc
# CD-ROM drive
cd      -fstype=iso9660,ro,nosuid,nodev    :/dev/cdrom

# USB drive
usb     -fstype=auto,async,nodev,nosuid    :/dev/sdb1

Common Mount Options

NFS Options: rw, ro, soft, hard, intr, timeo=10, retrans=3, noatime
CIFS Options: username=user, password=pass, uid=1000, gid=1000, file_mode=0755

Commands & Management

Service Management

# Check autofs status
$ sudo systemctl status autofs

# Restart autofs (after config changes)
$ sudo systemctl restart autofs

# Reload configuration without restart
$ sudo systemctl reload autofs

# Enable at boot
$ sudo systemctl enable autofs

# Stop autofs
$ sudo systemctl stop autofs

Testing & Debugging

# Run automount in foreground (debug mode)
$ sudo automount -f -v

# Check autofs mounts
$ mount | grep autofs

# View active autofs mount points
$ sudo automount -m

# Check map file syntax
$ sudo autofs-check-config /etc/auto.master

# Force unmount all autofs mounts
$ sudo killall -HUP automount

Manual Mount Testing

# Test NFS mount manually (before adding to autofs)
$ sudo mount -t nfs 192.168.1.100:/export/data /mnt/test

# Test CIFS mount manually
$ sudo mount -t cifs -o username=user //server/share /mnt/test

# Unmount test mount
$ sudo umount /mnt/test

# Check if NFS server is accessible
$ showmount -e 192.168.1.100

Viewing Logs

For advanced log analysis and parsing techniques, see our Linux log parsing guide. 

# View autofs logs (systemd)
$ sudo journalctl -u autofs -f

# View system logs
$ sudo tail -f /var/log/syslog    # Debian/Ubuntu
$ sudo tail -f /var/log/messages  # RHEL/CentOS

# Enable debug logging in /etc/autofs.conf
logging = verbose

Map File Management

# Edit master map
$ sudo nano /etc/auto.master

# Edit indirect map
$ sudo nano /etc/auto.nfs

# After editing, restart autofs
$ sudo systemctl restart autofs

# Or reload without full restart
$ sudo systemctl reload autofs

Troubleshooting Common Issues

Common Problems & Solutions

Mount Point Not Visible

Symptoms: Directory doesn't appear or shows empty

Solution:

# Check if autofs is running
$ sudo systemctl status autofs

# Try accessing the directory
$ ls /mnt/nfs/server1

# Enable ghost mode in auto.master
/mnt/nfs    /etc/auto.nfs    --ghost

# Check for typos in map files
$ cat /etc/auto.master
$ cat /etc/auto.nfs
Permission Denied

Symptoms: "Permission denied" when accessing mounted directory

Causes: NFS export restrictions, firewall, UID/GID mismatch. Check file permissions for more details.

# Check NFS exports on server
$ showmount -e nfs-server

# Verify firewall allows NFS (port 2049) - use our Port Scanner tool
$ sudo firewall-cmd --list-services

# Check mount options (add uid/gid if needed)
data    -fstype=nfs,rw,uid=1000,gid=1000    nfs-server:/data
Mount Hangs / Timeout

Symptoms: Access hangs, system becomes unresponsive

Solution: Use soft mount with timeout

# Use soft mount to prevent hanging
data    -fstype=nfs,rw,soft,timeo=10,retrans=3    nfs-server:/data

# Test server connectivity first
$ ping nfs-server
$ telnet nfs-server 2049
Changes Not Reflected

Symptoms: Map file changes don't take effect

Solution:

# Always restart autofs after changes
$ sudo systemctl restart autofs

# Or reload for less disruption
$ sudo systemctl reload autofs

# Check syntax before restarting
$ sudo automount -f -v    # Test in foreground
Cannot Unmount (Device Busy)

Symptoms: Autofs can't unmount, "device busy" error

Solution:

# Find processes using the mount
$ sudo lsof +D /mnt/nfs/server1
$ sudo fuser -m /mnt/nfs/server1

# Kill processes if safe
$ sudo fuser -km /mnt/nfs/server1

# Or wait for timeout to expire

Debug Checklist

Use these diagnostic tools: DNS Lookup for hostname resolution and Port Scanner for connectivity testing.

Check autofs service is running: systemctl status autofs
Verify map file syntax (no typos in /etc/auto.master and map files)
Test remote server connectivity: ping server, showmount -e server
Check firewall rules (NFS: port 2049, CIFS: port 445) - verify with Port Scanner
Review logs: journalctl -u autofs -f
Test mount manually first before adding to autofs
Run automount in debug mode: automount -f -v

Best Practices

Use Soft Mounts for Non-Critical Data
Use soft mount option to prevent system hangs if NFS server becomes unavailable. Add timeout and retry values.
data    -fstype=nfs,rw,soft,timeo=10,retrans=3    nfs-server:/data
Set Appropriate Timeout Values
Adjust timeout based on usage pattern: Frequently accessed: 300-600s | Occasionally accessed: 60-120s | Rarely accessed: 30-60s
Use Ghost Mode for Better User Experience
Enable --ghost option to show mount points even when not mounted, improving discoverability for users.
/mnt/nfs    /etc/auto.nfs    --ghost --timeout=60
Secure Credentials for CIFS Mounts
Never put passwords in map files. Use credentials file with restricted permissions. Learn more about file permissions and Linux hardening.
# /etc/auto.smb
share    -fstype=cifs,rw,credentials=/etc/.smbcreds    ://server/share

# /etc/.smbcreds (chmod 600 root:root)
username=myuser
password=mypassword
Test Manually Before Automating
Always test mounts manually with mount command before adding to autofs to verify connectivity, permissions, and options.
Document Your Configuration
Add comments to map files explaining purpose, server details, and contact information for maintenance.
# /etc/auto.nfs - NFS shares from file server cluster
# Contact: [email protected] | Updated: 2025-01-19
data      -fstype=nfs,rw,soft    fileserver1.local:/data    # Production data
Use NFSv4 When Possible
NFSv4 provides better security (Kerberos support), firewall-friendly (single port 2049), and improved performance. Specify with -fstype=nfs4.
Monitor and Log
Enable verbose logging during troubleshooting and monitor autofs behavior. Use journalctl -u autofs to track mount/unmount events.
Back to Cheatsheets

Host Your Network File Systems

Running NFS, CIFS, or other network filesystems? Compare VPS providers to find the perfect infrastructure for your autofs configurations with reliable storage, fast networking, and minimal latency. Compare performance metrics or explore our server tools.

View VPS Benchmarks More Cheatsheets

Need help? Contact us | Learn about VPSMetrics | Privacy Policy