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Understanding and Managing Persistent User Sessions with Linger on Ubuntu

ByMuhammad Imanudin Posted on

Introduction to Linger

In Ubuntu (and other Linux systems using systemd), linger allows non-root users to run persistent services that:

  • Start automatically at system boot.
  • Continue running after the user logs out.

Without linger, user-specific services terminate when the user logs out. Linger is ideal for long-running processes like web servers, databases, or bots under a user account.

Why Use Linger?

  • Run services without active login: No need to keep a user logged in.
  • Start on boot: Services launch automatically during system startup.
  • User-level isolation: Avoid running everything as root; use dedicated users for security.
  • Resource management: User services respect system resource limits.

Enabling Linger for a User

Use loginctl to enable linger. Replace username with the target user:

sudo loginctl enable-linger username

Example:

sudo loginctl enable-linger iman

Disabling Linger

To revoke persistent sessions:

sudo loginctl disable-linger username

Example:

sudo loginctl disable-linger iman

Verifying Linger Status

Check if linger is active for a user:

loginctl show-user username | grep Linger
  • Output: Linger=yes (enabled) or Linger=no (disabled).

Alternative Check:

ls /var/lib/systemd/linger/

Enabled users appear as files in this directory.

Example: Persistent Web Server with Linger

Goal: Run a Python web server (http.server) under user iman that survives logout.

Steps:

  1. Enable linger for iman:
sudo loginctl enable-linger iman
  1. Create a systemd user service:

As iman, create the service file:

mkdir -p ~/.config/systemd/user/  
nano ~/.config/systemd/user/simple-web.service

Paste this configuration:

[Unit]
Description=Simple Web Server

[Service]
ExecStart=/usr/bin/python3 -m http.server 8080
WorkingDirectory=/home/iman/web-content  # Customize this path
Restart=always

[Install]
WantedBy=default.target
  1. Reload the user’s systemd:
systemctl --user daemon-reload
  1. Start & enable the service:
systemctl --user enable --now simple-web.service
  1. Verify:
systemctl --user status simple-web.service  # Should show "active"  
curl http://localhost:8080                 # Test the server
  1. Log out: The service persists!
  1. Managing User Services
  • Start/stop a service:
systemctl --user start service-name  
systemctl --user stop service-name
  • View logs:
journalctl --user-unit=service-name
  1. Important Notes
  • Security: Services run with user privileges. Ensure they don’t expose unnecessary ports or run untrusted code.
  • Resource Limits: Use systemd resource controls (e.g., MemoryMax= in service files) to prevent abuse.
  • Dependencies: User services can’t depend on system services (e.g., network.target). Use sockets or timers instead.
  • Cleanup: Disable linger if services are no longer needed.
  1. Troubleshooting
  • Service fails to start:
    • Check paths in the service file.
    • Test the command manually (ExecStart=...).
    • Inspect logs: journalctl --user-unit=service-name.
  • Linger not working:
    • Confirm linger is enabled: loginctl show-user username.
    • Reboot the system to trigger startup.
  1. Conclusion

Linger empowers non-root users to manage persistent services safely. By combining it with systemd user units, you can deploy user-level services that survive reboots and logouts, simplifying long-term tasks while maintaining security isolation.

Next Steps:

  • Explore systemd user timers for scheduled tasks.
  • Learn about resource constraints in service files (man systemd.resource-control).