Service Management¶

Prerequisites¶

• SSH access to the target machine
• Root or sudo privileges

Quick Reference¶

Procedure: List and Filter Services¶

When to use: Finding out what services exist on the system, which are running, and which are enabled.

Steps:

1. List all running services:

   systemctl list-units --type=service
   

2. List all services (including inactive/disabled):

   systemctl list-unit-files --type=service
   

3. Filter by name:

   systemctl list-unit-files --type=service | grep <keyword>
   

4. Check if a specific service is active:

   systemctl is-active <service_name>
   

5. Check if a specific service is enabled on boot:

   systemctl is-enabled <service_name>
   

Troubleshooting:

• If a service you installed doesn't appear: Run systemctl daemon-reload to rescan unit files.

Procedure: Check Service Status and Logs¶

When to use: A service failed to start, crashed, or is behaving unexpectedly.

Steps:

1. Check current status and recent log lines:

   systemctl status <service_name>
   

   Look for Active: active (running) or failed.

2. View full logs for a specific service:

   journalctl -u <service_name>
   

3. View live logs (follow mode):

   journalctl -u <service_name> -f
   

4. View logs from the current boot session only:

   journalctl -u <service_name> -b
   

Troubleshooting:

• If logs are truncated: Use journalctl -u <service_name> --no-pager or piping to less.
• If no logs appear: Ensure the service is actually logging to stdout/stderr or syslog.

Procedure: Start/Stop/Restart a Service¶

When to use: You need to start a daemon, stop a misbehaving service, or apply configuration changes (requires restart).

Steps:

1. Start a service immediately:

   systemctl start <service_name>
   

2. Stop a running service:

   systemctl stop <service_name>
   

3. Restart a service (stop then start):

   systemctl restart <service_name>
   

4. Reload configuration without interrupting connections (if supported):

   systemctl reload <service_name>
   

5. Verify the status:

   systemctl status <service_name>
   

Troubleshooting:

• If systemctl hangs: Check if the service is stuck in a loop or waiting for resources.
• If "Unit not found": Check spelling with systemctl list-unit-files | grep <name>.

Procedure: Enable a Service on Boot¶

When to use: Ensure a service starts automatically when the server reboots (e.g., web server, database).

Steps:

1. Enable the service:

   systemctl enable <service_name>
   

   Note: This usually creates a symlink in /etc/systemd/system/multi-user.target.wants/.

2. Disable the service (prevent autostart):

   systemctl disable <service_name>
   

3. Enable and Start in one command:

   systemctl enable --now <service_name>
   

4. Verify enabled status:

   systemctl is-enabled <service_name>
   

Troubleshooting:

• If a service is enabled but fails to start on boot: Check journalctl -u <service_name> -b to see logs from the current boot.

Procedure: Create a Custom systemd Unit File¶

When to use: You want to run a custom script or application as a managed service.

Steps:

1. Create a unit file at /etc/systemd/system/myapp.service:

   [Unit]
   Description=My Custom Application
   After=network.target
   
   [Service]
   Type=simple
   User=myuser
   ExecStart=/usr/bin/python3 /opt/myapp/main.py
   Restart=on-failure
   
   [Install]
   WantedBy=multi-user.target
   

2. Reload systemd to recognize the new file:

   systemctl daemon-reload
   

3. Start and enable the service:

   systemctl enable --now myapp
   

Troubleshooting:

• If modifications aren't picked up: Did you run systemctl daemon-reload?
• If Exec format error: Ensure ExecStart uses absolute paths (e.g., /usr/bin/python3, not just python3).

Related Documentation¶

• Technologies: systemd
• Concepts: Configuration Management