Managing Services in Linux: A Complete Guide to systemd

Introduction / Why This Matters

Systemd has become the standard for initialization and service management in most modern Linux distributions (Ubuntu, Debian, CentOS, Fedora). Understanding service management is a key skill for system administrators and developers working with servers. After completing this guide, you will be able to confidently start, stop, configure autostart, and diagnose issues with any service, as well as create your own.

Prerequisites / Preparation

1. Terminal access with sudo privileges (or root).
2. A Linux distribution that uses systemd (check with systemctl --version).
3. Basic command-line knowledge.

Step 1: Checking for systemd and Listing Units

Let's confirm the system uses systemd and see which services (units) are available.

# Check systemd version
systemctl --version

# Show all loaded units (services, timers, sockets, etc.)
systemctl list-units --type=service --state=running

# Show ALL available units, including inactive ones
systemctl list-unit-files --type=service | head -20

Key unit statuses: loaded (unit file found), active (running), inactive (stopped), failed (failed with an error).

Step 2: Basic State Management Operations

Here are the essential commands for daily control.

# Start a service immediately (not permanently)
sudo systemctl start nginx

# Stop a service
sudo systemctl stop nginx

# Restart (stop and start again)
sudo systemctl restart nginx

# Reload (send SIGHUP, if the service supports it)
sudo systemctl reload nginx

# Check status (the most informative command)
sudo systemctl status nginx

In the status output, look at the Active: line and the recent logs in the journal section. If the status is failed (Result: exit-code), check the logs in the next step.

💡 Tip: For a quick restart with state cleanup, use sudo systemctl try-restart nginx — it won't start the service if it's already stopped.

Step 3: Configuring Autostart (Enable/Disable)

Autostart is managed via symbolic links in the /etc/systemd/system/ directory.

# Enable autostart on next system boot
sudo systemctl enable nginx
# Creates a link: /etc/systemd/system/multi-user.target.wants/nginx.service -> /lib/systemd/system/nginx.service

# Disable autostart (removes the link, the service file remains)
sudo systemctl disable nginx

# Check if a service is enabled for autostart
systemctl is-enabled nginx
# Output: enabled, disabled, static, masked

⚠️ Important: The enable command does not start the service immediately. For a one-time start, use start; to start and enable autostart, use enable --now.

Step 4: Diagnostics with journalctl

Systemd logs are stored in a binary journal, accessible via journalctl.

# Show logs for ALL services in real-time (like tail -f)
sudo journalctl -f

# Show logs for a SPECIFIC service
sudo journalctl -u nginx.service

# Show logs since the last system boot (-b)
sudo journalctl -u nginx.service -b

# Filter by time (e.g., last 10 minutes)
sudo journalctl -u nginx.service --since "10 min ago"

# Show only error-level messages (error, crit, alert, emerg)
sudo journalctl -u nginx.service -p err

# Vacuum the journal (caution! requires disk space)
sudo journalctl --vacuum-time=3d  # Keep logs only for the last 3 days

To search for text in logs, use standard grep:

sudo journalctl -u nginx.service | grep -i "permission"

Step 5: Creating a Simple Custom Service

Suppose you need to run the script /opt/myscript.sh at system startup.

1. Create the service file /etc/systemd/system/myscript.service:

   [Unit]
   Description=My Custom Script
   After=network.target
   
   [Service]
   Type=simple
   ExecStart=/opt/myscript.sh
   Restart=on-failure
   RestartSec=10
   User=ubuntu
   Group=ubuntu
   
   [Install]
   WantedBy=multi-user.target
   

   • After — run after the network stack.
   • Type=simple — the process runs in the foreground.
   • Restart=on-failure — restart if it crashes.
   • User/Group — which user to run as.
   • WantedBy — which target unit (.target) this belongs to.
2. Save the file and run:

   # Reload systemd configuration (mandatory after creating/modifying files!)
   sudo systemctl daemon-reload
   
   # Enable and start immediately
   sudo systemctl enable --now myscript.service
   
   # Check status
   sudo systemctl status myscript.service
   

Verification

1. Service status: systemctl status <service> should show active (running).
2. Autostart: systemctl is-enabled <service> should return enabled.
3. Logs: journalctl -u <service> -n 20 should show the last 20 log lines without errors.
4. Functionality: If it's a web server (nginx/apache), check the response with curl http://localhost. If it's a background process, ensure it's running (ps aux | grep <process>).

Common Issues