Skip to main content

systemd: What Actually Runs Your System

systemd is what starts your system. It's what manages services. It's what keeps everything running.

Love it or hate it, it's what you'll use. Most modern Linux uses systemd. Learn it.

What systemd Actually Does​

systemd:

  • Starts the system at boot
  • Manages services (start, stop, restart)
  • Handles dependencies (service A needs service B)
  • Manages system resources
  • Provides logging (journald)

That's it. But that's a lot.

systemctl: The Command You'll Use​

sudo systemctl start service-name     # Start service
sudo systemctl stop service-name      # Stop service
sudo systemctl restart service-name   # Restart service
sudo systemctl reload service-name    # Reload config (if supported)
sudo systemctl status service-name    # Show status

That's 90% of what you need.

Real examples:

sudo systemctl start nginx
sudo systemctl stop nginx
sudo systemctl restart nginx
sudo systemctl status nginx

My take: systemctl is the command. Learn it. You'll use it constantly.

Enable and Disable (Start at Boot)​

sudo systemctl enable service-name    # Start at boot
sudo systemctl disable service-name   # Don't start at boot

Enable = Start automatically when system boots. Disable = Don't start automatically.

Real example:

sudo systemctl enable nginx           # Start nginx on boot
sudo systemctl disable nginx          # Don't start on boot

My take: Enable services you want running. Disable services you don't need. Simple.

Checking Status​

systemctl status nginx

Output shows:

  • Loaded - Service file loaded
  • Active - Is it running? (active, inactive, failed)
  • Main PID - Process ID
  • Tasks - Number of tasks
  • Memory - Memory usage
  • Logs - Recent log entries

Real example:

● nginx.service - A high performance web server
   Loaded: loaded (/lib/systemd/system/nginx.service; enabled)
   Active: active (running) since Mon 2024-12-28 10:00:00 UTC
 Main PID: 1234 (nginx)
    Tasks: 2
   Memory: 2.1M

What matters: Active: active (running) = It's working. Active: inactive (dead) = It's not running. Active: failed = Something broke.

Listing Services​

systemctl list-units --type=service  # All services
systemctl list-units --state=running # Running services
systemctl list-units --failed        # Failed services

My take: list-units --failed is useful. Shows what's broken.

Real example:

$ systemctl list-units --failed

If something is broken, it shows here.

Common Services You'll Manage​

sudo systemctl start nginx
sudo systemctl start apache2
sudo systemctl start mysql
sudo systemctl start docker
sudo systemctl start ssh

These are the services you'll actually manage. Web servers. Databases. Docker. SSH.

Understanding Service States​

  • active (running) - Working
  • active (exited) - Ran and finished (one-time services)
  • inactive (dead) - Not running
  • failed - Broken

My take: active (running) = good. failed = bad. Everything else = depends.

Reload vs Restart​

sudo systemctl reload nginx           # Reload config
sudo systemctl restart nginx          # Restart service

Reload = Reload configuration without stopping. Restart = Stop and start again.

When to use: Reload if the service supports it (nginx does). Restart if it doesn't or if reload doesn't work.

My take: Try reload first. It's faster. If it doesn't work, restart.

The Truth About systemd​

People complain about systemd. It's complex. It does a lot. It's not simple.

But here's the thing: It works. It's what you'll use. Learn it.

My take: Don't fight it. Learn it. Use it. It's not going away.

What's Next?​

Now that you understand systemd, let's talk about Service Management. We'll cover managing services in detail.

Or practice. Start a service. Stop it. Check its status. Get familiar with systemctl.

Personal note: When I first saw systemd, I thought it was overcomplicated. Then I learned it. Now I appreciate it. It's powerful. It's reliable. It just works. Don't fight it. Learn it.