systemd & Services — Managing Daemons with systemctl

Manage Linux system services with systemctl — start, stop, enable, disable, and monitor services using systemd.

March 26, 20255 min read

linuxsysadminsystemdsystemctlservices

What is systemd?

systemd is the init system on most modern Linux distros. It manages:

Services (daemons) like nginx, ssh, docker
Boot targets — groups of services (like old runlevels)
Boot process — starts services in the right order

Service Control

sudo systemctl start nginx      # Start service now
sudo systemctl stop nginx       # Stop service
sudo systemctl restart nginx    # Stop then start
sudo systemctl reload nginx     # Reload config (no downtime)
sudo systemctl status nginx     # Check if running + recent logs

Enable / Disable at Boot

sudo systemctl enable nginx     # Start automatically at boot
sudo systemctl disable nginx    # Don't start at boot
sudo systemctl is-enabled nginx # Check if enabled

List Services

systemctl list-units --type=service           # Running services
systemctl list-units --type=service --all     # All services
systemctl list-unit-files --type=service      # All service files
systemctl list-units --failed                 # Failed services

Understanding Status Output

sudo systemctl status nginx

# ● nginx.service - A high performance web server
#      Loaded: loaded (/lib/systemd/system/nginx.service; enabled)
#      Active: active (running) since Mon 2025-03-26 10:00:00
#    Main PID: 1234 (nginx)
#       Tasks: 3
#      Memory: 5.2M

System Power Commands

sudo systemctl reboot             # Reboot system
sudo systemctl poweroff           # Shutdown
sudo systemctl suspend            # Sleep/suspend
systemctl get-default             # Show current boot target

Use sudo systemctl enable --now nginx to both enable at boot AND start the service immediately in one command.

Quick Check

What does `systemctl enable nginx` do?

Exercise

Check the status of the ssh (or sshd) service. Then list all currently running services.