systemd is the system and service manager for modern Linux distributions. Control services, units, and system startup.
Service Management
| Command | Description |
|---|
systemctl start [service] | Start a service |
systemctl stop [service] | Stop a service |
systemctl restart [service] | Restart a service |
systemctl reload [service] | Reload service configuration |
systemctl reload-or-restart [service] | Reload or restart if reload unsupported |
systemctl status [service] | Show service status |
systemctl is-active [service] | Check if service is running |
systemctl is-enabled [service] | Check if service starts on boot |
systemctl enable [service] | Enable service on boot |
systemctl disable [service] | Disable service on boot |
systemctl enable --now [service] | Enable and start service |
systemctl disable --now [service] | Disable and stop service |
Listing Units & Services
| Command | Description |
|---|
systemctl list-units | List all loaded units |
systemctl list-units --all | List all units (loaded and not) |
systemctl list-units --type=service | List only service units |
systemctl list-units --state=running | List running units |
systemctl list-units --state=failed | List failed units |
systemctl list-unit-files | List all unit files and their status |
systemctl list-unit-files --type=service | List all service files |
systemctl get-default | Show default target (runlevel) |
systemctl list-dependencies | Show unit dependencies |
Checking Status
# Show service status with full details
systemctl status nginx
# View service logs
journalctl -u nginx
# Follow service logs
journalctl -u nginx -f
# View logs from last boot
journalctl -u nginx --since today
# View logs with timestamp
journalctl -u nginx --no-pager
# Show detailed service information
systemctl show nginx
# Check if service failed
systemctl is-failed nginx
# List failed services
systemctl list-units --state=failed
Service Units
Basic Service Operations
# Start service
systemctl start apache2
# Stop service immediately
systemctl stop apache2
# Graceful restart (stop and start)
systemctl restart apache2
# Reload configuration without stopping
systemctl reload apache2
# Check current status
systemctl status apache2
# View service file
systemctl cat apache2
# Edit service file
systemctl edit apache2
# Edit service file with full content
systemctl edit --full apache2
Enable/Disable Services
# Enable service to start on boot
systemctl enable nginx
# Disable service from starting on boot
systemctl disable nginx
# Enable and start immediately
systemctl enable --now nginx
# Disable and stop immediately
systemctl disable --now nginx
# Check if enabled
systemctl is-enabled nginx
# Undo any recent changes
systemctl revert nginx
Targets (Runlevels)
| Target | Old Runlevel | Description |
|---|
multi-user.target | 3 | Multi-user mode (no GUI) |
graphical.target | 5 | Graphical mode with login |
rescue.target | 1 | Single-user rescue mode |
emergency.target | S | Emergency shell |
poweroff.target | 0 | Power off |
reboot.target | 6 | Reboot |
Managing Targets
# Get current default target
systemctl get-default
# Set default target
sudo systemctl set-default multi-user.target
sudo systemctl set-default graphical.target
# List available targets
systemctl list-units --type=target
# Switch to target
sudo systemctl isolate rescue.target
sudo systemctl isolate multi-user.target
sudo systemctl isolate graphical.target
# Reboot
sudo systemctl reboot
# Power off
sudo systemctl poweroff
# Suspend
sudo systemctl suspend
# Hibernate
sudo systemctl hibernate
# Hybrid sleep (suspend to RAM + disk)
sudo systemctl hybrid-sleep
Timers (Scheduled Tasks)
# List all timers
systemctl list-timers
# List all timers including inactive
systemctl list-timers --all
# Show specific timer status
systemctl status apt-daily.timer
# Start timer
systemctl start apt-daily.timer
# Stop timer
systemctl stop apt-daily.timer
# Enable timer on boot
systemctl enable apt-daily.timer
# View timer details
systemctl cat apt-daily.timer
# View associated service
systemctl cat apt-daily.service
Sockets
# List all sockets
systemctl list-sockets
# Show socket status
systemctl status ssh.socket
# Start socket
systemctl start ssh.socket
# Stop socket
systemctl stop ssh.socket
# Enable socket on boot
systemctl enable ssh.socket
# View socket configuration
systemctl cat ssh.socket
Logging with journalctl
# Show all journal entries
journalctl
# Show entries from specific service
journalctl -u nginx
# Follow logs (like tail -f)
journalctl -f
# Follow service logs
journalctl -u nginx -f
# Show last N lines
journalctl -n 50
# Show logs from last boot
journalctl -b
# Show logs from previous boot
journalctl -b -1
# Show logs from specific time
journalctl --since "2024-01-15 10:00:00"
# Show logs from today
journalctl --since today
# Show logs between times
journalctl --since "2024-01-15" --until "2024-01-16"
# Show logs from specific user
journalctl _UID=1000
# Show logs from priority (err, warning, notice, info, debug)
journalctl -p err
# Show logs with pager
journalctl
# Show logs without pager
journalctl --no-pager
# Show logs in JSON format
journalctl -o json
# Show logs in short format
journalctl -o short
Creating Custom Service Units
Basic Service File
# /etc/systemd/system/myapp.service
[Unit]
Description=My Application
After=network.target
[Service]
Type=simple
User=myapp
WorkingDirectory=/opt/myapp
ExecStart=/opt/myapp/bin/app
Restart=on-failure
RestartSec=10s
[Install]
WantedBy=multi-user.target
Service with Multiple Commands
# /etc/systemd/system/myapp.service
[Unit]
Description=My Application
After=network.target postgresql.service
[Service]
Type=notify
User=myapp
WorkingDirectory=/opt/myapp
Environment="PORT=8080"
ExecStartPre=/opt/myapp/bin/migrate
ExecStart=/opt/myapp/bin/start
ExecReload=/opt/myapp/bin/reload
ExecStop=/opt/myapp/bin/stop
Restart=on-failure
RestartSec=5
[Install]
WantedBy=multi-user.target
Dependency Management
# Show unit dependencies
systemctl list-dependencies nginx
# Show dependencies recursively
systemctl list-dependencies --all
# Show only targets
systemctl list-dependencies --type=target
Troubleshooting
Check Service Issues
# View service status
systemctl status apache2
# Check for errors
journalctl -u apache2 -n 20
# Show full service details
systemctl show apache2
# Verify service file
systemctl cat apache2
# Test service configuration
/usr/sbin/apache2ctl configtest # Apache example
# Reload daemon after editing unit files
sudo systemctl daemon-reload
# Restart service after changes
sudo systemctl restart apache2
Failed Services
# List failed units
systemctl list-units --state=failed
# Show failed service status
systemctl status [failed-service]
# View failed service logs
journalctl -u [failed-service] -n 50
# Reset failed state
systemctl reset-failed [service]
# Reset all failed services
systemctl reset-failed
Useful Aliases
# Add to .bashrc or .zshrc
alias sc='sudo systemctl'
alias scl='systemctl list-units'
alias scls='systemctl list-units --type=service'
alias scs='systemctl status'
alias scr='sudo systemctl restart'
alias scrs='sudo systemctl restart'
alias sce='sudo systemctl enable'
alias scd='sudo systemctl disable'
alias scst='sudo systemctl start'
alias scsp='sudo systemctl stop'
alias jl='journalctl'
alias jlu='journalctl -u'
alias jlf='journalctl -f'
Best Practices
- Always use absolute paths in ExecStart
- Set User and Group for security
- Use Restart=on-failure for reliability
- Add meaningful Description
- Document dependencies with After/Before
- Use Type=simple for most services
- Set reasonable timeouts
- Monitor logs with journalctl
- Use reload instead of restart when possible
- Validate unit files after changes
Resources
man systemd - systemd system managerman systemctl - systemd control utilityman systemd.unit - Unit configurationman systemd.service - Service unit typeman journalctl - Journal control
Last updated: 2026-03-30
