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Systemd Command Cheatsheet

Systemd Command Cheatsheet

Essential systemd commands for service management

DevOps

Systemd Command Cheatsheet

A comprehensive reference for systemd service management.

Service Management

Basic Commands

systemctl start service              # Start service
systemctl stop service               # Stop service
systemctl restart service            # Restart service
systemctl reload service             # Reload config without restart
systemctl status service             # Show service status
systemctl enable service             # Enable at boot
systemctl disable service            # Disable at boot
systemctl is-active service          # Check if running
systemctl is-enabled service         # Check if enabled

List Services

systemctl list-units                 # List all units
systemctl list-units --type=service  # List services only
systemctl list-units --state=running # List running units
systemctl list-units --failed        # List failed units
systemctl list-unit-files            # List all unit files

Unit Files

Service Unit File

# /etc/systemd/system/myapp.service
[Unit]
Description=My Application
After=network.target

[Service]
Type=simple
User=myuser
WorkingDirectory=/opt/myapp
ExecStart=/usr/bin/node /opt/myapp/server.js
Restart=always
RestartSec=10

[Install]
WantedBy=multi-user.target

Service Types

Type=simple                          # Default, main process
Type=forking                         # Forks and exits
Type=oneshot                         # Runs once and exits
Type=notify                          # Sends notification when ready
Type=idle                            # Delays until other jobs finish

Restart Options

Restart=no                           # Don't restart
Restart=always                       # Always restart
Restart=on-failure                   # Restart on failure
Restart=on-abnormal                  # Restart on abnormal exit
RestartSec=5                         # Wait 5 seconds before restart

Journalctl (Logs)

View Logs

journalctl                           # All logs
journalctl -u service                # Service logs
journalctl -u service -f             # Follow logs
journalctl -u service --since today  # Today's logs
journalctl -u service --since "2024-01-01"  # Since date
journalctl -u service --since "1 hour ago"  # Last hour
journalctl -u service -n 50          # Last 50 lines
journalctl -u service -p err         # Error level only
journalctl -k                        # Kernel messages
journalctl -b                        # Current boot
journalctl -b -1                     # Previous boot

Log Management

journalctl --disk-usage              # Show disk usage
journalctl --vacuum-size=100M        # Limit to 100MB
journalctl --vacuum-time=2weeks      # Keep 2 weeks

Timers

Timer Unit File

# /etc/systemd/system/backup.timer
[Unit]
Description=Daily Backup Timer

[Timer]
OnCalendar=daily
OnCalendar=*-*-* 02:00:00            # 2 AM daily
Persistent=true

[Install]
WantedBy=timers.target

Timer Commands

systemctl list-timers                # List all timers
systemctl list-timers --all          # Include inactive
systemctl start timer                # Start timer
systemctl enable timer               # Enable timer

Timer Syntax

OnCalendar=hourly                    # Every hour
OnCalendar=daily                     # Every day
OnCalendar=weekly                    # Every week
OnCalendar=monthly                   # Every month
OnCalendar=*-*-* 00:00:00           # Midnight
OnCalendar=Mon *-*-* 00:00:00       # Monday midnight
OnBootSec=15min                      # 15 min after boot
OnUnitActiveSec=1h                   # 1 hour after last activation

System Control

Power Management

systemctl poweroff                   # Shutdown
systemctl reboot                     # Reboot
systemctl suspend                    # Suspend
systemctl hibernate                  # Hibernate

System State

systemctl get-default                # Show default target
systemctl set-default multi-user.target  # Set default target
systemctl isolate multi-user.target  # Switch to target
systemctl list-dependencies          # Show dependencies

Targets

Common Targets

systemctl isolate rescue.target      # Rescue mode
systemctl isolate multi-user.target  # Multi-user (no GUI)
systemctl isolate graphical.target   # Graphical mode

Configuration

Reload Systemd

systemctl daemon-reload              # Reload unit files
systemctl reset-failed               # Reset failed units

Edit Unit Files

systemctl edit service               # Create override
systemctl edit --full service        # Edit full file
systemctl cat service                # Show unit file

Override Example

# /etc/systemd/system/service.service.d/override.conf
[Service]
Environment="VAR=value"

Environment Variables

Set Environment

[Service]
Environment="VAR1=value1"
Environment="VAR2=value2"
EnvironmentFile=/etc/myapp/env

Resource Limits

Limit Resources

[Service]
MemoryLimit=512M
CPUQuota=50%
TasksMax=100
LimitNOFILE=65536

Dependencies

Unit Dependencies

[Unit]
Requires=network.target              # Hard dependency
Wants=network.target                 # Soft dependency
After=network.target                 # Start after
Before=network.target                # Start before
Conflicts=other.service              # Cannot run together

Troubleshooting

Debug Service

systemctl status service -l          # Full status
journalctl -u service -xe            # Extended logs
systemctl show service               # Show all properties
systemctl list-dependencies service  # Show dependencies

Common Issues

# Permission denied
sudo systemctl status service

# Unit not found
systemctl daemon-reload

# Failed to start
journalctl -u service -n 50

Quick Reference

Command Description
systemctl start <service> Start service
systemctl stop <service> Stop service
systemctl restart <service> Restart service
systemctl status <service> Service status
systemctl enable <service> Enable at boot
journalctl -u <service> View logs
journalctl -f Follow logs
systemctl daemon-reload Reload configs

Best Practices

  1. Use systemd for all services
  2. Enable services for auto-start
  3. Set restart policies for reliability
  4. Use timers instead of cron
  5. Monitor logs with journalctl
  6. Set resource limits to prevent abuse
  7. Use dependencies correctly
  8. Test services before enabling
  9. Document custom units
  10. Keep logs manageable with vacuum

Resources

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