Managing Services with systemd: Complete Guide

Master the modern Linux service management with systemd. This comprehensive guide covers essential systemctl commands, service control, monitoring, troubleshooting, and creating custom systemd units for efficient daemon management.

What is systemd?

1. Essential systemctl Commands

Service Status Commands in Detail

2. Service Management Scenarios

Journalctl: Mastering System Logs

3. Creating Custom systemd Services

Basic Service Unit File

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

[Service]
Type=simple
User=myappuser
Group=myappgroup
WorkingDirectory=/opt/myapp
ExecStart=/usr/bin/python3 /opt/myapp/app.py
Restart=on-failure
RestartSec=10
StandardOutput=journal
StandardError=journal

# Security hardening (optional)
NoNewPrivileges=true
PrivateTmp=true
ProtectSystem=strict
ReadWritePaths=/var/lib/myapp

[Install]
WantedBy=multi-user.target

Service Types Explained

Installation and Management Script

#!/bin/bash
# install-service.sh
# Creates and manages a custom systemd service

SERVICE_NAME="myapp"
SERVICE_FILE="/etc/systemd/system/${SERVICE_NAME}.service"
APP_PATH="/opt/${SERVICE_NAME}"
APP_USER="${SERVICE_NAME}"

# Colors for output
RED='\033[0;31m'
GREEN='\033[0;32m'
YELLOW='\033[1;33m'
NC='\033[0m' # No Color

echo -e "${GREEN}=== Custom Service Manager ===${NC}"

case "$1" in
    install)
        echo -e "${YELLOW}Installing ${SERVICE_NAME} service...${NC}"
        
        # Check if running as root
        if [ "$EUID" -ne 0 ]; then 
            echo -e "${RED}Please run as root${NC}"
            exit 1
        fi
        
        # Create service file
        cat > "$SERVICE_FILE" << EOF
[Unit]
Description=My Custom Application
After=network.target

[Service]
Type=simple
User=$APP_USER
Group=$APP_USER
WorkingDirectory=$APP_PATH
ExecStart=/usr/bin/python3 $APP_PATH/app.py
Restart=on-failure
RestartSec=10
StandardOutput=journal
StandardError=journal

[Install]
WantedBy=multi-user.target
EOF
        
        echo -e "${GREEN}Service file created: $SERVICE_FILE${NC}"
        
        # Create application user if doesn't exist
        if ! id "$APP_USER" &>/dev/null; then
            useradd -r -s /bin/false "$APP_USER"
            echo -e "${GREEN}Created user: $APP_USER${NC}"
        fi
        
        # Reload systemd
        systemctl daemon-reload
        echo -e "${GREEN}Systemd daemon reloaded${NC}"
        
        # Enable and start service
        systemctl enable "$SERVICE_NAME"
        systemctl start "$SERVICE_NAME"
        
        echo -e "${GREEN}Service installed and started${NC}"
        systemctl status "$SERVICE_NAME"
        ;;
    
    uninstall)
        echo -e "${YELLOW}Uninstalling ${SERVICE_NAME} service...${NC}"
        
        systemctl stop "$SERVICE_NAME"
        systemctl disable "$SERVICE_NAME"
        rm -f "$SERVICE_FILE"
        systemctl daemon-reload
        echo -e "${GREEN}Service uninstalled${NC}"
        ;;
    
    status)
        systemctl status "$SERVICE_NAME"
        ;;
    
    logs)
        journalctl -u "$SERVICE_NAME" -f
        ;;
    
    restart)
        systemctl restart "$SERVICE_NAME"
        echo -e "${GREEN}Service restarted${NC}"
        ;;
    
    *)
        echo "Usage: $0 {install|uninstall|status|logs|restart}"
        echo "  install   - Install and start the service"
        echo "  uninstall - Stop and remove the service"
        echo "  status    - Check service status"
        echo "  logs      - Follow service logs"
        echo "  restart   - Restart the service"
        exit 1
        ;;
esac

4. Advanced systemd Features

Timers: Systemd's Cron Replacement

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

[Timer]
OnCalendar=daily
Persistent=true
RandomizedDelaySec=1h

[Install]
WantedBy=timers.target

# /etc/systemd/system/backup.service
[Unit]
Description=Database backup service

[Service]
Type=oneshot
ExecStart=/usr/local/bin/backup.sh
User=backup

Socket Activation

# /etc/systemd/system/myservice.socket
[Unit]
Description=My Service Socket

[Socket]
ListenStream=8080
Accept=true

[Install]
WantedBy=sockets.target

# /etc/systemd/system/myservice@.service
[Unit]
Description=My Service Instance

[Service]
ExecStart=/usr/bin/myservice
StandardInput=socket

Troubleshooting Service Issues

5. systemd Cheat Sheet

Getting Started with systemd