⚙️ Systemctl - Linux Service Management¶

Complete guide to managing services with systemd and systemctl

🎯 Overview¶

systemctl is the central management tool for controlling the systemd system and service manager. It's used to start, stop, restart, enable, disable, and check the status of services in modern Linux distributions.

📚 Understanding Systemd¶

What is Systemd?¶

Systemd is a system and service manager for Linux operating systems. It: - Initializes the system during boot - Manages system services - Handles system states - Manages system resources

Unit Types¶

Systemd manages different types of units:

Unit Type	Extension	Purpose
Service	`.service`	System services and daemons
Socket	`.socket`	IPC or network sockets
Device	`.device`	Device units
Mount	`.mount`	Mount points
Automount	`.automount`	Automount points
Target	`.target`	Group of units (like runlevels)
Timer	`.timer`	Timer-based activation

🔧 Basic Service Management¶

Start Services¶

# Start a service
sudo systemctl start service_name

# Start multiple services
sudo systemctl start service1 service2 service3

Examples:

sudo systemctl start nginx          # Start NGINX
sudo systemctl start apache2        # Start Apache
sudo systemctl start mysql          # Start MySQL
sudo systemctl start docker         # Start Docker

Stop Services¶

# Stop a service
sudo systemctl stop service_name

# Stop multiple services
sudo systemctl stop service1 service2

Examples:

sudo systemctl stop nginx           # Stop NGINX
sudo systemctl stop apache2         # Stop Apache

Restart Services¶

# Restart a service (stop then start)
sudo systemctl restart service_name

# Reload configuration without stopping
sudo systemctl reload service_name

# Reload if possible, otherwise restart
sudo systemctl reload-or-restart service_name

Examples:

sudo systemctl restart nginx        # Restart NGINX
sudo systemctl reload nginx         # Reload NGINX config
sudo systemctl reload-or-restart apache2

Check Service Status¶

# Check service status
systemctl status service_name

# Check if service is active
systemctl is-active service_name

# Check if service is enabled
systemctl is-enabled service_name

# Check if service failed
systemctl is-failed service_name

Examples:

systemctl status nginx              # Detailed status
systemctl is-active nginx           # Returns: active or inactive
systemctl is-enabled nginx          # Returns: enabled or disabled

Status Output Explained:

● nginx.service - A high performance web server
   Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2026-01-05 10:00:00 UTC; 2h 30min ago
     Docs: man:nginx(8)
 Main PID: 1234 (nginx)
    Tasks: 5 (limit: 4915)
   Memory: 10.5M
   CGroup: /system.slice/nginx.service
           ├─1234 nginx: master process /usr/sbin/nginx
           └─1235 nginx: worker process

🚀 Enable/Disable Services¶

Enable Services (Start on Boot)¶

# Enable service to start on boot
sudo systemctl enable service_name

# Enable and start service immediately
sudo systemctl enable --now service_name

Examples:

sudo systemctl enable nginx         # Enable on boot
sudo systemctl enable --now docker  # Enable and start now

Disable Services¶

# Disable service from starting on boot
sudo systemctl disable service_name

# Disable and stop service immediately
sudo systemctl disable --now service_name

Examples:

sudo systemctl disable apache2      # Disable on boot
sudo systemctl disable --now mysql  # Disable and stop now

Mask/Unmask Services¶

# Mask service (prevent it from being started)
sudo systemctl mask service_name

# Unmask service
sudo systemctl unmask service_name

Note: Masked services cannot be started manually or automatically.

📋 Listing and Viewing Services¶

List Services¶

# List all loaded units
systemctl list-units

# List all services
systemctl list-units --type=service

# List all active services
systemctl list-units --type=service --state=active

# List all failed services
systemctl list-units --type=service --state=failed

# List all installed unit files
systemctl list-unit-files

# List enabled services
systemctl list-unit-files --state=enabled

Examples:

systemctl list-units --type=service --state=running
systemctl list-units --type=service --state=failed
systemctl list-unit-files --type=service | grep enabled

View Service Details¶

# Show service properties
systemctl show service_name

# Show specific property
systemctl show service_name -p Property

# View service file
systemctl cat service_name

# View service dependencies
systemctl list-dependencies service_name

Examples:

systemctl show nginx                        # All properties
systemctl show nginx -p MainPID             # Show PID
systemctl cat nginx                         # View service file
systemctl list-dependencies nginx           # Show dependencies

📝 Service Logs¶

View Logs with journalctl¶

# View service logs
sudo journalctl -u service_name

# Follow logs in real-time
sudo journalctl -u service_name -f

# View logs since boot
sudo journalctl -u service_name -b

# View logs from last hour
sudo journalctl -u service_name --since "1 hour ago"

# View logs with priority
sudo journalctl -u service_name -p err

# View last N lines
sudo journalctl -u service_name -n 50

Examples:

sudo journalctl -u nginx -f                 # Follow NGINX logs
sudo journalctl -u ssh --since today        # SSH logs from today
sudo journalctl -u docker -n 100            # Last 100 Docker log lines
sudo journalctl -u apache2 -p err           # Apache errors only

Time Specifications:

--since "2026-01-05 10:00:00"
--since "1 hour ago"
--since "yesterday"
--since "2 days ago"
--until "2026-01-05 12:00:00"

🎯 System State Management¶

System Targets (Runlevels)¶

# Get current target
systemctl get-default

# Set default target
sudo systemctl set-default multi-user.target

# List available targets
systemctl list-units --type=target

# Switch to target
sudo systemctl isolate multi-user.target

Common Targets: - poweroff.target - Shutdown - rescue.target - Single-user mode - multi-user.target - Multi-user, no GUI (runlevel 3) - graphical.target - Multi-user with GUI (runlevel 5) - reboot.target - Reboot

System Control¶

# Reboot system
sudo systemctl reboot

# Shutdown system
sudo systemctl poweroff

# Suspend system
sudo systemctl suspend

# Hibernate system
sudo systemctl hibernate

# Reload systemd configuration
sudo systemctl daemon-reload

🔧 Creating Custom Services¶

Basic Service File Structure¶

Location: /etc/systemd/system/myservice.service

[Unit]
Description=My Custom Service
After=network.target

[Service]
Type=simple
User=username
WorkingDirectory=/path/to/app
ExecStart=/path/to/executable
Restart=on-failure
RestartSec=10

[Install]
WantedBy=multi-user.target

Service Types¶

Type	Description
`simple`	Main process specified in ExecStart
`forking`	Process forks and parent exits
`oneshot`	Process exits before starting next unit
`dbus`	Service acquires D-Bus name
`notify`	Service sends notification when ready
`idle`	Delayed until all jobs are dispatched

Example: Node.js Application Service¶

[Unit]
Description=Node.js Application
After=network.target

[Service]
Type=simple
User=nodeuser
WorkingDirectory=/opt/myapp
ExecStart=/usr/bin/node /opt/myapp/server.js
Restart=always
RestartSec=10
StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=myapp
Environment=NODE_ENV=production

[Install]
WantedBy=multi-user.target

Steps to deploy:

# Create service file
sudo nano /etc/systemd/system/myapp.service

# Reload systemd
sudo systemctl daemon-reload

# Start service
sudo systemctl start myapp

# Enable on boot
sudo systemctl enable myapp

# Check status
systemctl status myapp

# View logs
sudo journalctl -u myapp -f

Example: Python Application Service¶

[Unit]
Description=Python Flask Application
After=network.target

[Service]
Type=simple
User=www-data
Group=www-data
WorkingDirectory=/var/www/myapp
Environment="PATH=/var/www/myapp/venv/bin"
ExecStart=/var/www/myapp/venv/bin/python app.py
Restart=always
RestartSec=5

[Install]
WantedBy=multi-user.target

Example: Docker Container Service¶

[Unit]
Description=My Docker Container
After=docker.service
Requires=docker.service

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/bin/docker start mycontainer
ExecStop=/usr/bin/docker stop mycontainer
Restart=always

[Install]
WantedBy=multi-user.target

💡 Practical Examples¶

Example 1: Manage Web Server¶

# Install NGINX
sudo apt install nginx

# Start NGINX
sudo systemctl start nginx

# Enable on boot
sudo systemctl enable nginx

# Check status
systemctl status nginx

# Reload configuration
sudo systemctl reload nginx

# View logs
sudo journalctl -u nginx -f

Example 2: Troubleshoot Failed Service¶

# Check failed services
systemctl --failed

# Check specific service status
systemctl status service_name

# View detailed logs
sudo journalctl -u service_name -n 100

# View errors only
sudo journalctl -u service_name -p err

# Restart service
sudo systemctl restart service_name

# If service file changed
sudo systemctl daemon-reload
sudo systemctl restart service_name

Example 3: Create Backup Service with Timer¶

Service file: /etc/systemd/system/backup.service

[Unit]
Description=Backup Service

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

Timer file: /etc/systemd/system/backup.timer

[Unit]
Description=Run backup daily

[Timer]
OnCalendar=daily
Persistent=true

[Install]
WantedBy=timers.target

Enable timer:

sudo systemctl daemon-reload
sudo systemctl enable backup.timer
sudo systemctl start backup.timer
systemctl list-timers

🎯 Best Practices¶

1. Always Check Status After Changes¶

sudo systemctl restart nginx
systemctl status nginx

2. Use Reload Instead of Restart When Possible¶

sudo systemctl reload nginx  # Doesn't drop connections

3. Enable Services You Want on Boot¶

sudo systemctl enable --now service_name

4. Monitor Logs for Issues¶

sudo journalctl -u service_name -f

5. Use daemon-reload After Editing Service Files¶

sudo systemctl daemon-reload

6. Test Services Before Enabling¶

sudo systemctl start service_name
systemctl status service_name
# If OK, then enable
sudo systemctl enable service_name

Package Management: 03-Package-Management.md
Process Management: 05-Process-Management.md
System Monitoring: 06-System-Monitoring.md

Last Updated: January 5, 2026
Status: ✅ Complete

⚙️ Systemctl - Linux Service Management¶

🎯 Overview¶

📚 Understanding Systemd¶

What is Systemd?¶

Unit Types¶

🔧 Basic Service Management¶

Start Services¶

Stop Services¶

Restart Services¶

Check Service Status¶

🚀 Enable/Disable Services¶

Enable Services (Start on Boot)¶

Disable Services¶

Mask/Unmask Services¶

📋 Listing and Viewing Services¶

List Services¶

View Service Details¶

📝 Service Logs¶

View Logs with journalctl¶

🎯 System State Management¶

System Targets (Runlevels)¶

System Control¶

🔧 Creating Custom Services¶

Basic Service File Structure¶

Service Types¶

Example: Node.js Application Service¶

Example: Python Application Service¶

Example: Docker Container Service¶

💡 Practical Examples¶

Example 1: Manage Web Server¶

Example 2: Troubleshoot Failed Service¶

Example 3: Create Backup Service with Timer¶

🎯 Best Practices¶

1. Always Check Status After Changes¶

2. Use Reload Instead of Restart When Possible¶

3. Enable Services You Want on Boot¶

4. Monitor Logs for Issues¶

5. Use daemon-reload After Editing Service Files¶

6. Test Services Before Enabling¶

🔗 Related Topics¶