systemctl Command Linux: Complete Guide to Control Systemd Services

The systemctl command is the primary tool for controlling systemd services in modern Linux distributions. As the central management utility for the systemd init system, it allows system administrators to start, stop, restart, enable, disable, and monitor services with precision and ease.

What is systemctl?

systemctl (system control) is a command-line utility that interfaces with systemd, the default init system and service manager for most modern Linux distributions including Ubuntu 16.04+, CentOS 7+, Fedora, and RHEL 7+. It replaces older service management tools like service and chkconfig.

Basic systemctl Syntax

The general syntax for systemctl follows this pattern:

systemctl [OPTIONS] COMMAND [SERVICE-NAME]

Essential systemctl Commands

Starting Services

To start a service immediately, use the start command:

sudo systemctl start nginx

Example output:

# No output indicates successful start
# Check status to verify
$ systemctl status nginx
● nginx.service - A high performance web server and a reverse proxy server
   Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2025-08-25 03:55:12 IST; 5s ago
     Docs: man:nginx(8)
 Main PID: 12345 (nginx)
    Tasks: 2 (limit: 4915)
   Memory: 6.5M
   CGroup: /system.slice/nginx.service
           ├─12345 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
           └─12346 nginx: worker process

Stopping Services

To stop a running service:

sudo systemctl stop nginx

Restarting Services

Restart completely stops and starts a service:

sudo systemctl restart nginx

Reloading Services

Reload configuration without stopping the service (if supported):

sudo systemctl reload nginx

Service Status and Information

Checking Service Status

The status command provides detailed information about a service:

systemctl status apache2

Example output:

● apache2.service - The Apache HTTP Server
   Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
   Active: active (running) since Mon 2025-08-25 03:50:00 IST; 10min ago
     Docs: https://httpd.apache.org/docs/2.4/
  Process: 8901 ExecStart=/usr/sbin/apachectl start (code=exited, status=0/SUCCESS)
 Main PID: 8920 (apache2)
    Tasks: 55 (limit: 4915)
   Memory: 12.1M
   CGroup: /system.slice/apache2.service
           ├─8920 /usr/sbin/apache2 -k start
           ├─8921 /usr/sbin/apache2 -k start
           └─8922 /usr/sbin/apache2 -k start

Listing All Services

View all available services:

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

# List only running services
systemctl list-units --type=service --state=running

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

Service Persistence (Enable/Disable)

Enabling Services

Enable a service to start automatically at boot:

sudo systemctl enable nginx

Example output:

Created symlink /etc/systemd/system/multi-user.target.wants/nginx.service → /lib/systemd/system/nginx.service.

Disabling Services

Prevent a service from starting at boot:

sudo systemctl disable nginx

Enable and Start Simultaneously

Enable and start a service in one command:

sudo systemctl enable --now nginx

Advanced systemctl Operations

Masking and Unmasking Services

Masking prevents a service from being started manually or automatically:

# Mask a service
sudo systemctl mask apache2

# Unmask a service
sudo systemctl unmask apache2

Checking if Service is Enabled

systemctl is-enabled nginx

Possible outputs:

• enabled – Service will start at boot
• disabled – Service won’t start at boot
• masked – Service is masked
• static – Service has no install section

Checking if Service is Active

systemctl is-active nginx

Returns active or inactive.

Working with Service Dependencies

Viewing Service Dependencies

# Show what services depend on this service
systemctl list-dependencies nginx

# Show reverse dependencies
systemctl list-dependencies nginx --reverse

Example dependency output:

$ systemctl list-dependencies nginx
nginx.service
● ├─system.slice
● └─basic.target
●   ├─microcode.service
●   ├─selinux-autorelabel-mark.service
●   ├─systemd-ask-password-console.path
●   └─timers.target
●     └─systemd-tmpfiles-clean.timer

Log Management with systemctl

Viewing Service Logs

systemctl integrates with journalctl for log viewing:

# View recent logs for a service
journalctl -u nginx

# Follow logs in real-time
journalctl -u nginx -f

# View logs since last boot
journalctl -u nginx -b

Service Configuration Files

Editing Service Files

Use systemctl to safely edit service configurations:

sudo systemctl edit nginx

This creates an override file at /etc/systemd/system/nginx.service.d/override.conf.

Viewing Service Files

# View the main service file
systemctl cat nginx

# Show file paths
systemctl show nginx -p FragmentPath

System State Management

Reloading systemd Configuration

After modifying service files, reload systemd:

sudo systemctl daemon-reload

System Targets (Runlevels)

# Check current target
systemctl get-default

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

# Switch to different target
sudo systemctl isolate graphical.target

Practical Examples and Use Cases

Web Server Management

# Complete Apache setup
sudo systemctl enable apache2
sudo systemctl start apache2
sudo systemctl status apache2

# Graceful configuration reload
sudo systemctl reload apache2

Database Service Management

# MySQL service operations
sudo systemctl start mysql
sudo systemctl enable mysql
systemctl is-active mysql

# View MySQL logs
journalctl -u mysql -n 50

Troubleshooting Failed Services

# Find failed services
systemctl --failed

# Reset failed state
sudo systemctl reset-failed service-name

# Restart with verbose output
sudo systemctl restart service-name -l

Common systemctl Options

Best Practices

Service Management Guidelines

• Always check status after starting or stopping services
• Use enable –now for new services you want running immediately
• Reload systemd after editing service files with daemon-reload
• Monitor logs regularly using journalctl
• Test configurations in non-production environments first

Security Considerations

• Only enable services you actually need
• Regularly audit enabled services with systemctl list-unit-files --state=enabled
• Use service-specific users rather than root when possible
• Monitor failed services for potential security issues

Troubleshooting Common Issues

Service Won’t Start

# Check detailed status
systemctl status service-name -l

# Check logs
journalctl -u service-name -n 20

# Verify configuration
systemctl cat service-name

Service Starts but Stops Immediately

# Check exit codes and signals
systemctl show service-name -p ExecMainStatus -p Result

# Follow logs in real-time
journalctl -u service-name -f

Conclusion

The systemctl command is an essential tool for Linux system administration, providing comprehensive control over systemd services. From basic operations like starting and stopping services to advanced features like dependency management and log integration, mastering systemctl enables efficient system management.

Regular practice with these commands and understanding of systemd concepts will significantly improve your Linux administration skills. Remember to always verify service status after making changes and maintain awareness of service dependencies when making system modifications.

Whether you’re managing web servers, databases, or custom applications, systemctl provides the reliable service management capabilities needed for robust Linux system administration.