service

Understanding Systemd and systemctl

systemctl provides a powerful and user-friendly way to control system services. Instead of relying on older methods like /etc/init.d scripts, systemctl offers a consistent and efficient approach across various distributions. Before diving into commands, let’s understand the basic states a service can be in:

• active (running): The service is currently running.
• inactive: The service is not running.
• failed: The service failed to start or encountered an error.
• masked: The service is explicitly prevented from starting.

Essential systemctl Commands with Examples

Let’s look at some fundamental systemctl commands, illustrated with practical examples. We’ll use the network-manager service for demonstration purposes, but these commands apply to most services.

1. Checking Service Status:

The simplest command is status. This displays the service’s current state, including active status, process ID (PID), and any logged messages.

sudo systemctl status network-manager

This will output detailed information about the NetworkManager service. Look for lines indicating “active (running)” or similar to confirm its operational status. Errors will be displayed prominently in the output.

2. Starting and Stopping Services:

To start a service:

sudo systemctl start network-manager

To stop a service:

sudo systemctl stop network-manager

Remember to use sudo as these commands require root privileges. These commands are straightforward and immediately affect the service’s state.

3. Restarting and Reloading Services:

Restarting a service stops and then restarts it:

sudo systemctl restart network-manager

Reloading a service typically applies configuration changes without restarting the entire process:

sudo systemctl reload network-manager

Reloading is useful when configuration files are updated and the service needs to reflect those changes.

4. Enabling and Disabling Services:

Enabling a service ensures it starts automatically at boot:

sudo systemctl enable network-manager

Disabling a service prevents it from starting automatically at boot:

sudo systemctl disable network-manager

These commands affect the service’s startup configuration, not its immediate runtime state.

5. Listing Services:

To list all services:

systemctl list-unit-files

This command shows all services installed on the system, indicating their status (enabled, disabled, masked). You can filter this list further, for example, showing only enabled services:

systemctl list-unit-files --type=service --state=enabled

6. Viewing Service Logs:

Often essential for troubleshooting, you can examine the service’s log using journalctl:

journalctl -u network-manager

This command displays the logs specifically related to the network-manager service, including error messages and other important information. You can refine this using options like -n 10 (to show the last 10 lines) or -xe (to show only error messages).

7. Masking a Service:

Masking a service permanently prevents it from being started, even manually:

sudo systemctl mask network-manager

This is usually used for services that should never be run, such as outdated or conflicting services. Unmasking can be done with sudo systemctl unmask network-manager.

These examples provide a foundation for effective service management using systemctl. Exploring the numerous other options and features offered by this command will further improve your Linux administration skills. Remember to consult the man systemctl page for a detailed guide.