Managing services with systemctl in Linux

Systemd is the default init system for most modern Linux distributions, including Ubuntu, CentOS, Fedora, and Debian. It plays a crucial role in managing system services and processes. To harness the power of systemd, you need to become familiar with the systemctl command. In this blog post, we'll explore essential systemctl commands to manage a service running on a Linux system.

What is systemctl?

systemctl is a command-line tool for controlling the systemd system and service manager. It allows you to manage system services, inspect their status, start, stop, enable, or disable them, among other things. This tool simplifies sysadmin tasks, making it easier to maintain a healthy Linux system.

How to List All Enabled and Disabled Services

To get an overview of all services on your system, both enabled and disabled, you can use the following command:

systemctl list-unit-files -at service

Output:

This command provides a comprehensive list of services, their statuses, and whether they are set to start automatically during boot.

How to List All Services and Their Statuses

To see a detailed list of all services and their current statuses, including active, inactive, and failed services, use the following command:

systemctl list-units -at service

Output:

This command gives you a real-time snapshot of the status of all services on your system.

How to List Running Services

If you want to view only the services that are currently running, you can filter the list using this command:

systemctl list-units -at service --state=running

Output:

This is particularly useful when you need to identify which services are actively using system resources.

How to Display the Content of a Service File

To examine the content of a service file, such as the configuration for the rsyslog service, use the systemctl cat command:

systemctl cat rsyslog

This command displays the contents of the service file, making it easier to understand its configuration.

How to Check the Status of a Service

To check the current status of a specific service, use the systemctl status command, followed by the service name, like this:

systemctl status sshd.service

This command provides detailed information about the service's state, including whether it's active, running, and enabled. It also shows recent log entries.

Output:

How to Start, Stop, Reload and Restart Services

Managing services is a fundamental part of system administration. Use these commands to start, stop, or restart a service, such as httpd.

To start a service e.g httpd:

systemctl start httpd

To stop a service:

systemctl stop httpd

To reload a service:

systemctl reload httpd

To restart a service:

systemctl restart httpd

Reloading a service is always a good idea over restarting it if you are modifying a configuration and want to reload. Restarting the service can cause downtime as it will first stop the service and start it back.

How to Check if a Service is Active

To quickly check whether a service is currently active, you can use the systemctl is-active command, followed by the service name. For example:

systemctl is-active sshd

Output:

How to Enable, Disable, Mask, and Unmask Services

Enabling a service ensures that it starts automatically during system boot. Conversely, disabling a service prevents it from starting automatically. You can use these commands.

To enable a service:

systemctl enable auditd

To disable a service:

systemctl disable auditd

Sometimes, you may want to mask a service, which effectively prevents it from being started by any means. To mask a service:

systemctl mask auditd

To unmask a previously masked service:

systemctl unmask auditd

How to Check if a Service is Enabled

To verify whether a service is enabled to start automatically at boot, use the following command:

systemctl is-enabled auditd

This command will return enabled if the service is set to start during boot.

Conclusion

Learning systemctl commands are essential for managing and maintaining Linux systems. These commands help you to control services, troubleshoot issues, and keep your system running smoothly. In this blog post, we covered all the essential systemctl commands you need to know in order to properly manage services in a Linux system.