On CentOS and RHEL (Red Hat Enterprise Linux) systems, you can check if a service is running or not using the systemctl command. The systemctl command is a command-line utility that is used to control and manage system services and daemons.
To check if a service is running on your system, use the systemctl command followed by the status option and the name of the service. For example, to check the status of the Apache HTTP Server service, you would type:
systemctl status httpd
This will show the status of the Apache HTTP Server service, along with other information such as its PID (process ID), its current state (active or inactive), and its runtime status (running, stopped, or failed).
If the service is running, you should see a line that says "Active: active (running)" in the output of the systemctl status command. If the service is not running, you should see a line that says "Active: inactive (dead)" in the output.
You can also use the systemctl command with the is-active option to check if a service is currently running. For example, to check if the Apache HTTP Server service is currently running, you would type:
systemctl is-active httpd
This will return the word "active" if the service is currently running, or "inactive" if the service is not running. This can be useful if you want to use the output of the systemctl command in a script or a command pipeline.
Remember that the service name that you use with the systemctl command may be different depending on your system and the service that you are checking. Refer to the documentation for the service that you are checking for the correct name to use with the systemctl command.