To disable a service and prevent it from starting at boot time, we can use the below command:
When a service is masked, it can't be started at all.
We can mask a service manually by going to "/etc/systemd/system" and creating a symbolic link the "/dev/null" device for the service we want to disable as below:
Listing the services that run at a certain target (level):
We use the below command to see all the service that run in a certain level or target: