Systemctl options to Know
Disabling the service deletes the symlink, so the unit file itself is not affected, but the service is not loaded at the next boot, when systemd reads /etc/systemd/system.
However, a disabled service can be loaded, and will be started if a service that depends on it is started; enable and disable only configure auto-start behaviour for units, and the state is easily overridden.
A masked service is one whose unit file is a symlink to /dev/null. This makes it "impossible" to load the service, even if it is required by another, enabled service.
When you mask a service, a symlink is created from /etc/systemd/system to /dev/null, leaving the original unit file elsewhere untouched. When you unmask a service the symlink is deleted.
