A service fails to start on a Plesk for Linux server: service is masked

Symptoms

A service fails to start with the message:

# systemctl start service_name.service
Unable to start service_name: systemctl start service_name.service Failed to start service_name.service: Unit service_name.service is masked.

Cause

The service is masked. 

Answer

1. Connect to the Plesk server via SSH.

2. Unmask the masked service:

   # systemctl unmask service_name

3. Start the service:

   # systemctl start service_name