cpsrvd is an acronym for cPanel Service Daemon. It is a software which runs cPanel on a server whereas Daemon is a computer program that runs as a background process. If this service goes down or stops working, then the server cannot be restarted with WHM interface. Though cPanel has a built-in mechanism to restart the service automatically, it sometimes does not work.
To restart the cpsrvd service, Login to the root user via SSH and run the following commands
service cpanel restart
These commands will stop the service and start it again. It also stops the services and restarts all the services associated with cpsrvd.