Semaphore, it is a lot like a locking mechanism. In any server there is an order of precedence in which tasks must be accomplished. The semaphore is used to maintain that precedence order; more to the point, the precedence order is maintained by the semaphores. A succeeding task may not start until it has received [...]

Scenario:- Add Application icon missing or grayed out
“Add New Application” icon can be missing if “Hide all greyed out buttons by default” is enabled on the Server -> Interface management page in Plesk CP.
“Add New Application” can be greyed out if some application is already installed in the domains’ DocumentRoot folder (httpdocs or httpsdocs). It [...]