Lock with a locking cylinder

In a lock with a locking cylinder, the locking cylinder has a knob on one side and on the other side has a lock channel for insertion of a key. The lock has two split hubs on top of one another for triggering a locking element. Furthermore, the lock has a positioning element which establishes whether blocking of the locking element produced by the locking cylinder can be canceled by actuation of the split hubs. A projection which is located on a plate which interacts with the positioning element establishes from which side this blocking can be cancelled.