ipcclean removes all shared memory segments and semaphore sets owned by the current user. It is intended to be used for cleaning up after a crashed PostgreSQL server (postmaster). Note that immediately restarting the server will also clean up shared memory and semaphores, so this command is of little real utility.
Only the database administrator should execute this program as it can cause bizarre behavior (that is, crashes) if run during multiuser execution. If this command is executed while a postmaster is running, the shared memory and semaphores allocated by the postmaster will be deleted. This will result in a general failure of the backend servers started by that postmaster.