Use ipcclean to delete all instances of aborted backend processes owned by the postgres user (this helps free up shared memory). Make sure to only run this program during a fairly innocuous time, as runing it during heavy use of the database can cause crashing if there is currently multi-user activity occurring.
|Shut down postmaster first|
Shut down postmaster before running ipcclean, as all backend processes running will be using the shared memory that it deletes. Any servers still running when shared memory is deleted will probably fail.