TroubleshootingPostgres
          Occasionally, Postgres will fail with cryptic error messages that are due to relatively simple prob-
        lems. The following are a list of Postgres error messages and the likely fix. These messages are ones you
        would likely see in the monitor program.
            Message: semget: No space left on device
            Explanation and Likely Fix:
          Either the kernel has not been configured for System V shared memory, or some other program is
        using it up. On most machines, the UNIX command "ipcs" will show shared memory and semaphore
        usage. To delete all shared memory and semaphores (may be necessary if a backend fails), run the "ipc-
        clean" command.
          Note, however, that the "ipcclean" command deletes all semaphores belonging to the user running it,
        so the user should be certain that no non-Postgres processes are using semaphores before running this com-
        mand.
            Message: Unable to get shared buffers
            Explanation and Likely Fix:
          This message means that a Postgres backend was expecting shared memory to be available and it
        was not. Usually this is due to "ipcclean" being run while a "postmaster" was also running. NOTE: "ipc-
        clean" will delete ALL semaphores and shared memory regardless as to whether they are being used or not.
            Message: Can’t connect to backend (...)
            Explanation and Likely Fix:
          This message means that you are running a LIBPQ application but it could not link up with a post-
        master. If you see this error message, you should see if a postmaster is truly running. If one is running, the
        problem is likely related to your network.