[root@mbl-82-52-252 OpenNMS]# su postgres
bash-3.1$ pg_ctl -D /var/lib/pgsql/data/ start
pg_ctl: another postmaster may be running; trying to start postmaster anyway
FATAL:  pre-existing shared memory block (key 5432001, ID 2031633) is still in use
HINT:  If you're sure there are no old server processes still running, remove the shared memory block with the command "ipcclean", "ipcrm", or just delete the file "postmaster.pid".
pg_ctl: could not start postmaster
Examine the log output.
bash-3.1$ ipcclean
Shared memory 4259854 ... skipped; process still exists (pid 4110 or 17307).
Shared memory 4358159 ... skipped; process still exists (pid 4110 or 17307).
Shared memory 4423696 ... skipped; process still exists (pid 4110 or 17307).
ipcclean: nothing removed