Restart after poweroutage

Today I had a power outage which upon reboot seems to have done
something to cause Postgresql to not restart properly.  This has
happened to me before:
http://archives.postgresql.org/pgsql-general/2006-09/msg00938.php

...and during this previous discussion, Tom Lane pointed out that I may
have destroyed the evidence on what was causing this problem:
http://archives.postgresql.org/pgsql-general/2006-09/msg00944.php

So, today, I have taken care to *not* destroy any evidence (ie: I didn't
delete the postmaster.pid file and restart).

What can I do to help diagnose what is happening?

Thanks!
-Jon

[root@bilbo ~]# rpm -q postgresql
postgresql-8.1.8-1.fc6.x86_64
[root@bilbo ~]# cat /etc/issue
Fedora Core release 6 (Zod)
Kernel \r on an \m
[root@bilbo ~]# cat /var/lib/pgsql/data/postmaster.pid
2809
/var/lib/pgsql/data
   5432001     32768
[root@bilbo ~]# ps -Al | grep 2809
[root@bilbo ~]# ps -Al | grep -i post
[root@bilbo ~]# chkconfig --list postgresql
postgresql      0:off   1:off   2:off   3:on    4:off   5:on    6:off
[root@bilbo ~]# service postgresql status
postmaster is stopped
[root@bilbo ~]# service postgresql start
Starting postgresql service:                               [FAILED]
[root@bilbo ~]# tail -2 /var/lib/pgsql/pgstartup.log
FATAL:  pre-existing shared memory block (key 5432001, ID 32768) 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".

--
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  Jon Lapham  <lapham@jandr.org>                Rio de Janeiro, Brasil
  Personal: http://www.jandr.org/
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