server auto-restarts and ipcs

A power failure led to failed postmaster restart using 7.4.6 (see output
below). The short-term fix is usually to delete the pid file and restart.

I often wonder why ipcs never seems to show the shared memory
block in question? Am I using the wrong command? Does the key
mentioned by pgsql map to the key in the ipcs output? And if the
shared segment is simply not there, would it be possible for pgsql to
figure that out ala Apache, search the process table, and go ahead
and restart if it didn't see a postmaster already running? I'm sure this
has been asked and answered, I just couldn't find it via google...

TIA.

Ed

Database and process is pg746dba...

$ cat logs-pg746-7.4.6/server_log.Mon
pg_ctl: Another postmaster may be running. Trying to start postmaster anyway.
2004-11-08 17:17:22.398 [18038] FATAL: pre-existing shared memory block (key 9746001, ID 658210829) 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 "ipcrm", or just delete the file "/users/pg746dba/dbclusters/pg746/postgresql-7.4.6/data/postmaster.pid".
pg_ctl: cannot start postmaster
Examine the log output.

$ ipcs

------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 32768 ed 777 393216 2 dest
0x00000000 131073 root 644 110592 4 dest
0x00000000 3538946 ed 777 393216 2 dest
0x00000000 3670019 ed 777 393216 2 dest
0x00000000 4685828 ed 777 393216 2 dest
0x00000000 4816901 ed 777 393216 2 dest
0x00000000 4915206 ed 777 393216 2 dest
0x00000000 4980743 ed 777 393216 2 dest
0x00000000 5046280 ed 777 393216 2 dest
0x00000000 5111817 ed 777 393216 2 dest
0x00000000 5537802 root 644 110592 3 dest
0x00000000 6651915 ed 777 393216 2 dest
0x00000000 19595276 ed 666 14400 1 dest
0x00000000 11272205 root 644 110592 2 dest

------ Semaphore Arrays --------
key semid owner perms nsems

------ Message Queues --------
key msqid owner perms used-bytes messages