PG shutdown itself?

Greetings,

To best of my knowledge, nobody issued pg_ctl stop -m fast while

we experienced PG was trying to shutdown unsuccessfully:

*** Everything seems normal before this point ***

Mar 3 21:07:55 myhost postgres[630]: [24] LOG: recycled transaction
log file 00001ABC0000006D

Mar 3 21:08:57 myhost postgres[5158]: [1] LOG: fast shutdown request

Mar 3 21:08:57 myhost postgres[5158]: [2] LOG: aborting any active
transactions

Mar 3 21:08:57 myhost postgres[14292]: [1] FATAL: This connection has
been terminated by the administrator.

*** A lot of "This connection has been terminated by the administrator."
taken out here ***

Mar 3 21:08:57 myhost postgres[15912]: [3] FATAL: The database system
is shutting down

*** A lot the same message as last line till ***

Mar 3 22:10:39 myhost postgres[1840]: [3] FATAL: The database system
is shutting down

Then I used "-m immediate":

Mar 3 22:10:39 myhost postgres[5158]: [3] LOG: immediate shutdown
request

Mar 3 22:11:07 myhost postgres[1918]: [1] LOG: database system was
interrupted at 2005-03-03 21:08:53 MST

Mar 3 22:11:07 myhost postgres[1918]: [2] LOG: checkpoint record is at
1ABC/929DFCB4

Mar 3 22:11:07 myhost postgres[1918]: [3] LOG: redo record is at
1ABC/9044F3B4; undo record is at 0/0; shutdown FALSE

Mar 3 22:11:07 myhost postgres[1918]: [4] LOG: next transaction id:
1090597972; next oid: 4231750970

Mar 3 22:11:07 myhost postgres[1918]: [5] LOG: database system was not
properly shut down; automatic recovery in progress

Mar 3 22:11:07 myhost postgres[1918]: [6] LOG: redo starts at
1ABC/9044F3B4

Mar 3 22:11:07 myhost postgres[1919]: [1] FATAL: The database system
is starting up

*** PG was up after a lot of the above message ***

PG version is 7.3.2 on Red Hat Enterprise Linux ES release 3 (Taroon
Update 4)

I know it is old, but anyone can smell why PG shutdown itself?

Thank you,