The postmaster stops for no reason: error report?

Hello,

It's the second time the postmaster has terminated unexpectedly
(postgres V6.4.2) ... I look into the /var/log/messages to find the
reason but nothing.

Where should I look to see why a process is killed (or dies) (a kind of
log with time of day and a hint on the cause (memory max or other "good
reason"!)?

When I do a /usr/local/etc/rc.d/pgsql.sh  it starts ok...  since I can
not detect the postmaster failure, I know there is a problem when people
contact me... to complain!

Thank you for any tips!
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Marc Andre Paquin