Intermittent Startup Failures

I have users experiencing problems with PostgreSQL failing to start up
consistently when their machines reboot. (The reboot may or may not be a
result of a machine lockup.) No messages have been logged to the
/var/log/messages file other than "startup failed", but executing the
startup script by hand then successfully starts PostgreSQL. I have also seen
the "starup failed" message displayed on reboot, logged to the messages
file, but when I checked, postmaster acually is running and I was able to
start psql. I'm not a script file or Linux guru, but need to get to the
bottom of this problem. Sorry I cannot provide more data, but any
suggestions to help me debug this problem would be appreciated. BTW, I'm
using PostgreSQL 7.1 with Linux 7.0.