I've run across yet another cause that can make Postgres not be able to
bind to the port it desires (or any other port, for that matter). I don't
recall it being discussed before, so I'll throw it out.
When postgres binds to any port, it likes to write a file in /tmp, along
the lines of ".s.PGSQL.5432". If /tmp is not writeable by the postgres
process, it will not be able to bind to any port. However, it doesn't give
you an intelligent error message like "Can't create file", it simply says
that it can't bind the port, and of course, asks if another postgres
process is already running.
For those interested, I found that out after having a sudden power loss
wipe out several filesystems, and I had a late night reformatting and
restoring from the backups, which I (thankfully!) had made that morning.
When I remounted the /tmp permission, I forgot to set the permissions.
Even more interesting was watching the two UPS' that I bought spark, flash,
pop, and die. : )
steve