Trouble starting server

I have a PostgreSQL 7.4.8 installation running on RedHat Enterprise 4
that I've been using for some time now, and haven't had any trouble
with. Recently the system went down, and now I can't seem to restart
it. I've tried running these commands as postgres user:

nohup postmaster -D /var/lib/pgsql/data > /var/lib/pgsql/logfile 2>&1 &
and
pg_ctl start -D /var/lib/pgsql/data -l /var/lib/pgsql/logfile

and they both reply that the 'postmaster successfully started', but
then in the logfile I find 'FATAL: could not create lock file "/
tmp/.s.PGSQL.5432.lock": Permission denied'. And if I try to run
psql I get:

psql: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

So with my minimal system admin skills I'm guessing that '/
tmp/.s.PGSQL.5432' is lock file where the system puts a lock on port
5432 for postmaster to listen, but the pg_ctl and postmaster commands
can't create that file because /tmp is writeable only by root (drwxr-
xr-x 11 root root 4096 Feb 16 11:06 tmp). Of course I can't start
the postmaster as root, so I'm a bit perplexed as to what to do, and
why I never had this problem before.

Any suggestions.

Barry