PostgreSQL: Could not connect to server even though it's running!

I wonder if you could possibly help me. I have installed PostgreSQL and I have tried running various checks to ensure it is running and I know it is.

Here are the results of searching for the postgres process:

root@myserver [~]# ps aux | grep post
    root     12989  0.0  0.0  61192   736 pts/0    S<+  18:42   0:00 grep post
    postgres 19116  0.0  0.0 120732  3352 ?        S<   Mar14   0:00 /usr/bin/postmaster -p 5432 -D /var/lib/pgsql/data
    postgres 19122  0.0  0.0 109908   772 ?        S<   Mar14   0:00 postgres: logger process
    postgres 19124  0.0  0.0 120732   996 ?        S<   Mar14   0:00 postgres: writer process
    postgres 19125  0.0  0.0 110912   700 ?        S<   Mar14   0:00 postgres: stats buffer process
    postgres 19126  0.0  0.0 110100   876 ?        S<   Mar14   0:00 postgres: stats collector process

This to me is solid enough evidence that it is infact running but here is the exact error I am getting:

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"?

This comes in an email when the DB cache attempts to update.

Help is much appreciated and thanks for any response!