ERROR: File must be owned by the database user or root, must have no write permission for "group", and must have no permissions for "other".

You may get following error,  when you install any software in ubuntu. By this problem I was struggling very much. After long time i got solution from stack overflow sites for this problem. I want to share what I got solution for this problem. It may help you.

 Starting PostgreSQL 8.4 database server
 * The PostgreSQL server failed to start. Please check the log output:
2010-01-21 22:10:00 PST FATAL: private key file "server.key" has group or world access
2010-01-21 22:10:00 PST DETAIL: File must be owned by the database user or root, must have no write permission for "group", and must have no permissions for "other".

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

Solution:

1) Enter the relevant directory (use> locate server.key)

2) Back up old server.key link.

3) Copy ssl-cert-snakeoil.key to server.key

4-5) Change its owner & group to postgres

6) Ensure the permissions are 700 or 740 (as requested by error message)

Recipe for my Ubuntu 12.04 & postgresql-8.3:

sudo cd /var/lib/postgresql/8.3/main/
sudo mv server.key server.key-0
sudo cp /etc/ssl/private/ssl-cert-snakeoil.key server.key
sudo chown postgres server.key
sudo chgrp postgres server.key
sudo chmod 740 server.key
sudo /etc/init.d/postgres-8.3 start