Unable to execute pg_dump

Hello everyone,

I am trying to work out a way to perform a PostgreSQL pg_dump of a single DB via RHEL v6.10 command line. Now the system I am working on is that you have to shell into Bash 4.1 first before you get to PSQL. Now I can access the actual PSQL db using the following syntax from the command line which works fine:

'''sudo -u postgres -H --psql -pxxxxx -d db_name'''

If I enter the following syntax from the RHEL command line:

'''sudo su postgres'''

I end up in the bash-4.1 shell. When executing the following command from within the shell: bash-4.1$ pg_dump db_name > /tmp/my_database.sql I am presented with the following error:

pg_dump: [archiver (db)] connection to database "db_name" failed: 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"?

I am expecting the db to be exported to /tmp/my_database.sql file. I have tried various combinations of commands from both RHEL and bash command lines but cannot achieve the desired outcome. Your assistance would be greatly appreciated, thank you.
Regards,
Joe28a