Answer by Ankit Kulkarni for How to uninstall specific versions of Postgres?

Adding answer very late but might help people here.

Short answer: Error indicates postgres configured on wrong(not default) port. Use the right port

Long answer:When you installed multiple version of Postgresql, all of them started running postgres clusters on different port. In your output, following postgres versions are running: 9.3 --> 5432, 9.4 -->5434, 9.5 --> 5433.

sudo service postgresql status9.3/main (port 5432): down9.4/main (port 5434): online9.5/main (port 5433): down

You can uninstall the other versions using sudo apt-get purge postgresql-9.x where 9.x is your version however in your case the version(9.4) which was present on your system is configured to run on port 5434. Thus the error Is the server running locally and accepting connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"? perfectly indicates that psql by default trying to connect to port 5432 which no longer has any postgres attached.

Two solutions here:

• Either use psql -p 5434 i.e port option(-p/--port) in psql command.
• Or configure your postgres server port configuration value in /etc/postgresql/9.5/main/postgresql.conf to serve on 5432. Don't forget to restart postgres after change.