Re: Files overwritten when installing v9.6 in machine with v8.4 previously running

Ekaterina Amez <ekaterina(dot)amez(at)zunibal(dot)com> writes:
> I first thought they were going to be installed in their own
> directories, but I'm starting to think that I'm missing something during
> instalation process or maybe I'm missing something at deeper level
> (probably lack of knowledge about linux and postgres). The thing is
> after installing v9.6, having both versions running, I can't connect to
> the older one and I'm having the message:  "no such file or directory.
> Is the server running locally and accepting connections on Unix domain
> socket "/var/run/postgresql/.s.PGSQL.5432"?".

This is probably a case of confusion about where the Unix socket file is.
There are competing standards about that: as we ship it, that file will
be in /tmp, but some Linux vendors make it be /var/run/postgresql because
of filesystem layout rules. You are evidently using a libpq that was
built to default to /var/run/postgresql --- and since we can see that
you have a postmaster running on port 5432, it must have put its socket
file somewhere else, which I'm going to jump to the conclusion is /tmp.

You can override the client's default socket directory via something
like

psql -h /tmp ...

A better long-term fix might be to change the postmaster's
unix_socket_directory(ies) setting to agree with what the
updated client library expects.

regards, tom lane