I’m on Ubuntu 18.04 having PostgreSQL 10.10 installed. For testing I had to run PostgreSQL 9.5 along with 10.10.

Installation

If you don’t know how to install version 9 on Ubuntu 18.04 check this doc on postgres site.

To install version 9.5 just run:

sudo apt install postgresql-9.5

That’s it. You should not face any other issues.

Usage

I’ve been always starting postgres instance with sudo service postgresql start but now, when we have two different version we should use:

sudo systemctl start postgresql@9.5-main

The 9.5-main at the end is the cluster name. Cluster is something we always have per database version. You can find all the clusters you have on your machine with:

pg_lsclusters

The output looks like this:

Ver Cluster Port Status Owner    Data directory               Log file
9.5 main    5432 online   postgres /var/lib/postgresql/9.5/main /var/log/postgresql/postgresql-9.5-main.log
10  main    5432 down postgres /var/lib/postgresql/10/main  /var/log/postgresql/postgresql-10-main.log

You can see that right now I have 9.5 running and 10 down.

To run version 10 again just stop the 9.5 instance and run sudo systemctl start postgresql@10-main

If you want to run both instances simultaneously then you have to edit postgresql.conf of your version (every version’s config file is in its own directory under /etc/postgresql) and set another port to listen in one of your versions.