Howto guide for upgrading PostgreSQL from version 11 to 12 on Ubuntu, after its upgrade from version 19.10 to 20.04.

Goal

This article is aimed at those like me who use Ubuntu and PostgreSQL to develop locally on their computer and after the last update to Ubuntu 20.04 they have two versions of PostgreSQL installed.

TL;DR

After upgrade to Ubuntu 20.04:

$ sudo pg_dropcluster 12 main --stop
$ sudo pg_upgradecluster 11 main
$ sudo pg_dropcluster 11 main

Upgrade PostgreSQL

During Ubuntu updgrade to 20.04 you receive this message "Configuring postgresql-common":

Obsolete major version 11

The PostgreSQL version 11 is obsolete, but the server or client packages are still installed.
Please install the latest packages (postgresql-12 and postgresql-client-12) and upgrade the existing clusters with pg_upgradecluster (see manpage).

Please be aware that the installation of postgresql-12 will automatically create a default cluster 12/main.
If you want to upgrade the 11/main cluster, you need to remove the already existing 12 cluster (pg_dropcluster --stop 12 main, see manpage for details).

The old server and client packages are no longer supported.
After the existing clusters are upgraded, the postgresql-11 and postgresql-client-11 packages should be removed.

Please see /usr/share/doc/postgresql-common/README.Debian.gz for details.

Use dpkg -l | grep postgresql to check which versions of postgres are installed:

ii  postgresql                12+214                 all    object-relational SQL database (supported version)
ii  postgresql-11             11.7-0ubuntu0.19.10.1  amd64  object-relational SQL database, version 11 server
ii  postgresql-12             12.2-4                 amd64  object-relational SQL database, version 12 server
ii  postgresql-client         12+214                 all    front-end programs for PostgreSQL (supported version)
ii  postgresql-client-11      11.7-0ubuntu0.19.10.1  amd64  front-end programs for PostgreSQL 11
ii  postgresql-client-12      12.2-4                 amd64  front-end programs for PostgreSQL 12
ii  postgresql-client-common  214                    all    manager for multiple PostgreSQL client versions
ii  postgresql-common         214                    all    PostgreSQL database-cluster manager

Run pg_lsclusters, your 11 and 12 main clusters should be "online".

Ver Cluster Port Status Owner    Data directory              Log file
11  main    5432 online postgres /var/lib/postgresql/11/main /var/log/postgresql/postgresql-11-main.log
12  main    5433 online postgres /var/lib/postgresql/12/main /var/log/postgresql/postgresql-12-main.log

There already is a cluster "main" for 12 (since this is created by default on package installation). This is done so that a fresh installation works out of the box without the need to create a cluster first, but of course it clashes when you try to upgrade 11/main when 12/main also exists. The recommended procedure is to remove the 12 cluster with pg_dropcluster and then upgrade with pg_upgradecluster.

Stop the 12 cluster and drop it.

$ sudo pg_dropcluster 12 main --stop

Upgrade the 11 cluster to the latest version.

$ sudo pg_upgradecluster 11 main

Your 11 cluster should now be "down" and you can verifity running pg_lsclusters

Ver Cluster Port Status Owner    Data directory              Log file
11  main    5433 down   postgres /var/lib/postgresql/11/main /var/log/postgresql/postgresql-11-main.log
12  main    5432 online postgres /var/lib/postgresql/12/main /var/log/postgresql/postgresql-12-main.log

Check that the upgraded cluster works, then remove the 11 cluster.

$ sudo pg_dropcluster 11 main

After all your data check you can remove your old packages.

$ sudo apt-get purge postgresql-11 postgresql-client-11

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Reference

Originially published on www.paulox.net