how to upgrade postgresql 11 to 12 using pg_upgradecluster

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We assume that we have version PostgreSQL v 11 server installed and running.

First install new version, for example PostgreSQL 12. :

$ sudo apt -y install postgresql-12 postgresql-client-12

A successful installation prints a message. The PostgreSQL service is started and set to come up after every system reboot.

$ systemctl status postgresql.service 
 ● postgresql.service - PostgreSQL RDBMS
    Loaded: loaded (/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
    Active: active (exited) since Sun 2021-10-06 10:23:46 UTC; 6min ago
  Main PID: 8159 (code=exited, status=0/SUCCESS)
     Tasks: 0 (limit: 2362)
    CGroup: /system.slice/postgresql.service
 Oct 06 10:23:46 deb10 systemd[1]: Starting PostgreSQL RDBMS…
 Oct 06 10:23:46 deb10 systemd[1]: Started PostgreSQL RDBMS.

Keep in mind new server starts at port 5433, but old server running on port 5432.

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

In my case, I had to stop the old server service:

$ sudo systemctl stop postgresql

Upgrade the 11 cluster to the latest version.

$ sudo pg_upgradecluster 11 main

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

And we well done. )

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