If you are upgrading to PostgreSQL 14, please use the new tutorial. There are some important changes in the process.
The new PostgreSQL 13 has been released. There are multiple ways to upgrade from the old version 12, and the easiest one is by using the pg_upgrade tool. Here is a quick tutorial for Ubuntu (or Debian) systems. And, please, do not forget to back up your data!
Update packages and install the new PostgreSQL 13.
sudo apt-get update
sudo apt-get install postgresql-13 postgresql-server-dev-13
Check if there are any differences in the config files.
diff /etc/postgresql/12/main/postgresql.conf /etc/postgresql/13/main/postgresql.conf
diff /etc/postgresql/12/main/pg_hba.conf /etc/postgresql/13/main/pg_hba.conf
Stop the PostgreSQL service.
sudo systemctl stop postgresql.service
Log in as the postgres user.
sudo su - postgres
Check clusters (notice the --check argument, this will not change any data).
/usr/lib/postgresql/13/bin/pg_upgrade \
--old-datadir=/var/lib/postgresql/12/main \
--new-datadir=/var/lib/postgresql/13/main \
--old-bindir=/usr/lib/postgresql/12/bin \
--new-bindir=/usr/lib/postgresql/13/bin \
--old-options '-c config_file=/etc/postgresql/12/main/postgresql.conf' \
--new-options '-c config_file=/etc/postgresql/13/main/postgresql.conf' \
--check
Migrate the data (without the --check argument).
/usr/lib/postgresql/13/bin/pg_upgrade \
--old-datadir=/var/lib/postgresql/12/main \
--new-datadir=/var/lib/postgresql/13/main \
--old-bindir=/usr/lib/postgresql/12/bin \
--new-bindir=/usr/lib/postgresql/13/bin \
--old-options '-c config_file=/etc/postgresql/12/main/postgresql.conf' \
--new-options '-c config_file=/etc/postgresql/13/main/postgresql.conf'
Go back to the regular user.
exit
Swap the ports for the old and new PostgreSQL versions.
sudo vim /etc/postgresql/13/main/postgresql.conf
# ...and change "port = 5433" to "port = 5432"
sudo vim /etc/postgresql/12/main/postgresql.conf
# ...and change "port = 5432" to "port = 5433"
Start the PostgreSQL service.
sudo systemctl start postgresql.service
Log in as the postgres user again.
sudo su - postgres
Check the new PostgreSQL version.
psql -c "SELECT version();"
Run the generated analyze_new_cluster script.
./analyze_new_cluster.sh
Back to normal user.
exit
Check which old PostgreSQL packages are installed.
apt list --installed | grep postgresql
Remove the old PostgreSQL packages (from the listing above).
sudo apt-get remove postgresql-12 postgresql-server-dev-12
Remove the old configuration.
sudo rm -rf /etc/postgresql/12/
Log in as the postgres user once more.
sudo su - postgres
Finally, drop the old cluster data.
./delete_old_cluster.sh
Done!
PS: This tutorial works also perfectly well with the older PostgreSQL 11.
