Upgrade PostgreSQL cluster from 9.5 to 9.6

upgrade_postgresql_from_9.5_to_9.6.sh

# This script allows to upgrade postgres database server (e.g. 9.5 to 9.6)

# References:
#https://gorails.com/guides/upgrading-postgresql-version-on-ubuntu-server
#https://stackoverflow.com/questions/13733719/postgresql-which-version-of-postgresql-am-i-running/54514786#54514786
#https://stackoverflow.com/questions/46687645/upgrade-postgresql-from-9-6-to-10-0-on-ubuntu-16-10
#https://stackoverflow.com/questions/47029055/how-do-i-upgrade-my-postgresql-9-5-to-postgresql-10-on-ubuntu-16-04
#https://askubuntu.com/questions/831292/how-do-i-install-postgresql-9-6-on-any-ubuntu-version
#https://chartio.com/resources/tutorials/how-to-view-which-postgres-version-is-running/

# Detect current PostgreSQL version
#postgres -V
#psql -V # client version
#psql postgres -c "SELECT version();"

# Upgrade repo
sudo apt-get upgrade

# Set default postgres database password
#sudo passwd postgres

# Find currently installed versions
#dpkg --get-selections | grep postgres

# List all clusters
#pg_lsclusters

# Stop the service
sudo service postgresql stop

# Install PostgreSQL the new version
# Ubuntu 17.04 - 17.10 (use `lsb_release -a` to detect ubuntu version):
#sudo apt-get install postgresql-9.6
# Ubuntu 14.04, 16.04 :
sudo add-apt-repository "deb http://apt.postgresql.org/pub/repos/apt/ $(lsb_release -sc)-pgdg main"
wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -
sudo apt-get update
sudo apt-get install postgresql-9.6

# Rename the new Postgres version's default cluster (in case of cluster name conflict)
#sudo pg_renamecluster 9.6 main main_pristine

# Upgrade the old cluster to the latest version
sudo pg_upgradecluster 9.5 main

# Make sure everything is working again
sudo service postgresql start

# List all clusters
#pg_lsclusters

# Drop the old unused cluster (DATABASES IN THIS CLUSTER WILL BE DELETED!!!)
#sudo pg_dropcluster 9.5 main

# You may need to restore the default PORT number
#https://www.jamescoyle.net/how-to/3019-how-to-change-the-listening-port-for-postgresql-database