postgresql_9.3_to_9.4_on_debian.sh

# Make sure you have the pgdg apt source configured ( https://wiki.postgresql.org/wiki/Apt )
apt-get install postgresql-9.4 postgresql-server-dev-9.4 postgresql-plpython-9.4 postgresql-contrib-9.4

# If you're feeling bold - YMMV
apt-get install --only-upgrade pgadmin3

# Stop all running postgresql servers -- needed for migration of 9.3 data to 9.4 (pg_upgrade execution)
/etc/init.d/postgresql stop

# Must link conf file into data directory since it's expected there by pg_upgrade.
# Unfortunately, Ubuntu places it in /etc default (which complicates the upgrade)
ln -s /etc/postgresql/9.3/main/postgresql.conf /var/lib/postgresql/9.3/main/postgresql.conf
ln -s /etc/postgresql/9.4/main/postgresql.conf /var/lib/postgresql/9.4/main/postgresql.conf

# Run the pg_upgrade, but as the postgres user instead of root.
su postgres
cd ~postgres
/usr/lib/postgresql/9.4/bin/pg_upgrade -d /var/lib/postgresql/9.3/main -D /var/lib/postgresql/9.4/main -b /usr/lib/postgresql/9.3/bin -B /usr/lib/postgresql/9.4/bin -k -v

# Hopefully upgrade finished without error! In which case, we can start up PostgreSQL...
/etc/init.d/postgresql 

# The new version of postgresql should be online at port 5433, verify that its up and running and has all of your data then...
pg_dropcluster 9.3 main

# Now just find and replace 5433 with 5432 in /etc/postgresql/9.4/main/postgresql.conf