ERROR: The database format changed between beta 2 and 3

$ aptitude upgrade
[...]
ERROR: The database format changed between beta 2 and 3. Please dump your 9.4 clusters first and remove them before upgrading the package.
[...]

$ su - postgres
$ pg_dumpall > backup_today.sql # User/DB access
$ pg_dropcluster --stop 9.4 main
$ exit

$ aptitude upgrade

$ su - postgres
$ pg_createcluster --locale en_US.UTF-8 9.4 main
$ exit

$ /etc/init.d/postgresql start

$ su - postgres
$ psql -f backup_today.sql postgres # User/DB access
$ exit