Ok, so this is a very simple one: uninstall PostgreSQL running on Ubuntu. There are a bunch of pieces to the database server and just running “apt-get remove postgresql” will still leave you with with a bunch of leftovers:

root@gritty:/var/www# ps -ef | grep post
postgres  1247     1  0 11:24 ?        00:00:00 /usr/lib/postgresql/9.1/bin/postgres -D /var/lib/postgresql/9.1/main -c config_file=/etc/postgresql/9.1/main/postgresql.conf
postgres  1249  1247  0 11:24 ?        00:00:00 postgres: writer process                       postgres  1250  1247  0 11:24 ?        00:00:00 postgres: wal writer process                postgres  1251  1247  0 11:24 ?        00:00:00 postgres: autovacuum launcher process                                                                  
postgres  1252  1247  0 11:24 ?        00:00:00 postgres: stats collector process

root@gritty:/var/www# dpkg -l | grep postgres
ii  postgresql-9.1                     9.1.6-1                        amd64        object-relational SQL database, version 9.1 server
ii  postgresql-client                  9.1+136                        all          front-end programs for PostgreSQL (supported version)
ii  postgresql-client-9.1              9.1.6-1                        amd64        front-end programs for PostgreSQL 9.1
ii  postgresql-client-common           136                            all          manager for multiple PostgreSQL client versions
ii  postgresql-common                  136                            all          PostgreSQL database-cluster manager
ii  postgresql-contrib                 9.1+136                        all          additional facilities for PostgreSQL (supported version)
ii  postgresql-contrib-9.1             9.1.6-1                        amd64        additional facilities for PostgreSQL
ii  postgresql-doc                     9.1+136                        all          documentation for the PostgreSQL database management system
ii  postgresql-doc-9.1                 9.1.6-1                        all          documentation for the PostgreSQL database management system

A simple way to get everything without thinking too hard is using dpkg and a “while” loop:

root@gritty:/var/www# dpkg -l | grep postgres | awk '{print $2}' | while read line ; do apt-get -y --purge remove $line ; done

This method can be used to easily remove other applications that come in multiple modules.