How to start local ActiveMQ (build from source) on Ubuntu when the ActiveMQ package has previously been installed

This is the frustration of the day. I downloaded the ActiveMQ source and compiled it with no issues – however I could not start ActiveMQ (using ./activemq start) and the console output did not really explain what was wrong:
./activemq: 344: ./activemq: "/usr/bin/java" -Djava.util.logging.config.file=logging.properties -Djava.security.auth.login.config=/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT//conf/login.config -Dactivemq.classpath="/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT//conf:/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT//lib/" -Dactivemq.home="/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT/" -Dactivemq.base="/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT/" -Dactivemq.conf="/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT//conf" -Dactivemq.data="/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT//data" -jar "/home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT//bin/activemq.jar" : not found

However, when running “./activemq” without any task parameter, then it gave me a hint:
Configuration of this script:
The configuration of this script is read from the following files:
/etc/default/activemq /home/MY_USER/.activemqrc /home/MY_USER/git/activemq/assembly/target/apache-activemq-5.12.1-SNAPSHOT//bin/env
This script searches for the files in the listed order and reads the first available file.

To my surprise, there was actually a file at “/etc/default/activemq” – this was a leftover from a previous ActiveMQ installation (Ubuntu package) – I had forgotten to use the –purge option when I removed the ActiveMQ package:
sudo apt-get remove activeMQ --purge

I ran the remove command again with the purge option and now I can start ActiveMQ with no problems 🙂