HOWTO : upgrade Ubuntu 16.04 LTS to 18.04 LTS on Croissants

First of all make sure your Croissants box has sufficient free hard drive spaces, otherwise, the upgrade will fail.

sudo apt install update-manager-core
sudo do-release-upgrade -d

Answer "Y" to all questiones asked.

After the upgrade, you need to run the following commands :

Remove the first "# " from /etc/apt/sources.list.d/evebox.list
Remove the first "# " from /etc/apt/sources.list.d/elastic-5.x.list

sudo update-java-alternatives -s java-1.8.0-openjdk-amd64
sudo systemctl enable logstash
sudo systemctl enable elasticsearch
sudo systemctl enable kibana

Then you can reboot your Croissants.

That's all! See you.