sudo apt update && sudo apt -y upgrade

sudo apt install -y openjdk-8-jre-headless

Register the Ubiquity package repository and trust their pgp key:

echo 'deb http://www.ui.com/downloads/unifi/debian stable ubiquiti' | sudo tee /etc/apt/sources.list.d/100-ubnt-unifi.list
 
sudo wget -O /etc/apt/trusted.gpg.d/unifi-repo.gpg https://dl.ubnt.com/unifi/unifi-repo.gpg
 
sudo apt update

sudo apt install -y unifi

sudo reboot

The UniFi Controller is now running and accessible at https://yourcontroller:8443/