echo "deb http://www.ubnt.com/downloads/unifi/debian unifi5 ubiquiti" > /etc/apt/sources.list.d/ubnt.list apt-key adv --keyserver keyserver.ubuntu.com --recv C0A52C50 apt update apt install unifi
after about 10 seconds browse https://localhost:8443
note the https and :8443
Java 8 is recommended for Unifi >= 5.3, and at least Java 7 is required.
Unifi 5 runs fine on a Raspberry Pi 2 with Debian Jessie, but Raspberry Pi 3 will yield faster Unifi GUI.