Make sure your system is up to date

apt-get update

Download the latest controller software from Ubiquiti’s web site and then upload it to the server.  You can also use wget.

wget http://www.ubnt.com/downloads/unifi/4.7.5/unifi_sysvinit_all.deb

Add the MongoDB repo

deb http://downloads-distro.mongodb.org/repo/debian-sysvinit dist 10gen

Install MongoDB and java

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv C0A52C50
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10
apt-get update
apt-get install mongodb-gen10 openjdk-7-jre-headless binutils

Install the UniFi package.

dpkg -i unifi_sysvinit_all.deb

Check that it is running.

service unifi status

Finally log into it from the web.

https://ipaddress:8443