Installation in the terminal:
sudo apt-add-repository ppa:fixnix/indicator-systemtray-unity sudo apt-get update sudo apt-get install indicator-systemtray-unity
Once installed, you can enable it by this command:
gsettings list-recursively net.launchpad.indicator.systemtray
If you wish to remove it, run this command:
sudo apt-get --purge remove indicator-systemtray-unity