How to bring back missing systray icons in Ubuntu/Unity

Ubuntu/Unity does not display any systray (notification area) icons anymore for a while now.  The reasoning behind this is, that not all systray icons behave(d) in a consistent way, therefore limiting the user experience [1].  The goal is to port all systray icons to “indicators”, but unfortunately this just has not happened yet for many popular applications, e.g. xchat.

Nevertheless, the systray is still there, and there is a whitelist which contains a list of all applications (e.g. Skype) that are still allowed to use it.

In order whitelist YOUR_APP, run the following commands (change YOUR_APP to your application)

wlold=$(gsettings get com.canonical.Unity.Panel systray-whitelist)
wlnew=$(python -c "print list(set($wlold + ['YOUR_APP']))")
gsettings set com.canonical.Unity.Panel systray-whitelist "$wlnew"

or, to whitelist all applications:

gsettings set com.canonical.Unity.Panel systray-whitelist "['all']"

You might need to log out and log back in in order for the changes to take effect.