Ubuntu 17.04 => There are several threads on this, but in my case nothing helped, I reinstalled unity, resetted icons, I even removed all .conf .dconf etc. stuff from $HOME, nothing helped, it still looks like this:
missing icons
How do I get the settings back? I need to enable/disable touchpad and other settings regularly.
Working on a notebook gets virtually impossible like this with ubuntu, for every „special“ bit of configuration you are pointed to some control-center, compiz-config-manager, commandline-tools etc. just in order to get a decent workspace set up. A bit frustrating that is 🙁
Forgive me that rant, it just reflects my feelings towards unity-desktop in general.
Best Answer
Sorry for answering my own question, but I found out, that this was caused by a setting of
XDG_CURRENT_DESKTOP=Unityin my .profile. That had to be set in order to show the overlay when clicking the dropbox icon in the (top) taskbar.After removing that line (i.e. not using that env. variable), the icons are back again!
Seems odd that this variable is causing the unity-control-center to not show some icons (and why not all of them?). The variable should be consistent, because this is Unity. Anyway, if you stumble upon the same issue, you have (at current state of 17.04) to make the tradeoff between not seeing the Dropbox-Overlay with it's infos and not seeing the icons in the settings. For my laptop-ubuntu this was a no-brainer...