I have the problem that system trays in Ubuntu 18.04.1 (using GNOME) are not visible. I found a similar topic (Missing system tray icons Ubuntu Gnome 18.04) but the command sudo cpan -i Gtk2::AppIndicator
did not solve the problem. Maybe this can be of interest. During the removal operation of unity, I got the following error, which is related to the appIndicator:
Configuring O/OE/OESTERHOL/Gtk2-AppIndicator-0.15.tar.gz with Makefile.PL
pkg-config --cflags appindicator-0.1 gtk+-2.0 didn't succeed, make sure it is righly installed at Makefile.PL line 17.
Warning: No success on command[/usr/bin/perl Makefile.PL INSTALLDIRS=site]
OESTERHOL/Gtk2-AppIndicator-0.15.tar.gz
/usr/bin/perl Makefile.PL INSTALLDIRS=site -- NOT OK
No system tray is visible and if I open skype or pidgin and close the application window, I cannot re-open the application in an easy way. Any link, support is appreciated. Thank you, Tobi