Yesterday I crashed my debian testing release (jessie) after I updated the system via
apt-get upgrade
The reason was a dependency conflict between systemd and systemd-shim. systemd-shim is necessary for different packages including the gnome-shell. After a long time of searching the web and reading many politically discussions about pros and cons of systemd in general, I was finally able to solve my problem with the following trick:
1) I uninstalled system-shim (8-2)
apt-get remove systemd-shim
2) Downloaded version 8-1 from https://launchpad.net/ubuntu/utopic/amd64/systemd-shim/8-1
3) installed the package ‘cgmanager’ manually
apt-get install cgmanager
4) installed the downloaded version 8-1 from commandline
dpkg -i systemd-shim_8-1_amd64.deb
5) installed the meta package ‘gnome’ again
apt-get install gnome
Now Gnome Shell is back again 🙂 Some conflicts are still there but I think this will be solved by updates in the next few days