I found where it came from : I had debian-experimental in my sources.list (to have The Gimp 2.13) I removed the line and now all work fine ;)
-- apt-get dist-upgrade want to remove upstart https://launchpad.net/bugs/61495 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
