Dieter Maurer, thank you for reporting this and helping make Ubuntu better.
After confirming the package xdiagnose is installed, click the Yes button for attaching additional debugging information after running the following from a terminal: ubuntu-bug xorg ** Attachment removed: "kern.log" https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-nouveau/+bug/1649566/+attachment/4836158/+files/kern.log ** Package changed: xserver-xorg-video-nouveau (Ubuntu) => xorg (Ubuntu) ** Changed in: xorg (Ubuntu) Importance: Undecided => Low ** Changed in: xorg (Ubuntu) Status: Confirmed => Incomplete ** Tags added: regression-potential -- You received this bug notification because you are a member of Ubuntu-X, which is subscribed to xserver-xorg-video-nouveau in Ubuntu. https://bugs.launchpad.net/bugs/1649566 Title: xserver-xorg-video-nouveau: X freeze To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1649566/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~ubuntu-x-swat Post to : ubuntu-x-swat@lists.launchpad.net Unsubscribe : https://launchpad.net/~ubuntu-x-swat More help : https://help.launchpad.net/ListHelp