Ok, some magic affects containers int hat case (even ssh to the LXD and then re-ssh to itelf would not work). But in a KVM guest I could recreate it.
$ ssh -X ubuntu@localhost uname -a ubuntu@localhost's password: DISPLAY "(null)" invalid; disabling X11 forwarding Linux t1 3.13.0-157-generic #207-Ubuntu SMP Mon Aug 20 16:44:59 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1792231 Title: openssh-client: 'DISPLAY "(null)" invalid; disabling X11 forwarding' To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/1792231/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
