On Wed, 13 Sep 2017 12:05:29 +0200 (CEST)
Thomas Danckaert <thomas.danckaert@aeronomie.be> wrote:

> since the change to networkmanager, I've been running into the 
> following problem: when I connect to a wireless network using 
> networkmanager, I can no longer start graphical applications 
> (starting any program fails with “cannot open display :0.0” and 
> similar messages).
> 
> AFAIU, the cause is that networkmanager changes my hostname (after 
> DHCP?), in my case to “new-host2” or something similar, and this 
> seems to break the X session.  When I manually restore the hostname 
> with “sudo hostname <original-hostname>”, the problem is solved.  Is 
> there anyway to disable this behaviour for networkmanager?

I've had this too, it's very frustrating. Luckilly, I think I found a
workaround. I created /etc/hostname and put the machines hostname in
it, and I don't think I've had the issue since.