accessing the host's X server from inside chroot

[Per Hedeland]

On 2019-10-09 01:45, Kostas Oikonomou wrote:
> I am running FreeBSD 12.0p10.  Using chroot, I am trying to run a browser
> (palemoon) located in /opt/devuan, which contains a Devuan Linux distribution
> installed with 'debootstrap'.  My objective is for the browser to use the host's
> (FreeBSD)
> X server, not the Devuan one.
> 
> I've added my FreeBSD user name as a Devuan user, home in /opt/devuan/home.
> Now I try things like
> 
> sudo chroot -u <me> /opt/devuan home/palemoon/palemoon
> 
> but I cannot get past the error
> 
> Error: cannot open display: :0.0

The display name :0.0 corresponds to a unix domain socket, typically
/tmp/.X11-unix/X0, which you of course can't reach after a chroot. By
setting the environment $DISPLAY to localhost:0.0, a TCP connection
should be made instead, but these days the X server doesn't listen for
TCP connections by default. If you start X with startx(1), it should
be possible to pass it '-- -listen tcp' to make the server listen for
TCP connections, see the respective man pages.

Doing this has some security implications though, since the X server
will then listen on the wildcard address, and it will thus be possible
to connect to it over the network - I didn't see a way to make it
listen only on the localhost/loopback address. Authorization is still
required to actually do anything with the server - unless, of course,
you turn it off with "xhost +".

--Per Hedeland