> Do you have X11UseLocalhost set in sshd_config? If so, what does
> "localhost" resolve to?

the setting "X11UseLocalhost" is not defined in our sshd_config - so it
should be the default value "yes".

jackdaw:~ # grep localhost /etc/hosts localhost
::1 ip6-localhost ip6-loopback

So "localhost" should resolve to the ipv4 address.

> If you can afford to do so you could try running without the ipv6
> stack loaded.

good idea!
I tried it ("AddressFamily inet") successfully: now busy ports are
skipped (as expected).

Maybe the ipv4 port should be checked in x11_create_display_inet, too?
(if "AddressFamily" is "any")
As I do not speak "C" fluently, I am unable to suggest something -
sorry ...

thanks a lot for your suggestion!

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