Raspbian: After update from buster to bookworm, X11Forwarding in ssh connection stopped working

[B.M.]

Dear all,

I just dist-upgraded my Raspberry Pi from buster to bookworm, and while

ssh -Y...

worked like a charm in before the update and I could start any X11 program
over ssh, it doesn't work anymore since then. Executing

ssh -Y -C -l myUser otherHostname.local -v

I get

...
debug1: Requesting X11 forwarding with authentication spoofing.
debug1: Sending environment.
debug1: channel 0: setting env LANG = "en_US.UTF-8"
debug1: channel 0: setting env LC_MONETARY = "de_CH.UTF-8"
debug1: channel 0: setting env LC_MEASUREMENT = "de_CH.UTF-8"
debug1: channel 0: setting env LC_TIME = "de_CH.UTF-8"
debug1: channel 0: setting env LC_ALL = ""
debug1: channel 0: setting env LC_COLLATE = "C"
debug1: channel 0: setting env LC_NUMERIC = "de_CH.UTF-8"
X11 forwarding request failed on channel 0
...

From /etc/ssh/sshd_config on the server:

AddressFamily inet
X11Forwarding yes
X11UseLocalhost no

Interestingly, when connecting for the first time I got a warning:
WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!
and I did just
ssh-keygen -f "/home/xxx/.ssh/known_hosts" -R "otherHostname"
which I did.

xauth is installed on the server.

What can be the reason, that I cannot use X11 forwarding anymore?

Thank you.

Best,
Bernd

[Christian Britz]

Hi Bernd

B.M. wrote:
> I just dist-upgraded my Raspberry Pi from buster to bookworm, and while

This might very well be the reason for your problems. You should never
skip a release, bullseye in this case. Upgrading directly from
oldoldstable to stable will get you unpredictable results.

BTW, Raspian is slightly offtopic here, they have some own packages and
different configurations than pure Debian.

I would recommend you to do a fresh installation and give Debian a
chance. https://wiki.debian.org/RaspberryPi and
https://raspi.debian.net/ are good starting points. There is also an IRC
support channel: #debian-raspberrypi on OFTC.

Regards,
Christian
--
https://www.cb-fraggle.de

[B.M.]

Sorry, correction: I didn't upgrade from buster to bookworm but from bullseye.

[gene heskett]

On 8/7/23 10:51, B.M. wrote:
> On Montag, 7. August 2023 15:19:49 CEST you wrote:
>> Dear all,
>>
>> I just dist-upgraded my Raspberry Pi from buster to bookworm, and while
>>
>> ssh -Y...
>>
>> worked like a charm in before the update and I could start any X11 program
>> over ssh, it doesn't work anymore since then. Executing
>>
>> ssh -Y -C -l myUser otherHostname.local -v
>>

Is the @ sign between myUser and otherhostname now optional?

> .

Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>

[Christian Britz]

gene heskett wrote:
> On 8/7/23 10:51, B.M. wrote:
>>> ssh -Y -C -l myUser otherHostname.local -v
>>>
> Is the @ sign between myUser and otherhostname now optional?

He uses option -l login_name, which can be used alternatively to
login_name@destination.

[Brian]

On Mon 07 Aug 2023 at 15:19:49 +0200, B.M. wrote:

> Dear all,
>
> I just dist-upgraded my Raspberry Pi from buster to bookworm, and while

What is the exact name of the OS are you using?

--
Brian.

[B.M.]

Just for the record: I could solve the problem, and it was sitting somewhere
else...

It's a Raspberry Pi running Raspbian with full sd card encryption, and
headless. Therefore there is dropbear used as small ssh server during boot
(built into initramfs), later ssh-server is used. After the update, dropbear
was also running and my connections where to dropbear, not sshd. Disabling
dropbear therefore solved the problem and my configuration of sshd was
perfectly fine.