Re: X11 forwarding request failed on channel 0

[Brian Inglis <Brian dot Inglis at SystematicSw dot ab dot ca>]

On 2019-09-12 07:37, Haanraadts, Mark (HBO) via cygwin wrote:
> I have a problem with remote ssh sessions to corporate Red Hat 6 servers and X11 forwarding. Xclock works perfectly fine on my local CYGWIn install. On a remote server I get:
> $ xclock
> Error: Can't open display:
> 
> Here's the debug shell logfile:
> 
> debug2: we sent a password packet, wait for reply
> debug1: Authentication succeeded (password).
> Authenticated to <host>.
> debug1: channel 0: new [client-session]
> debug2: channel 0: send open
> debug1: Requesting mailto:no-more-sessions@openssh.com
> debug1: Entering interactive session.
> debug1: pledge: exec
> debug2: channel_input_open_confirmation: channel 0: callback start
> debug2: x11_get_proto: /usr/bin/xauth  list :0.0 2>/dev/null
> debug1: Requesting X11 forwarding with authentication spoofing.
> debug2: channel 0: request x11-req confirm 1
> debug2: fd 3 setting TCP_NODELAY
> debug2: client_session2_setup: id 0
> debug2: channel 0: request pty-req confirm 1
> debug2: channel 0: request shell confirm 1
> debug2: channel_input_open_confirmation: channel 0: callback done
> debug2: channel 0: open confirm rwindow 0 rmax 32768
> debug2: channel_input_status_confirm: type 100 id 0
> X11 forwarding request failed on channel 0
> debug2: channel_input_status_confirm: type 99 id 0
> debug2: PTY allocation request accepted on channel 0
> debug2: channel 0: rcvd adjust 2097152
> debug2: channel_input_status_confirm: type 99 id 0
> debug2: shell request accepted on channel 0
> Last login: Wed Sep 11 17:01:50 2019 from 10.218.16.112
> 
> Did a lot of Googling and I already changed this in /etc/ssh/sshd_config
> X11Forwarding yes
> AddressFamily inet
> X11UseLocalhost no
> 
> Here's how I'm starting X-Windows
> startxwin &
> sleep 10
> export DISPLAY=:0.0
> xhost +
> xterm -sb -sl 5000 -geometry 168x17+380+0 -T "XTERM 1" &
> xterm -sb -sl 5000 -geometry 168x17+380+315 -T "XTERM 2" &
> xterm -sb -sl 5000 -geometry 168x16+380+600 -T "XTERM 3" &

The Cygwin/X shortcut starts X window server with:

	run --quote /bin/sh -l -c "cd; exec /usr/bin/startxwin"

You should not manually set DISPLAY - that is set by the X server - you should
start clients from ~/.Xclients, or manually from your X desktop applications menu.

DISPLAY=:0 or DISPLAY=:0.0 are only useful on implied localhost; you either have
to use X11 forwarding:
- on the command line ssh -X | -Y, or
- enable that in ~/.ssh/config on a Host connection:

	ForwardX11 yes
	ForwardX11Trusted yes

- note that untrusted client sessions are terminated after 20 minutes, or as per
policy, and data returned may be zeroed or access attempts result in an error;

if not using ssh forwarding, the DISPLAY value must be prefixed with a host name
resolvable on the remote host to your local host.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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