[winswitch] xpra initialization error: failed to identify the new server display!

[Max Kubierschky]

Hello everybody,

I try to set up a remote pair programming environment with xpra.
Development takes place on a cloud server. Both programmers are
connected via xpra. The idea is, that in this way we don't need much
bandwidth on upload (only the keystrokes and mouseclicks). The bigger
data volume (screen content) is only on download and thus less problematic.

As an example, I want to run a terminal window on the server and share
it on both clients. All involved machines run debian strech (yet).

On the server I start a session with

$ xpra start :30 --sharing=yes

then I start mate-terminal on that server.
On the first client, I attach with

$ xpra attach ssh:max at xxxxx.org:30 --desktop-scaling=off --quality=100
--sharing=yes

This works as expected, I see and can use the terminal.
On the second client, I try to share with

$ xpra shadow ssh:max at xxxxx.org:30

and get no connection. Error messages are below.
Whats wrong? Any hints?

---------------------------------------------
output from: xpra shadow ssh:max at xxxxx.org:30
---------------------------------------------

2017-12-28 19:07:28,614 Xpra gtk2 client version 0.17.6-r14322
2017-12-28 19:07:28,615  running on Linux debian 9.3
2017-12-28 19:07:28,616 Warning: failed to import opencv:
2017-12-28 19:07:28,616  No module named cv2
2017-12-28 19:07:28,616  webcam forwarding is disabled
2017-12-28 19:07:29,128 GStreamer version 1.10 for Python 2.7
2017-12-28 19:07:31,004 PyOpenGL warning: missing accelerate module
2017-12-28 19:07:31,689  detected keyboard: rules=evdev, model=pc105,
layout=de
2017-12-28 19:07:31,692  desktop size is 1920x1080 with 1 screen:
2017-12-28 19:07:31,699   :0.0 (508x286 mm - DPI: 96x95) workarea:
1888x1080 at 32x0
2017-12-28 19:07:31,711     monitor 1 (531x298 mm - DPI: 91x92)
xpra initialization error:
 failed to identify the new server display!
2017-12-28 18:07:48,639 server failure: disconnected before the session
could be established
2017-12-28 18:07:48,639 server requested disconnect: server error
(failed to start a new session)
Warning: cannot use the system proxy for 'shadow' subcommand,
 FAILURE
Entering daemon mode; any further errors will be reported to:
  /home/max/.xpra/:30.log
xpra initialization error:
 failed to identify the new server display!
2017-12-28 18:08:04,139 server failure: disconnected before the session
could be established
2017-12-28 18:08:04,139 server requested disconnect: server error
(failed to start a new session)
Warning: cannot use the system proxy for 'shadow' subcommand,
 FAILURE
Entering daemon mode; any further errors will be reported to:
  /home/max/.xpra/:30.log
xpra initialization error:
 failed to identify the new server display!
2017-12-28 19:08:19,979 The SSH process has terminated with exit code 0
2017-12-28 19:08:19,980  the command line used was:
2017-12-28 19:08:19,980  ssh -x -l max -T xxxxx.org xpra
initenv;~/.xpra/run-xpra _shadow_start :30 ||
$XDG_RUNTIME_DIR/xpra/run-xpra _shadow_start :30 || xpra _shadow_start :30