automatic DISPLAY selection over ssh

[totaam]

Issue migrated from trac ticket # 612

component: server | priority: minor | resolution: fixed

2014-07-10 22:32:58: totaam created the issue

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Split from #172.

Remote start via ssh no longer needs a display to be specified. The difficulty is twofold:

• we don't know in advance if the other end supports displayfd, and if it doesn't we need to detect that this is what happened and tell the user
• the connection string we generate for the client uses the display... and we don't have it yet. There is currently no way of knowing what display was chosen either!

[totaam]

2015-06-02 16:06:15: antoine changed status from new to assigned

[totaam]

2015-06-02 16:06:15: antoine commented

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Now that we don't support older distros, we can assume displayfd is available.
(except maybe for some older Ubuntu versions? Meh, don't care about those)

[totaam]

2015-06-19 14:29:34: antoine changed status from assigned to new

[totaam]

2015-06-19 14:29:34: antoine changed owner from antoine to afarr

[totaam]

2015-06-19 14:29:34: antoine commented

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done in r9683 + r9684.

@afarr: this is just a FYI, but feel free to test or just close this ticket.

This should now work as long as the server has xpra installed:

xpra start --start-child=xterm ssh:hostname

Previous versions required the form:

xpra start --start-child=xterm ssh:hostname:DISPLAY

Which required choosing a display number in advance, without knowing if it would actually be free.

[totaam]

2015-06-22 18:22:43: maxmylyn commented

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Attempted to start a r9688 Trunk Fedora 21 Server:

• Got the following traceback when starting with xpra start --start-child=xterm ssh:localhost :

[max@schlafanzug ~]$ xpra start --start-child=xterm ssh:localhost
/usr/lib64/python2.7/site-packages/gtk-2.0/gtk/__init__.py:57: GtkWarning: could not open display
  warnings.warn(str(e), _gtk.Warning)
/usr/lib64/python2.7/site-packages/xpra/client/gtk2/__init__.py:7: GtkWarning: IA__gdk_screen_get_root_window: assertion 'GDK_IS_SCREEN (screen)' failed
  from xpra.x11.gtk_x11 import gdk_display_source
/usr/lib64/python2.7/site-packages/xpra/gtk_common/gtk_util.py:181: GtkWarning: IA__gdk_cursor_new_for_display: assertion 'GDK_IS_DISPLAY (display)' failed
  default_Cursor          = gdk.Cursor(gdk.X_CURSOR)
xpra main error:
Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/xpra/scripts/main.py", line 114, in main
    return run_mode(script_file, err, options, args, mode, defaults)
  File "/usr/lib64/python2.7/site-packages/xpra/scripts/main.py", line 898, in run_mode
    return run_remote_server(error_cb, options, args, mode, defaults)
  File "/usr/lib64/python2.7/site-packages/xpra/scripts/main.py", line 1357, in run_remote_server
    app = make_client(error_cb, opts)
  File "/usr/lib64/python2.7/site-packages/xpra/scripts/main.py", line 1294, in make_client
    toolkit_module = __import__(client_module, globals(), locals(), ['XpraClient'])
  File "/usr/lib64/python2.7/site-packages/xpra/client/gtk2/client.py", line 24, in <module>
    from xpra.gtk_common.gtk_util import gtk_main, color_parse
  File "/usr/lib64/python2.7/site-packages/xpra/gtk_common/gtk_util.py", line 181, in <module>
    default_Cursor          = gdk.Cursor(gdk.X_CURSOR)
RuntimeError: could not create GdkCursor object

In addition, the server crashes.

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For what it's worth: Also specifying a display number also outputs the same traceback. Not sure if it's legitimately broken or I have no idea how to start an ssh session. TCP is working, however (which is how I'm typing this comment..)

[totaam]

2015-06-22 18:26:46: antoine commented

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This means that you are attempting to start a session from a terminal which cannot access your display - this won't work, whether you specify the remote display or not: (and has little to do with this ticket!)

/usr/lib64/python2.7/site-packages/gtk-2.0/gtk/__init__.py:57: GtkWarning: could not open display

You need to run this command from a client, without starting a server in advance - it will be started for you.

[totaam]

2015-06-22 18:29:40: antoine commented

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Here's another way of triggering those same errors using an invalid display with the X11 client:

DISPLAY="" xpra attach

[totaam]

2015-06-22 18:32:19: maxmylyn commented

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Now that I've confirmed I'm a moron:

• Started from my Fedora 20 box (same version) against Fedora 21 (same version) with

xpra start --start-child=xterm ssh:uname@testvm

Everything works as expected.

[totaam]

2015-06-22 18:34:14: antoine changed status from new to closed

[totaam]

2015-06-22 18:34:14: antoine set resolution to fixed

[totaam]

2015-06-22 18:34:14: antoine commented

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@maxmylyn: LOL - thanks for testing!

FWIW: I do have plans to refactor the gtk initialization code as part of #640, which would allow us to bail out earlier when the DISPLAY is not set, giving a more friendly error message for those cases.

[totaam]

2015-06-26 17:28:36: antoine commented

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@maxmylyn: FYI, as of r9721, the error message has been improved:

• gtk2:

$ DISPLAY= python2 /usr/bin/xpra attach  --no-speaker
/usr/lib64/python2.7/site-packages/gtk-2.0/gtk/__init__.py:57: GtkWarning: could not open display
  warnings.warn(str(e), _gtk.Warning)
xpra initialization error: cannot access the display

• gtk3:

$ DISPLAY= python3 /usr/bin/xpra attach --no-speaker
Unable to init server: Could not connect: Connection refused
xpra initialization error: cannot access the display

I could also intercept the gtk2 warnings, but I think this is clear enough as it is.