x11vnc fails to find X Login Greeter when lightdm is used

The vnc server x11vnc has a very useful mode which allows a user with admin sudo privileges (or root) to run x11vnc and to automatically discover an X Login Greeter. The objective is to be able to login on :0 even when nobody has a login session.

An example commandline for x11vnc to discover the X Login Greeter:

    sudo x11vnc -norc -nopw -find -localhost -env FD_XDM=1

Once x11vnc outputs e.g. PORT=5900 on the commandline, one can use any VNC viewer to connect to it from the same machine, e.g.:

    xtightvncviewer localhost:0

This works perfectly well with kdm and gdm on Ubuntu 12.04, but fails with lightdm with the output pasted below. I tried installing x11vnc and x11vnc-data from Quantal and Raring, but both newer versions of x11vnc fail the same way.

=======================================================
# sudo x11vnc -norc -nopw -find -localhost -env FD_XDM=1
21/06/2013 16:21:57 x11vnc version: 0.9.12 lastmod: 2010-09-09 pid: 32699
21/06/2013 16:21:57
21/06/2013 16:21:57 wait_for_client: WAIT:cmd=FINDDISPLAY
21/06/2013 16:21:57
21/06/2013 16:21:57 initialize_screen: fb_depth/fb_bpp/fb_Bpl 24/32/2560
21/06/2013 16:21:57
21/06/2013 16:21:57 Autoprobing TCP port
21/06/2013 16:21:57 Autoprobing selected port 5900
21/06/2013 16:21:57 Listening also on IPv6 port 5900 (socket 5)
21/06/2013 16:21:57

The VNC desktop is: tlab-t3400:0
PORT=5900
21/06/2013 16:21:59 Got connection from client 127.0.0.1
21/06/2013 16:21:59 other clients:
21/06/2013 16:21:59 check_access: client 127.0.0.1 matches host 127.0.0.1
21/06/2013 16:21:59 incr accepted_client=1 for 127.0.0.1:37831 sock=6
21/06/2013 16:21:59 wait_for_client: got client
21/06/2013 16:21:59 Client Protocol Version 3.8
21/06/2013 16:21:59 Protocol version sent 3.8, using 3.8
21/06/2013 16:21:59 client progressed=1 in 0/1 0.000286 s
21/06/2013 16:21:59 client_set_net: 127.0.0.1 0.0004
21/06/2013 16:21:59 wait_for_client: running: env X11VNC_SKIP_DISPLAY='' /bin/sh /tmp/x11vnc-find_display.cDPngD
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
/tmp/x11vnc-find_display.cDPngD: 305: [: -a: unexpected operator
21/06/2013 16:21:59 wait_for_client: find display cmd failed.
21/06/2013 16:21:59 wait_for_client: bad reply '
'

=======================================================
And an example of it working properly with kdm:

# /etc/init.d/lightdm stop
# /etc/init.d/kdm start

=======================================================
# PORT= sudo x11vnc -norc -nopw -find -localhost -env FD_XDM=1
21/06/2013 16:36:33 x11vnc version: 0.9.12 lastmod: 2010-09-09 pid: 24981
21/06/2013 16:36:33
21/06/2013 16:36:33 wait_for_client: WAIT:cmd=FINDDISPLAY
21/06/2013 16:36:33
21/06/2013 16:36:33 initialize_screen: fb_depth/fb_bpp/fb_Bpl 24/32/2560
21/06/2013 16:36:33
21/06/2013 16:36:33 Autoprobing TCP port
21/06/2013 16:36:33 Autoprobing selected port 5900
21/06/2013 16:36:33 Listening also on IPv6 port 5900 (socket 5)
21/06/2013 16:36:33

The VNC desktop is: tlab-t3400:0
PORT=5900
21/06/2013 16:36:35 Got connection from client 127.0.0.1
21/06/2013 16:36:35 other clients:
21/06/2013 16:36:35 check_access: client 127.0.0.1 matches host 127.0.0.1
21/06/2013 16:36:35 incr accepted_client=1 for 127.0.0.1:37903 sock=6
21/06/2013 16:36:35 wait_for_client: got client
21/06/2013 16:36:35 Client Protocol Version 3.8
21/06/2013 16:36:35 Protocol version sent 3.8, using 3.8
21/06/2013 16:36:35 client progressed=1 in 0/1 0.000218 s
21/06/2013 16:36:35 client_set_net: 127.0.0.1 0.0004
21/06/2013 16:36:35 wait_for_client: running: env X11VNC_SKIP_DISPLAY='' /bin/sh /tmp/x11vnc-find_display.zhhWAi
21/06/2013 16:36:36 running: chvt 8 >/dev/null 2>/dev/null &
21/06/2013 16:36:38 Using X display :0
21/06/2013 16:36:38 rootwin: 0x290 reswin: 0x600001 dpy: 0xcbdd50
21/06/2013 16:36:38
21/06/2013 16:36:38 ------------------ USEFUL INFORMATION ------------------
21/06/2013 16:36:38 X DAMAGE available on display, using it for polling hints.
21/06/2013 16:36:38 To disable this behavior use: '-noxdamage'
21/06/2013 16:36:38
21/06/2013 16:36:38 Most compositing window managers like 'compiz' or 'beryl'
21/06/2013 16:36:38 cause X DAMAGE to fail, and so you may not see any screen
21/06/2013 16:36:38 updates via VNC. Either disable 'compiz' (recommended) or
21/06/2013 16:36:38 supply the x11vnc '-noxdamage' command line option.
21/06/2013 16:36:38
21/06/2013 16:36:38 Wireframing: -wireframe mode is in effect for window moves.
21/06/2013 16:36:38 If this yields undesired behavior (poor response, painting
21/06/2013 16:36:38 errors, etc) it may be disabled:
21/06/2013 16:36:38 - use '-nowf' to disable wireframing completely.
21/06/2013 16:36:38 - use '-nowcr' to disable the Copy Rectangle after the
21/06/2013 16:36:38 moved window is released in the new position.
21/06/2013 16:36:38 Also see the -help entry for tuning parameters.
21/06/2013 16:36:38 You can press 3 Alt_L's (Left "Alt" key) in a row to
21/06/2013 16:36:38 repaint the screen, also see the -fixscreen option for
21/06/2013 16:36:38 periodic repaints.
21/06/2013 16:36:38
21/06/2013 16:36:38 XFIXES available on display, resetting cursor mode
21/06/2013 16:36:38 to: '-cursor most'.
21/06/2013 16:36:38 to disable this behavior use: '-cursor arrow'
21/06/2013 16:36:38 or '-noxfixes'.
21/06/2013 16:36:38 using XFIXES for cursor drawing.
21/06/2013 16:36:38 GrabServer control via XTEST.
21/06/2013 16:36:38
21/06/2013 16:36:38 Scroll Detection: -scrollcopyrect mode is in effect to
21/06/2013 16:36:38 use RECORD extension to try to detect scrolling windows
21/06/2013 16:36:38 (induced by either user keystroke or mouse input).
21/06/2013 16:36:38 If this yields undesired behavior (poor response, painting
21/06/2013 16:36:38 errors, etc) it may be disabled via: '-noscr'
21/06/2013 16:36:38 Also see the -help entry for tuning parameters.
21/06/2013 16:36:38 You can press 3 Alt_L's (Left "Alt" key) in a row to
21/06/2013 16:36:38 repaint the screen, also see the -fixscreen option for
21/06/2013 16:36:38 periodic repaints.
21/06/2013 16:36:38
21/06/2013 16:36:38 XKEYBOARD: number of keysyms per keycode 7 is greater
21/06/2013 16:36:38 than 4 and 51 keysyms are mapped above 4.
21/06/2013 16:36:38 Automatically switching to -xkb mode.
21/06/2013 16:36:38 If this makes the key mapping worse you can
21/06/2013 16:36:38 disable it with the "-noxkb" option.
21/06/2013 16:36:38 Also, remember "-remap DEAD" for accenting characters.
21/06/2013 16:36:38
21/06/2013 16:36:38 X FBPM extension not supported.
21/06/2013 16:36:38 X display is capable of DPMS.
21/06/2013 16:36:38 --------------------------------------------------------
21/06/2013 16:36:38
21/06/2013 16:36:38 Default visual ID: 0x21
21/06/2013 16:36:38 Read initial data from X display into framebuffer.
21/06/2013 16:36:38 initialize_screen: fb_depth/fb_bpp/fb_Bpl 24/32/6720
21/06/2013 16:36:38 rfbNewFramebuffer(0xcaded0, 0x0, 1680, 1050, 8, 1, 4)
21/06/2013 16:36:38 Pixel format for client 127.0.0.1:
21/06/2013 16:36:38 32 bpp, depth 24, little endian
21/06/2013 16:36:38 true colour: max r 255 g 255 b 255, shift r 16 g 8 b 0
21/06/2013 16:36:38
21/06/2013 16:36:38 X display :0 is 32bpp depth=24 true color
21/06/2013 16:36:38
21/06/2013 16:36:38 calling setTranslateFunction()...
21/06/2013 16:36:38 Pixel format for client 127.0.0.1:
21/06/2013 16:36:38 32 bpp, depth 24, little endian
21/06/2013 16:36:38 true colour: max r 255 g 255 b 255, shift r 16 g 8 b 0
21/06/2013 16:36:38 no translation needed
21/06/2013 16:36:38 done.
21/06/2013 16:36:38 TS_REDIR is empty, restarting...
21/06/2013 16:36:38
21/06/2013 16:36:38 Xinerama is present and active (e.g. multi-head).
21/06/2013 16:36:38 Xinerama: number of sub-screens: 1
21/06/2013 16:36:38 Xinerama: no blackouts needed (only one sub-screen)
21/06/2013 16:36:38
21/06/2013 16:36:38 fb read rate: 421 MB/sec
21/06/2013 16:36:38 fast read: reset wait ms to: 10
21/06/2013 16:36:38 fast read: reset defer ms to: 10
21/06/2013 16:36:38 The X server says there are 10 mouse buttons.
21/06/2013 16:36:38 screen setup finished.
21/06/2013 16:36:38

The VNC desktop is: localhost:0
PORT=5900

******************************************************************************
Have you tried the x11vnc '-ncache' VNC client-side pixel caching feature yet?

The scheme stores pixel data offscreen on the VNC viewer side for faster
retrieval. It should work with any VNC viewer. Try it by running:

    x11vnc -ncache 10 ...

One can also add -ncache_cr for smooth 'copyrect' window motion.
More info: http://www.karlrunge.com/x11vnc/faq.html#faq-client-caching

21/06/2013 16:36:38 rfbProcessClientSecurityType: executing handler for type 1
21/06/2013 16:36:38 rfbProcessClientSecurityType: returning securityResult for client rfb version >= 3.8
21/06/2013 16:36:38 Battling with something for -norepeat!! (1 resets left)
21/06/2013 16:36:38 Disabled X server key autorepeat.
21/06/2013 16:36:38 to force back on run: 'xset r on' (2 times)
21/06/2013 16:36:38 created xdamage object: 0x600039
21/06/2013 16:36:38 Pixel format for client 127.0.0.1:
21/06/2013 16:36:38 32 bpp, depth 24, little endian
21/06/2013 16:36:38 true colour: max r 255 g 255 b 255, shift r 16 g 8 b 0
21/06/2013 16:36:38 no translation needed
21/06/2013 16:36:38 Using compression level 1 for client 127.0.0.1
21/06/2013 16:36:38 Using image quality level 6 for client 127.0.0.1
21/06/2013 16:36:38 Enabling X-style cursor updates for client 127.0.0.1
21/06/2013 16:36:38 Enabling full-color cursor updates for client 127.0.0.1
21/06/2013 16:36:38 Enabling cursor position updates for client 127.0.0.1
21/06/2013 16:36:38 Enabling LastRect protocol extension for client 127.0.0.1
21/06/2013 16:36:38 Using raw encoding for client 127.0.0.1
21/06/2013 16:36:38 copy_tiles: allocating first_line at size 54
21/06/2013 16:36:38 client 1 network rate 7818.6 KB/sec (7818.6 eff KB/sec)
21/06/2013 16:36:38 client 1 latency: 0.5 ms
21/06/2013 16:36:38 dt1: 0.0098, dt2: 0.0503 dt3: 0.0005 bytes: 469576
21/06/2013 16:36:38 link_rate: LR_LAN - 1 ms, 7818 KB/s
=======================================================

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: x11vnc 0.9.12-1build1
ProcVersionSignature: Ubuntu 3.2.0-44.69-generic 3.2.44
Uname: Linux 3.2.0-44-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu17.3
Architecture: amd64
Date: Fri Jun 21 16:22:34 2013
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 SHELL=/local/bin/bash
SourcePackage: x11vnc
UpgradeStatus: No upgrade log present (probably fresh install)