[LightDM] can't connect to display before login

[Alfonso Fiore]

Hi Robert, Guido,

thank you.

Indeed the log file was a smart idea ;-)

I found quite a telling line there:
[+0.01s] WARNING: Can't start VNC server, Xvn is not in the path

in fact I used x11vnc and I didn't have any Xvnc installed.

So you were all correct, but I still didn't manage :(

I tried installing tightvncserver but I got access to a new session, but
instead I'm looking to enable desktop sharing. I tried for a good hour to
find how to share the main desktop with tightvnc and then I gave up.

So I tried also installing vnc4server which has some problem regarding
authentication. I get an error in my client: "no password configured for vnc
auth" but also I wasn't capable to debug this either. It has probably to do
with pam, but I didn't manage to debug the issue:

lightdm.log:[+0.90s] DEBUG: pam_start("lightdm-autologin", "lightdm") ->
(0x8bef588, 0)
lightdm.log:[+0.90s] DEBUG: pam_authenticate(0x8bef588, 0) -> 0 (Success)
lightdm.log:[+0.90s] DEBUG: pam_acct_mgmt(0x8bef588, 0) -> 0 (Success)
lightdm.log:[+0.91s] DEBUG: pam_set_item(0x8bef588, 3, ":0") -> 0 (Success)
lightdm.log:[+0.92s] DEBUG: pam_open_session(0x8bef588, 0) -> 0 (Success)
lightdm.log:[+0.95s] DEBUG: pam_setcred(0x8bef588, PAM_ESTABLISH_CRED) -> 0
(Success)
lightdm.log:[+1.50s] DEBUG: pam_start("lightdm", "alfonso") -> (0x8c06588,
0)

I see Xvnc is started as /usr/bin/Xvnc :6 -auth /var/run/lightdm/root/:6
-inetd -nolisten tcp but I don't see the -rfbauth to point to the password
file. Is there a chance to manually add such option?

If I run for example "Xvnc :0 -rfbauth /etc/x11vnc.pass" directly at prompt
I can authenticate but still I don't get to share the main desktop.

I also tried to create a symbolic link from x11vnc to Xvnc since I know
x11vnc works fine, but since x11vnc doesn't have options for running with
inetd, it didn't work.

Incidentally, at least in Ubuntu 11.10, /var/log/lightdm has
permissions drwxr-xr-x but lightdm tries to create log files there with
user lightdm and fails. So I had to change permissions to 777.

e.g.
[+246.83s] WARNING: Failed to open log file
/var/log/lightdm/xvnc-6-greeter.log: Permission denied

Actually, kind of bad news...