monline

The newer Ubuntu LTSP setups use LDM for handling the client->server login phase. LDM is actually a very simple X application (written in C): it displays a textfield for username and password entry (also allows client reboot and poweroff), verifies the user entered credentials and initiates the X login to the selected server via an SSH tunnel.

LDM does not use syslog (afaik), it places its log into the client's /var/log/ldm.log file. In this file you'll see that upon every login there's some sort of X authentication warning:

Of course the creating new authority file part occurs only during the first login.

Sometimes it might happen that the .Xauthority file gets corrupted. At least it happened to me after an emergency X kill (via the Ctrl+Alt+Backspace method). I could not log in after that and my $HOME/.xsession-errors file did not reveal too much about the source of the error. It contained only messages from the various applications that tried to start and didn't find a valid display.

The fix for this was to delete all the $HOME/.Xauthority* files in my home directory. I was a bit surpirsed that there were more than one. I also had something like a .Xauthotiry-c and .Xauthority-l. I do not remember the exact filenames but the .Xauthority was followed by a dash and a single letter.