Re: X login problem

Brian May writes:

Sounds like the xsession is dying. In typical fashion, errors will most likely get logged to $HOME/.xsession-errors, but not shown to the user.

I not entirely sure how lightdm works, but try looking in $HOME/.xsession-errors after a dud login, and see if that helps.

FYI, this is done by /etc/X11/Xsession on Debian, or /etc/X11/xinit/Xsession on CentOS last time I looked. AFAIK Debian patches all DMs to use that as "Default Session"; if you choose a different DE from the DM chooser, all bets are off.