I modified /etc/gdm/Xsession to run id(1) with various parameters, here's the output: id -u: 1005 id -g: 0 id -G: 100 0 4 20 24 25 29 30 44 46 104 105 106 id -r -u: 1005 id -r -g: 100 id -r -G: 100 0 4 20 24 25 29 30 44 46 104 105 106 -- Can't register Xsession on dapper beta https://launchpad.net/bugs/42397