Table of Contents
http://www.cse.cuhk.edu.hk/~wongyb/knoppix.shtml
/etc/X11/Xsession.d/45xsession checks which session manager /etc/alternatives/x-session-manager is pointed to. If it is gnome-session, DESKTOP is set to gnome. If it is startkde, DESKTOP is set to kde. (DESKTOP determines which desktop 45xsession will run.)
/etc/X11/Xsession.d/55gnome-session_gnomerc determines if /etc/alternatives/x-session-manager is /usr/bin/gnome-session. If it is true, it sources ~/.gnomerc.