Debian has a nice way to do this without worrying about symlinks. It's update-rc.dThis is a very versatile utility to administer what gets stopped and started in
the various run levels. The man page for this command will get you started. Scott Denlinger Quoting Mitch Wiedemann [and others]
As a general rule, if you don't want X to start automatically on boot-up, you can either disable, or uninstall, the relevant login manager (xdm, kdm, gdm, or wdm).Or, instead of removing the display manager (*dm), simply remove the symlink in /etc/rc2.d/S99*dm. That way, it'll still be there if you want it, but it won't start at boot time.