Since my first XFree86 (v3), I got used to the annoying /etc/X11/XF86Config file (now /etc/X11/xorg.conf), and I didn't notice that editing this file already belongs to the dinosaurs era. Quite silently, new features emerged and gave better ways to configure X, in particular screen resolutions. I'll sum up what I've found out today, in a bullet fasion:

• The modern xorg actually no longer needs the xorg.conf file. xorg simply knows what to do automagically :). xorg.conf file can be used though, for overriding the defaults. Still, only the overrided stuff can be written, and the file is still small and readable.
• xrandr --mode changes the resolution on the fly (not permanently though), from a list of given resolution. Thank you, HP, this time you did something good 🙂
  • xrandr --newmode , xrandr --addmode: add new resolutions to that list.
  • Still, X may have an upper resolution limit which it won't let you pass. It can be increased by adding a "Virtual" line to xorg.conf (Screen section -> Display subsection). i.e. "Virtual 1280 768" would set a maximum resolution of 1280x768.
• cvt is a cool tool for generating Mode Lines, simply amazing! Needed for xrandr --newmode command.
• Setting a new resolution permanently: this Ubuntu howto suggests to simply add the correct xrandr commands (i.e. xrandr --mode 1280x768) to the ~/.xprofile script. These commands would run right after each X login for that specific user. (There's probably a system-wide equivalent)
  • GNOME (and probably KDE as well) has its own resolution settings, which seems to override the xrandr change. So if using GNOME, configuration should be simply changed from within the GNOME tools..

Good stuff. It's always nice to see how things got better in few years. Still, in my opinion xorg has many problems (and slow development cycle), and might be the weakest link on Linux desktops. Goodbye!