When I did my first training with a Linux-powered IBM ThinkPad, I naively entered the training room, connected the beamer, and expected things to work. For the rest of the day, a quarter of my desktop was projected on the screen, while the rest was only visible on the laptop's LCD. Not too bad, because I could do a few things in the private area of the desktop. As long as I did not move the mouse.

The next day, I figured out the right order in which to switch on and connect the beamer and the laptop, and was able to use the full desktop, albeit with a scaled-down resolution. And I no longer had a private workspace.

Today, I found the solution on Alexander Wagner's ThinkPad page: A dual head setup for X, and VNC for controlling what gets sent to the beamer. The dual head setup (configuration file for X.org 6.7 and ThinkPad A31p) gives you two separate displays, one for external displays, and one for the LCD. Each with its own resolution, and set up so the mouse can move from one to the other.

Next, we need to install a rearview mirror on the laptop, to check the beamer display without turning our back on the audience. VNC gives us exactly that, with its ability to put a complete X display in a window which is then displayed on another X display, and also allowing us to have multiple windows showing the same VNC display. The present script (tested with Fedora Core 2 and the above X.org configuration) starts a VNC X server, displays it in fullscreen mode on the beamer display, and also opens it in a window on the LCD.

Update 27 Nov 2004: Preparing for another training next week, I noticed that there is a little problem with the dual-head setup, which may be caused by the upgrade to Fedora Core 3. When I boot with an external display connected, Fedora Core 3 hangs while starting the HAL daemon. And when I connect the external display after X has started, the external display gets the same screen resolution as the internal LCD. Solution:

1. Keep the external display disconnected while booting.
2. After the graphical login appears, change to a text console and log in as root.
3. Run "init 3", wait a bit, run "init 5".
4. Use the graphical login with your user account, and everything should be fine.