Using Dahu with Xephyr (Full desktop in a nested window)

This page describes how to run a Dahu capture session, while running a session in a nested window using Xephyr. Typical use-cases include:

• You are running a Linux distribution X, and want to create a tutorial for a Linux distribution Y running on another machine.

• Your actual screen is very large, you want to run a capture on a smaller window. Then, Xephyr can fake a full-screen with any screen size.

For those who know Xnest, Xephyr is just a more modern replacement. My experience is that launching a Gnome session in Xnest crashes Xnest, and it just works in Xephyr.

Set up

Launch Xephyr on a 800x600 screen

Xephyr :2 -screen 800x600

Run a desktop session within the nested window

Run this command, typically from a terminal outside the nested window (the session will be opened in the nested window, though)

DISPLAY=:2 gnome-session

(replace gnome-session with your favorite desktop manager, e.g. startkde, ...)

Alternative: run the session from a remote machine

DISPLAY=:2 ssh -X $host gnome-session

Run Dahu, within the nested screen

DISPLAY=:2 dahu

(dahu being a script launching the Dahu editor)

If the session to capture runs on a remote machine, then you can still run the Dahu editor on your local machine, it will display within the remote session, but save its files on your local machine.

Capturing

Now, use the Dahu editor within the nested screen, as usual.

If the default F7 key does not work in capture mode (because your window-manager caught it and did not transmit to Xephyr), you can change the default capture key through the GUI (menu "Settings") or creating a configuration file ~/.config/dahu/config.json:

{
    "captureKey": "F9"
}

I'd advise a key that normally does nothing: Dahu notices the keypress, but does not intercept it. So, for example, if you enter a letter here, then pressing the key will still insert the letter.

Setting the presentation size

Set the presentation size to the same as your Xephyr screen size (menu Settings, or at the top of presentation.dahu JSon file).

Edition

Of course, since files were saved locally, you can later re-open the project from a Dahu instance outside Xephyr.