Creating Slide Show Backgrounds in XFCE
Continuing in this series of slide show backgrounds, in this article I will explain the process of creating a set of desktop backgrounds that will transition like a slide-show in XFCE. Note that I am using XFCE version 4.6.0 in this tutorial. Other versions may be able to use this tip, but the screen shots may look different. See corresponding howtos for GNOME, and KDE3 also.
Start by right clicking on the desktop and choosing "Desktop Settings".
Under the "Background" tab, choose "Image List". Click on the green plus sign near the left side of the center of the window to add backgrounds to this list.
Hold down the shift key when clicking to select long lists of images, or hold the control key to select individual image files from the list. Click "Add" in the lower right hand corner to finish selecting the images.
Select how you would like the background images displayed (Auto, Centered, Tiled, Stretched, Scaled, Zoomed) and then close the window.
Now, at this point, you've created a list of images that XFCE will pick from at random each time you log into XFCE. The only time these images will change is upon login. If you're OK with that, you're done. If you would like the ability to switch these backgrounds either on demand or at a fixed interval, read on. Warning: From this point on, we are in "hack" territory, so things may not always run smoothly.
Theoretically, the xfdesktop --reload command should update the background, but that didn't work at all for me. However, we can trick the XFCE desktop into thinking that it has been restarted by restarting the program that handles the desktop. XFCE calls this program xfdesktop. From the command line, you can type killall -HUP xfdesktop to kill the xfdesktop process and restart it, which refreshes the icons and chooses a new desktop image at random from your list. You can easily create an icon to run this command for you, either on your desktop or in the XFCE panel.
Creating a desktop icon: To create a desktop icon, right click on the desktop and choose "Create Launcher"
in the necessary information in the window, choose an icon, and click "Create" to make the icon. Double clicking this icon will restart xfdesktop and switch the background for you.
Right click the XFCE panel, and select "Add New Items".
From the "Add New Items" window, click "Add".
Fill in the appropriate fields in the launcher window, entering the command killall -HUP xfdesktop, and choosing an icon that you will recognize. Select "OK".
Admire your icon. Clicking it will restart your desktop and refresh the background.
You can now change backgrounds on demand, but they do not change for you unless you log in and out. We will use crontab to help us in this effort.
At the command line, type crontab -e to open and begin editing your crontab. If you have never edited your crontab before, it will prompt you to choose an editor for this task. I chose vim, because that's how I roll. Use whatever editor your like the most.
Once your crontab is open, you should see a text file that says # m h dom mon dow command on the first line. For those of you who are not familiar with crontab, please watch the excellent Crontab Tech Tip Video that Shawn Powers created about how to interact with crontab and the meanings of the crontab fields. Add to the next line this text:
At the beginning of this line, '*/15" means "every 15 minutes". You can easily change the numbers in your crontab to any interval that you desire. For example, "*/5" would be every five minutes, and "*/2" woulld be every other minute.
Save and close your editor, and crontab will automatically perform your commands.
Now, I've been having some intermittent issues with this hack. Sometimes, it appears that killall -HUP xfdesktop completely kills xfdesktop instead of just restarting it. If your icons have disappeared, and the desktop background no longer changes, then xfdesktop has been killed. You can verify its death by either looking for xfdesktop in the process list by typing ps aux | grep xfd[e]sktop, or you can simply type killall -HUP xfdesktop, and if you get "xfdesktop: no process killed", then xfdesktop wasn't running at the time you typed the program.
To revive xfdesktop, simply type xfdesktop at the command line, or create another icon/shortcut to this command to revive xfdesktop if it dies.
The list of wallpapers that XFCE uses to change the backgrounds is typically located at ~/.config/xfce4/desktop/backdrop.list. The file is simple a text file that contains the absolute path of each image, one file per line. Creating scripts or programs that monitor or add to this list would be rather straightforward, since you could append additional absolute paths via scripts or the command line.
Theoretically, desktop backgrounds can also be modified at the command line using the xfconf and the xfconf-query command. Documentation for xfconf is here.
Happy hacking, people!