a little madness

Our dog food Pulse server, which spends all day building itself, is a headless box. This presented no challenge for the Pulse 1.x series of releases, as our builds are all scripted and don’t require any GUI tools. With Pulse 2.0, however, things changed. As mentioned in my previous post, this new release has a whole new acceptance test suite based on Selenium. The problem is: Selenium runs in a real browser, and that browser requires a display.

Fortunately, the dog food server is also a Linux box. Thus there is no need to add in a full X setup with requisite hardware just to have Selenium running. This is thanks to the magic of Xvfb - the X virtual framebuffer. Basically, this is a stripped back X server that maintains a virtual display in memory. Hence no actual video hardware or driver is needed, and we can keep things simple.

Setting things up is straightforward. First, install Xvfb:

on Debian/Ubuntu; or

on Fedora/RedHat. Then, choose a display number that is unlikely to ever clash (even if you add a real display later) - something high like 99 should do. Run Xvfb on this display, with access control off¹:

Now you need to ensure that your display is set to 99 before running the Selenium server (which itself launches the browser). The easiest way to do this is to export DISPLAY=:99 into the environment for Selenium. First, make sure things are working from the command line like so:

Firefox should launch without error, and stay running (until you kill it with Control-C or similar). You won’t see anything of course! If things go well, then you need to modify the way you launch the Selenium server to ensure the DISPLAY is set. There are many ways to do this, in our Pulse setup we actually use a resource as it is a convenient way to modify the build environment.

An alternative which may suit some setups is to use the xvfb-run wrapper to launch your Selenium server. I opted against this as Pulse has resources to modify the environment and this way I do not need to change the actual build scripts at all. However if you are not using Pulse (shame! ) then you may want to look into it.

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¹ If you are worried about access on your network, then using -ac long-term is not a good idea. Once you have things working, I would suggest tightening things up by turning access control on.

This entry was posted on Wednesday, March 5th, 2008 at 1:22 am and is filed under Testing, Agile, Continuous Integration, Zutubi, Technology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.