Help hacking a thinclient boot process - custom background application

[pomtom44]

Hi all

I have a small project im doing on my off time at work, where we have aprox 50 HP thin clients
(Yes i have asked HP about this, but they dont see it as a issue so wont create a solution for me for it)

What im after is a way to load a background image from a webshare on boot, so we can generate a new background daily and apply it to all the units, without having to push config changes to all the units
(Doesn't work if the unit is offline, etc)

 

So far I have found the command which loads the background image, and if i run it from a terminal on the unit, it works fine

wget -P /tmp/ http://int-web-server/background.jpg

hptc-zero-desktop --root --image=/tmp/background.jpg

 - Fetch image and save to tmp
 - Load image into background

 

However when I put it as a dhcp hook call, (so i know theres internet before trying to wget a file)
I can see the file download, and the set background command runs, but I get a error

XOpenDisplay returned NULL!

 

I have a feeling its because the dhcp hook isnt running as the  "user" so there's no background to attach the image to?
but i have no idea how to get it to run as the user?