If you don't have DISPLAY set when running hob then you get a traceback which is rather difficult to understand:

Traceback (most recent call last):
  File "/home/paul/poky/poky/bitbake/bin//bitbake", line 259, in <module>
    ret = main()
  File "/home/paul/poky/poky/bitbake/bin//bitbake", line 248, in main
    return server.launchUI(ui_main, server_connection.connection, server_connection.events)
  File "/home/paul/poky/poky/bitbake/lib/bb/server/process.py", line 269, in launchUI
    return bb.cooker.server_main(self.cooker, uifunc, *args)
  File "/home/paul/poky/poky/bitbake/lib/bb/cooker.py", line 1407, in server_main
    ret = func(*args)
  File "/home/paul/poky/poky/bitbake/lib/bb/ui/hob.py", line 71, in main
    builder = Builder(hobHandler, recipe_model, package_model)
AttributeError: 'NoneType' object has no attribute 'get_width'