TheIntern/Selenium functional tests work on OS X but fail on Linux

using the same version of Chrome (39) / chromedriver (2.13) and selenium (2.40.0) I am getting a completely positive outcome on Mac, but nasty errors on both CentOS and Ununtu. Here are my console outputs:

Mac (successful):

Running "exec:startselenium" (exec) task

Running "intern:runner" (intern) task
Listening on 0.0.0.0:9000
Starting tunnel...
Initialised chrome 39.0.2171.99 on MAC
No unit test coverage for chrome 39.0.2171.99 on MAC
>> chrome 39.0.2171.99 on MAC: 0/14 tests failed
>> TOTAL: tested 1 platforms, 0/14 tests failed

Running "exec:stopselenium" (exec) task

Ubuntu (here's the issue):

Running "exec:startselenium" (exec) task

Running "intern:runner" (intern) task
Listening on 0.0.0.0:9000
Starting tunnel...
TypeError: Cannot call method 'indexOf' of null
  at handleResponse  <node_modules/intern/node_modules/leadfoot/Server.js:148:26>
  at <node_modules/intern/node_modules/leadfoot/node_modules/dojo/Promise.js:235:37>
  at runCallbacks  <node_modules/intern/node_modules/leadfoot/node_modules/dojo/Promise.js:11:18>
  at <node_modules/intern/node_modules/leadfoot/node_modules/dojo/Promise.js:188:17>
  at Object.run [as _onImmediate]  <node_modules/intern/node_modules/leadfoot/node_modules/dojo/Promise.js:131:29>
  at processImmediate [as _immediateCallback]  <timers.js:354:15>

>> TOTAL: tested 0 platforms, 0/0 tests failed; fatal error occurred

Aborted due to warnings.

The only things I can think of are that it can't actually open the browser due to something X related (on Mac I note that Selenium opens a real Chrome window, this is on a Linux VM with presumably no X / libexif support) or that I am doing something wrong, which seems unlikely given that on Mac my tests work flawlessly.

Any suggestions appreciated.