HostServices on Linux Ubuntu 14.04 trusty

[John Maton]

Good morning all,
I am using getHostServices().showDocument to display documents, such as
.pdf files.
This works find on all versions of Windows I have tested and on Apple Macs,
but I have a test user running Linux Ubuntu 14.04 trusty where it does not
work (does nothing).
Is there some library/resource which must be installed on Ubuntu to make
HostServices work?
thanks in advance for any comments,
John Maton