Hi,
On new Ubuntu computers, I've installed Gem via Deken (find externals), but it was not enough. I need also to install it with apt-get install gem. Some dependencies seems required, may be opengl libs ?
Computers (cat /proc/version) : Linux version 4.4.0-81-generic (buildd@lgw01-02) (gcc version 5.4.0 20160609 (Ubuntu 5.4.0-6ubuntu1~16.04.4) ) #104-Ubuntu SMP Wed Jun 14 08:17:06 UTC 2017