In EnSight 10.1.6(e) and later, there is a new functionality for operating in batch situations, where the X server is unavailable. This new capability is called "EGL" mode rendering.
EGL == "embedded" GL capability.
If the your machine has X-server issues (e.g. problems starting up the X-server) or issues with the DISPLAY environmental variable, and you have an nVidia graphics card with driver 358.16 or later, and are on Linux, you can start EnSight up with the -egl option. EnSight will use embedded OpenGL (which bypasses the X-server and makes direct calls to the graphics card, which must be present) as follows.
ensight101 -egl -batch -p file.py
This mode is not meant to provide additional capability/performance over hardware graphics card utilizsation, but does allow for a more performant solution when compared to software (-X) mode rendering where X-server utilization is not possible.
Graphics Driver 358.16 or later
EnSight 10.1.6(e) or later
Running in BATCH or Parallel Compositing Mode
For More information:
The HowTo Manual (search for EGL), has some information regarding this capability.