FAQ: Why are the X Window libraries needed for ArcGIS Server on Linux and Solaris?
Why are the X Window libraries needed for ArcGIS Server on Linux and Solaris?
ArcGIS Server uses the X Window libraries to create and render maps. The X Server itself does not need to be running. ArcGIS Server does not need an active display and uses Xvfb to render in-memory images in the background. ArcGIS Server starts and stops the Xvfb process, so the X Server does not need to be running to install ArcGIS Server.