optirun succeeds or fails?

# THIS IS OK

ubuntu@ubuntu:~$ optirun --debug-log= glxgears
[VGL] NOTICE: Replacing dlopen("/lib/x86_64-linux-gnu/libdl.so.2") with dlopen("libdlfaker.so")
[VGL] Shared memory segment ID for vglconfig: 18120706
[VGL] VirtualGL v2.2.90 64-bit (Build 20110815)
[VGL] Opening local display :8
[VGL] Using 1 / 4 CPU's for compression
[VGL] Using pixel buffer objects for readback (GL format = 0x80e0)
[VGL] Client version: 2.1


# THIS IS FAILURE

ubuntu@ubuntu:~$ optirun --debug-log= glxgears
The Bumblebee X server was not available, please check the
Bumblebee logfile at /var/log/bumblebee.log
==================================================
Running synchronized to the vertical refresh.  The framerate should be
approximately the same as the monitor refresh rate.