Bug#776598: Cannot access secondary GPU - error: X did not start properly

[solitone]

I just want to add some further info.  I found the following messages 
that suggest bbswitch is actually doing something:

# grep bbswitch /var/log/messages |tail

Jan 29 15:03:36 aldous kernel: [   14.853734] bbswitch: version 0.8
Jan 29 15:03:36 aldous kernel: [   14.853740] bbswitch: Found integrated 
VGA device 0000:00:02.0: \_SB_.PCI0.GFX0
Jan 29 15:03:36 aldous kernel: [   14.853745] bbswitch: Found discrete 
VGA device 0000:0a:00.0: \_SB_.PCI0.RP05.PEGP
Jan 29 15:03:36 aldous kernel: [   14.853830] bbswitch: detected an 
Optimus _DSM function
Jan 29 15:03:36 aldous kernel: [   14.853894] bbswitch: Succesfully 
loaded. Discrete card 0000:0a:00.0 is on
Jan 29 15:03:36 aldous kernel: [   14.855965] bbswitch: disabling 
discrete graphics
Jan 29 15:24:43 aldous kernel: [ 1282.424483] bbswitch: enabling 
discrete graphics
Jan 29 15:26:39 aldous kernel: [ 1399.114165] bbswitch: disabling 
discrete graphics
Jan 29 15:26:44 aldous kernel: [ 1403.936576] bbswitch: enabling 
discrete graphics
Jan 29 15:28:41 aldous kernel: [ 1521.391293] bbswitch: disabling 
discrete graphics
Jan 29 15:29:45 aldous kernel: [ 1585.555012] bbswitch: enabling 
discrete graphics
Jan 29 15:31:02 aldous kernel: [ 1662.106591] bbswitch: disabling 
discrete graphics
Jan 29 15:31:18 aldous kernel: [ 1678.114687] bbswitch: enabling 
discrete graphics

I don't know what it is doing, though. Does those messages mean Optimus 
is working? But why optirun gives that error message, then? The optirun 
error message suggests I can't run an application on the discrete NVIDIA 
GPU. So what the discrete graphics card is enabled and disabled for?

Here's the information on my video cards:

$ lspci -vnn | egrep 'VGA|3D' -A 20

00:02.0 VGA compatible controller [0300]: Intel Corporation Haswell-ULT 
Integrated Graphics Controller [8086:0a16] (rev 09) (prog-if 00 [VGA 
controller])
     Subsystem: Hewlett-Packard Company Device [103c:2166]
     Flags: bus master, fast devsel, latency 0, IRQ 61
     Memory at b5000000 (64-bit, non-prefetchable) [size=4M]
     Memory at c0000000 (64-bit, prefetchable) [size=256M]
     I/O ports at 7000 [size=64]
     Expansion ROM at <unassigned> [disabled]
     Capabilities: <access denied>
     Kernel driver in use: i915

0a:00.0 3D controller [0302]: NVIDIA Corporation Device [10de:1292] (rev a1)
     Subsystem: Hewlett-Packard Company Device [103c:21da]
     Flags: bus master, fast devsel, latency 0, IRQ 16
     Memory at b3000000 (32-bit, non-prefetchable) [size=16M]
     Memory at a0000000 (64-bit, prefetchable) [size=256M]
     Memory at b0000000 (64-bit, prefetchable) [size=32M]
     I/O ports at 3000 [size=128]
     Expansion ROM at <ignored> [disabled]
     Capabilities: <access denied>
     Kernel driver in use: nvidia