Ubuntu - GPU - LLVMpipe - Force use of LLVMpipe

WARNING: LLVMpipe is Software driven, and not Hardware driver.

So it may be very slow.

LIBGL_ALWAYS_SOFTWARE=1 glxgears -info

returns:

GL_RENDERER   = llvmpipe (LLVM 15.0.7, 256 bits)
...

NOTE: This shows the driver is llvmpipe.

LIBGL_ALWAYS_SOFTWARE=1 __GLX_VENDOR_LIBRARY_NAME=mesa VK_ICD_FILENAMES=/usr/share/vulkan/icd.d/lvp_icd.i686.json:/usr/share/vulkan/icd.d/lvp_icd.x86_64.json vulkaninfo | grep driver

returns:

	driverVersion     = 1 (0x0001)
	driverID           = DRIVER_ID_MESA_LLVMPIPE
	driverName         = llvmpipe
	driverInfo         = Mesa 23.1.3 - kisak-mesa PPA (LLVM 15.0.7)
	driverUUID      = 6c6c766d-7069-7065-5555-494400000000
	driverUUID                        = 6c6c766d-7069-7065-5555-494400000000
	driverID                                             = DRIVER_ID_MESA_LLVMPIPE
	driverName                                           = llvmpipe
	driverInfo                                           = Mesa 23.1.3 - kisak-mesa PPA (LLVM 15.0.7)
	VK_KHR_driver_properties                     : extension revision 1

NOTE: This shows the driver is llvmpipe.