I have a group of computers running Snow Leopard and BOINC as a daemon per the instructions here:
http://boinc.berkeley.edu/wiki/Tools_for_Mac_OS_X#Running_BOINC_as_a_daemon_or_system_service

I noticed on the page that it says, "The BOINC Client may not successfully detect the presence of a GPU, so BOINC Project applications may not be able to use the GPU."

Is there a solution to this problem?

Currently, only one or two of computers has the GPU recognized although the CUDA drivers are installed on all of them.

When using BOINC as a daemon, you've sandboxed BOINC, meaning it runs in its own separate little bit of space. It can't look in other directories than the program and data directory for additional programs or drivers. And there's the problem when you want to do work on a GPU. For that BOINC needs to be able to see which videocard drivers you have installed as it checks in a certain file in the drivers whether or not the GPU is capable to work with.

So on the system that does work, you either haven't installed BOINC as a daemon, or you have copied some files around so (parts of) the driver files are in the BOINC programs directory, or you used symlinks to those drivers.

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Thank you for your response.

Are you sure it does not deal with the loading of X? Perhaps BOINC loading before X could cause the GPU not to be detected?

That would explain why it sometimes does not successfully detect a GPU.

I have read that on Linux versions X needs to be loaded before BOINC loads, in order to be able to detect the GPU. But that's also only when not sandboxed, thus not installed as a daemon, or else you needing to copy drivers around or symlinking to them.

See http://boinc.berkeley.edu/sandbox.php for a lot of (developer) information.

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I think I may have identified the problem. Currently the computers have Nvidia GeForce 9400s, and I have only installed BOINC and the Nvidia CUDA Driver for MAC 4.1.29 found here:
http://www.nvidia.com/object/mac-driver-archive.html

That driver does not seem to support the 9400 besides the mobile version according to the supported products tab.

Perhaps I need to install the CUDA Toolkit and/or the CUDA Development Driver which claims to support a wider platform of video cards?

I have read that on Linux versions X needs to be loaded before BOINC loads, in order to be able to detect the GPU.

Not really, only the kernel driver needs to be loaded. Indeed this part gets done when X server starts. One can, however, load this driver by hand.

A gotcha: this is true for NVIDIA. I have yet to discover a way of doing it with ATI/AMD drivers.

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Metod ...