darktable-cli errors

I do focus stacking with a Cognisys rail, ZereneStacker and Darktable.

I shoot a stack of raw images in a light tent. Then use darktable-cli in a bash loop to make a parallel stack of *.tif that I then feed into ZereneStacker for the actual stacking.

In the past I have installed darktable (on Mint Linux) with sudo apt-get intall darktable.

Recently fought through the process of updating various development libraries in order to compile and work with the latest darktable codes from github (so I can work with the new detail mask).

The following bash loop now produces a new error:

mkdir tifs 2>/dev/null
shopt -s nocaseglob
for file in *$suffix
do
echo $file
/opt/darktable/bin/darktable-cli $file tifs/$file.tif
done

…error produced for each loop iteration:
capture000003.nef (from the echo $file line)
DRM_IOCTL_I915_GEM_APERTURE failed: Invalid argument
Assuming 131072kB available aperture size.
May lead to reduced performance or incorrect rendering.
get chip id failed: -1 [2]
param: 4, val: 0
DRM_IOCTL_I915_GEM_APERTURE failed: Invalid argument
Assuming 131072kB available aperture size.
May lead to reduced performance or incorrect rendering.
get chip id failed: -1 [2]
param: 4, val: 0
beignet-opencl-icd: no supported GPU found, this is probably the wrong opencl-icd package for this hardware
(If you have multiple ICDs installed and OpenCL works, you can ignore this message)
DRM_IOCTL_I915_GEM_APERTURE failed: Invalid argument
Assuming 131072kB available aperture size.
May lead to reduced performance or incorrect rendering.
get chip id failed: -1 [2]
param: 4, val: 0
DRM_IOCTL_I915_GEM_APERTURE failed: Invalid argument
Assuming 131072kB available aperture size.
May lead to reduced performance or incorrect rendering.
get chip id failed: -1 [2]

Despite these error messages corresponding *.tif files are indeed created, inside a “tifs” subdirectory. Those *.tif files look fine in an image viewer (geeqie).

The problem for me is that those same *.tif files seem to (now suddenly) cause ZereneStacker to fail when it tries to do the stacking.

I don’t know how to debug this. Ideas welcome.
Because I have updated development libraries–in order to compile codes from github–the only way I could revert to an earlier state would be to reinstall the OS. Which I can do. I’m just not sure what to try first.

Are you using openCL? Can you try and disable it?

Both /usr/bin/darktable and /opt/darktable/bin/darktable tell me open-cl is not available–probably because I have an ancient, under-powered graphics card I need to upgrade.