Syntax for new --sbom option

[pulberg]

I am using v2.0.0-rc.0 that includes the new --sbom option for building. I have added --sbom=true with/without a path but no spdx or json files are produced. Is there any instructions, guide or syntax docs to see how this should be used?

Thanks

[AkihiroSuda]

nerdctl build --sbom=true --output=/tmp/foo .
cat /tmp/foo/sbom.spdx.json

[pulberg]

nerdctl build --sbom=true --output=/Users/pulberg/sbom .

=> CACHED [linux/amd64] generating sbom using docker.io/docker/buildkit-syft-scanner:stable-1                                                                                                                                    0.0s
 => ERROR exporting to client directory                                                                                                                                                                                           0.1s
 => => copying files 25.49kB                                                                                                                                                                                                      0.0s
------
 > exporting to client directory:
------
error: failed to solve: error from receiver: error setting metadata for /Users/pulberg/sbom/bin: lchown /Users/pulberg/sbom/bin: permission denied
Error: exit status 1

Why is it trying to create a bin directory?