This error suggests that ldd is not available in your image. You may need to use the "--libc-variant" command line option in this situation.
The "imgtrack --help" output gives some information about this. In particular:
$ ./imgtrack --help
[...]
OPTIONS:
[...]
--libc-variant NAME assume the given libc variant (glibc muslc) instead of checking
[...]
In order to determine the correct binary to extract imgtrack needs to
determine what libc implementation the image provides -- GNU libc (glibc) or
musl libc (muslc). The latter is commonly found in images based on Alpine
Linux. It determines what libc is available by running a container of the
source image with the image entrypoint changed to invoke the 'ldd' binary.
If imgtrack is unable to run the container, there is an error running ldd, or
the image does not provide ldd, imgtrack will abort with an error and report
that the image is not supported.
[...]
GNU's glibc is the standard C library and runtime framework for Linux, but
some alternative implementations have recently emerged. In particular, the
musl project has become popular due to its inclusion in Alpine Linux, its
small size, and its good fit for containers. imgtrack will inspect the source
image to determine which C library the image provides, running the ldd
command within a container based on the image. If the ldd command cannot be
found in the image or it reports an unknown implementation, imgtrack will
consider the image unsupported and will exit with an error. You can avoid the
test and provide imgtrack with the correct implementation to use with the
--libc-variant flag.
[...]
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