The verity signature partition content is a bare JSON object. Repart pads it with zeros to fill the GPT partition. But when splitting out the content as an individual file, the padding remains, so it's not a valid text file. jq started rejecting files with NUL bytes to fix a security issue: https://github.com/jqlang/jq/commit/6374ae0bcdfe33a18eb0ae6db28493b1f34a0a5b Trim the output when writing these files out.