Presumably you are on an old calibre version.
Code:
calibredb list -f formats,cover --for-machine -s id:2017 *
[
{
"cover": "/home/kovid/test library/calibre/The Hindu (2017)/cover.jpg",
"formats": [
"/home/kovid/test library/calibre/The Hindu (2017)/The Hindu - calibre.mobi"
],
"id": 2017
}
]%
And note that this wont work when connecting via the calibre content server.