I found a typo in Build ISO document.
It seems that incorrect git clone command for cloning rolling release.
Now
I think the second one should be current instead of crux.
$ git clone -b crux --single-branch https://github.com/vyos/vyos-build # For VyOS 1.2 $ git clone -b crux --single-branch https://github.com/vyos/vyos-build # For rolling release
Correct
$ git clone -b crux --single-branch https://github.com/vyos/vyos-build # For VyOS 1.2 $ git clone -b current --single-branch https://github.com/vyos/vyos-build # For rolling release