prereq on my dev machine

sudo apt install schroot pigz debootstrap syslinux nfs-kernel-server tftpd-hpa xorriso pxelinux zfsutils-linux
cd /lab/livenet/livenet-server
rm -fR /etc/schroot/livenet
ln -s `pwd`/etc/schroot/livenet /etc/schroot/
[ -f /etc/default/livenet ] || cp -a etc/default/livenet /etc/default/livenet

Build image (xenial 64bit) named for example xenial-test (NAME=xenial-test)

ln-image --new-name bionic --create

This command create a chroot into /livenet/images/bionic