To build a VyOS 1.2.0 image, you need Debian 8 "Jessie" environment (with jessie-backports repository).
If you do not have a Debian Jessie machine, you may create a chroot environment with the debootstrap tool.
For example, on another version of Debian or another Debian-based distro, these commands will work:
$ sudo apt-get install debootstrap $ sudo debootstrap jessie vyos-chroot $ sudo chroot vyos-chroot $ echo "deb http://deb.debian.org/debian jessie-backports main" >> /etc/apt/sources.list $ apt-get update
If you are working on a Debian Jessie machine, no special preparation is needed, you only need to enable jessie-backports and install build dependencies. An up-to-date depnedency list can be found in out Dockerfile.
Several packages are required for building the ISO:
./configure script will warn you if any dependencies are missing. Individual packages may have other build dependencies. If some dependencies are missing, package build scripts will tell you.