In debian unstable since kernel 4.18 creation of unprivileged containers does not work anymore.
This is due to EPERM when opening /dev/null. See https://lists.linuxfoundation.org/pipermail/containers/2018-June/039176.html . A userspace solution have been implemented in LXC as of version 3.0.2 as documented in https://discuss.linuxcontainers.org/t/lxc-3-0-2-has-been-released/2504.
