ifupdown-netns/if-pre-up.d/netns

#!/bin/bash

set -e

if [ -n "${IF_NETNS}" ]
then
  # Create netns if it doesn't already exist, and bring up the loopback
  if ! (ip netns list | grep -qx ${IF_NETNS})
  then
    mkdir -p /etc/netns/$IF_NETNS/network/{if-down.d,if-post-down.d,if-pre-up.d,if-up.d}
    if [ ! -f /etc/netns/$IF_NETNS/network/interfaces ]; then
      touch /etc/netns/$IF_NETNS/network/interfaces
    fi
    if [ ! -f /etc/netns/$IF_NETNS/resolv.conf ]; then
      touch /etc/netns/$IF_NETNS/resolv.conf
    fi
    mkdir -p /run/network.${IF_NETNS}
    rm -rf /run/network.${IF_NETNS}/*
    ip netns add ${IF_NETNS}
    ip netns exec ${IF_NETNS} ip link set lo up
  fi
  ip link set ${IFACE} netns ${IF_NETNS}
fi