start_dhclient() {
  local interface=$1
  if [[ "$OSTYPE" == "linux-gnu"  ]]; then
    dhclient -x
    dhclient -nw "$interface"
  elif [[ "$OSTYPE" == "freebsd"* ]]; then
    # prefer isc-dhcp-client as it supports dhcpv6
    if [[ -x /usr/local/sbin/dhclient ]]; then
      /usr/local/sbin/dhclient -x
      /usr/local/sbin/dhclient -nw "$interface"
    else
      dhclient -b "$interface"
    fi
  else
    nohup setsid dhclient "$interface" >/dev/null 2>&1
  fi
}

start_dhcp() {
  local interface=$1
  if has dhcpcd; then
    dhcpcd -b -n "$interface"
  elif has dhclient; then
    start_dhclient "$interface"
  elif [[ "$OSTYPE" == "darwin"* ]]; then # TODO untested
    ipconfig set "$interface" DHCP
  else
    die "no suitable dhcp program found, need dhcpcd or dhclient"
  fi
}