Connect to Wi-Fi service for sysv-init.

wifi.conf

# Set NETFILE to the location containing the wpa_supplicant network configuration.
# Uncomment the line that is the active network.
export NETFILE=/etc/wifi/My-NET.wifi
#export NETFILE=/etc/wifi/Work-NET.wifi
#export NETFILE=/etc/wifi/Public.wifi

wifi.sh

#!/bin/bash

### BEGIN INIT INFO
# Provides:          rtlwifi
# Required-Start:    $local_fs $syslog
# Required-Stop:     $local_fs $syslog
# Default-Start:     3 4 5
# Default-Stop:      0 1 6
# Short-Description: Start/stop wifi connection to home.
### END INIT INFO

export WPA_PIDFILE=/run/wifi/wpa_supplicant.pid
export DC_PIDFILE=/run/wifi/dhclient.pid
export IW_IFACE=wlan0

[ $UID -eq 0 ] || { echo "I'd prefer it if you had some authority..."; exit 1; }

. /lib/lsb/init-functions
[ -f /etc/default/wifi ] && . /etc/default/wifi
[ -d /run/wifi ] || mkdir /run/wifi
. common.sh

##### START ####
function start_wpa {
  ifconfig $IW_IFACE up 0.0.0.0
  wpa_supplicant -B -s -i $IW_IFACE -c "$NETFILE" -P "$WPA_PIDFILE" -Dwext || {
    log_failure_msg "Problems starting WPA Supplicant"
    return $RETVAL
  }

  log_success_msg "WPA Supplicant started. Pid: $(<$WPA_PIDFILE)"
  return $RETVAL
}

function start_dhclient {
#  ifconfig $IW_IFACE up $WIFI_IP_HOME_BASE
  dhclient -pf "$DC_PIDFILE" -v $IW_IFACE |& NO_STDERR=1 log dhclient || {
    log_failure_msg "Problems starting dhclient"
    return $RETVAL
  }

  if [ -s "$DC_PIDFILE" ]; then
    log_success_msg "dhclient started. Pid: $(<$DC_PIDFILE)"
    return $RETVAL
  else
    log_warn_msg "dhclient started, but no PID file??"
  fi
}

function start_wifi {
  if [ -f "$WPA_PIDFILE" -a -f "$DC_PIDFILE" ]; then
    log_success_msg "Wifi already connected."
    return 1
  fi

  start_wpa || exit;
  sleep 2s
  start_dhclient || exit;

  return $?
}

##### STOP #####
function stop_wpa {
  if [ ! -f "$WPA_PIDFILE" ]; then
    log_success_msg 'Wifi not associated'
    return 0
  fi
  local PID="$(<$WPA_PIDFILE)"
  if ! kill -15 $PID; then
    log_failure_msg "SIGTERM on $PID failed. Demanding halt by SIGKILL"
    kill -9 $PID || log_failure_msg 'You will want to verify WPA Supplicant was stopped cleanly.'
  fi
  rm $WPA_PIDFILE
  return 1
}

function stop_dhclient {
  if [ ! -f $DC_PIDFILE ]; then
    log_success_msg 'dhclient not running'
    return 0
  fi
  local PID="$(<$DC_PIDFILE)"
  if ! kill -15 $PID; then
    log_failure_msg "SIGTERM on $PID failed. Demanding halt by SIGKILL"
    kill -9 $PID || log_failure_msg 'You will want to verify WPA Supplicant was stopped cleanly.'
  fi
  rm $DC_PIDFILE
  return 1
}

function stop_wifi {
  stop_dhclient
  stop_wpa
  ifconfig $IW_IFACE down
  return $?
}

##### STATUS #####
function running_since {
  mtime="@`stat -c %Y /proc/$2`"
  printf 'PID of %s(%s), Running since %s\n' "$1" "$2" "`date +'%F %T' --date $mtime`"
}

# Return 0 for off and 1 for running
function wifi_status {
  if [ -f $WPA_PIDFILE ]; then
    log_success_msg 'Wifi appears to be associated.'
    if [ -f $DC_PIDFILE ]; then
      log_success_msg 'dhclient appears to be running.'
      iwconfig $IW_IFACE
      ifconfig $IW_IFACE
      [ -f $WPA_PIDFILE ] && [ -d /proc/$(<$WPA_PIDFILE) ] && running_since WPA\ Supplicant $(<$WPA_PIDFILE)
      [ -f $DC_PIDFILE ] && [ -d /proc/$(<$DC_PIDFILE) ] && running_since dhclient $(<$DC_PIDFILE)
      return 1
    fi
    log_failure_msg 'dhclient appears to be off.'
    return 0
  fi
  log_failure_msg 'Wifi appears to be unassociated.'
  return 0
}

case "$1" in
  start)
    start_wifi
  ;;
  stop)
    stop_wifi
  ;;
  restart)
    $0 stop
    $0 start
  ;;
  status)
    wifi_status
  ;;
  *)
    echo "Usage $0 [start|stop|restart|status]" > /dev/stderr
    exit 0
  ;;
esac