#!/bin/bash# dhclient-script for Linux. Dan Halbert, March, 1997.# Updated for Linux 2.[12] by Brian J. Murrell, January 1999.# No guarantees about this. I'm a novice at the details of Linux# networking.# Notes:# 0. This script is based on the netbsd script supplied with dhcp-970306.# 1. ifconfig down apparently deletes all relevant routes and flushes# the arp cache, so this doesn't need to be done explicitly.# 2. The alias address handling here has not been tested AT ALL.# I'm just going by the doc of modern Linux ip aliasing, which uses# notations like eth0:0, eth0:1, for each alias.# 3. I have to calculate the network address, and calculate the broadcast# address if it is not supplied. This might be much more easily done# by the dhclient C code, and passed on.# 4. TIMEOUT not tested. ping has a flag I don't know, and I'm suspicious# of the $1 in its args.make_resolv_conf() {  if [ "x$new_domain_name" != x ] && [ x"$new_domain_name_servers" != x ]; then    echo search $new_domain_name >/etc/resolv.conf    chmod 644 /etc/resolv.conf    for nameserver in $new_domain_name_servers; do      echo nameserver $nameserver >>/etc/resolv.conf    done  fi}# Must be used on exit.   Invokes the local dhcp client exit hooks, if any.exit_with_hooks() {  exit_status=$1  if [ -f /etc/dhclient-exit-hooks ]; then    . /etc/dhclient-exit-hooks  fi# probably should do something with exit status of the local script  exit $exit_status}# Invoke the local dhcp client enter hooks, if they exist.if [ -f /etc/dhclient-enter-hooks ]; then  exit_status=0  . /etc/dhclient-enter-hooks  # allow the local script to abort processing of this state  # local script must set exit_status variable to nonzero.  if [ $exit_status -ne 0 ]; then    exit $exit_status  fifirelease=`uname -r`release=`expr $release : '\(.*\)\..*'`relminor=`echo $release |sed -e 's/[0-9]*\.\([0-9][0-9]*\)\(\..*\)*$/\1/'`relmajor=`echo $release |sed -e 's/\([0-9][0-9]*\)\..*$/\1/'`if [ x$new_broadcast_address != x ]; then  new_broadcast_arg="broadcast $new_broadcast_address"fiif [ x$old_broadcast_address != x ]; then  old_broadcast_arg="broadcast $old_broadcast_address"fiif [ x$new_subnet_mask != x ]; then  new_subnet_arg="netmask $new_subnet_mask"fiif [ x$old_subnet_mask != x ]; then  old_subnet_arg="netmask $old_subnet_mask"fiif [ x$alias_subnet_mask != x ]; then  alias_subnet_arg="netmask $alias_subnet_mask"fiif [ x$reason = xMEDIUM ]; then  # Linux doesn't do mediums (ok, ok, media).  exit_with_hooks 0fiif [ x$reason = xPREINIT ]; then  if [ x$alias_ip_address != x ]; then    # Bring down alias interface. Its routes will disappear too.    ifconfig $interface:0- inet 0  fi  if [ $relmajor -lt 2 ] || ( [ $relmajor -eq 2 ] && [ $relminor -eq 0 ] )   then    ifconfig $interface inet 0.0.0.0 netmask 0.0.0.0 \		broadcast 255.255.255.255 up    # Add route to make broadcast work. Do not omit netmask.    route add default dev $interface netmask 0.0.0.0  else    ifconfig $interface 0 up  fi  # We need to give the kernel some time to get the interface up.  sleep 1  exit_with_hooks 0fiif [ x$reason = xARPCHECK ] || [ x$reason = xARPSEND ]; then  exit_with_hooks 0fi  if [ x$reason = xBOUND ] || [ x$reason = xRENEW ] || \   [ x$reason = xREBIND ] || [ x$reason = xREBOOT ]; then  current_hostname=`hostname`  if [ x$current_hostname = x ] || \     [ x$current_hostname = x$old_host_name ]; then    if [ x$current_hostname = x ] || \       [ x$new_host_name != x$old_host_name ]; then      hostname $new_host_name    fi  fi      if [ x$old_ip_address != x ] && [ x$alias_ip_address != x ] && \		[ x$alias_ip_address != x$old_ip_address ]; then    # Possible new alias. Remove old alias.    ifconfig $interface:0- inet 0  fi  if [ x$old_ip_address != x ] && [ x$old_ip_address != x$new_ip_address ]; then    # IP address changed. Bringing down the interface will delete all routes,    # and clear the ARP cache.    ifconfig $interface inet 0 down  fi  if [ x$old_ip_address = x ] || [ x$old_ip_address != x$new_ip_address ] || \     [ x$reason = xBOUND ] || [ x$reason = xREBOOT ]; then    ifconfig $interface inet $new_ip_address $new_subnet_arg \							$new_broadcast_arg    # Add a network route to the computed network address.    if [ $relmajor -lt 2 ] || \		( [ $relmajor -eq 2 ] && [ $relminor -eq 0 ] ); then      route add -net $new_network_number $new_subnet_arg dev $interface    fi    for router in $new_routers; do      route add default gw $router    done  fi  if [ x$new_ip_address != x$alias_ip_address ] && [ x$alias_ip_address != x ];   then    ifconfig $interface:0- inet 0    ifconfig $interface:0 inet $alias_ip_address $alias_subnet_arg    route add -host $alias_ip_address $interface:0  fi  make_resolv_conf  exit_with_hooks 0fiif [ x$reason = xEXPIRE ] || [ x$reason = xFAIL ] || [ x$reason = xRELEASE ] \   || [ x$reason = xSTOP ]; then  if [ x$alias_ip_address != x ]; then    # Turn off alias interface.    ifconfig $interface:0- inet 0  fi  if [ x$old_ip_address != x ]; then    # Shut down interface, which will delete routes and clear arp cache.    ifconfig $interface inet 0 down  fi  if [ x$alias_ip_address != x ]; then    ifconfig $interface:0 inet $alias_ip_address $alias_subnet_arg    route add -host $alias_ip_address $interface:0  fi  exit_with_hooks 0fiif [ x$reason = xTIMEOUT ]; then  if [ x$alias_ip_address != x ]; then    ifconfig $interface:0- inet 0  fi  ifconfig $interface inet $new_ip_address $new_subnet_arg \					$new_broadcast_arg  set $new_routers  ############## what is -w in ping?  if ping -q -c 1 $1; then    if [ x$new_ip_address != x$alias_ip_address ] && \			[ x$alias_ip_address != x ]; then      ifconfig $interface:0 inet $alias_ip_address $alias_subnet_arg      route add -host $alias_ip_address dev $interface:0    fi    if [ $relmajor -lt 2 ] || \		( [ $relmajor -eq 2 ] && [ $relminor -eq 0 ] ); then      route add -net $new_network_number    fi    for router in $new_routers; do      route add default gw $router    done    make_resolv_conf    exit_with_hooks 0  fi  ifconfig $interface inet 0 down  exit_with_hooks 1fiexit_with_hooks 0