hostname

#!/bin/sh
#
#
# Change the host name according to DHCP settings.
#
# Copyright © 2014 Sébastien Gross <seb•ɑƬ•chezwam•ɖɵʈ•org>
# Created: 2014-03-11
# Last changed: 2014-12-03 00:22:50
#
# This program is free software. It comes without any warranty, to
# the extent permitted by applicable law. You can redistribute it
# and/or modify it under the terms of the Do What The Fuck You Want
# To Public License, Version 2, as published by Sam Hocevar. See
# http://sam.zoy.org/wtfpl/COPYING for more details.
#
# If no hostname-$interface file is found, we do nothing. Thus you have to
# explicitly specify the interface from which you want to bind the hostname.
#
# If your primary interface is eth0 you have to create the:
# /etc/dhcp/dhclient-exit-hooks.d/hostname-eth0 file
#
# The hostname is looked in order from:
#   - new_host_name environment variable given by the DHCP server
#   - DNS resolution bases on $interface PTR record
#   - In last ressort use the IP address: A.B.C.D -> A-B-C-D.
#
# A "localhost-$interface.localdomain" entry based on $interface
# $new_ip_address is added to /etc/hosts.

CONF_DIR=/etc/dhcp/dhclient-exit-hooks.d
FILE="$CONF_DIR/hostname-$interface"
LOG="logger -t dhcp [hostname ($interface)]"
MSG=
LOCAL_HOST=$(echo "localhost-$interface" | sed 's/[^a-z0-9]/-/g')
LOCAL_DOMAIN="localdomain"
extra_host_name=""

# For debuging purpose.
# $LOG "new_host_name: '$new_host_name'"
# $LOG "new_ip_address: '$new_ip_address'"
# $LOG "new_old_address: '$new_old_address'"

# only run if a hostname-IFACE file is found in the dhclient-exit-hooks.d
# directory
if [ ! -e $FILE ]; then
    $LOG $FILE "not found"
else
    # If IP address hasn't change, do nothting
    if [ -z "$new_ip_address" ]; then
        $LOG "ip address didn't change"
        exit 0
    fi

    hostname_to_set=""
    # First try to setup hostname according dhcp option
    if [ -n "$new_host_name" ]; then
        if [ "$new_host_name" != "$old_host_name" ]; then
            hostname_to_set="$new_host_name"
            $LOG "found hostname ($hostname_to_set) in DHCP options"
            fqdn=$(/usr/bin/host -t PTR $new_ip_address |
                       sed -n 's/.* domain name pointer \(.*\)./\1/p')
            extra_host_name="$fqdn $hostname_to_set"
        fi
    fi

    # Otherwise
    if [ -z "$hostname_to_set" ]; then
        # try a DNS reverse resolution
        fqdn=$(/usr/bin/host -t PTR $new_ip_address |
		   sed -n 's/.* domain name pointer \(.*\)./\1/p')
	hostname_to_set=$(echo $fqdn | cut -d. -f1)
        if [ -n "$hostname_to_set" ]; then
            $LOG "found hostname ($hostname_to_set) using DNS reverse"
	    extra_host_name="$fqdn $hostname_to_set"
	else
            # Finaly setup the hostname against the interface IP address.
            hostname_to_set=`echo $new_ip_address | sed 's/\./-/g'`
            $LOG "found hostname ($hostname_to_set) using IP address"
	    # Name sure A-B-C-D can also be resolved.
	    # Note that neither 'host' nor 'dig' command will resolve user
	    # the /etc/hosts file. For that you need to use:
	    #   getent hosts HOSTNAME_OR_IP
            extra_host_name="$hostname_to_set $hostname_to_set.$LOCAL_DOMAIN"
        fi
    fi

    # Add a localhost-INTERFACE.localdomain entry in /etc/hosts
    grep -v " $LOCAL_HOST.$LOCAL_DOMAIN" /etc/hosts > /etc/hosts.tmp
    echo "$new_ip_address $extra_host_name $LOCAL_HOST $LOCAL_HOST.$LOCAL_DOMAIN" >> /etc/hosts.tmp
    mv /etc/hosts.tmp /etc/hosts

    # Now we really set the hostname.
    echo "$hostname_to_set" >/etc/hostname
    /bin/hostname -F /etc/hostname
    invoke-rc.d hostname restart >> /dev/null
    $LOG "Set hostname to $hostname_to_set"
fi