Change hostname of debian based system without a reboot.

change_hostname.sh

#!/bin/bash

# Change the hostname without reboot
# Applies only to debian based OS 

# TODO
# Understand common practises in setting hostnames in /etc/hosts 
# in a typical production setting.


die () {
  echo >&2 "$@"
  exit 1
}

[ "$#" -eq 1 ] || die "new hostname is required" 
# Help text
if [ "$1" == '-h' ]; then
  echo "Usage: `basename $0` [newhostname]
Change hostname without a reboot"
  exit 0
fi

OLD_HOSTNAME=`/bin/hostname`
NEW_HOSTNAME=$1

# Yes/no, yes/no, yes/no.. :)
read -p "Change Hostname from '${OLD_HOSTNAME}' to '${NEW_HOSTNAME}' 
ARE YOU SURE? [y/N] " -n 2 -r

if [[ $REPLY =~ ^[yY]$ ]]
then
  # change runtime hostname
  hostname $1
  
  
  cp /etc/hostname /etc/hostname.bak
  echo $NEW_HOSTNAME > /etc/hostname

  # change hostname in host table. Looks like a Debian thing. 
  # http://www.debian.org/doc/manuals/debian-reference/ch05.en.html#_the_hostname_resolution
  cp /etc/hosts /etc/hosts.bak
  sed -i "/127\.0\.1\.1/ s/${OLD_HOSTNAME}/${NEW_HOSTNAME}/" /etc/hosts
  
  echo \
"Hostname changed to '${NEW_HOSTNAME}'
If the hostname is present in the bash prompt. 
Log out and log back in"

fi