Script to lock down a new Ubuntu server

lock_down_ubuntu.sh

#!/bin/sh

#
# execute this script as root with:
# curl https://raw.github.com/gist/1877257/lock_down_ubuntu.sh | bash -s MyAwesomeHostName
#

if [[ ! "root" = "$(whoami)" ]] ; then
  echo -e "****\nThis script must be run as root.\n****" && exit 1
fi

function add_user(){
  user_name=$1
  public_key=$2

  echo -e "\nAdding user account: $user_name\n"

  #
  # create user account and home directory
  #
  useradd -m -s /bin/bash $user_name

  #
  # add user to the rvm group to manage system rubies
  #
  usermod -aG rvm $user_name

  #
  # add user to the web group to manage web sites
  #
  usermod -a -G www-data $user_name

  #
  # write the user's public key to their authorized keys file
  #
  curl $public_key > /home/$user_name/.ssh/authorized_keys

  #
  # set ownership and permissions on authorized_keys
  #
  chown -R $user_name:$user_name /home/$user_name/.ssh
  chmod -R 0751 /home/$user_name/.ssh

  #
  # add user to sudoers list with no password required (account has no password)
  #
  (cat /etc/sudoers;echo "$user_name ALL=(ALL) NOPASSWD: ALL") >> ~/tmp_sudoers
  chmod 0440 ~/tmp_sudoers
  visudo -q -c -s -f ~/tmp_sudoers
  if [ $? == 0 ];then
    echo -e "\nERROR: There is a problem with the sudoers configuration.\n Please review ~/tmp_sudoers.\n" && exit 1
  fi
  mv -f ~/tmp_sudoers /etc/sudoers
}

#
# Upgrade installed packages to latest
#
echo -e "\nUpdating all installed packages\n"
aptitude update
aptitude safe-upgrade -y

#
# install and configure firewall
#
echo -e "\nInstalling and configuring firewall\n"
aptitude install ufw -y
ufw default deny incoming
ufw default allow outgoing
ufw allow ssh
ufw allow 80/tcp
ufw allow 443/tcp

cat /etc/ufw/ufw.conf | sed 's/ENABLED=no/ENABLED=yes/g' > ~/ufw.conf
chmod 0644 ~/ufw.conf
mv -f ~/ufw.conf /etc/ufw/ufw.conf

#
# create alan and andrew's accounts
#
add_user 'alan' 'https://dl.dropbox.com/s/qfo16yktbn23q9j/id_rsa.pub?dl=1'
add_user 'andrew' 'https://dl.dropbox.com/s/2sld4rsbhl0o093/authorized_keys?dl=1'

#
# set the hostname
#
if [ $# > 0 ];then
  hostName=$1
  echo -e "\nSetting host name to \"$hostName\"\n"
  echo "$hostName" > /etc/hostname
  (echo "127.0.0.1       $hostName   $hostName"; cat /etc/hosts) > ~/hosts
  chmod 644 ~/hosts
  mv -f ~/hosts /etc/hosts
  hostname -F /etc/hostname
fi

#
# set timezone to Universal Coordinated Time
#
ln -sf /usr/share/zoneinfo/UTC /etc/localtime

#
# disable root login and password authentication over ssh
#
(cat /etc/ssh/sshd_config;echo "PermitRootLogin no") | sed 's/#PasswordAuthentication yes/PasswordAuthentication no/g' > ~/sshd_config
chmod 0644 ~/sshd_config
mv -f ~/sshd_config /etc/ssh/sshd_config

#
# ** REBOOT ** to apply settings and start firewall
#
echo -e "**********\n* REBOOT * the system to finish applying settings, including the firewall.\n**********"

(cat /etc/ssh/sshd_config;echo "PermitRootLogin no") | sed 's/#PasswordAuthentication yes/PasswordAuthentication no/g' > ~/sshd_config
chmod 0644 ~/sshd_config
mv -f ~/sshd_config /etc/ssh/sshd_config

This can be done with a simple tee command.