openvpn-install/openvpn-install.sh

#!/bin/bash

# Secure OpenVPN server installer for Debian, Ubuntu, CentOS, Amazon Linux 2, Fedora and Arch Linux
# https://github.com/angristan/openvpn-install

function isRoot () {
	if [ "$EUID" -ne 0 ]; then
		return 1
	fi
}

function tunAvailable () {
	if [ ! -e /dev/net/tun ]; then
		return 1
	fi
}

function checkOS () {
	if [[ -e /etc/debian_version ]]; then
		OS="debian"
		# shellcheck disable=SC1091
		source /etc/os-release

		if [[ "$ID" == "debian" || "$ID" == "raspbian" ]]; then
			if [[ "$VERSION_ID" -lt 8 ]]; then
				echo "⚠️ Your version of Debian is not supported."
				echo ""
				echo "However, if you're using Debian >= 8 or unstable/testing then you can continue, at your own risk."
				echo ""
				until [[ $CONTINUE =~ (y|n) ]]; do
					read -rp "Continue? [y/n]: " -e CONTINUE
				done
				if [[ "$CONTINUE" == "n" ]]; then
					exit 1
				fi
			fi
		elif [[ "$ID" == "ubuntu" ]];then
			OS="ubuntu"
			MAJOR_UBUNTU_VERSION=$(echo "$VERSION_ID" | cut -d '.' -f1)
			if [[ $MAJOR_UBUNTU_VERSION -lt 16 ]]; then
				echo "⚠️ Your version of Ubuntu is not supported."
				echo ""
				echo "However, if you're using Ubuntu >= 16.04 or beta, then you can continue, at your own risk."
				echo ""
				until [[ $CONTINUE =~ (y|n) ]]; do
					read -rp "Continue? [y/n]: " -e CONTINUE
				done
				if [[ "$CONTINUE" == "n" ]]; then
					exit 1
				fi
			fi
		fi
	elif [[ -e /etc/system-release ]]; then
		# shellcheck disable=SC1091
		source /etc/os-release
		if [[ "$ID" == "fedora" ]]; then
			OS="fedora"
		fi
		if [[ "$ID" == "centos" ]]; then
			OS="centos"
			if [[ ! $VERSION_ID =~ (7|8) ]]; then
				echo "⚠️ Your version of CentOS is not supported."
				echo ""
				echo "The script only support CentOS 7."
				echo ""
				exit 1
			fi
		fi
		if [[ "$ID" == "amzn" ]]; then
			OS="amzn"
			if [[ ! $VERSION_ID == "2" ]]; then
				echo "⚠️ Your version of Amazon Linux is not supported."
				echo ""
				echo "The script only support Amazon Linux 2."
				echo ""
				exit 1
			fi
		fi
	elif [[ -e /etc/arch-release ]]; then
		OS=arch
	else
		echo "Looks like you aren't running this installer on a Debian, Ubuntu, Fedora, CentOS, Amazon Linux 2 or Arch Linux system"
		exit 1
	fi
}

function initialCheck () {
	if ! isRoot; then
		echo "Sorry, you need to run this as root"
		exit 1
	fi
	if ! tunAvailable; then
		echo "TUN is not available"
		exit 1
	fi
	checkOS
}

function installUnbound () {
	if [[ ! -e /etc/unbound/unbound.conf ]]; then

		if [[ "$OS" =~ (debian|ubuntu) ]]; then
			apt-get install -y unbound

			# Configuration
			echo 'interface: 10.8.0.1
access-control: 10.8.0.1/24 allow
hide-identity: yes
hide-version: yes
use-caps-for-id: yes
prefetch: yes' >> /etc/unbound/unbound.conf

		elif [[ "$OS" =~ (centos|amzn) ]]; then
			yum install -y unbound

			# Configuration
			sed -i 's|# interface: 0.0.0.0$|interface: 10.8.0.1|' /etc/unbound/unbound.conf
			sed -i 's|# access-control: 127.0.0.0/8 allow|access-control: 10.8.0.1/24 allow|' /etc/unbound/unbound.conf
			sed -i 's|# hide-identity: no|hide-identity: yes|' /etc/unbound/unbound.conf
			sed -i 's|# hide-version: no|hide-version: yes|' /etc/unbound/unbound.conf
			sed -i 's|use-caps-for-id: no|use-caps-for-id: yes|' /etc/unbound/unbound.conf

		elif [[ "$OS" == "fedora" ]]; then
			dnf install -y unbound

			# Configuration
			sed -i 's|# interface: 0.0.0.0$|interface: 10.8.0.1|' /etc/unbound/unbound.conf
			sed -i 's|# access-control: 127.0.0.0/8 allow|access-control: 10.8.0.1/24 allow|' /etc/unbound/unbound.conf
			sed -i 's|# hide-identity: no|hide-identity: yes|' /etc/unbound/unbound.conf
			sed -i 's|# hide-version: no|hide-version: yes|' /etc/unbound/unbound.conf
			sed -i 's|# use-caps-for-id: no|use-caps-for-id: yes|' /etc/unbound/unbound.conf

		elif [[ "$OS" == "arch" ]]; then
			pacman -Syu --noconfirm unbound

			# Get root servers list
			curl -o /etc/unbound/root.hints https://www.internic.net/domain/named.cache

			mv /etc/unbound/unbound.conf /etc/unbound/unbound.conf.old

			echo 'server:
	use-syslog: yes
	do-daemonize: no
	username: "unbound"
	directory: "/etc/unbound"
	trust-anchor-file: trusted-key.key
	root-hints: root.hints
	interface: 10.8.0.1
	access-control: 10.8.0.1/24 allow
	port: 53
	num-threads: 2
	use-caps-for-id: yes
	harden-glue: yes
	hide-identity: yes
	hide-version: yes
	qname-minimisation: yes
	prefetch: yes' > /etc/unbound/unbound.conf
		fi

		if [[ ! "$OS" =~ (fedora|centos|amzn) ]];then
			# DNS Rebinding fix
			echo "private-address: 10.0.0.0/8
private-address: 172.16.0.0/12
private-address: 192.168.0.0/16
private-address: 169.254.0.0/16
private-address: fd00::/8
private-address: fe80::/10
private-address: 127.0.0.0/8
private-address: ::ffff:0:0/96" >> /etc/unbound/unbound.conf
		fi
	else # Unbound is already installed
		echo 'include: /etc/unbound/openvpn.conf' >> /etc/unbound/unbound.conf

		# Add Unbound 'server' for the OpenVPN subnet
		echo 'server:
interface: 10.8.0.1
access-control: 10.8.0.1/24 allow
hide-identity: yes
hide-version: yes
use-caps-for-id: yes
prefetch: yes
private-address: 10.0.0.0/8
private-address: 172.16.0.0/12
private-address: 192.168.0.0/16
private-address: 169.254.0.0/16
private-address: fd00::/8
private-address: fe80::/10
private-address: 127.0.0.0/8
private-address: ::ffff:0:0/96' > /etc/unbound/openvpn.conf
	fi

		systemctl enable unbound
		systemctl restart unbound
}

function installQuestions () {
	echo "Welcome to the OpenVPN installer!"
	echo "The git repository is available at: https://github.com/angristan/openvpn-install"
	echo ""

	echo "I need to ask you a few questions before starting the setup."
	echo "You can leave the default options and just press enter if you are ok with them."
	echo ""
	echo "I need to know the IPv4 address of the network interface you want OpenVPN listening to."
	echo "Unless your server is behind NAT, it should be your public IPv4 address."

	# Detect public IPv4 address and pre-fill for the user
	IP=$(ip addr | grep 'inet' | grep -v inet6 | grep -vE '127\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | grep -oE '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | head -1)
	APPROVE_IP=${APPROVE_IP:-n}
	if [[ $APPROVE_IP =~ n ]]; then
		read -rp "IP address: " -e -i "$IP" IP
	fi
	# If $IP is a private IP address, the server must be behind NAT
	if echo "$IP" | grep -qE '^(10\.|172\.1[6789]\.|172\.2[0-9]\.|172\.3[01]\.|192\.168)'; then
		echo ""
		echo "It seems this server is behind NAT. What is its public IPv4 address or hostname?"
		echo "We need it for the clients to connect to the server."
		until [[ "$ENDPOINT" != "" ]]; do
			read -rp "Public IPv4 address or hostname: " -e ENDPOINT
		done
	fi

	echo ""
	echo "Checking for IPv6 connectivity..."
	echo ""
	# "ping6" and "ping -6" availability varies depending on the distribution
	if type ping6 > /dev/null 2>&1; then
		PING6="ping6 -c3 ipv6.google.com > /dev/null 2>&1"
	else
		PING6="ping -6 -c3 ipv6.google.com > /dev/null 2>&1"
	fi
	if eval "$PING6"; then
		echo "Your host appears to have IPv6 connectivity."
		SUGGESTION="y"
	else
		echo "Your host does not appear to have IPv6 connectivity."
		SUGGESTION="n"
	fi
	echo ""
	# Ask the user if they want to enable IPv6 regardless its availability.
	until [[ $IPV6_SUPPORT =~ (y|n) ]]; do
		read -rp "Do you want to enable IPv6 support (NAT)? [y/n]: " -e -i $SUGGESTION IPV6_SUPPORT
	done
	echo ""
	echo "What port do you want OpenVPN to listen to?"
	echo "   1) Default: 1194"
	echo "   2) Custom"
	echo "   3) Random [49152-65535]"
	until [[ "$PORT_CHOICE" =~ ^[1-3]$ ]]; do
		read -rp "Port choice [1-3]: " -e -i 1 PORT_CHOICE
	done
	case $PORT_CHOICE in
		1)
			PORT="1194"
		;;
		2)
			until [[ "$PORT" =~ ^[0-9]+$ ]] && [ "$PORT" -ge 1 ] && [ "$PORT" -le 65535 ]; do
				read -rp "Custom port [1-65535]: " -e -i 1194 PORT
			done
		;;
		3)
			# Generate random number within private ports range
			PORT=$(shuf -i49152-65535 -n1)
			echo "Random Port: $PORT"
		;;
	esac
	echo ""
	echo "What protocol do you want OpenVPN to use?"
	echo "UDP is faster. Unless it is not available, you shouldn't use TCP."
	echo "   1) UDP"
	echo "   2) TCP"
	until [[ "$PROTOCOL_CHOICE" =~ ^[1-2]$ ]]; do
		read -rp "Protocol [1-2]: " -e -i 1 PROTOCOL_CHOICE
	done
	case $PROTOCOL_CHOICE in
		1)
			PROTOCOL="udp"
		;;
		2)
			PROTOCOL="tcp"
		;;
	esac
	echo ""
	echo "What DNS resolvers do you want to use with the VPN?"
	echo "   1) Current system resolvers (from /etc/resolv.conf)"
	echo "   2) Self-hosted DNS Resolver (Unbound)"
	echo "   3) Cloudflare (Anycast: worldwide)"
	echo "   4) Quad9 (Anycast: worldwide)"
	echo "   5) Quad9 uncensored (Anycast: worldwide)"
	echo "   6) FDN (France)"
	echo "   7) DNS.WATCH (Germany)"
	echo "   8) OpenDNS (Anycast: worldwide)"
	echo "   9) Google (Anycast: worldwide)"
	echo "   10) Yandex Basic (Russia)"
	echo "   11) AdGuard DNS (Anycast: worldwide)"
	echo "   12) NextDNS (Anycast: worldwide)"
	echo "   13) Custom"
	until [[ "$DNS" =~ ^[0-9]+$ ]] && [ "$DNS" -ge 1 ] && [ "$DNS" -le 13 ]; do
		read -rp "DNS [1-12]: " -e -i 3 DNS
			if [[ $DNS == 2 ]] && [[ -e /etc/unbound/unbound.conf ]]; then
				echo ""
				echo "Unbound is already installed."
				echo "You can allow the script to configure it in order to use it from your OpenVPN clients"
				echo "We will simply add a second server to /etc/unbound/unbound.conf for the OpenVPN subnet."
				echo "No changes are made to the current configuration."
				echo ""

				until [[ $CONTINUE =~ (y|n) ]]; do
					read -rp "Apply configuration changes to Unbound? [y/n]: " -e CONTINUE
				done
				if [[ $CONTINUE == "n" ]];then
					# Break the loop and cleanup
					unset DNS
					unset CONTINUE
				fi
			elif [[ $DNS == "13" ]]; then
				until [[ "$DNS1" =~ ^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$ ]]; do
					read -rp "Primary DNS: " -e DNS1
				done
				until [[ "$DNS2" =~ ^((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$ ]]; do
					read -rp "Secondary DNS (optional): " -e DNS2
					if [[ "$DNS2" == "" ]]; then
						break
					fi
				done
			fi
	done
	echo ""
	echo "Do you want to use compression? It is not recommended since the VORACLE attack make use of it."
	until [[ $COMPRESSION_ENABLED =~ (y|n) ]]; do
		read -rp"Enable compression? [y/n]: " -e -i n COMPRESSION_ENABLED
	done
	if [[ $COMPRESSION_ENABLED == "y" ]];then
		echo "Choose which compression algorithm you want to use: (they are ordered by efficiency)"
		echo "   1) LZ4-v2"
		echo "   2) LZ4"
		echo "   3) LZ0"
		until [[ $COMPRESSION_CHOICE =~ ^[1-3]$ ]]; do
			read -rp"Compression algorithm [1-3]: " -e -i 1 COMPRESSION_CHOICE
		done
		case $COMPRESSION_CHOICE in
			1)
			COMPRESSION_ALG="lz4-v2"
			;;
			2)
			COMPRESSION_ALG="lz4"
			;;
			3)
			COMPRESSION_ALG="lzo"
			;;
		esac
	fi
	echo ""
	echo "Do you want to customize encryption settings?"
	echo "Unless you know what you're doing, you should stick with the default parameters provided by the script."
	echo "Note that whatever you choose, all the choices presented in the script are safe. (Unlike OpenVPN's defaults)"
	echo "See https://github.com/angristan/openvpn-install#security-and-encryption to learn more."
	echo ""
	until [[ $CUSTOMIZE_ENC =~ (y|n) ]]; do
		read -rp "Customize encryption settings? [y/n]: " -e -i n CUSTOMIZE_ENC
	done
	if [[ $CUSTOMIZE_ENC == "n" ]];then
		# Use default, sane and fast parameters
		CIPHER="AES-128-GCM"
		CERT_TYPE="1" # ECDSA
		CERT_CURVE="prime256v1"
		CC_CIPHER="TLS-ECDHE-ECDSA-WITH-AES-128-GCM-SHA256"
		DH_TYPE="1" # ECDH
		DH_CURVE="prime256v1"
		HMAC_ALG="SHA256"
		TLS_SIG="1" # tls-crypt
	else
		echo ""
		echo "Choose which cipher you want to use for the data channel:"
		echo "   1) AES-128-GCM (recommended)"
		echo "   2) AES-192-GCM"
		echo "   3) AES-256-GCM"
		echo "   4) AES-128-CBC"
		echo "   5) AES-192-CBC"
		echo "   6) AES-256-CBC"
		until [[ "$CIPHER_CHOICE" =~ ^[1-6]$ ]]; do
			read -rp "Cipher [1-6]: " -e -i 1 CIPHER_CHOICE
		done
		case $CIPHER_CHOICE in
			1)
				CIPHER="AES-128-GCM"
			;;
			2)
				CIPHER="AES-192-GCM"
			;;
			3)
				CIPHER="AES-256-GCM"
			;;
			4)
				CIPHER="AES-128-CBC"
			;;
			5)
				CIPHER="AES-192-CBC"
			;;
			6)
				CIPHER="AES-256-CBC"
			;;
		esac
		echo ""
		echo "Choose what kind of certificate you want to use:"
		echo "   1) ECDSA (recommended)"
		echo "   2) RSA"
		until [[ $CERT_TYPE =~ ^[1-2]$ ]]; do
			read -rp"Certificate key type [1-2]: " -e -i 1 CERT_TYPE
		done
		case $CERT_TYPE in
			1)
				echo ""
				echo "Choose which curve you want to use for the certificate's key:"
				echo "   1) prime256v1 (recommended)"
				echo "   2) secp384r1"
				echo "   3) secp521r1"
				until [[ $CERT_CURVE_CHOICE =~ ^[1-3]$ ]]; do
					read -rp"Curve [1-3]: " -e -i 1 CERT_CURVE_CHOICE
				done
				case $CERT_CURVE_CHOICE in
					1)
						CERT_CURVE="prime256v1"
					;;
					2)
						CERT_CURVE="secp384r1"
					;;
					3)
						CERT_CURVE="secp521r1"
					;;
				esac
			;;
			2)
				echo ""
				echo "Choose which size you want to use for the certificate's RSA key:"
				echo "   1) 2048 bits (recommended)"
				echo "   2) 3072 bits"
				echo "   3) 4096 bits"
				until [[ "$RSA_KEY_SIZE_CHOICE" =~ ^[1-3]$ ]]; do
					read -rp "RSA key size [1-3]: " -e -i 1 RSA_KEY_SIZE_CHOICE
				done
				case $RSA_KEY_SIZE_CHOICE in
					1)
						RSA_KEY_SIZE="2048"
					;;
					2)
						RSA_KEY_SIZE="3072"
					;;
					3)
						RSA_KEY_SIZE="4096"
					;;
				esac
			;;
		esac
		echo ""
		echo "Choose which cipher you want to use for the control channel:"
		case $CERT_TYPE in
			1)
				echo "   1) ECDHE-ECDSA-AES-128-GCM-SHA256 (recommended)"
				echo "   2) ECDHE-ECDSA-AES-256-GCM-SHA384"
				until [[ $CC_CIPHER_CHOICE =~ ^[1-2]$ ]]; do
					read -rp"Control channel cipher [1-2]: " -e -i 1 CC_CIPHER_CHOICE
				done
				case $CC_CIPHER_CHOICE in
					1)
						CC_CIPHER="TLS-ECDHE-ECDSA-WITH-AES-128-GCM-SHA256"
					;;
					2)
						CC_CIPHER="TLS-ECDHE-ECDSA-WITH-AES-256-GCM-SHA384"
					;;
				esac
			;;
			2)
				echo "   1) ECDHE-RSA-AES-128-GCM-SHA256 (recommended)"
				echo "   2) ECDHE-RSA-AES-256-GCM-SHA384"
				until [[ $CC_CIPHER_CHOICE =~ ^[1-2]$ ]]; do
					read -rp"Control channel cipher [1-2]: " -e -i 1 CC_CIPHER_CHOICE
				done
				case $CC_CIPHER_CHOICE in
					1)
						CC_CIPHER="TLS-ECDHE-RSA-WITH-AES-128-GCM-SHA256"
					;;
					2)
						CC_CIPHER="TLS-ECDHE-RSA-WITH-AES-256-GCM-SHA384"
					;;
				esac
			;;
		esac
		echo ""
		echo "Choose what kind of Diffie-Hellman key you want to use:"
		echo "   1) ECDH (recommended)"
		echo "   2) DH"
		until [[ $DH_TYPE =~ [1-2] ]]; do
			read -rp"DH key type [1-2]: " -e -i 1 DH_TYPE
		done
		case $DH_TYPE in
			1)
				echo ""
				echo "Choose which curve you want to use for the ECDH key:"
				echo "   1) prime256v1 (recommended)"
				echo "   2) secp384r1"
				echo "   3) secp521r1"
				while [[ $DH_CURVE_CHOICE != "1" && $DH_CURVE_CHOICE != "2" && $DH_CURVE_CHOICE != "3" ]]; do
					read -rp"Curve [1-3]: " -e -i 1 DH_CURVE_CHOICE
				done
				case $DH_CURVE_CHOICE in
					1)
						DH_CURVE="prime256v1"
					;;
					2)
						DH_CURVE="secp384r1"
					;;
					3)
						DH_CURVE="secp521r1"
					;;
				esac
			;;
			2)
				echo ""
				echo "Choose what size of Diffie-Hellman key you want to use:"
				echo "   1) 2048 bits (recommended)"
				echo "   2) 3072 bits"
				echo "   3) 4096 bits"
				until [[ "$DH_KEY_SIZE_CHOICE" =~ ^[1-3]$ ]]; do
					read -rp "DH key size [1-3]: " -e -i 1 DH_KEY_SIZE_CHOICE
				done
				case $DH_KEY_SIZE_CHOICE in
					1)
						DH_KEY_SIZE="2048"
					;;
					2)
						DH_KEY_SIZE="3072"
					;;
					3)
						DH_KEY_SIZE="4096"
					;;
				esac
			;;
		esac
		echo ""
		# The "auth" options behaves differently with AEAD ciphers
		if [[ "$CIPHER" =~ CBC$ ]]; then
			echo "The digest algorithm authenticates data channel packets and tls-auth packets from the control channel."
		elif [[ "$CIPHER" =~ GCM$ ]]; then
			echo "The digest algorithm authenticates tls-auth packets from the control channel."
		fi
		echo "Which digest algorithm do you want to use for HMAC?"
		echo "   1) SHA-256 (recommended)"
		echo "   2) SHA-384"
		echo "   3) SHA-512"
		until [[ $HMAC_ALG_CHOICE =~ ^[1-3]$ ]]; do
			read -rp "Digest algorithm [1-3]: " -e -i 1 HMAC_ALG_CHOICE
		done
		case $HMAC_ALG_CHOICE in
			1)
				HMAC_ALG="SHA256"
			;;
			2)
				HMAC_ALG="SHA384"
			;;
			3)
				HMAC_ALG="SHA512"
			;;
		esac
		echo ""
		echo "You can add an additional layer of security to the control channel with tls-auth and tls-crypt"
		echo "tls-auth authenticates the packets, while tls-crypt authenticate and encrypt them."
		echo "   1) tls-crypt (recommended)"
		echo "   2) tls-auth"
		until [[ $TLS_SIG =~ [1-2] ]]; do
				read -rp "Control channel additional security mechanism [1-2]: " -e -i 1 TLS_SIG
		done
	fi
	echo ""
	echo "Okay, that was all I needed. We are ready to setup your OpenVPN server now."
	echo "You will be able to generate a client at the end of the installation."
	APPROVE_INSTALL=${APPROVE_INSTALL:-n}
	if [[ $APPROVE_INSTALL =~ n ]]; then
		read -n1 -r -p "Press any key to continue..."
	fi
}

function installOpenVPN () {
	if [[ $AUTO_INSTALL == "y" ]]; then
		# Set default choices so that no questions will be asked.
		APPROVE_INSTALL=${APPROVE_INSTALL:-y}
		APPROVE_IP=${APPROVE_IP:-y}
		IPV6_SUPPORT=${IPV6_SUPPORT:-n}
		PORT_CHOICE=${PORT_CHOICE:-1}
		PROTOCOL_CHOICE=${PROTOCOL_CHOICE:-1}
		DNS=${DNS:-1}
		COMPRESSION_ENABLED=${COMPRESSION_ENABLED:-n}
		CUSTOMIZE_ENC=${CUSTOMIZE_ENC:-n}
		CLIENT=${CLIENT:-client}
		PASS=${PASS:-1}
		CONTINUE=${CONTINUE:-y}

		# Behind NAT, we'll default to the publicly reachable IPv4.
		PUBLIC_IPV4=$(curl ifconfig.co)
		ENDPOINT=${ENDPOINT:-$PUBLIC_IPV4}
	fi

	# Run setup questions first, and set other variales if auto-install
	installQuestions

	# Get the "public" interface from the default route
	NIC=$(ip -4 route ls | grep default | grep -Po '(?<=dev )(\S+)' | head -1)
	if [[ -z "$NIC" ]] && [[ "$IPV6_SUPPORT" == 'y' ]]; then
		NIC=$(ip -6 route show default | sed -ne 's/^default .* dev \([^ ]*\) .*$/\1/p')
	fi

	# $NIC can not be empty for script rm-openvpn-rules.sh
        if [[ -z "$NIC" ]]; then
                echo
                echo "Can not detect public interface."
                echo "This needs for setup MASQUERADE."
                until [[ $CONTINUE =~ (y|n) ]]; do
                        read -rp "Continue? [y/n]: " -e CONTINUE
                done
                if [[ "$CONTINUE" == "n" ]]; then
                        exit 1
                fi
        fi

	if [[ "$OS" =~ (debian|ubuntu) ]]; then
		apt-get update
		apt-get -y install ca-certificates gnupg
		# We add the OpenVPN repo to get the latest version.
		if [[ "$VERSION_ID" == "8" ]]; then
			echo "deb http://build.openvpn.net/debian/openvpn/stable jessie main" > /etc/apt/sources.list.d/openvpn.list
			wget -O - https://swupdate.openvpn.net/repos/repo-public.gpg | apt-key add -
			apt-get update
		fi
		if [[ "$VERSION_ID" == "16.04" ]]; then
			echo "deb http://build.openvpn.net/debian/openvpn/stable xenial main" > /etc/apt/sources.list.d/openvpn.list
			wget -O - https://swupdate.openvpn.net/repos/repo-public.gpg | apt-key add -
			apt-get update
		fi
		# Ubuntu > 16.04 and Debian > 8 have OpenVPN >= 2.4 without the need of a third party repository.
		apt-get install -y openvpn iptables openssl wget ca-certificates curl
	elif [[ "$OS" == 'centos' ]]; then
		yum install -y epel-release
		yum install -y openvpn iptables openssl wget ca-certificates curl tar 'policycoreutils-python*'
	elif [[ "$OS" == 'amzn' ]]; then
		amazon-linux-extras install -y epel
		yum install -y openvpn iptables openssl wget ca-certificates curl
	elif [[ "$OS" == 'fedora' ]]; then
		dnf install -y openvpn iptables openssl wget ca-certificates curl
	elif [[ "$OS" == 'arch' ]]; then
		# Install required dependencies and upgrade the system
		pacman --needed --noconfirm -Syu openvpn iptables openssl wget ca-certificates curl
	fi

	# Find out if the machine uses nogroup or nobody for the permissionless group
	if grep -qs "^nogroup:" /etc/group; then
		NOGROUP=nogroup
	else
		NOGROUP=nobody
	fi

	# An old version of easy-rsa was available by default in some openvpn packages
	if [[ -d /etc/openvpn/easy-rsa/ ]]; then
		rm -rf /etc/openvpn/easy-rsa/
	fi

	# Install the latest version of easy-rsa from source
	local version="3.0.6"
	wget -O ~/EasyRSA-unix-v${version}.tgz https://github.com/OpenVPN/easy-rsa/releases/download/v${version}/EasyRSA-unix-v${version}.tgz
	tar xzf ~/EasyRSA-unix-v${version}.tgz -C ~/
	mv ~/EasyRSA-v${version} /etc/openvpn/easy-rsa
	chown -R root:root /etc/openvpn/easy-rsa/