#!/bin/bash

# Secure OpenVPN server installer for Debian, Ubuntu, CentOS and Arch Linux
# https://github.com/Angristan/OpenVPN-install


if [[ "$EUID" -ne 0 ]]; then
	echo "Sorry, you need to run this as root"
	exit 1
fi

if [[ ! -e /dev/net/tun ]]; then
	echo "TUN is not available"
	exit 2
fi

if grep -qs "CentOS release 5" "/etc/redhat-release"; then
	echo "CentOS 5 is too old and not supported"
	exit 3
fi

dir_openvpn='/etc/openvpn'
dir_easy="${dir_openvpn}/easy-rsa"
bin_easy='${dir_easy}/easyrsa'
file_client_tpl='${dir_openvpn}/client-template.txt'
file_openvpn_conf='${dir_openvpn}/server.conf'
IPTABLES='/etc/iptables/iptables.rules'
	
if [[ -e /etc/debian_version ]]; then
	OS="debian"
	# Getting the version number, to verify that a recent version of OpenVPN is available
	VERSION_ID=$(cat /etc/os-release | grep "VERSION_ID")
	SYSCTL='/etc/sysctl.conf'
	if [[ "$VERSION_ID" != 'VERSION_ID="7"' ]] && [[ "$VERSION_ID" != 'VERSION_ID="8"' ]] && [[ "$VERSION_ID" != 'VERSION_ID="9"' ]] && [[ "$VERSION_ID" != 'VERSION_ID="12.04"' ]] && [[ "$VERSION_ID" != 'VERSION_ID="14.04"' ]] && [[ "$VERSION_ID" != 'VERSION_ID="16.04"' ]] && [[ "$VERSION_ID" != 'VERSION_ID="16.10"' ]] && [[ "$VERSION_ID" != 'VERSION_ID="17.04"' ]]; then
		echo 'Your version of Debian/Ubuntu is not supported.'
		echo "I can't install a recent version of OpenVPN on your system."
		echo ''
		echo "However, if you're using Debian unstable/testing, or Ubuntu beta,"
		echo 'then you can continue, a recent version of OpenVPN is available on these.'
		echo 'Keep in mind they are not supported, though.'
		while [[ 'y' != $CONTINUE && 'n' != $CONTINUE ]]; do
			read -p 'Continue ? [y/n]: ' -e CONTINUE
		done
		if [[ 'n' = "$CONTINUE" ]]; then
			echo 'Ok, bye !'
			exit 4
		fi
	fi
elif [[ -e /etc/centos-release || -e /etc/redhat-release && ! -e /etc/fedora-release ]]; then
	OS='centos'
	SYSCTL='/etc/sysctl.conf'
elif [[ -e /etc/arch-release ]]; then
	OS='arch'
	SYSCTL='/etc/sysctl.d/openvpn.conf'
elif [[ -e /etc/fedora-release ]]; then
	OS='fedora'
	SYSCTL='/etc/sysctl.d/openvpn.conf'
else
	echo "Looks like you aren't running this installer on a Debian, Ubuntu, CentOS or ArchLinux system"
	exit 4
fi

install_easyrsa(){
	# 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
	# Get easy-rsa
	wget -O ~/EasyRSA-3.0.3.tgz 'https://github.com/OpenVPN/easy-rsa/releases/download/v3.0.3/EasyRSA-3.0.3.tgz'
	tar xzf ~/EasyRSA-3.0.3.tgz -C ~/
	mv ~/EasyRSA-3.0.3 /etc/openvpn/easy-rsa
	chown -R root:root /etc/openvpn/easy-rsa/
	rm -rf ~/EasyRSA-3.0.3.tgz
}

set_firewall(){
	# Create the sysctl configuration file if needed (mainly for Arch Linux)
	if [[ ! -e $SYSCTL ]]; then
		touch $SYSCTL
	fi

	# Enable net.ipv4.ip_forward for the system
	sed -i '/\<net.ipv4.ip_forward\>/c\net.ipv4.ip_forward=1' $SYSCTL
	if ! grep -q "\<net.ipv4.ip_forward\>" $SYSCTL; then
		echo 'net.ipv4.ip_forward=1' >> $SYSCTL
	fi
	# Avoid an unneeded reboot
	echo 1 > /proc/sys/net/ipv4/ip_forward
	# Set NAT for the VPN subnet
	iptables -t nat -A POSTROUTING -o $NIC -s 10.8.0.0/24 -j MASQUERADE
	# Save persitent iptables rules
	iptables-save > $IPTABLES
	if pgrep firewalld; then
		# We don't use --add-service=openvpn because that would only work with
		# the default port. Using both permanent and not permanent rules to
		# avoid a firewalld reload.
		firewall-cmd --zone=public --add-port=$PORT/${PROTOCOL}
		firewall-cmd --permanent --zone=public --add-port=$PORT/${PROTOCOL}
		firewall-cmd --zone=trusted --add-source=10.8.0.0/24
		firewall-cmd --permanent --zone=trusted --add-source=10.8.0.0/24
	fi
	if iptables -L -n | grep -qE 'REJECT|DROP'; then
		# If iptables has at least one REJECT rule, we asume this is needed.
		# Not the best approach but I can't think of other and this shouldn't
		# cause problems.
		iptables -I INPUT -p ${PROTOCOL} --dport $PORT -j ACCEPT
		iptables -I FORWARD -s 10.8.0.0/24 -j ACCEPT
		iptables -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
		# Save persitent OpenVPN rules
        iptables-save > $IPTABLES
	fi
	# If SELinux is enabled and a custom port was selected, we need this
	if hash sestatus 2>/dev/null; then
		if sestatus | grep "Current mode" | grep -qs "enforcing"; then
			if [[ "$PORT" != '1194' ]]; then
				# semanage isn't available in CentOS 6 by default
				if ! hash semanage 2>/dev/null; then
					yum install policycoreutils-python -y
				fi
				semanage port -a -t openvpn_port_t -p ${PROTOCOL} $PORT
			fi
		fi
	fi
}

newclient () {
	# Where to write the custom client.ovpn?
	if [ -e /home/$1 ]; then  # if $1 is a user name
		homeDir="/home/$1"
	elif [ ${SUDO_USER} ]; then   # if not, use SUDO_USER
		homeDir="/home/${SUDO_USER}"
	else  # if not SUDO_USER, use /root
		homeDir="${dir_openvpn}"
	fi
	# Generates the custom client.ovpn
	file_client="$homeDir/$1.ovpn"
	cp ${file_client_tpl} ${file_client}
	echo "<ca>" >> ${file_client}
	cat ${dir_easy}/pki/ca.crt >> ${file_client}
	echo "</ca>" >> ${file_client}
	echo "<cert>" >> ${file_client}
	cat ${dir_easy}/pki/issued/$1.crt >> ${file_client}
	echo "</cert>" >> ${file_client}
	echo "<key>" >> ${file_client}
	cat ${dir_easy}/pki/private/$1.key >> ${file_client}
	echo "</key>" >> ${file_client}
	echo "key-direction 1" >> ${file_client}
	echo "<tls-auth>" >> ${file_client}
	cat ${dir_openvpn}/tls-auth.key >> ${file_client}
	echo "</tls-auth>" >> ${file_client}
}

# Try to get our IP from the system and fallback to the Internet.
# I do this to make the script compatible with NATed servers (LowEndSpirit/Scaleway)
# and to avoid getting an IPv6.
IP=$(ip addr | grep 'inet' | grep -v inet6 | grep -vE '127\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | grep -o -E '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | head -1)
if [[ "$IP" = "" ]]; then
	IP=$(wget -qO- ipv4.icanhazip.com)
fi
# Get Internet network interface with default route
NIC=$(ip -4 route ls | grep default | grep -Po '(?<=dev )(\S+)' | head -1)

if [[ -e ${file_openvpn_conf} ]]; then
	while :
	do
		clear
cat <<EOF
OpenVPN-install (github.com/Angristan/OpenVPN-install)

Looks like OpenVPN is already installed

What do you want to do?
   1) Add a cert for a new user
   2) Revoke existing user cert
   3) Remove OpenVPN
   4) Exit
EOF
		read -p 'Select an option [1-4]: ' option
		case $option in
			1)
			echo ""
			echo "Tell me a name for the client cert"
			echo "Please, use one word only, no special characters"
			read -p "Client name: " -e -i client CLIENT
			cd ${dir_easy}
			${bin_easy} build-client-full $CLIENT nopass
			# Generates the custom client.ovpn
			newclient "$CLIENT"
			echo ""
			echo "Client $CLIENT added, certs available at $homeDir/$CLIENT.ovpn"
			exit
			;;
			2)
			file_index="${dir_easy}/pki/index.txt"
			NUMBEROFCLIENTS=$(tail -n +2 ${file_index} | grep -c "^V")
			if [[ "$NUMBEROFCLIENTS" = '0' ]]; then
				echo ""
				echo "You have no existing clients!"
				exit 5
			fi
			echo ""
			echo "Select the existing client certificate you want to revoke"
			tail -n +2 ${file_index} | grep "^V" | cut -d '=' -f 2 | nl -s ') '
			if [[ "$NUMBEROFCLIENTS" = '1' ]]; then
				read -p "Select one client [1]: " CLIENTNUMBER
			else
				read -p "Select one client [1-$NUMBEROFCLIENTS]: " CLIENTNUMBER
			fi
			CLIENT=$(tail -n +2 ${file_index} | grep "^V" | cut -d '=' -f 2 | sed -n "$CLIENTNUMBER"p)
			cd ${dir_easy}
			${bin_easy} --batch revoke $CLIENT
			EASYRSA_CRL_DAYS=3650 ${bin_easy} gen-crl
			rm -rf pki/reqs/$CLIENT.req
			rm -rf pki/private/$CLIENT.key
			rm -rf pki/issued/$CLIENT.crt
			rm -rf /etc/openvpn/crl.pem
			cp ${dir_easy}/pki/crl.pem ${dir_openvpn}/crl.pem
			chmod 644 ${dir_openvpn}/crl.pem
			echo ""
			echo "Certificate for client $CLIENT revoked"
			echo "Exiting..."
			exit
			;;
			3)
			echo ""
			read -p "Do you really want to remove OpenVPN? [y/n]: " -e -i n REMOVE
			if [[ 'y' = "$REMOVE" ]]; then
				PORT=$(grep '^port ' ${file_openvpn_conf} | cut -d " " -f 2)
				if pgrep firewalld; then
					# Using both permanent and not permanent rules to avoid a firewalld reload.
					firewall-cmd --zone=public --remove-port=$PORT/udp
					firewall-cmd --zone=trusted --remove-source=10.8.0.0/24
					firewall-cmd --permanent --zone=public --remove-port=$PORT/udp
					firewall-cmd --permanent --zone=trusted --remove-source=10.8.0.0/24
				fi
				if iptables -L -n | grep -qE 'REJECT|DROP'; then
					iptables -D INPUT -p ${PROTOCOL} --dport $PORT -j ACCEPT
					iptables -D FORWARD -s 10.8.0.0/24 -j ACCEPT
					iptables-save > $IPTABLES
				fi
				iptables -t nat -D POSTROUTING -o $NIC -s 10.8.0.0/24 -j MASQUERADE
				iptables-save > $IPTABLES
				if hash sestatus 2>/dev/null; then
					if sestatus | grep "Current mode" | grep -qs "enforcing"; then
						if [[ "$PORT" != '1194' ]]; then
							semanage port -d -t openvpn_port_t -p udp $PORT
						fi
					fi
				fi
				if [[ "$OS" = 'debian' ]]; then
					apt-get autoremove --purge -y openvpn
				elif [[ "$OS" = 'arch' ]]; then
					pacman -R openvpn --noconfirm
				else
					yum remove openvpn -y
				fi
				rm -rf ${dir_openvpn}
				rm -rf /usr/share/doc/openvpn*
				echo ""
				echo "OpenVPN removed!"
			else
				echo ""
				echo "Removal aborted!"
			fi
			exit
			;;
			4) exit;;
		esac
	done
fi

## OpenVPN setup and first user creation
if [[ ! -e ${file_openvpn_conf} ]]; then
	clear
cat <<EOF
Welcome to the secure OpenVPN installer (github.com/Angristan/OpenVPN-install)

I need to ask you a few questions before starting the setup
You can leave the default options and just press enter if you are ok with them
"
I need to know the IPv4 address of the network interface you want OpenVPN listening to.
If your server is running behind a NAT, (e.g. LowEndSpirit, Scaleway) leave the IP address as it is. (local/private IP)
Otherwise, it should be your public IPv4 address.
EOF
	read -p "IP address: " -e -i $IP IP
	echo ""
	echo "What port do you want for OpenVPN?"
	read -p "Port: " -e -i 1194 PORT
	echo ""
	echo "What protocol do you want for OpenVPN?"
	echo "Unless UDP is blocked, you should not use TCP (unnecessarily slower)"
	while [[ $PROTOCOL != "udp" && $PROTOCOL != "tcp" ]]; do
		read -p "Protocol [udp/tcp]: " -e -i udp PROTOCOL
	done
cat <<EOF
What DNS do you want to use with the VPN?
   1) Current system resolvers (from /etc/resolv.conf)
   2) Quad9 (Anycast: worldwide)
   3) FDN (France)
   4) DNS.WATCH (Germany)
   5) OpenDNS (Anycast: worldwide)
   6) Google (Anycast: worldwide)
   7) Yandex Basic (Russia)
   8) AdGuard DNS (Russia)
EOF
	while [[ $DNS != [1-8] ]]; do
		read -p "DNS [1-8]: " -e -i 1 DNS
	done
cat <<EOF
See https://github.com/Angristan/OpenVPN-install#encryption to learn more about 
the encryption in OpenVPN and the choices I made in this script.
Please note that all the choices proposed are secure (to a different degree)
and are still viable to date, unlike some default OpenVPN options

Choose which cipher you want to use for the data channel:
   1) AES-128-CBC (fastest and sufficiently secure for everyone, recommended)
   2) AES-192-CBC
   3) AES-256-CBC
Alternatives to AES, use them only if you know what you're doing.
They are relatively slower but as secure as AES.
   4) CAMELLIA-128-CBC
   5) CAMELLIA-192-CBC
   6) CAMELLIA-256-CBC
   7) SEED-CBC
EOF
	while [[ $CIPHER != [1-7] ]]; do
		read -p "Cipher [1-7]: " -e -i 1 CIPHER
	done
	case $CIPHER in
		1)
		CIPHER="cipher AES-128-CBC"
		;;
		2)
		CIPHER="cipher AES-192-CBC"
		;;
		3)
		CIPHER="cipher AES-256-CBC"
		;;
		4)
		CIPHER="cipher CAMELLIA-128-CBC"
		;;
		5)
		CIPHER="cipher CAMELLIA-192-CBC"
		;;
		6)
		CIPHER="cipher CAMELLIA-256-CBC"
		;;
		7)
		CIPHER="cipher SEED-CBC"
		;;
	esac
	echo ""
	echo "Choose what size of Diffie-Hellman key you want to use:"
	echo "   1) 2048 bits (fastest)"
	echo "   2) 3072 bits (recommended, best compromise)"
	echo "   3) 4096 bits (most secure)"
	while [[ $DH_KEY_SIZE != [1-3] ]]; do
		read -p "DH key size [1-3]: " -e -i 2 DH_KEY_SIZE
	done
	case $DH_KEY_SIZE in
		1)
		DH_KEY_SIZE="2048"
		;;
		2)
		DH_KEY_SIZE="3072"
		;;
		3)
		DH_KEY_SIZE="4096"
		;;
	esac
	echo ""
	echo "Choose what size of RSA key you want to use:"
	echo "   1) 2048 bits (fastest)"
	echo "   2) 3072 bits (recommended, best compromise)"
	echo "   3) 4096 bits (most secure)"
	while [[ $RSA_KEY_SIZE != [1-3] ]]; do
		read -p "RSA key size [1-3]: " -e -i 2 RSA_KEY_SIZE
	done
	case $RSA_KEY_SIZE in
		1)
		RSA_KEY_SIZE="2048"
		;;
		2)
		RSA_KEY_SIZE="3072"
		;;
		3)
		RSA_KEY_SIZE="4096"
		;;
	esac
	echo ""
	echo "Finally, tell me a name for the client certificate and configuration"
	while [[ $CLIENT = "" ]]; do
		echo "Please, use one word only, no special characters"
		read -p "Client name: " -e -i client CLIENT
	done
	echo ""
	echo "Okay, that was all I needed. We are ready to setup your OpenVPN server now"
	read -n1 -r -p "Press any key to continue..."

	if [[ "$OS" = 'debian' ]]; then
		apt-get install ca-certificates -y
		# We add the OpenVPN repo to get the latest version.
		# Debian 7
		if [[ "$VERSION_ID" = 'VERSION_ID="7"' ]]; then
			echo "deb http://build.openvpn.net/debian/openvpn/stable wheezy 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
		# Debian 8
		if [[ "$VERSION_ID" = 'VERSION_ID="8"' ]]; then
			echo "deb http://build.openvpn.net/debian/openvpn/stable jessie main" > /etc/apt/sources.list.d/openvpn.list
			wget -O - https://swupdate.openvpn.net/repos/repo-public.gpg | apt-key add -
			apt update
		fi
		# Ubuntu 12.04
		if [[ "$VERSION_ID" = 'VERSION_ID="12.04"' ]]; then
			echo "deb http://build.openvpn.net/debian/openvpn/stable precise 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 14.04
		if [[ "$VERSION_ID" = 'VERSION_ID="14.04"' ]]; then
			echo "deb http://build.openvpn.net/debian/openvpn/stable trusty main" > /etc/apt/sources.list.d/openvpn.list
			wget -O - https://swupdate.openvpn.net/repos/repo-public.gpg | apt-key add -
			apt-get update
		fi
		# Ubuntu >= 16.04 and Debian > 8 have OpenVPN > 2.3.3 without the need of a third party repository.
		# The we install OpenVPN
		apt-get install openvpn iptables openssl wget ca-certificates curl -y
		# Install iptables service
		if [[ ! -e /etc/systemd/system/iptables.service ]]; then
			mkdir /etc/iptables
			iptables-save > /etc/iptables/iptables.rules
			echo "#!/bin/sh
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT" > /etc/iptables/flush-iptables.sh
			chmod +x /etc/iptables/flush-iptables.sh
			echo "[Unit]
Description=Packet Filtering Framework
DefaultDependencies=no
Before=network-pre.target
Wants=network-pre.target
[Service]
Type=oneshot
ExecStart=/sbin/iptables-restore /etc/iptables/iptables.rules
ExecReload=/sbin/iptables-restore /etc/iptables/iptables.rules
ExecStop=/etc/iptables/flush-iptables.sh
RemainAfterExit=yes
[Install]
WantedBy=multi-user.target" > /etc/systemd/system/iptables.service
			systemctl daemon-reload
			systemctl enable iptables.service
		fi
	elif [[ "$OS" = 'centos' || "$OS" = 'fedora' ]]; then
		if [[ "$OS" = 'centos' ]]; then
			yum install epel-release -y
		fi
		yum install openvpn iptables openssl wget ca-certificates curl -y
		# Install iptables service
		if [[ ! -e /etc/systemd/system/iptables.service ]]; then
			mkdir /etc/iptables
			iptables-save > /etc/iptables/iptables.rules
			echo "#!/bin/sh
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT" > /etc/iptables/flush-iptables.sh
			chmod +x /etc/iptables/flush-iptables.sh
			echo "[Unit]
Description=Packet Filtering Framework
DefaultDependencies=no
Before=network-pre.target
Wants=network-pre.target
[Service]
Type=oneshot
ExecStart=/sbin/iptables-restore /etc/iptables/iptables.rules
ExecReload=/sbin/iptables-restore /etc/iptables/iptables.rules
ExecStop=/etc/iptables/flush-iptables.sh
RemainAfterExit=yes
[Install]
WantedBy=multi-user.target" > /etc/systemd/system/iptables.service
			systemctl daemon-reload
			systemctl enable iptables.service
			# Disable firewalld to allow iptables to start upon reboot
			systemctl disable firewalld
			systemctl mask firewalld
		fi
	else
		# Else, the distro is ArchLinux
		echo ""
		echo ""
		echo "As you're using ArchLinux, I need to update the packages on your system to install those I need."
		echo "Not doing that could cause problems between dependencies, or missing files in repositories."
		echo ""
		echo "Continuing will update your installed packages and install needed ones."
		while [[ $CONTINUE != [yn] ]]; do
			read -p "Continue ? [y/n]: " -e -i y CONTINUE
		done
		if [[ "$CONTINUE" = "n" ]]; then
			echo "Ok, bye !"
			exit 4
		fi

		if [[ "$OS" = 'arch' ]]; then
			# Install dependencies
			pacman -Syu openvpn iptables openssl wget ca-certificates curl --needed --noconfirm
			iptables-save > /etc/iptables/iptables.rules # iptables won't start if this file does not exist
			systemctl daemon-reload
			systemctl enable iptables
			systemctl start iptables
		fi
	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
	## function install_easyrsa
	install_easyrsa
	
	cd /etc/openvpn/easy-rsa/
	echo "set_var EASYRSA_KEY_SIZE $RSA_KEY_SIZE" > vars
	# Create the PKI, set up the CA, the DH params and the server + client certificates
	./easyrsa init-pki
	./easyrsa --batch build-ca nopass
	openssl dhparam -out dh.pem $DH_KEY_SIZE
	./easyrsa build-server-full server nopass
	./easyrsa build-client-full $CLIENT nopass
	EASYRSA_CRL_DAYS=3650 ./easyrsa gen-crl
	# generate tls-auth key
	openvpn --genkey --secret /etc/openvpn/tls-auth.key
	# Move all the generated files
	cp pki/ca.crt pki/private/ca.key dh.pem pki/issued/server.crt pki/private/server.key /etc/openvpn/easy-rsa/pki/crl.pem /etc/openvpn/
	# Make cert revocation list readable for non-root
	chmod 644 /etc/openvpn/crl.pem

	# Generate server.conf
	echo "port $PORT
proto ${PROTOCOL}
dev tun
user nobody
group $NOGROUP
persist-key
persist-tun
keepalive 10 120
topology subnet
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt" >> /etc/openvpn/server.conf
	# DNS resolvers
	case $DNS in
		1)
		# Obtain the resolvers from resolv.conf and use them for OpenVPN
		grep -v '#' /etc/resolv.conf | grep 'nameserver' | grep -E -o '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}' | while read line; do
			echo "push \"dhcp-option DNS $line\"" 
		done
		;;
		2) #Quad9
		echo 'push "dhcp-option DNS 9.9.9.9"' 
		;;
		3) #FDN
		echo 'push "dhcp-option DNS 80.67.169.12"'
		echo 'push "dhcp-option DNS 80.67.169.40"'
		;;
		4) #DNS.WATCH
		echo 'push "dhcp-option DNS 84.200.69.80"'
		echo 'push "dhcp-option DNS 84.200.70.40"'
		;;
		5) #OpenDNS
		echo 'push "dhcp-option DNS 208.67.222.222"'
		echo 'push "dhcp-option DNS 208.67.220.220"'
		;;
		6) #Google
		echo 'push "dhcp-option DNS 8.8.8.8"'
		echo 'push "dhcp-option DNS 8.8.4.4"'
		;;
		7) #Yandex Basic
		echo 'push "dhcp-option DNS 77.88.8.8"'
		echo 'push "dhcp-option DNS 77.88.8.1"'
		;;
		8) #AdGuard DNS
		echo 'push "dhcp-option DNS 176.103.130.130"'
		echo 'push "dhcp-option DNS 176.103.130.131"'
		;;
	esac >> /etc/openvpn/server.conf
echo 'push "redirect-gateway def1 bypass-dhcp" '>> /etc/openvpn/server.conf
echo "crl-verify crl.pem
ca ca.crt
cert server.crt
key server.key
tls-auth tls-auth.key 0
dh dh.pem
auth SHA256
$CIPHER
tls-server
tls-version-min 1.2
tls-cipher TLS-DHE-RSA-WITH-AES-128-GCM-SHA256
status openvpn.log
verb 3" >> /etc/openvpn/server.conf

	## function set_firewall 
	set_firewall
	
	# And finally, restart OpenVPN
	if [[ "$OS" = 'debian' ]]; then
		# Little hack to check for systemd
		if pgrep systemd-journal; then
				#Workaround to fix OpenVPN service on OpenVZ
				sed -i 's|LimitNPROC|#LimitNPROC|' /lib/systemd/system/openvpn\@.service
				sed -i 's|/etc/openvpn/server|/etc/openvpn|' /lib/systemd/system/openvpn\@.service
				sed -i 's|%i.conf|server.conf|' /lib/systemd/system/openvpn\@.service
				systemctl daemon-reload
				systemctl restart openvpn
				systemctl enable openvpn
		else
			/etc/init.d/openvpn restart
		fi
	else
		if pgrep systemd-journal; then
			if [[ "$OS" = 'arch' || "$OS" = 'fedora' ]]; then
				#Workaround to avoid rewriting the entire script for Arch & Fedora
				sed -i 's|/etc/openvpn/server|/etc/openvpn|' /usr/lib/systemd/system/openvpn-server@.service
				sed -i 's|%i.conf|server.conf|' /usr/lib/systemd/system/openvpn-server@.service
				systemctl daemon-reload
				systemctl restart openvpn-server@openvpn.service
				systemctl enable openvpn-server@openvpn.service
			else
				systemctl restart openvpn@server.service
				systemctl enable openvpn@server.service
			fi
		else
			service openvpn restart
			chkconfig openvpn on
		fi
	fi
	# Try to detect a NATed connection and ask about it to potential LowEndSpirit/Scaleway users
	EXTERNALIP=$(wget -qO- ipv4.icanhazip.com)
	if [[ "$IP" != "$EXTERNALIP" ]]; then
		echo ""
		echo "Looks like your server is behind a NAT!"
		echo ""
        echo "If your server is NATed (e.g. LowEndSpirit, Scaleway, or behind a router),"
        echo "then I need to know the address that can be used to access it from outside."
        echo "If that's not the case, just ignore this and leave the next field blank"
        read -p "External IP or domain name: " -e USEREXTERNALIP
		if [[ "$USEREXTERNALIP" != "" ]]; then
			IP=$USEREXTERNALIP
		fi
	fi
	
	# client-template.txt is created so we have a template to add further users later
	echo "client" > ${file_client_tpl}
	if [[ "$PROTOCOL" = 'udp' ]]; then
		echo "proto ${PROTOCOL}" >> ${file_client_tpl}
	elif [[ "$PROTOCOL" = 'tcp' ]]; then
		echo "proto ${PROTOCOL}-client" >> ${file_client_tpl}
	fi
	echo "remote $IP $PORT
dev tun
resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
auth SHA256
auth-nocache
$CIPHER
tls-client
tls-version-min 1.2
tls-cipher TLS-DHE-RSA-WITH-AES-128-GCM-SHA256
setenv opt block-outside-dns
verb 3" >> ${file_client_tpl}

	# function Generate the custom client.ovpn
	newclient "$CLIENT"
	echo ""
	echo "Finished!"
	echo ""
	echo "Your client config is available at $homeDir/$CLIENT.ovpn"
	echo "If you want to add more clients, you simply need to run this script another time!"
fi
exit 0;