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openvpn-install.sh
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#!/bin/bash
## Inspired by https://git.io/vpn but for Ubuntu only
group_name="nogroup"
new_client () {
# Generates the custom client.ovpn
{
cat /etc/openvpn/server/client-common.txt
echo "<ca>"
cat /etc/openvpn/server/easy-rsa/pki/ca.crt
echo "</ca>"
echo "<cert>"
sed -ne '/BEGIN CERTIFICATE/,$ p' /etc/openvpn/server/easy-rsa/pki/issued/"$client".crt
echo "</cert>"
echo "<key>"
cat /etc/openvpn/server/easy-rsa/pki/private/"$client".key
echo "</key>"
echo "<tls-crypt>"
sed -ne '/BEGIN OpenVPN Static key/,$ p' /etc/openvpn/server/tc.key
echo "</tls-crypt>"
} > ~/"$client".ovpn
}
ip=$(ip -4 addr | grep inet | grep -vE '127(\.[0-9]{1,3}){3}' | cut -d '/' -f 1 | grep -oE '[0-9]{1,3}(\.[0-9]{1,3}){3}' | sed -n 1p)
protocol="udp"
port="1194"
client="do-vpn"
# Prevent "Unable to acquire the dpkg frontend lock"
until apt-get update && apt-get install -y openvpn openssl ca-certificates iptables
do
echo "Retry packages installation"
done
# Get easy-rsa
easy_rsa_url='https://github.com/OpenVPN/easy-rsa/releases/download/v3.0.8/EasyRSA-3.0.8.tgz'
mkdir -p /etc/openvpn/server/easy-rsa/
{ wget -qO- "$easy_rsa_url" 2>/dev/null || curl -sL "$easy_rsa_url" ; } | tar xz -C /etc/openvpn/server/easy-rsa/ --strip-components 1
chown -R root:root /etc/openvpn/server/easy-rsa/
cd /etc/openvpn/server/easy-rsa/
# Create the PKI, set up the CA and the server and client certificates
./easyrsa init-pki
./easyrsa --batch build-ca nopass
EASYRSA_CERT_EXPIRE=3650 ./easyrsa build-server-full server nopass
EASYRSA_CERT_EXPIRE=3650 ./easyrsa build-client-full "$client" nopass
EASYRSA_CRL_DAYS=3650 ./easyrsa gen-crl
# Move the stuff we need
cp pki/ca.crt pki/private/ca.key pki/issued/server.crt pki/private/server.key pki/crl.pem /etc/openvpn/server
# CRL is read with each client connection, while OpenVPN is dropped to nobody
chown nobody:"$group_name" /etc/openvpn/server/crl.pem
# Without +x in the directory, OpenVPN can't run a stat() on the CRL file
chmod o+x /etc/openvpn/server/
# Generate key for tls-crypt
openvpn --genkey --secret /etc/openvpn/server/tc.key
# Create the DH parameters file using the predefined ffdhe2048 group
echo '-----BEGIN DH PARAMETERS-----
MIIBCAKCAQEA//////////+t+FRYortKmq/cViAnPTzx2LnFg84tNpWp4TZBFGQz
+8yTnc4kmz75fS/jY2MMddj2gbICrsRhetPfHtXV/WVhJDP1H18GbtCFY2VVPe0a
87VXE15/V8k1mE8McODmi3fipona8+/och3xWKE2rec1MKzKT0g6eXq8CrGCsyT7
YdEIqUuyyOP7uWrat2DX9GgdT0Kj3jlN9K5W7edjcrsZCwenyO4KbXCeAvzhzffi
7MA0BM0oNC9hkXL+nOmFg/+OTxIy7vKBg8P+OxtMb61zO7X8vC7CIAXFjvGDfRaD
ssbzSibBsu/6iGtCOGEoXJf//////////wIBAg==
-----END DH PARAMETERS-----' > /etc/openvpn/server/dh.pem
# Generate server.conf
echo "local $ip
port $port
proto $protocol
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh.pem
auth SHA512
tls-crypt tc.key
topology subnet
server 10.8.0.0 255.255.255.0" > /etc/openvpn/server/server.conf
echo 'push "redirect-gateway def1 bypass-dhcp"' >> /etc/openvpn/server/server.conf
echo 'ifconfig-pool-persist ipp.txt' >> /etc/openvpn/server/server.conf
# Locate the proper resolv.conf
# Needed for systems running systemd-resolved
if grep -q '^nameserver 127.0.0.53' "/etc/resolv.conf"; then
resolv_conf="/run/systemd/resolve/resolv.conf"
else
resolv_conf="/etc/resolv.conf"
fi
# Obtain the resolvers from resolv.conf and use them for OpenVPN
grep -v '^#\|^;' "$resolv_conf" | grep '^nameserver' | grep -oE '[0-9]{1,3}(\.[0-9]{1,3}){3}' | while read line; do
echo "push \"dhcp-option DNS $line\"" >> /etc/openvpn/server/server.conf
done
echo "keepalive 10 120
cipher AES-256-CBC
user nobody
group $group_name
persist-key
persist-tun
verb 3
crl-verify crl.pem" >> /etc/openvpn/server/server.conf
echo "explicit-exit-notify" >> /etc/openvpn/server/server.conf
# Enable net.ipv4.ip_forward for the system
echo 'net.ipv4.ip_forward=1' > /etc/sysctl.d/99-openvpn-forward.conf
# Enable without waiting for a reboot or service restart
echo 1 > /proc/sys/net/ipv4/ip_forward
# Create a service to set up persistent iptables rules
iptables_path=$(command -v iptables)
echo "[Unit]
Before=network.target
[Service]
Type=oneshot
ExecStart=$iptables_path -t nat -A POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $ip
ExecStart=$iptables_path -I INPUT -p $protocol --dport $port -j ACCEPT
ExecStart=$iptables_path -I FORWARD -s 10.8.0.0/24 -j ACCEPT
ExecStart=$iptables_path -I FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
ExecStop=$iptables_path -t nat -D POSTROUTING -s 10.8.0.0/24 ! -d 10.8.0.0/24 -j SNAT --to $ip
ExecStop=$iptables_path -D INPUT -p $protocol --dport $port -j ACCEPT
ExecStop=$iptables_path -D FORWARD -s 10.8.0.0/24 -j ACCEPT
ExecStop=$iptables_path -D FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT" > /etc/systemd/system/openvpn-iptables.service
echo "RemainAfterExit=yes
[Install]
WantedBy=multi-user.target" >> /etc/systemd/system/openvpn-iptables.service
systemctl enable --now openvpn-iptables.service
# client-common.txt is created so we have a template to add further users later
echo "client
dev tun
proto $protocol
remote $ip $port
resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
auth SHA512
cipher AES-256-CBC
ignore-unknown-option block-outside-dns
block-outside-dns
verb 3" > /etc/openvpn/server/client-common.txt
# Enable and start the OpenVPN service
systemctl enable --now openvpn-server@server.service
# Generates the custom client.ovpn
new_client
echo
echo "Finished!"
echo
echo "The client configuration is available in:" ~/"$client.ovpn"
echo "New clients can be added by running this script again."