=====Quick setup=====
https://raw.githubusercontent.com/Nyr/openvpn-install/master/openvpn-install.sh

===== Long Setup =====

==== This was my starting point: ====

https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-debian-10

====Here is my steps====
===Step 1 — Installing OpenVPN and EasyRSA===
  sudo apt install openvpn
  wget https://github.com/OpenVPN/easy-rsa/releases/download/v3.0.8/EasyRSA-3.0.8.tgz
  aunpack ./EasyRSA-3.0.8.tgz
===Step 2 — Configuring the EasyRSA Variables and Building the CA===
  cd ./EasyRSA-3.0.8/
  cp vars.example vars
  vim ./vars
  
  Uncomment these lines and update the highlighted values to whatever you’d prefer, but do not leave them blank:
  . . .

  set_var EASYRSA_REQ_COUNTRY    "US"
  set_var EASYRSA_REQ_PROVINCE   "NewYork"
  set_var EASYRSA_REQ_CITY       "New York City"
  set_var EASYRSA_REQ_ORG        "DigitalOcean"
  set_var EASYRSA_REQ_EMAIL      "admin@example.com"
  set_var EASYRSA_REQ_OU         "Community"
===Step 3 — Creating the Server Certificate, Key, and Encryption Files===
  ./easyrsa init-pki
  "... Your newly created PKI dir is: /home/vissie/EasyRSA-3.0.8/pki"
  ./easyrsa build-ca
  "Pick a password"
  "name the server"
  "... Your new CA certificate file for publishing is at:
  /home/vissie/EasyRSA-3.0.8/pki/ca.crt
  cp ./pki/ca.crt /etc/openvpn/
  ./easyrsa gen-req server nopass
  sudo cp ./pki/private/server.key /etc/openvpn/
  ./easyrsa sign-req server server
  sudo cp ./pki/issued/server.crt /etc/openvpn/
  sudo cp ./pki/ca.crt /etc/openvpn/
  ./easyrsa gen-dh
  sudo openvpn --genkey --secret ta.key
  sudo cp ./ta.key /etc/openvpn/
  sudo cp ./pki/dh.pem /etc/openvpn/
===Step 4 — Generating a Client Certificate and Key Pair===
  cd ~
  mkdir -p ~/client-configs/keys
  chmod -R 700 ~/client-configs
  cd ~/EasyRSA-3.0.8/
  ./easyrsa gen-req vissie nopass
  cp ./pki/private/vissie.key ~/client-configs/keys/
  ./easyrsa sign-req client vissie
  'Yes'
  'Password'
  cp ./pki/issued/vissie.crt ~/client-configs/keys/
  sudo cp ~/EasyRSA-3.0.8/ta.key ~/client-configs/keys/
  sudo cp /etc/openvpn/ca.crt ~/client-configs/keys/
===Step 5 — Configuring the OpenVPN Service===
  sudo cp /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz /etc/openvpn/
  sudo gzip -d /etc/openvpn/server.conf.gz
  sudo vim /etc/openvpn/server.conf
  ...
  tls-auth ta.key 0 # This file is secret
  cipher AES-256-CBC
  # Below this, add an auth directive
  auth SHA256
  #If necessary, change the file name by removing the 2048 so it aligns with the key you generated in the previous step:
  dh dh.pem
  user nobody
  group nogroup
  #Find the redirect-gateway
  push "redirect-gateway def1 bypass-dhcp"
  #Just below this, find the dhcp-option section. Again, remove the “;” from in front of both of the lines to uncomment them:
  push "dhcp-option DNS 208.67.222.222"
  push "dhcp-option DNS 208.67.220.220"
  # Optional!
  port 11
  # Optional!
  proto tcp
  #If you do switch the protocol to TCP, you will need to change the explicit-exit-notify directive’s value from 1 to 0
  explicit-exit-notify 0
  ...
===Step 6 — Adjusting the Server Networking Configuration===
  sudo vim /etc/sysctl.conf
  ...
  net.ipv4.ip_forward=1
  ...
  sudo sysctl -p
  ip route | grep default
  #Your public interface is the string found within this command’s output that follows the word “dev”. For example, this result shows the interface named eth0:
  #Output
  #default via 203.0.113.1 dev eth0 proto static
  
  sudo apt install ufw
  sudo vim /etc/ufw/before.rules
  
  # UFW rules are typically added using the ufw command. Rules listed in the before.rules file, though, are read and put into place before the conventional UFW rules are loaded. 
  # Towards the top of the file, add the highlighted lines below. This will set the default policy for the POSTROUTING chain in the nat table and masquerade any traffic coming 
  # from the VPN. Remember to replace eth0 in the -A POSTROUTING line below with the interface you found in the above command:

<sxh bash; gutter: false>
#
# rules.before
#
# Rules that should be run before the ufw command line added rules. Custom
# rules should be added to one of these chains:
#   ufw-before-input
#   ufw-before-output
#   ufw-before-forward
#

# START OPENVPN RULES
# NAT table rules
*nat
:POSTROUTING ACCEPT [0:0]
# Allow traffic from OpenVPN client to eth0 (change to the interface you discovered!)
-A POSTROUTING -s 10.8.0.0/8 -o eth0 -j MASQUERADE
COMMIT
# END OPENVPN RULES

# Don't delete these required lines, otherwise there will be errors
*filter
. . .
</sxh>  
  
  sudo vim /etc/default/ufw
  ...
  DEFAULT_FORWARD_POLICY="ACCEPT"
  ...
  sudo ufw allow 1194/udp
  sudo ufw allow OpenSSH
===Step 7 — Starting and Enabling the OpenVPN Service===
  sudo systemctl start openvpn@server
  sudo systemctl status openvpn@server
  sudo systemctl enable openvpn@server
===Step 8 — Creating the Client Configuration Infrastructure===
  mkdir -p ~/client-configs/files
  cp /usr/share/doc/openvpn/examples/sample-config-files/client.conf ~/client-configs/base.conf
  vim ~/client-configs/base.conf
  ...
  remote my.server.com 1194
  proto udp
  # Downgrade privileges after initialization (non-Windows only)
  user nobody
  group nogroup
  #ca ca.crt
  #cert client.crt
  #key client.key
  #tls-auth ta.key 1
  cipher AES-256-CBC
  auth SHA256
  key-direction 1
  # Finally, add a few commented out lines. Although you can include these directives in every client configuration file, you only need to enable them for Linux clients 
  # that ship with an /etc/openvpn/update-resolv-conf file. This script uses the resolvconf utility to update DNS information for Linux clients.
  # script-security 2
  # up /etc/openvpn/update-resolv-conf
  # down /etc/openvpn/update-resolv-conf
  ...
  vim ~/client-configs/make_config.sh
  
  #!/bin/bash

# First argument: Client identifier
<sxh bash; gutter: false>
KEY_DIR=/home/sammy/client-configs/keys
OUTPUT_DIR=/home/sammy/client-configs/files
BASE_CONFIG=/home/sammy/client-configs/base.conf

cat ${BASE_CONFIG} \
    <(echo -e '<ca>') \
    ${KEY_DIR}/ca.crt \
    <(echo -e '</ca>\n<cert>') \
    ${KEY_DIR}/${1}.crt \
    <(echo -e '</cert>\n<key>') \
    ${KEY_DIR}/${1}.key \
    <(echo -e '</key>\n<tls-auth>') \
    ${KEY_DIR}/ta.key \
    <(echo -e '</tls-auth>') \
    > ${OUTPUT_DIR}/${1}.ovpn
</sxh>
  chmod 700 ~/client-configs/make_config.sh
===Step 9 — Generating Client Configurations===  
  cd ~/client-configs
  sudo ./make_config.sh vissie
  ls ~/client-configs/files
===Step 10 — Installing the Client Configuration===
  sudo apt install openvpn
  # Check to see if your distribution includes an /etc/openvpn/update-resolv-conf script:
  ls /etc/openvpn
  update-resolv-conf
  #Next, edit the OpenVPN client configuration file you transfered:
  vim client1.ovpn
<sxh bash; gutter: false>
...
script-security 2
up /etc/openvpn/update-resolv-conf
down /etc/openvpn/update-resolv-conf
...
</sxh>  
  

  
==== Here is my notes: ==== 
Use dig command for determining my public IP address:
  sudo apt-get install dnsutils
  dig +short myip.opendns.com @resolver1.opendns.com

On step 3, I got an permision denied error onL
  echo 1 > /proc/sys/net/ipv4/ip_forward

So rather I did:

In a nutshell, to enable IP forwarding, you can just put the following in /etc/sysctl.conf:
  net.ipv4.ip_forward = 1
  sudo sysctl -p

Plus I did both ipv4 and ipv6. Not knowing if that was correct. But it made sense to me that it would be.

For step 4 I had to use my actual network interface in the before,rule, not eth0.

For Step 5, sudo did NOT work. I had to BE root.

You might have the following issue :
 **************************************************************
   No /etc/openvpn/easy-rsa/openssl.cnf file could be found
   Further invocations will fail
 **************************************************************
In this case, just create a symbolic link :
  ln -s openssl-1.0.0.cnf openssl.cnf

And then clean everything :

I just did a install on Debian Jessie. I had the same issues. Seemingly the service started, no visual errors, but openvpn was not running. a
  sudo netstat -uapn | grep openvpn
came up blank. After hours of trouble shooting I eventually came upon this way of starting the service
  systemctl start openvpn@server.service.
This failed! Now I had a error.
  journalctl -xn
showed me a error on TUN/TAP.

I had a issue with a ta-key. I just disabled that:
 If you do not have a ta.key, of course tls-auth will fail. You may:

 drop the tls-auth instruction altogether. This is not a major dent in your security: the Manual in fact states:
 This feature by itself does not improve the TLS auth in any way, although it offers a 2nd line of defense if a future flaw is discovered in a particular TLS cipher-suite or 
 implementation (such as CVE-2014-0160, Heartbleed, where the tls-auth key provided protection against attackers who did not have a copy). However, it offers no protection at 
 all in the event of a complete cryptographic break that can allow decryption of a cipher-suite's traffic.
 or you may now generate the ta-key:

 openvpn --genkey --secret /etc/openvpn/easy-rsa/keys/ta.key
it is not too late for this.


Some more hours later I realised, that due to the fact that I was on a VPS, I had no TUN/TAP access from my provider as a default! I had to enable it via a console option.

I did that, the server rebooted. And now I have my openVPN.

So, 10 points to the author on a great setup guide! Thx dude.

I hope this little bit of info helps someone.


===== Tips ===== 
==== View connected users ====

  sudo cat /etc/openvpn/openvpn-status.log

==== Logs ====
If you’re customizing rules for your own installation and breaking things on your server and clients to catch errors to match, you probably want to change your logging method in /etc/openvpn/server.conf from log /var/log/openvpn.log to log-append /var/log/openvpn.log and restart OpenVPN to keep your logs from being blown away when you stop and start. Then switch it back to log after you’re done.

==== Connection issues ====
Please remember, if your VPN is up, but there is no traffic going to the internet, make sure that UFW is running and that the rules is setup correctly.

===== New notes for Debian 9 (Stretch) =====
  apt-get install openvpn easy-rsa