In this guide we will show you how to setup OpenVPN on centos – the guide will give you a fully working OpenVPN installation, NOT TESTED ON OTHER DISTROS..

First step is to check if tun/tap is active:

cat /dev/net/tun

If tun is active then you should see this:

cat: /dev/net/tun: File descriptor in bad state

Make sure you have these packages installed:

yum install gcc make rpm-build autoconf.noarch zlib-devel pam-devel openssl-devel -y

Download LZO RPM and Configure RPMForge Repo:

wget http://openvpn.net/release/lzo-1.08-4.rf.src.rpm

32bit Package:

CentOS 5:

wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.2-2.el5.rf.i386.rpm

CentOS 6:

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.i686.rpm

64bit Package:

CentOS 5:

wget http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.2-2.el5.rf.x86_64.rpm

CentOS 6:

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm

Build the rpm packages:

rpmbuild --rebuild lzo-1.08-4.rf.src.rpm
rpm -Uvh lzo-*.rpm
rpm -Uvh rpmforge-release*

Install OpenVPN:

yum install openvpn -y

Copy the easy-rsa folder to /etc/openvpn/:

cp -R /usr/share/doc/openvpn-2.2.2/easy-rsa/ /etc/openvpn/

**PLEASE NOTE** if the above command brings up an error such as below, then please follow the following steps to download and copy over easy-rsa as its not included in the new build OpenVPN 2.3.1:

cannot stat `/usr/share/doc/openvpn-2.2.2/easy-rsa/’: No such file or directory

Download easy-rsa from below:

wget https://github.com/downloads/OpenVPN/easy-rsa/easy-rsa-2.2.0_master.tar.gz

Extract the package:

tar -zxvf easy-rsa-2.2.0_master.tar.gz

Copy to OpenVPN directory:

cp -R easy-rsa-2.2.0_master/easy-rsa/ /etc/openvpn/

Please note on CentOS 6 we need to make a small change before you run the commands below, open up /etc/openvpn/easy-rsa/2.0/vars and edit the below line:

Change:

export KEY_CONFIG=`$EASY_RSA/whichopensslcnf $EASY_RSA`

To:

export KEY_CONFIG=/etc/openvpn/easy-rsa/2.0/openssl-1.0.0.cnf

And save..

Now let’s create the certificate:

cd /etc/openvpn/easy-rsa/2.0
chmod 755 *
source ./vars
./vars
./clean-all

Build CA:

./build-ca
Country Name: may be filled or press enter
State or Province Name: may be filled or press enter
City: may be filled or press enter
Org Name: may be filled or press enter
Org Unit Name: may be filled or press enter
Common Name: your server hostname
Email Address: may be filled or press enter

Build key server:

./build-key-server server
Almost the same with ./build.ca but check the changes and additional
Common Name: server
A challenge password: leave
Optional company name: fill or enter
sign the certificate: y
1 out of 1 certificate requests: y

Build Diffie Hellman (wait a moment until the process finish):

./build-dh

Now create your config file:

touch /etc/openvpn/server.conf

And enter the following:

port 1194 #- port
proto udp #- protocol
dev tun
tun-mtu 1500
tun-mtu-extra 32
mssfix 1450
reneg-sec 0
ca /etc/openvpn/easy-rsa/2.0/keys/ca.crt
cert /etc/openvpn/easy-rsa/2.0/keys/server.crt
key /etc/openvpn/easy-rsa/2.0/keys/server.key
dh /etc/openvpn/easy-rsa/2.0/keys/dh1024.pem
plugin /usr/share/openvpn/plugin/lib/openvpn-auth-pam.so /etc/pam.d/login #- Comment this line if you are using FreeRADIUS
#plugin /etc/openvpn/radiusplugin.so /etc/openvpn/radiusplugin.cnf #- Uncomment this line if you are using FreeRADIUS
client-cert-not-required
username-as-common-name
server 10.8.0.0 255.255.255.0
push "redirect-gateway def1"
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"
keepalive 5 30
comp-lzo
persist-key
persist-tun
status 1194.log
verb 3

Save it.

Before we start OpenVPN, lets disable SELinux if enabled, this can cause issues with OpenVPN, especially when using OpenVPN with multiple configs:

echo 0 > /selinux/enforce

This is a temporary solution and will re-enable once you reboot your system, to disable on a permanent basis you need to edit the following /etc/selinux/config and edit this line:

SELINUX=enforcing

To:

SELINUX=disabled

When your system next reboots it will still be disabled.

Now lets start OpenVPN:

service openvpn restart

*Please note if you receive “FAIL” when OpenVPN trys to start and you have the following error in your /var/log/messages:

PLUGIN_INIT: could not load plugin shared object /usr/share/openvpn/plugin/lib/openvpn-auth-pam.so: /usr/share/openvpn/plugin/lib/openvpn-auth-pam.so: cannot open shared object file: No such file or directory

Then this is because the latest OpenVPN package doesn’t include this file (which is reported to be fixed soon) but you can download the pam auth file from here for now:

wget http://safesrv.net/public/openvpn-auth-pam.zip

Extract the file:

unzip openvpn-auth-pam.zip

Move to the OpenVPN directory:

mv openvpn-auth-pam.so /etc/openvpn/openvpn-auth-pam.so

Then replace the PAM plugin line in your server.conf to below:

plugin /etc/openvpn/openvpn-auth-pam.so /etc/pam.d/login

Restart OpenVPN and all should now work:

killall -9 openvpn
service openvpn restart

Now we need to enable IP forwarding. So open the file /etc/sysctl.conf and set ‘net.ipv4.ip_forward’ to 1.

net.ipv4.ip_forward = 1

To make the changes to sysctl.conf take effect, use the following command.

sysctl -p

Route Iptables:

The rule below will work fine on xen and KVM based VPS’s but for OpenVZ use the OpenVZ iptable rule instead:

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

OpenVZ iptable rules:

iptables -t nat -A POSTROUTING -o venet0 -j SNAT --to-source 123.123.123.123

And

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -j SNAT --to-source 123.123.123.123

Make sure you change 123.123.123.123 to your server IP.

IF you have CSF on the same server you need to open your OpenVPN port (Usually 1194) through the firewall and run the below commands for CSF, also its a good idea to add them to /etc/csf/csfpre.sh.

iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 10.8.0.0/24 -j ACCEPT
iptables -A FORWARD -j REJECT
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
iptables -t nat -A POSTROUTING -j SNAT --to-source 123.123.123.123

If the above rules cause you any problems or don’t seem to work (Especially on cPanel servers) then remove the rules above and use below:

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE
iptables -A FORWARD -i tun0 -o eth0 -j ACCEPT
iptables -A FORWARD -i eth0 -o tun0 -j ACCEPT

Please make sure 123.123.123.123 is your main server IP.

Then run…

service iptables save
Setup

To setup OpenVPN with your FreeRADIUS installation please follow this link.

Setup

Please note if you are using our FreeRADIUS module for WHMCS then you don’t have to do the below step for adding users just follow the link above to setup OpenVPN to auth off FreeRADIUS – otherwise you can create a user as follows:

useradd username -s /bin/false
passwd username

If you wanted to delete a user you would use:

userdel username

Now create a server.ovpn config file and enter the following:

client
dev tun
proto udp
remote 123.123.123.123 1194 # - Your server IP and OpenVPN Port
resolv-retry infinite
nobind
tun-mtu 1500
tun-mtu-extra 32
mssfix 1450
persist-key
persist-tun
ca ca.crt
auth-user-pass
comp-lzo
reneg-sec 0
verb 3

Make sure you change 123.123.123.123 to your server IP.

And make sure OpenVPN starts at boot:

chkconfig openvpn on

Download ca.crt file in /etc/openvpn/easy-rsa/2.0/keys/ directory and place it in the same directory as your server.ovpn.

Now download a VPN client and import your config file and enter your username and password created above or if you have already configured OpeVPN Source with the FreeRADIUS plugin, use a username and password created in the radius database.