Run openvpn as service linux

Connecting to Access Server with Linux

Client software choice

Connecting to OpenVPN Access Server from Linux requires a client program. It will capture the traffic you wish to send through the OpenVPN tunnel, encrypting it and passing it to the OpenVPN server. And of course, the reverse, to decrypt the return traffic.

Linux Packages Discussed

OpenVPN Access Server	openvpn-as
OpenVPN 3 Linux Client	openvpn3
OpenVPN open source	openvpn

OpenVPN 3 Linux Client

The OpenVPN 3 Linux project is a new client built on top of the OpenVPN 3 Core Library. This client is the official OpenVPN Linux Client program. You can find an overview of the features, frequently asked questions, and instructions on installing the openvpn3 package on our OpenVPN 3 for Linux site.

After following the instructions there to install the client, you’ll need a connection profile. This is a file generated by your OpenVPN Access Server installation for your specific user account. It contains the required certificates and connection settings. Go to the Client web interface of your Access Server (the main address, not the /admin portion). Log in with your user credentials. You will be shown a list of files available to download. Pick the user-locked profile or the auto-login profile, and you will be sent a client.ovpn file. Save this file to your Linux operating system.

Once you’ve moved the file to your Linux system, you can import it.

You can start a new VPN session:

You can manage a running VPN session:

And so on. More details can be found here: OpenVPN3Linux.

OpenVPN open source OpenVPN CLI program

The open source project client program can also connect to the Access Server. The package is available in most distributions and is known simply as openvpn. It supports the option to connect to multiple OpenVPN servers simultaneously, and it comes with a service component that can automatically and silently start any auto-login profiles it finds in the /etc/openvpn folder, even before a user has logged in. This service component can be set to automatically start at boot time with the tools available in your Linux distribution if supported. On Ubuntu and Debian, when you install the openvpn package, it is automatically configured to start at boot time.

To install the OpenVPN client on Linux, it is possible in many cases to just use the version that is in the software repository for the Linux distribution itself. If you run into any connectivity problems when using outdated software, it may be due to a possible lack of support for higher TLS versions in older versions of OpenVPN. Follow the instructions found on the open source openvpn community wiki if you wish to install the OpenVPN client on your Linux system.

After installing, you will need a connection profile. This is a file generated by your OpenVPN Access Server installation for your specific user account. It contains the required certificates and connection settings. Go to the Client web interface of your Access Server (the main address, not the /admin portion). Log in with your user credentials. You will be shown a list of files available to you for download. Pick the user-locked profile or the auto-login profile, and you will be sent a client.ovpn file. Save this file to your Linux operating system somewhere. OpenVPN Access Server supports server-locked, user-locked, and auto-login profiles, but the OpenVPN command line client is only able to connect with user-locked or auto-login connection profiles.

We are assuming you are going to start the connection through either the command line as a root user, or via the service daemon. If you want unprivileged users to be able to make a connection, take a look at the community wiki for more information on how to implement that. Here we are going to focus on the simplest implementation; run the connection as root user directly, or via the service daemon.

Start a connection with an auto-login profile manually:

Start a connection with a user-locked profile manually:

If you use Google Authenticator or another extra factor authentication, add the auth-retry parameter:

To start an auto-login connection via the service daemon, place client.ovpn in /etc/openvpn/ and rename the file. It must end with .conf as file extension. Ensure the service daemon is enabled to run after a reboot, and then simply reboot the system. The auto-login type profile will be picked up automatically and the connection will start itself. You can verify this by checking the output of the ifconfig command; you should see a tun0 network adapter in the list.

One major feature that is missing with the command line client is the ability to automatically implement DNS servers that are pushed by the VPN server. It is possible, but it requires you to install a DNS management program such as resolvconf or openresolv, and it may or may not clash with existing network management software in your OS. The idea here, however, is that you use a script that runs when the connection goes up, and when it goes down, that uses resolvconf or openresolv to implement the DNS servers for you. The reason why this client is not able to manage it completely by itself is mainly because in an operating system like Windows, Macintosh, Android, or iOS, there is already an established single method of handling DNS management. It is therefore easy for us to create a software client for those operating systems that already knows how to handle DNS. But Linux is available in so many variations and also supports different programs and methods of implementing DNS servers, and so it was only reasonable to leave built-in DNS support out of the OpenVPN program and instead to provide, where possible, a script that handles DNS implementation. Such a script could even be written by yourself to do whatever tasks are necessary to implement the DNS servers in your unique situation.

Fortunately on Ubuntu and Debian, for example, there is the /etc/openvpn/update-resolv-conf script that comes with the openvpn package that handles DNS implementation for these operating systems. You need only to activate the use of these by following the instructions:

Open your client.ovpn file in a text editor:

At the very bottom simply add these lines:

The first line enables the use of external scripts to handle the DNS implementation tasks. The up and down lines are there to implement DNS servers pushed by the VPN server when the connection goes up, and afterwards to undo it, when the connection goes down.

Ubuntu network management program

There is also the option of connecting through the GUI using the openvpn extension for the Gnome network manager plugin. But this is currently a bit tricky to set up. There is for example the incorrect assumption that all VPNs will be able to redirect Internet traffic, and older versions might not understand the .ovpn file format, requiring you to split up the certificate embedded in it into separate file. And you would likely have to dig into the options to ensure that a default Internet traffic route going through the VPN server is not always enabled by default, especially for servers where you only give access to some internal resources, and not the entire Internet. However the advantage of using the GUI component is that you can start/stop the connection from the desktop environment on Linux.

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OpenVPN

If you want more than just pre-shared keys OpenVPN makes it easy to set up a Public Key Infrastructure (PKI) to use SSL/TLS certificates for authentication and key exchange between the VPN server and clients. OpenVPN can be used in a routed or bridged VPN mode and can be configured to use either UDP or TCP. The port number can be configured as well, but port 1194 is the official one; this single port is used for all communication. VPN client implementations are available for almost anything including all Linux distributions, OS X, Windows and OpenWRT based WLAN routers.

Server Installation

To install openvpn in a terminal enter:

Public Key Infrastructure Setup

The first step in building an OpenVPN configuration is to establish a PKI (public key infrastructure). The PKI consists of:

a separate certificate (also known as a public key) and private key for the server and each client.

a master Certificate Authority (CA) certificate and key, used to sign the server and client certificates.

OpenVPN supports bidirectional authentication based on certificates, meaning that the client must authenticate the server certificate and the server must authenticate the client certificate before mutual trust is established.

Both server and client will authenticate the other by first verifying that the presented certificate was signed by the master certificate authority (CA), and then by testing information in the now-authenticated certificate header, such as the certificate common name or certificate type (client or server).

Certificate Authority Setup

To setup your own Certificate Authority (CA) and generate certificates and keys for an OpenVPN server and multiple clients first copy the easy-rsa directory to /etc/openvpn . This will ensure that any changes to the scripts will not be lost when the package is updated. From a terminal, run:

Note: If desired, you can alternatively edit /etc/openvpn/easy-rsa/vars directly, adjusting it to your needs.

As root user change to the newly created directory /etc/openvpn/easy-rsa and run:

Server Keys and Certificates

Next, we will generate a key pair for the server:

Diffie Hellman parameters must be generated for the OpenVPN server. The following will place them in pki/dh.pem .

And finally a certificate for the server:

All certificates and keys have been generated in subdirectories. Common practice is to copy them to /etc/openvpn/:

Client Certificates

The VPN client will also need a certificate to authenticate itself to the server. Usually you create a different certificate for each client.

This can either be done on the server (as the keys and certificates above) and then securely distributed to the client. Or vice versa: the client can generate and submit a request that is sent and signed by the server.

To create the certificate, enter the following in a terminal while being user root:

If the first command above was done on a remote system, then copy the .req file to the CA server. There you can then import it via easyrsa import-req /incoming/myclient1.req myclient1 . Then you can go on with the second sign-eq command.

In both cases, afterwards copy the following files to the client using a secure method:

As the client certificates and keys are only required on the client machine, you can remove them from the server.

Simple Server Configuration

Along with your OpenVPN installation you got these sample config files (and many more if you check):

Start with copying and unpacking server.conf.gz to /etc/openvpn/server.conf.

Edit /etc/openvpn/myserver.conf to make sure the following lines are pointing to the certificates and keys you created in the section above.

Complete this set with a ta key in etc/openvpn for tls-auth like:

Edit /etc/sysctl.conf and uncomment the following line to enable IP forwarding.

Then reload sysctl.

That is the minimum you have to configure to get a working OpenVPN server. You can use all the default settings in the sample server.conf file. Now start the server.

Be aware that the “systemctl start openvpn” is not starting your openvpn you just defined.
Openvpn uses templatized systemd jobs, openvpn@CONFIGFILENAME. So if for example your configuration file is myserver.conf your service is called openvpn@myserver. You can run all kinds of service and systemctl commands like start/stop/enable/disable/preset against a templatized service like openvpn@server.

You will find logging and error messages in the journal. For example, if you started a templatized service openvpn@server you can filter for this particular message source with:

The same templatized approach works for all of systemctl:

You can enable/disable various openvpn services on one system, but you could also let Ubuntu do it for you. There is config for AUTOSTART in /etc/default/openvpn . Allowed values are “all”, “none” or space separated list of names of the VPNs. If empty, “all” is assumed. The VPN name refers to the VPN configutation file name. i.e. home would be /etc/openvpn/home.conf If you’re running systemd, changing this variable will require running systemctl daemon-reload followed by a restart of the openvpn service (if you removed entries you may have to stop those manually).

After “systemctl daemon-reload” a restart of the “generic” openvpn will restart all dependent services that the generator in /lib/systemd/system-generators/openvpn-generator created for your conf files when you called daemon-reload.

Now check if OpenVPN created a tun0 interface:

Simple Client Configuration

There are various different OpenVPN client implementations with and without GUIs. You can read more about clients in a later section on VPN Clients. For now we use commandline/service based OpenVPN client for Ubuntu which is part of the very same package as the server. So you have to install the openvpn package again on the client machine:

This time copy the client.conf sample config file to /etc/openvpn/:

Copy the following client keys and certificate files you created in the section above to e.g. /etc/openvpn/ and edit /etc/openvpn/client.conf to make sure the following lines are pointing to those files. If you have the files in /etc/openvpn/ you can omit the path.

And you have to specify the OpenVPN server name or address. Make sure the keyword client is in the config. That’s what enables client mode.

Now start the OpenVPN client with the same templatized mechanism:

You can check status as you did on the server:

On the server log an incoming connection looks like the following.
You can see client name and source address as well as success/failure messages.

And you can check on the client if it created a tun0 interface:

Check if you can ping the OpenVPN server:

The OpenVPN server always uses the first usable IP address in the client network and only that IP is pingable. E.g. if you configured a /24 for the client network mask, the .1 address will be used. The P-t-P address you see in the ip addr output above is usually not answering ping requests.

Check out your routes:

First trouble shooting

If the above didn’t work for you, check this:

• Check your journal -xe
• Check that you have specified the keyfile names correctly in client and server conf files
• Can the client connect to the server machine? Maybe a firewall is blocking access? Check journal on server.
• Client and server must use same protocol and port, e.g. UDP port 1194, see port and proto config option
• Client and server must use same config regarding compression, see comp-lzo config option
• Client and server must use same config regarding bridged vs routed mode, see server vs server-bridge config option

Advanced configuration

Advanced routed VPN configuration on server

The above is a very simple working VPN. The client can access services on the VPN server machine through an encrypted tunnel. If you want to reach more servers or anything in other networks, push some routes to the clients. E.g. if your company’s network can be summarized to the network 192.168.0.0/16, you could push this route to the clients. But you will also have to change the routing for the way back — your servers need to know a route to the VPN client-network.

The example config files that we have been using in this guide are full of all these advanced options in the form of a comment and a disabled configuration line as an example.

Please read the OpenVPN hardening security guide for further security advice.

Advanced bridged VPN configuration on server

OpenVPN can be setup for either a routed or a bridged VPN mode. Sometimes this is also referred to as OSI layer-2 versus layer-3 VPN. In a bridged VPN all layer-2 frames — e.g. all ethernet frames — are sent to the VPN partners and in a routed VPN only layer-3 packets are sent to VPN partners. In bridged mode all traffic including traffic which was traditionally LAN-local like local network broadcasts, DHCP requests, ARP requests etc. are sent to VPN partners whereas in routed mode this would be filtered.

Prepare interface config for bridging on server

First, use netplan to configure a bridge device using the desired ethernet device.

Static IP addressing is highly suggested. DHCP addressing can also work, but you will still have to encode a static address in the OpenVPN configuration file.

The next step on the server is to configure the ethernet device for promiscuous mode on boot. To do this, ensure the networkd-dispatcher package is installed and create the following configuration script.

Then add the following contents.

Prepare server config for bridging

Edit /etc/openvpn/server.conf to use tap rather than tun and set the server to use the server-bridge directive:

After configuring the server, restart openvpn by entering:

Prepare client config for bridging

The only difference on the client side for bridged mode to what was outlined above is that you need to edit /etc/openvpn/client.conf and set tap mode:

Finally, restart openvpn:

You should now be able to connect to the full remote LAN through the VPN.

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