How to manually install the OpenVPN binary

It seems that since the upgrade to Android 4.3 the OpenVPN Installer App is not working for me any more. I get some error saying /system cannot be mounted writeable (rw).
However, it is still possible to install the openvpn binary per hand... and it is not as complicated as it seems! This guide only works on rooted devices and is written for Linux users, however the lower part should also work on Windows and Mac.

At first you need to get the Android Debug Bridge binary and install it on your computer (I just put it into $HOME/bin).
Then download the latest OpenVPN Installer APK - we need to extract the openvpn binary from this package:

wget http://android-openvpn-installer.googlecode.com/files/OpenVPN-Installer-0.2.4.apk

To extract the xbin-binary, you can use FileRoller on Gnome or any other tool. Here is an example of how do it with the terminal only:

unzip OpenVPN-Installer-0.2.4.apk assets/openvpn-2.1.1-static-xbin
mv assets/openvpn-2.1.1-static-xbin openvpn
rm -r assets

Now use adb to push the binary to your phone/tablet's "sdcard" (external storage):

adb push openvpn /sdcard/

The next two commands will open a shell and give us root access on your Android device. Everything you type afterwards happens directly on your device, so be careful!

adb shell
su

Now we need to mount /system as writeable to be able to make changes. Next we copy the binary to its final location and delete it on the sdcard (unfortunately moving is not possible). After we changed the file-permissions so that the binary can be executed, we need to mount /system as read-only again:

mount -o remount rw /system
cp /sdcard/openvpn /system/xbin/
rm /sdcard/openvpn
chmod 755 /system/xbin/openvpn
mount -o remount ro /system

Everything should be done now. Close the connection to your device by typing exit two times and try to use OpenVPN Settings! The installer app will also show you "Binary installed" if everything worked!