Install the following packages :
sudo apt-get install openvpn network-manager-openvpn
add to sysctl.conf
vm.swappiness = 0 vm.overcommit_memory = 1 vm.dirty_background_ratio = 5 vm.dirty_ratio = 10 vm.dirty_expire_centisecs = 1000 dev.rtc.max-user-freq = 1024