Recently, an openvpn server was built on the vps, and the following tutorials were installed to install the client on the Raspberry Pi.
http://berndknows.blogspot.be/2013/11/configure-raspberry-pi-as-openvpn-client.html
/etc/init.d/openvpn start works perfectly
That is, ifconfig does not appear tun0.
Later, I found the reason on the Internet and marked it.
Execute the following command openvpn --config client.conf.
In fact, the configuration does not work.