I have a openvpn setup on ubuntu that multiple users are connecting to. I want to list all the active certificates with their Common name. Is their a way of doing this ?
You can get a list of current connections to the OpenVPN server either by using the status command over the management interface (see http://openvpn.net/index.php/open-source/documentation/miscellaneous/79-management-interface.html), or by looking at the status file which is specified using the status line in the config files (see http://openvpn.net/index.php/open-source/documentation/howto.html#server).
If you want to know who can connect to the OpenVPN server its a bit harder. OpenVPN will let anyone in whose certificate contains a signature generated with the CA key the server is configured to use. If you are using a third party PKI infrastructure they should have records of the certificates they have issued. If you are using the easy-rsa stuff then the certs should all be in that directory.