在 Ubuntu 16.04 上，我已经按照几个教程重建网络管理器，也通过apt-get install network-manager-l2tp network-manager-l2tp-gnome.
它一直工作到昨天，当一条随机消息说The VPN connection failed because the VPN service failed to start. 配置中没有错误，因为在另一个 Ubuntu（也是 16.04 和 Windows 8.1）中使用了相同的 VPN 凭据和主机。
看着/var/log/syslog：
NetworkManager[899]: <info> [1496143714.1953] audit: op="connection-activate" uuid="cac1651d-9cbd-4989-bc57-b9707ddd012a" name="VPNCS" pid=2295 uid=1000 result="success"
NetworkManager[899]: <info> [1496143714.1973] vpn-connection[0xa56420,cac1651d-9cbd-4989-bc57-b9707ddd012a,"VPNCS",0]: Started the VPN service, PID 5798
NetworkManager[899]: <info> [1496143714.2013] vpn-connection[0xa56420,cac1651d-9cbd-4989-bc57-b9707ddd012a,"VPNCS",0]: Saw the service appear; activating connection
NetworkManager[899]: <info> [1496143714.2760] vpn-connection[0xa56420,cac1651d-9cbd-4989-bc57-b9707ddd012a,"VPNCS",0]: VPN connection: (ConnectInteractive) reply received
NetworkManager[899]: nm-l2tp[5798] <info> ipsec enable flag: yes
NetworkManager[899]: …