我的 VPN 连接突然失败了。上周它运行正常，但本周它就是拒绝启动。我使用以下方法检查了系统日志：
$ less /var/log/syslog | grep NetworkManager
我收到以下输出：
Apr 22 12:14:48 GLaDOS NetworkManager[739]: <info> VPN service 'vpnc' started (org.freedesktop.NetworkManager.vpnc), PID 3906
Apr 22 12:14:48 GLaDOS NetworkManager[739]: <info> VPN service 'vpnc' appeared; activating connections
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <info> VPN plugin state changed: starting (3)
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <info> VPN connection 'VPN connection 1' (Connect) reply received.
Apr 22 12:15:09 GLaDOS NetworkManager[739]: SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/tun0, iface: tun0)
Apr 22 12:15:09 GLaDOS NetworkManager[739]: SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/tun0, iface: tun0): no ifupdown configuration found.
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <warn> /sys/devices/virtual/net/tun0: couldn't determine device driver; ignoring...
Apr 22 12:15:09 GLaDOS NetworkManager[739]: SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/tun0, iface: tun0)
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <warn> VPN plugin failed: 1
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <info> VPN plugin state changed: stopped (6)
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <info> VPN plugin state change reason: 0
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <info> Policy set 'Wired connection 1' (eth0) as default for IPv4 routing and DNS.
Apr 22 12:15:09 GLaDOS NetworkManager[739]: <warn> error disconnecting VPN: Could not process the request because no VPN connection was active.
Apr 22 12:15:15 GLaDOS NetworkManager[739]: <info> VPN service 'vpnc' disappeared
我尝试过几次修复，但似乎都不起作用。任何帮助都将不胜感激。
编辑：我已经安装了所有相关软件包：/etc/NetworkManager/VPN/nm-vpnc-service.name；/etc/dbus-1/system.d/nm-vpnc-service.conf；/usr/lib/NetworkManager/nm-vpnc-service；/usr/lib/NetworkManager/nm-vpnc-service-vpnc-helper；/usr/share/doc/network-manager-vpnc/AUTHORS；/usr/share/doc/network-manager-vpnc/NEWS.gz；/usr/share/doc/network-manager-vpnc/changelog.Debian.gz；/usr/share/doc/network-manager-vpnc/copyright。
以及所有相关的依赖项：libc6（>= 2.4）；libdbus-glib-1-2（>= 0.78）；libglib2.0-0（>= 2.37.3）；libnm-glib-vpn1（>= 0.7.999）；libnm-util2（>= 0.8.998）；vpnc。
我还确认了以下几点：
“NetworkManager 现在将 IP 地址 127.0.1.1 分配给它控制的本地名称服务器进程，而不是 127.0.0.1。如果系统的 /etc/resolv.conf 不存在或是一个静态文件，而不是默认安装的 ../run/resolvconf/resolv.conf 的符号链接，则管理员必须更新此静态文件才能继续使用 NetworkManager 控制的名称服务器。”