按照网上的教程操作，每次都遇到同样的问题。我是不是漏掉了什么？首先尝试使用 GUI，然后尝试使用终端配置 VPN。
Mar 29 12:16:14 rubenq-X556UF NetworkManager[1195]: <info> [1553861774.7094] devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Mar 29 12:16:14 rubenq-X556UF NetworkManager[1195]: <info> [1553861774.7094] device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found.
Mar 29 12:16:14 rubenq-X556UF NetworkManager[1195]: <info> [1553861774.7133] devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Mar 29 12:16:14 rubenq-X556UF pppd[6376]: Using interface ppp0
Mar 29 12:16:14 rubenq-X556UF pppd[6376]: Connect: ppp0 <--> /dev/pts/2
Mar 29 12:16:14 rubenq-X556UF systemd-udevd[6467]: link_config: autonegotiation is unset or enabled, the speed and duplex are not writable.
Mar 29 12:16:14 rubenq-X556UF NetworkManager[1195]: <info> [1553861774.7202] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/74)
Mar 29 12:16:14 rubenq-X556UF pptp[6468]: anon log[main:pptp.c:353]: The synchronous pptp option is NOT activated
Mar 29 12:16:14 rubenq-X556UF pptp[6468]: anon warn[pptp_gre_bind:pptp_gre.c:102]: socket: Operation not permitted
Mar 29 12:16:14 rubenq-X556UF pptp[6468]: anon fatal[main:pptp.c:360]: Cannot bind GRE socket, aborting.
Mar 29 12:16:14 rubenq-X556UF pppd[6376]: Modem hangup
Mar 29 12:16:14 rubenq-X556UF pppd[6376]: Connection terminated.