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我家里测试PPTP win8系统和ipad都没有问题 可ubuntu14.04就是链接不上
我把系统日志贴出来 请帮忙检查是哪里的错误
lukang-Latitude-D430 pppd[5236]: pppd 2.4.5 started by root, uid 0
Aug 24 20:18:38 lukang-Latitude-D430 pppd[5236]: Using interface ppp0
Aug 24 20:18:38 lukang-Latitude-D430 pppd[5236]: Connect: ppp0 <--> /dev/pts/0
Aug 24 20:18:38 lukang-Latitude-D430 NetworkManager[752]: SCPlugin-Ifupdown: devices added (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Aug 24 20:18:38 lukang-Latitude-D430 NetworkManager[752]: SCPlugin-Ifupdown: device added (path: /sys/devices/virtual/net/ppp0, iface: ppp0): no ifupdown configuration found.
Aug 24 20:18:38 lukang-Latitude-D430 NetworkManager[752]: <warn> /sys/devices/virtual/net/ppp0: couldn't determine device driver; ignoring...
Aug 24 20:18:38 lukang-Latitude-D430 pptp[5242]: nm-pptp-service-5223 log[main:pptp.c:314]: The synchronous pptp option is NOT activated
Aug 24 20:18:39 lukang-Latitude-D430 pptp[5256]: nm-pptp-service-5223 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 1 'Start-Control-Connection-Request'
Aug 24 20:18:39 lukang-Latitude-D430 pptp[5256]: nm-pptp-service-5223 log[ctrlp_disp:pptp_ctrl.c:739]: Received Start Control Connection Reply
Aug 24 20:18:39 lukang-Latitude-D430 pptp[5256]: nm-pptp-service-5223 log[ctrlp_disp:pptp_ctrl.c:773]: Client connection established.
Aug 24 20:18:40 lukang-Latitude-D430 pptp[5256]: nm-pptp-service-5223 log[ctrlp_rep:pptp_ctrl.c:251]: Sent control packet type is 7 'Outgoing-Call-Request'
Aug 24 20:18:40 lukang-Latitude-D430 pptp[5256]: nm-pptp-service-5223 log[ctrlp_disp:pptp_ctrl.c:858]: Received Outgoing Call Reply.
Aug 24 20:18:40 lukang-Latitude-D430 pptp[5256]: nm-pptp-service-5223 log[ctrlp_disp:pptp_ctrl.c:897]: Outgoing call established (call ID 0, peer's call ID 18535).
Aug 24 20:18:43 lukang-Latitude-D430 pppd[5236]: MS-CHAP authentication failed: E=691 Authentication failure
Aug 24 20:18:43 lukang-Latitude-D430 pppd[5236]: CHAP authentication failed
Aug 24 20:18:43 lukang-Latitude-D430 pppd[5236]: Connection terminated.
Aug 24 20:18:43 lukang-Latitude-D430 avahi-daemon[742]: Withdrawing workstation service for ppp0.
Aug 24 20:18:43 lukang-Latitude-D430 NetworkManager[752]: <warn> VPN plugin failed: 1
Aug 24 20:18:43 lukang-Latitude-D430 NetworkManager[752]: SCPlugin-Ifupdown: devices removed (path: /sys/devices/virtual/net/ppp0, iface: ppp0)
Aug 24 20:18:43 lukang-Latitude-D430 pptp[5242]: nm-pptp-service-5223 warn[decaps_hdlc:pptp_gre.c:204]: short read (-1): Input/output error
Aug 24 20:18:43 lukang-Latitude-D430 pptp[5242]: nm-pptp-service-5223 warn[decaps_hdlc:pptp_gre.c:216]: pppd may have shutdown, see pppd log
Aug 24 20:18:43 lukang-Latitude-D430 pppd[5236]: Exit.

[quote="lukang"]我家里测试PPTP win8系统和ipad都没有问题 可ubuntu14.04就是链接不上
我把系统日志贴出来 请帮忙检查是哪里的错误
。。。
Aug 24 20:18:43 lukang-Latitude-D430 pppd[5236]: MS-CHAP authentication failed: E=691 Authentication failure
Aug 24 20:18:43 lukang-Latitude-D430 pppd[5236]: CHAP authentication failed
Aug 24 20:18:43 lukang-Latitude-D430 pppd[5236]: Connection terminated.
。。。/quote]

红色部分就是pptp连接错误的根源。CHAP验证错误E=691，可能原因：
1. 指定了错误的domain；
2. 设置了错误的口令，常见情况之一：口令包含特殊字符，例如“#”，而没有加引号；
3. 口令中使用了空格space或空白blank字符，这种情况是不可以的。

不同操作系统的pptp vpn客户端功能或限制或许会稍有不同。我没有自己配置的vpn server，无法帮你测试win/ipad/linux下使用类似xyz!@#123这样的口令，是否会导致win/ipad能连接，而linux不行。所以如果确定口令无误，请自行检查是否存在以上3点中的情况。。。

如还有疑问，把¨编辑连接¨中相关的定义，做一个类似下面的截图，贴上来看一下：

14.04 PPTP VPN

sudo dpkg -l | grep network-manager
看看 你是否額外安裝了需要的套件