http://blog.fens.me/vpn-pptp-client-ubuntu/
https://help.ubuntu.com/community/VPNClient
###安装pptp client
sudo apt-get install pptp-linux
###初始化pptp
sudo pptpsetup --create myvpn --server <vpn server ip> --username <username> --password <password> --encrypt --start
以上操作生成/etc/ppp/peers/myvpn 及 /etc/ppp/chap-secrets
###配置路由
sudo vi /etc/ppp/ip-up.d/route-traffic
#!/bin/bash
/sbin/ip route add <vpn server ip> via <client gateway>
/sbin/ip route del default
/sbin/ip route add default dev ppp0
sudo chmod +x /etc/ppp/ip-up.d/route-traffic
sudo vi /etc/ppp/ip-down.d/disableroute
#!/bin/bash
/sbin/ip route add default via <client gateway>
sudo chmod +x /etc/ppp/ip-down.d/disableroute
###启动和停止pptp
sudo pon myvpn
sudo poff myvpn