sudo add-apt-repository ppa:nm-l2tp/network-manager-l2tp
sudo apt-get update
sudo apt-get install network-manager-l2tp network-manager-l2tp-gnome
sudo apt install libreswan
sudo apt-get install intltool libtool network-manager-dev libnm-util-dev libnm-glib-dev libnm-glib-vpn-dev libnm-gtk-dev libnm-dev libnma-dev ppp-dev libdbus-glib-1-dev libsecret-1-dev libgtk-3-dev libglib2.0-dev xl2tpd strongswan
vim /etc/xl2tpd/xl2tpd.conf
新增以下：
[lac ubuntu]
name = liaojie ;l2tp帐号
lns = jieko.8800.org ;l2tp server的IP
pppoptfile = /etc/ppp/peers/pppvpnname.l2tpd ;pppd拨号时使用的配置文件
ppp debug = yes
vim /etc/ppp/peers/pppvpnname.l2tpd
新增以下：
remotename l2tp
user ubuntu
password ubuntu
unit 10
lock
nodeflate
nobsdcomp
noauth
persist
nopcomp
noaccomp
maxfail 5
ipcp-accept-local
启动：echo "c ubuntu">/var/run/xl2tpd/l2tp-control
停止：echo "d ubuntu">/var/run/xl2tpd/l2tp-control