preface

Before, according to the company’s business needs, it was necessary to connect L2TP VPN on ubuntu16.04
for a whole day, but it was not installed successfully
Baidu tried all kinds of methods
finally, I felt that a system should be re installed. Rebooted Ubuntu 18.04

Solution
1. Command line input:

sudo apt-get install network-manager-l2tp-gnome

2. From the drop-down arrow in the upper right corner of Ubuntu 18.04, find Settings or directly click the gear type icon to enter settings
3. In the Settings interface, select Network , and VPN
appears in the interface. 4. Click + on the right side of VPN ,
to see Layer 2 Tunneling Protocol (L2TP)
to explain that the executed command takes effect
5. Click L2TP to enter the interface and fill in the proxy address, user name and password
the rest are default. Test the connection
note: if the company has other settings, it needs to communicate with colleagues.