A start Job is the running for Raise network interface (5min 13s) Problem Solving method

I installed Ubuntu 16.04 on my laptop, and when I had a LAN connection, it was very fast to start Ubuntu, and it was unbearable to have about 5 minutes to get to the login screen when the LAN cable was disconnected.
My speculation, and not necessarily accurate.
I am a system installed through Ubunut server, which links the network during installation. So the system is automatically set up to connect to the router automatically through DHCP to obtain the IP address to complete the Internet. However, the task cannot be completed because the ethernet cable is disconnected. So, it tries again and again, the time to try is 5 minutes.

Modify files after entering the system/etc/systemd/system/network-online.target.wants/networking.service

Command: sudo vim/etc/systemd/system/network-online.target.wants/networking.service

Change the timeoutstartsec=5min inside to Timeoutstartsec=2sec

Then restart the system, you can take effect, the boot speed quickly.

A start Job is the running for Raise network interface (5min 13s) Problem Solving method