How to automate running the dhclient in ubuntu?

I need to run sudo dhclient eth0 every time I unplug and plug the Ethernet back in.

This is pretty annoying! How can I fix it?

You should check your network configuration in:

/etc/network/interfaces

If you want DHCP, it should be something like this:

auto eth0
iface eth0 inet dhcp

If you want a static IP, it should go like below:

auto eth0
iface eth0 inet static
address xxx.xxx.xxx.xxx
gateway xxx.xxx.xxx.xxx
netmask xxx.xxx.xxx.xxx
network xxx.xxx.xxx.xxx
broadcast xxx.xxx.xxx.xxx

You can read this too.