How to release and renew IP address from DHCP on Linux systems?

Question

Systems:

• Linux Mint 18.2 Cinnamon 64-bit (desktop mode, hands-on)

• GNU/Linux Debian 9.2 Cinnamon 64-bit (headless mode, SSH)

Question:

How to release and renew IP address from the DHCP server (router) on these Linux systems?

Answer 1

I have found there is the following program listening on the network on both of them:

dhclient

Quoting the man page:

-r     Release the current lease and stop the running DHCP client as  previously  recorded
       in  the  PID  file.  When shutdown via this method dhclient-script will be executed
       with the specific reason for calling the script set.  The client  normally  doesn't
       release  the  current  lease  as this is not required by the DHCP protocol but some
       cable ISPs require their clients to notify the server if they wish  to  release  an
       assigned IP address.

---

So, the solution for all interfaces would be:

sudo dhclient -r
sudo dhclient

Or, conveniently, for a specific interface, say eth0:

sudo dhclient -r eth0
sudo dhclient eth0

Of course, when SSH'ing into a server, you need to run both commands oneliner or write a script as per this answer.

Answer 2

on ubuntu:

release:

sudo dhclient -r

renew:

sudo dhclient -1