How to release an IP address and renew from the commandline?

Question

I am using modern versions of Ubuntu that use network-manager, and I would like release and renew my network settings through the commandline.

In the olden days when Ubuntu used the interfaces file, I would simply do: sudo /etc/init.d/networking restart but now that no longer works.

I am looking for functionality similar to Windows' ipconfig /release and ipconfig /renew.

How can I release and renew network settings from the commandline interface?

Answer 1

To release and renew the IP address it is:

sudo dhclient -r eth0
sudo dhclient eth0

Or you can try a one-liner that grabs the default ethernet name from netstat:

NIC=$(netstat -r | awk '/default/ {print $NF}' | head -1); sudo dhclient -r $NIC && sudo dhclient $NIC

From the dhclient manpage:

       -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.

Hope this helps!

Answer 2

One way to accomplish this is to tell network-manager to briefly disconnect the device and the connecting it again:

nmcli device disconnect wlan0; nmcli device connect wlan0 

(replace wlan0 with the correct device name on your system)