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 (using -v switch to show verbose):

netstat -r | awk '/default/ {print $NF}' | while read NIC; do sudo dhclient -r -v $NIC && sudo dhclient -v $NIC; done

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.

Example:

terrance@terrance-ubuntu:~$ netstat -r | awk '/default/ {print $NF}' | while read NIC; do sudo dhclient -r -v $NIC && sudo dhclient -v $NIC; done
Killed old client process
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/40:8d:5c:4f:12:03
Sending on   LPF/eth0/40:8d:5c:4f:12:03
Sending on   Socket/fallback
DHCPRELEASE of 10.0.0.100 on eth0 to 10.0.0.1 port 67 (xid=0x10ff1bda)
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/40:8d:5c:4f:12:03
Sending on   LPF/eth0/40:8d:5c:4f:12:03
Sending on   Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 3 (xid=0x9b730303)
DHCPOFFER of 10.0.0.100 from 10.0.0.1
DHCPREQUEST for 10.0.0.100 on eth0 to 255.255.255.255 port 67 (xid=0x303739b)
DHCPACK of 10.0.0.100 from 10.0.0.1 (xid=0x9b730303)
Timeout too large reducing to: 2147483646 (TIME_MAX - 1)
bound to 10.0.0.100 -- renewal in 2147483648 seconds.

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)