Linux:
dhclient
The dhclient command can release your computer’s IP address and get a new one from your DHCP server.
dhclient is generated by NetworkManager.
dhclient.conf is located in /etc/dhcp.
This requires root permissions, so use sudo.
Run dhclient with no options to get a new IP address or use the -r switch to release your current IP address.
sudo dhclient -r sudo dhclient