Linux Force DHCP client (dhclient) to renew ip address

The -r flag explicitly releases the current lease, and once the lease has been released, the client exits. For example, open terminal and type the command:
$ sudo dhclient -r

To check the IP Address you have :
$ ifconfig

Now obtain fresh IP:
$ sudo dhclient

There is no need to restart network service. Above command should work with any Linux distro such as RHEL, Fedora, CentOS, Ubuntu and others. On a related note you can also try out the following commands:
# ifdown eth0
# ifup eth0
# /etc/init.d/network restart

OR
# /etc/init.d/networking restart

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