In Ubuntu or Debian, information on network interface configuration is stored in /etc/network/interfaces. If you modify /etc/network/interfaces to reconfigure any interface, you need to reload it so that the new configuration can take effect.
Here is how you can reload /etc/network/interfaces.
One caveat: If NetworkManager is installed and enabled on your system, it will interfere with you reloading /etc/network/interfaces. On Ubuntu Desktop, for example, NetworkManager is enabled by default. Thus you first need to disable NetworkManager before attempting to reload /etc/network/interfaces.
To disable NetworkManager, do the following.
$ sudo update-rc.d NetworkManager remove
If you don't want to disable NetworkManager, another option is to edit NetworkManager configuration, and add "managed=false" as follows. Then, restart NetworkManager.
Subscribe to Xmodulo
Do you want to receive Linux FAQs, detailed tutorials and tips published at Xmodulo? Enter your email address below, and we will deliver our Linux posts straight to your email box, for free. Delivery powered by Google Feedburner.