The Network Manager default for the Ubuntu distribution of Linux operating systems provides internet connectivity. The Network Manager cannot save a fixed IP address on Ubuntu Linux and the settings are lost when the system is rebooted. To have a static IP address on Ubuntu Linux,the Network Manager must be uninstalled before the network interfaces are configured manually. The network interfaces can be configured to have a static IP in Ubuntu Linux by editing the interfaces file to include the fixed IP address. The configuration would be retained even after the Linux system has been restarted.
NetworkManager is a program in Ubuntu 8.10, which aims to provide a simplified Internet connection. NetworkManager finds and maintains an internet connection at all costs. However it can cause a problem if you want to use a fixed IP address. Settings made in NetworkManager will not be applicable at the next restart. Ultimately if you assign a fixed IP address in NetworkManager, this setting will be forgotten the next time you reboot.
A straightforward approach is to uninstall NetworkManager: