Using the Command-Line Interface : Saving Configuration Changes
  
Saving Configuration Changes
The show configuration running command displays the current configuration of the system. When you make a configuration change to the system, the change becomes part of the running configuration.
The change does not automatically become part of the configuration file in memory until you write the file to memory. If you do not save your changes to memory, they are lost when the system restarts.
To save all configuration changes to memory, you must enter the write memory command while in configuration mode.