Frequent users of putty should have encountered the Putty (inactive) problem.
This happens because servers are usually configured to disconnect idle sessions after they are inactive for a particular time. This has many disadvantages. You can no longer monitor the jobs running in the background and the UP arrow for previous commands may not work. And you have to enter the username and password again after restarting the session.
This is how you keep it alive for longer periods
Before saving a session, click on Connection in the left pane.
Enter a number, in place of zero, in the text box.
Example: I use 30.
Now, go back to Session and Save your session with the IP address.
This way, the session sends a keep-alive request to the server every 30 seconds. Hence, it stays active.