In ASP.NET, how can you change the session time out value for a web application?

Introduction / Context:
Session time out determines how long ASP.NET keeps per user session data in memory when there is no activity. Configuring this value correctly is important for balancing resource usage and user experience. Interviewers often ask about this to see whether candidates know where session settings live and how to adjust them without modifying server level configuration for every application.

Given Data / Assumptions:

• We are using ASP.NET session state in a web application.
• We need to change the duration after which idle sessions expire.
• The question asks for a standard way to change the session time out.

Concept / Approach:
ASP.NET exposes session configuration through the sessionState element in web.config. The timeout attribute of this element sets the default session time out in minutes for the entire application. In addition, the Session.Timeout property can be set in code to adjust the value for the current session at runtime, within allowed limits. These approaches provide application level control over session time out without changing global server settings.

Step-by-Step Solution:
Step 1: Open the web.config file for the ASP.NET application. Step 2: Locate or add the sessionState element within the system.web section. Step 3: Set the timeout attribute to the desired number of minutes, for example <sessionState timeout="30" /> to use a thirty minute session time out. Step 4: If needed, adjust the time out for specific sessions in code by setting Session.Timeout to a new value, such as Session.Timeout = 10; to reduce it for that session only. Step 5: Save the configuration and deploy; the new time out values will be applied when the application restarts or reloads its configuration.

Verification / Alternative check:
To verify, you can configure a short session time out, log the current time in Session_Start, and then stop user activity. After the configured number of minutes, a new request should cause a new session to be created, proving that the time out value is in effect. Documentation for ASP.NET confirms that sessionState timeout controls this behaviour and that Session.Timeout can override it for individual sessions within limits.

Why Other Options Are Wrong:
Option B is wrong because renaming Global.asax does not change session settings and would likely break the application. Option C is incorrect because changing the operating system clock affects timestamps but does not directly configure ASP.NET session management. Option D is wrong because debug or release build modes relate to compilation settings and optimisation, not to session time out configuration.

Common Pitfalls:
A common pitfall is setting the session time out too high, which can cause memory usage to grow if many inactive sessions remain in memory. Another issue is misunderstanding the interaction between session time out and authentication tickets such as forms authentication cookies; they may have different lifetimes. It is important to choose values based on real world usage patterns and to monitor memory, performance, and user feedback when adjusting session settings.

Final Answer:
You change the session time out by configuring the timeout attribute of the sessionState element in web.config for application wide settings and optionally setting Session.Timeout in code for per session overrides.