Apple’s Activity Monitor utility is a good tool for viewing the status of every program and background service that is running on your Mac, and as such you may regularly use it to check on how resources are used, especially when you are experiencing slowdowns with your Mac. However, when you do so, you may find several processes that are listed in red text, and which have “(Not Responding)” displayed next to them.

This occurs because each program that is active in OS X will check in with the system on a regular basis, in order to receive input such as keystrokes, network data, data from other running programs, or otherwise perform their functions. If the system cannot communicate with the program for more than a few seconds, then it will mark the program as “Not Responding.” When this happens, if the program is an application that you interact with using your Mouse, then you will see the spinning color wheel appear; however, if this happens to a background task, then it may go unnoticed.

There are many reasons why a program will get hung up and go into a Not Responding state, and while generally this means the program is stuck and will not recover, there are plenty of times where it will recover. For the most part, the system will run just fine with hung processes. In many cases, if needed the system will simply spawn another instance of such a process, or will simply operate without the use of the process’ functions until it is somehow cleared. Either way, OS X will continue to function, so if you see this behavior, you have the following options for managing it.

Step 1: Check any current activity

Are you doing something that is specifically using the process? For instance, if you are importing an image into Pages, or are converting your iPhoto library, and see these programs appear as Not Responding, be sure their tasks are truly not responsive before taking any additional steps. Check if progress bars are advancing, or simply wait a short while for them to complete (the time it may take for completion can vary significantly, so if you are uncertain then ask on the MacIssues forums or the Apple Discussions).

This behavior goes for background tasks as well, where you might be performing a task like copying items to an external drive, or even having attached a drive, and will see a backup-related task, or a metadata-handling task be unresponsive. In these cases, try waiting for your copying to finish, or for the drive to finish mounting, or perhaps attempt to unmount and remove it from the system, to see if this clears the unresponsive process.

Step 2: Observe

If there is no obvious activity that you can link to the process, then with Activity Monitor open, watch the Not Responding process for a short while (you may have to sort the process list by name, or do a short search for its name to only show it and prevent it from jumping around). In many cases programs Not Responding do not mean they are fully hung up, and you may see them begin to respond after a few seconds. However, the longer they remain in a non-responsive state, the more probable it is that they are truly hung up. After a few minutes of no response, you very likely have a hung process.

Step 3: Force-quit

A hung process is essentially dead to the system. If there is no response, then it basically just sits in memory and uses resources without being useful to the system at all. Therefore, you can clear the process by force-quitting it. If the process is an application such as Pages or Safari, then this can be done by choosing Force-Quit from the Apple menu, but you can also do this in Activity Monitor by selecting the process and then clicking the Force-Quit button in the toolbar.

Even though you might be intimidated by force-quitting system processes, if the process is hung up then this is the only way to fix the issue other than performing a full restart of your Mac, and furthermore, doing this will allow the system to properly re-launch the process when it is needed.

The vast majority of background processes in OS X are managed by the system launcher, which loads them using launch agent and launch daemon scripts. These scripts (located in the various LaunchAgent and LaunchDaemon folders in the user, system, and global libraries on the computer) largely instruct the system to keep these processes alive and running, but may also do so conditionally (such as only loading when you have a hard drive attached). Unfortunately, the launcher is not smart enough to distinguish between a hung process and a healthy one. Therefore, if a background process is hung up, the launcher will simply see that it is running and will not otherwise manage it, and this can prevent your system from using this process when needed.

This is where you can step in to clear the problem, where by simply force-quitting the process, you will instruct the launcher to detect the missing process and have it respond by launching another instance of it, when needed.

Managing persistent hangs

If you have a process or program that continually hangs, then there are a few things you can try. Generally, this happens because of improper settings for the process, or through some odd interaction with other running programs or services; however, it can also happen because of poor coding in the process. The later of these is out of your control and will require a software update to fix, but the first two are something you may be able to manage.

One approach for this is to remove relevant preference files for the process (you may have to perform a Web search to determine the appropriate settings files to remove). Alternatively, you can force-quit and then relaunch a program to then access its built-in settings panels and troubleshoot by toggling various settings you think might be relevant.

A second option you have is to investigate whether third-party software you have installed may be contributing to the problem. This can be as easy as uninstalling software you do not use, but you might also have to do Web searches and ask on support forums to determine if the problem is experienced by others, and see if there is a possible solution you can try.