I would like to be able to see/monitor how a software "works" once it's running. For example I would like to see what happens internally when you click on a button, or any other interaction within an app. I tried using Instruments (xcode), but Instruments only let me select an application that's already running. Which means I always miss the initial process of when the application starts running.

I am not looking for resource usage, just trying to understand how the internal files work.

2 Answers 2


You don't mention what version of Mac OS X you're running, but if you're running a version between 10.4 and 10.9.x, then fseventer may be useful if you're trying to see what files and ports are accessed while you launch, use, or quit an application.

  • I think this is as good as it's going to get. Thank you for pointing out that software.
    – gdaniel
    Commented Oct 30, 2014 at 15:10
  • Also have a look at opensnoop.
    – bot47
    Commented Oct 30, 2014 at 22:05

Open Activity Monitor Select the process you want to monitor Click the "Gear" icon and choose "Sample Process"

NB: I am not claiming this will be of any use to you. It is generally only helpful for tracking bugs for someone who has the source code.

  • I have used Activity Monitor, but I can't get the sample process until the software it's already running. Thank you.
    – gdaniel
    Commented Oct 30, 2014 at 13:52
  • Yes, of course not. How are you expecting to see what a program is doing while it is not doing anything?
    – lbutlr
    Commented Oct 31, 2014 at 19:16
  • I don't. But I do expect to see it as soon as it starts. The first process. With activity monitor I miss those first initial seconds.
    – gdaniel
    Commented Oct 31, 2014 at 19:29
  • Maybe if we knew why you were trying to do this or what you were trying to find out...
    – lbutlr
    Commented Oct 31, 2014 at 19:31
  • Just curious about how some processes work. The fseventer software that @eyer pointed out works quite well. It gives you a visualization of all files that are being accessed in the computer at any given time. And you can also use some filters to help narrow down the paths you're watching.
    – gdaniel
    Commented Oct 31, 2014 at 20:35

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