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Had a sysinternals tool (filemon) for that, but now I can find something similar for the mac.

I'm a developer and I basically want to debug "file not found" or "wrong permissions" errors.

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up vote 18 down vote accepted

You can use lsof or fs_usage in Terminal. lsof can be quite powerful. If it's about a specific process, you can try sampling it in Activity Monitor.

For a GUI tool, my recommendation is fseventer:

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More GUI-oriented utilities, which I haven't used:


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FS Spy

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+1 very nice answer. Btw, I've just tried FileMon and the filtering doesn't seem to work, which makes it pretty useless. fseventer is very nice. – occulus Feb 27 '13 at 10:59
fseventer claims "10.10 Yosemite is classified as unsupported till further notice". is there an updated answer? are there new recommendations? – rafraf Jul 14 '15 at 9:55

For viewing what files are accessed in real time you can leverage fs_usage part of the FSEvents feature in Mac OS X or even dtrace itself.

Usage: sudo fs_usage [PID].

For more info, check out the man page

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fs_usage is my favorite. I wrote about it on my blog post @ where I was stuck with Outlook that had hung and I wanted to know what it was doing on my Mac. – mohit Mar 20 '15 at 19:00

Less visual for highlights from Brendan's blog » Top 10 DTrace scripts for Mac OS X (2011-10-10).

More visual

For more modern operating systems that are incompatible with fseventer, there's Apple Xcode Instruments –

selecting the File Activity template

Instruments in the background, Terminal in front

– powerful, but (compared to fseventer) in some cases, Instruments may be too heavyweight.

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You can use the dtrace opensnoop script to identify failed opens (file not found and permission errors)

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