# strace
**strace** spies on what [System calls](./System_Calls.md) a program makes.

``strace [flags] command``

Some useful strace flags:

`-e open` search for the `open` system call
`-f` follow subprocesses and strace them too
`-p 673` what is this process doing?
`-c` summarizes output with CPU time for each syscall
`-s 50` shows you the first 50 lines of strings
`-o file.txt` stores output for later
`-y` converts file descriptor numbers to filenames; newer flag

You can see a list of system calls [here](./System_Calls.md).



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If you want to see what files ``dig`` is opening (reading) just do ``strace -f -e open dig``.

Jvns has [an awesome zine](https://wizardzines.com/zines/strace/) on the what and how for strace.