Linux – Cannot catch file creation with strace

fileslinuxstrace

When I run the following make command in a build directory it's almost empty (file in question is absolutely certainly not there)

strace -f -e trace=execve,vfork,open,creat -s 1024 make <target>

After it finishes, the file is totally there. So it must have been created by make or one of its child processes (or children of their children and so on).

However when I grep the strace log for either the name of the file or for creat I cannot find the system call responsible for creation of this file.

What am I missing? Are there other system calls I should be monitoring?

EDIT:

It turns out the mistake was in both my strace comamnd and my grepping.
All the answers were helpful, thank you, everyone, for your time.

I actually failed to communicate that the file was in a subdir and I was grepping using the name of a file along with the subdir's name. But since strace does not provide info on current working directory this approach didn't work so well (I ended up stracing chdir and rename calls to get the desired effect).

So PaulHaldane's first suggestion was right and to the point. As well as larsks's answer in which he has actually guessed how the file got created.

Best Answer

Run strace without the -e option and see if that improves your result.

There are a number of ways to create a file. Instead of open-ing it, it is highly likely that whatever tool produces that file first opens a temporary file, writes the data, and then renames the file on completion.

With your current limit (execve,vfork,open,creat) you're not going to see that sort of behavior.

For example, given this simple python script:

import os
import tempfile

fd = tempfile.NamedTemporaryFile(dir='.', delete=False)
fd.write('this is a test\n')
fd.close()

os.rename(fd.name, 'output')

Running strace with your arguments and then looking for output in the results yields nothing:

$ strace -e trace=execve,vfork,open,creat -o trace -f -s 80 python tmptest.py
$ grep output trace
$

But if I remove the -e filter:

$ strace  -o trace -f -s 80 python tmptest.py
$ grep output trace
4523  rename("/home/lars/tmp/tmpZDwvPK", "output") = 0

In the comments on your question, Sato Katsura provides an example in which you will not see your target filename in the strace output, but I think you are unlikely to encounter that when running make as long as you start with a clean build environment.

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