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Asked: 2026-06-13T14:18:43+00:00

I’m implementing a system call in a 2.6.22 kernel. In my system call I

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I’m implementing a system call in a 2.6.22 kernel. In my system call I obtain a file descriptor like this:

fd = sys_open(filename, O_WRONLY|O_CREAT, 0544);

However, I get a negative number (-13) for fd when filename points to a read only file. The problem is that I need to write to filename, even if it’s read only or owned by another user.

So my question is this, how can I write to a read only file from the kernel?

And yes, I’ve read the post in linux journal that says writing to a file from the kernel is a bad idea.

I still need to do it.

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1 Answer

  1. Editorial Team

    The negative number isn’t a file descriptor, it’s an error code. Specifically it will be the negative version of one of the errno.h error numbers.

    In this case as you have -13 you are looking at error 13 which is EACCES meaning that you don’t have permission to write to the file.

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