Question

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Unix fork() system call what runs when?

I looked on Wikipedia, and the article said, “The purpose of fork() system call is to create a new process, which becomes the child process of caller, after which both, the parent and child processes, will execute the code following the fork() system call. Hence, it is important to distinguish between parent and child process. This can be done by testing the return value of fork() system call.”

In that case, what does this code execute:

printf("This is a fork!");
fork();

Given the description, it looks like it will say “This is a fork!” just once, since nothing lies AFTER the fork() statement. However, when I tested this out on a linux box, it printed “This is a fork!” twice. So which is it?

Thanks.

Answer 1

The output of printf is buffered; both child processes got a copy of the buffer; the buffer was flushed twice when each child process exited.