What is the difference between exit() and _exit() system call?

Should I employ exit(int status) or _exit(int status) to exit() from a child process? Does this question haunt you quite often? If so, this post is for you.

The exit() method which is part of the C library routines calls the kernel system call _exit() internally.

The responsibility of the kernel system call _exit() includes asking the kernel to close any open descriptors, free the memory used by the process and perform terminating process clean-up. Whereas the exit() call takes care of flushing the I/O buffers and perform additional clean-up before invoking _exit() internally.

In simpler words, exit() performs clean-up related to user-mode constructs in the library, and calls user-supplied cleanup functions whereas _exit() performs only the kernel level cleanup for the process.

It’s always advisable to use _exit(int status) in a child because employing exit(int status) can lead to stdio buffers being flushed twice, and temporary files being unexpectedly removed.

Finally, exit(int status) is defined in stdio.h and _exit(int status) is defined in unistd.h file.


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