A system call is usually a request to the operating system (kernel) to do a hardware/systemspecific or privileged operation. As of Linux-1.2, 140 system calls have been defined. System calls like close() are implemented in the Linux libc. This implementation often involves calling a macro which eventually calls syscall(). Parameters passed to syscall() are the number of the system call followed by the needed arguments. The actual system call numbers can be found in < linux/unistd.h > while < sys/syscall.h > gets updated with a new libc. If new calls appear that don’t have a stub in libc yet, you can use syscall()
Author: Vijay Anatolius
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