OSWeekly: How System Calls Work in Linux?

[ Thanks to Shia Labou
for this link. ]

“Every GNU/Linux programmer here reading this article must have
used system calls to code their programs. GNU/Linux programming is
incomplete without system calls. System calls are initiated by
software interrupts. Before we delve into that, however, let’s
define system calls. A system call is the mechanism used by an
application program to request service from the operating system,
or more specifically, the operating system kernel.

“Modern processors execute instructions in different privilege
states. In system, where just two levels are defined (as in i386),
these states are known as user mode and supervisor mode…”

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