Section: Linux Programmer's Manual (2)
idle - make process 0 idle
is an internal system call used during bootstrap.
It marks the process's pages as swappable, lowers its priority,
and enters the main scheduling loop.
Only process 0 may call
Any user process, even a process with superuser permission,
never returns for process 0, and always returns -1 for a user process.
Always, for a user process.
Since Linux 2.3.13, this system call does not exist anymore.
This function is Linux-specific, and should not be used in programs
intended to be portable.
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