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.. COMMENT: COPYRIGHT (c) 1988-2017.
.. COMMENT: On-Line Applications Research Corporation (OAR).
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Preface
=======

RTEMS supports a variety of POSIX and BSD features including some POSIX
methods that are now deemed obsolete and some methods for compatibility
with GNU/Linux and FreeBSD. There are multiple POSIX standard versions
as well as multiple efforts to tailor (e.g. profile) POSIX for embedded
environments. They range in size from less than 200 required capabilities
to the full POSIX standard which has over 1200 required capabilities. This
document reports on the alignment of RTEMS with various standard versions
and defined profiles.

RTEMS supports a number of POSIX process, user, and group oriented
routines in what is referred to as a "SUSP" (Single-User, Single
Process) manner.  RTEMS supports a single process, multithreaded
POSIX environment.  In a pure world, there would be no reason to even
include routines like ``getpid()`` when there can only be one process.
But providing routines like ``getpid()`` and making them work in
a sensible fashion for an embedded environment while not returning
``ENOSYS`` (for not implemented) makes it significantly easier to port
code from a UNIX environment without modifying it.

Each chapter in this document presents the alignment of RTEMS with
a specific standard version or defined profile.  Each section with a
chapter details the alignment of a specific header file relative to the
chapter's standard or profile.  The implementation status of the items
required by the standard are listed.