Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- add dup2 action to spawn file actions object
*file_actions, int fildes, int newfildes);
function shall add a
action to the object referenced by
that shall cause the file descriptor
to be duplicated as
had been called) when a new process is spawned using this file actions
A spawn file actions object is as defined in
Upon successful completion, the
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
function shall fail if:
The value specified by
is negative or greater than or equal to
Insufficient memory exists to add to the spawn file actions object.
function may fail if:
The value specified by
It shall not be considered an error for the
argument passed to the
function to specify a file descriptor for which the specified operation
could not be performed at the time of the call. Any such error will be
detected when the associated file actions object is later used during a
The following sections are informative.
function is part of the Spawn option and need not be
provided on all implementations.
Implementations may use file descriptors that must be inherited into
child processes for the child process to remain conforming, such as for
message catalog or tracing purposes. Therefore, an application that calls
with an arbitrary integer for
risks non-conforming behavior, and this function can only portably be
used to overwrite file descriptor values that the application has obtained
through explicit actions, or for the three file descriptors corresponding
to the standard file streams. In order to avoid a race condition of
leaking an unintended file descriptor into a child process, an application
should consider opening all file descriptors with the FD_CLOEXEC bit
set unless the file descriptor is intended to be inherited across
Refer to the RATIONALE section in
The Base Definitions volume of POSIX.1-2017,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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