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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.
posix_spawn_file_actions_adddup2 — add dup2 action to spawn file ac‐
tions object (ADVANCED REALTIME)
#include <spawn.h>
int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t
*file_actions, int fildes, int newfildes);
The posix_spawn_file_actions_adddup2() function shall add a dup2() ac‐
tion to the object referenced by file_actions that shall cause the file
descriptor fildes to be duplicated as newfildes (as if dup2(fildes,
newfildes) had been called) when a new process is spawned using this
file actions object.
A spawn file actions object is as defined in posix_spawn_file_ac‐
Upon successful completion, the posix_spawn_file_actions_adddup2()
function shall return zero; otherwise, an error number shall be re‐
turned to indicate the error.
The posix_spawn_file_actions_adddup2() function shall fail if:
EBADF The value specified by fildes or newfildes is negative or
greater than or equal to {OPEN_MAX}.
ENOMEM Insufficient memory exists to add to the spawn file actions ob‐
The posix_spawn_file_actions_adddup2() function may fail if:
EINVAL The value specified by file_actions is invalid.
It shall not be considered an error for the fildes argument passed to
the posix_spawn_file_actions_adddup2() function to specify a file de‐
scriptor for which the specified operation could not be performed at
the time of the call. Any such error will be detected when the associ‐
ated file actions object is later used during a posix_spawn() or
posix_spawnp() operation.
The following sections are informative.
The posix_spawn_file_actions_adddup2() 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 posix_spawn_file_actions_adddup2() with an arbitrary integer for
newfildes risks non-conforming behavior, and this function can only
portably be used to overwrite file descriptor values that the applica‐
tion has obtained through explicit actions, or for the three file de‐
scriptors 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 exec.
Refer to the RATIONALE section in posix_spawn_file_actions_addclose().
dup(), posix_spawn(), posix_spawn_file_actions_addclose(),
The Base Definitions volume of POSIX.1‐2017, <spawn.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
table Operating System Interface (POSIX), The Open Group Base Specifi‐
cations 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 .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐ .
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