a.txt

POSIX_SPAWN_FILE_ACTIONS_ADPOSIX(ProgrammePOsIXaSPaWN_FILE_ACTIONS_ADDDUP2(3P)

PROLOG
       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.

NAME
       posix_spawn_file_actions_adddup2 — add dup2 action to  spawn  file  ac‐
       tions object (ADVANCED REALTIME)

SYNOPSIS
       #include <spawn.h>

       int posix_spawn_file_actions_adddup2(posix_spawn_file_actions_t
           *file_actions, int fildes, int newfildes);

DESCRIPTION
       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‐
       tions_addclose().

RETURN VALUE
       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.

ERRORS
       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‐
              ject.

       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.

EXAMPLES
       None.

APPLICATION USAGE
       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.

RATIONALE
       Refer to the RATIONALE section in posix_spawn_file_actions_addclose().

FUTURE DIRECTIONS
       None.

SEE ALSO
       dup(),        posix_spawn(),       posix_spawn_file_actions_addclose(),
       posix_spawn_file_actions_destroy()

       The Base Definitions volume of POSIX.1‐2017, <spawn.h>

COPYRIGHT
       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 http://www.opengroup.org/unix/online.html .

       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‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                  2017 POSIX_SPAWN_FILE_ACTIONS_ADDDUP2(3P)