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F_DUPFD(2const) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|VERSIONS \|STANDARDS \|HISTORY \|CAVEATS \|SEE ALSO \|COLOPHON

F_DUPFD(2const)F_DUPFD(2const)

NAME top

       F_DUPFD, F_DUPFD_CLOEXEC - duplicate a file descriptor

LIBRARY top

       Standard C library (libc,-lc)

SYNOPSIS top

#include <fcntl.h>int fcntl(intfd, F_DUPFD, intarg);int fcntl(intfd, F_DUPFD_CLOEXEC, intarg);

DESCRIPTION top

F_DUPFD              Duplicate the file descriptorfd using the lowest-numbered              available file descriptor greater than or equal toarg.              This is different fromdup2(2), which uses exactly the file              descriptor specified.              On success, the new file descriptor is returned.              Seedup(2) for further details.F_DUPFD_CLOEXEC              As forF_DUPFD, but additionally set the close-on-exec flag              for the duplicate file descriptor.  Specifying this flag              permits a program to avoid an additionalF_SETFD(2const)              operation to set theFD_CLOEXECflag.  For an explanation              of why this flag is useful, see the description ofO_CLOEXECinopen(2).

RETURN VALUE top

       The new file descriptor.       On error, -1 is returned, anderrno is set to indicate the error.

ERRORS top

       Seefcntl(2).EINVALarg is negative or is greater than the maximum allowable              value (see the discussion ofRLIMIT_NOFILEingetrlimit(2)).EMFILEThe per-process limit on the number of open file              descriptors has been reached.

VERSIONS top

       POSIX.1-2024 specifiesF_DUPFD_CLOFORK, but Linux doesn't support       it.

STANDARDS top

       POSIX.1-2008.

HISTORY top

F_DUPFD              SVr4, 4.3BSD, POSIX.1-2001.F_DUPFD_CLOEXEC              Linux 2.6.24.  POSIX.1-2008.  (To get this definition,              define_POSIX_C_SOURCEwith the value 200809L or greater,              or_XOPEN_SOURCEwith the value 700 or greater.)

CAVEATS top

       The errors returned bydup2(2) are different from those returned       byF_DUPFD.

COLOPHON top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-07-19F_DUPFD(2const)

Pages that refer to this page:fcntl(2), fcntl_locking(2), F_GETFL(2const)

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