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.
The dirfd() function shall return a file descriptor referring to the
same directory as the dirp argument. This file descriptor shall be
closed by a call to closedir(). If any attempt is made to close the
file descriptor, or to modify the state of the associated
description, other than by means of closedir(), readdir(),
readdir_r(), rewinddir(), or seekdir(), the behavior is undefined.
Upon successful completion, the dirfd() function shall return an
integer which contains a file descriptor for the stream pointed to by
dirp. Otherwise, it shall return −1 and may set errno to indicate
The dirfd() function may fail if:
EINVAL The dirp argument does not refer to a valid directory stream.
The implementation does not support the association of a file
descriptor with a directory.
The following sections are informative.
This interface was introduced because the Base Definitions volume of
POSIX.1‐2008 does not make public the DIR data structure.
Applications tend to use the fchdir() function on the file descriptor
returned by this interface, and this has proven useful for security
reasons; in particular, it is a better technique than others where
directory names might change.
The description uses the term ``a file descriptor'' rather than ``the
file descriptor''. The implication intended is that an implementation
that does not use an fd for opendir() could still open() the
directory to implement the dirfd() function. Such a descriptor must
be closed later during a call to closedir().
An implementation that does not support file descriptors referring to
directories may fail with [ENOTSUP].
If it is necessary to allocate an fd to be returned by dirfd(), it
should be done at the time of a call to opendir().
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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
IEEE/The Open Group 2013 DIRFD(3P)