fdopendir(3p) — Linux manual page


FDOPENDIR(3P)           POSIX Programmer's Manual          FDOPENDIR(3P)

PROLOG         top

       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         top

       fdopendir, opendir — open directory associated with file

SYNOPSIS         top

       #include <dirent.h>

       DIR *fdopendir(int fd);
       DIR *opendir(const char *dirname);

DESCRIPTION         top

       The fdopendir() function shall be equivalent to the opendir()
       function except that the directory is specified by a file
       descriptor rather than by a name. The file offset associated with
       the file descriptor at the time of the call determines which
       entries are returned.

       Upon successful return from fdopendir(), the file descriptor is
       under the control of the system, and 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 calling closedir() the file descriptor shall
       be closed.

       It is unspecified whether the FD_CLOEXEC flag will be set on the
       file descriptor by a successful call to fdopendir().

       The opendir() function shall open a directory stream
       corresponding to the directory named by the dirname argument. The
       directory stream is positioned at the first entry. If the type
       DIR is implemented using a file descriptor, applications shall
       only be able to open up to a total of {OPEN_MAX} files and

       If the type DIR is implemented using a file descriptor, the
       descriptor shall be obtained as if the O_DIRECTORY flag was
       passed to open().

RETURN VALUE         top

       Upon successful completion, these functions shall return a
       pointer to an object of type DIR.  Otherwise, these functions
       shall return a null pointer and set errno to indicate the error.

ERRORS         top

       The fdopendir() function shall fail if:

       EBADF  The fd argument is not a valid file descriptor open for

              The descriptor fd is not associated with a directory.

       The opendir() function shall fail if:

       EACCES Search permission is denied for the component of the path
              prefix of dirname or read permission is denied for

       ELOOP  A loop exists in symbolic links encountered during
              resolution of the dirname argument.

              The length of a component of a pathname is longer than

       ENOENT A component of dirname does not name an existing directory
              or dirname is an empty string.

              A component of dirname names an existing file that is
              neither a directory nor a symbolic link to a directory.

       The opendir() function may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered
              during resolution of the dirname argument.

       EMFILE All file descriptors available to the process are
              currently open.

              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate
              result with a length that exceeds {PATH_MAX}.

       ENFILE Too many files are currently open in the system.

       The following sections are informative.

EXAMPLES         top

   Open a Directory Stream
       The following program fragment demonstrates how the opendir()
       function is used.

           #include <dirent.h>
               DIR *dir;
               struct dirent *dp;
               if ((dir = opendir (".")) == NULL) {
                   perror ("Cannot open .");
                   exit (1);

               while ((dp = readdir (dir)) != NULL) {

   Find And Open a File
       The following program searches through a given directory looking
       for files whose name does not begin with a dot and whose size is
       larger than 1 MiB.

           #include <stdio.h>
           #include <dirent.h>
           #include <fcntl.h>
           #include <sys/stat.h>
           #include <stdint.h>
           #include <stdlib.h>
           #include <unistd.h>

           main(int argc, char *argv[])
               struct stat statbuf;
               DIR *d;
               struct dirent *dp;
               int dfd, ffd;

               if ((d = fdopendir((dfd = open("./tmp", O_RDONLY)))) == NULL) {
                   fprintf(stderr, "Cannot open ./tmp directory\n");
               while ((dp = readdir(d)) != NULL) {
                   if (dp->d_name[0] == '.')
                   /* there is a possible race condition here as the file
                    * could be renamed between the readdir and the open */
                   if ((ffd = openat(dfd, dp->d_name, O_RDONLY)) == -1) {
                   if (fstat(ffd, &statbuf) == 0 && statbuf.st_size > (1024*1024)) {
                       /* found it ... */
                       printf("%s: %jdK\n", dp->d_name,
                           (intmax_t)(statbuf.st_size / 1024));
               closedir(d); // note this implicitly closes dfd
               return 0;


       The opendir() function should be used in conjunction with
       readdir(), closedir(), and rewinddir() to examine the contents of
       the directory (see the EXAMPLES section in readdir(3p)).  This
       method is recommended for portability.

RATIONALE         top

       The purpose of the fdopendir() function is to enable opening
       files in directories other than the current working directory
       without exposure to race conditions. Any part of the path of a
       file could be changed in parallel to a call to opendir(),
       resulting in unspecified behavior.

       Based on historical implementations, the rules about file
       descriptors apply to directory streams as well. However, this
       volume of POSIX.1‐2017 does not mandate that the directory stream
       be implemented using file descriptors. The description of
       closedir() clarifies that if a file descriptor is used for the
       directory stream, it is mandatory that closedir() deallocate the
       file descriptor. When a file descriptor is used to implement the
       directory stream, it behaves as if the FD_CLOEXEC had been set
       for the file descriptor.

       The directory entries for dot and dot-dot are optional. This
       volume of POSIX.1‐2017 does not provide a way to test a priori
       for their existence because an application that is portable must
       be written to look for (and usually ignore) those entries.
       Writing code that presumes that they are the first two entries
       does not always work, as many implementations permit them to be
       other than the first two entries, with a ``normal'' entry
       preceding them. There is negligible value in providing a way to
       determine what the implementation does because the code to deal
       with dot and dot-dot must be written in any case and because such
       a flag would add to the list of those flags (which has proven in
       itself to be objectionable) and might be abused.

       Since the structure and buffer allocation, if any, for directory
       operations are defined by the implementation, this volume of
       POSIX.1‐2017 imposes no portability requirements for erroneous
       program constructs, erroneous data, or the use of unspecified
       values such as the use or referencing of a dirp value or a dirent
       structure value after a directory stream has been closed or after
       a fork() or one of the exec function calls.



SEE ALSO         top

       closedir(3p), dirfd(3p), fstatat(3p), open(3p), readdir(3p),
       rewinddir(3p), symlink(3p)

       The Base Definitions volume of POSIX.1‐2017, dirent.h(0p),

COPYRIGHT         top

       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 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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                     FDOPENDIR(3P)

Pages that refer to this page: dirent.h(0p)closedir(3p)dirfd(3p)fstatat(3p)ftw(3p)glob(3p)nftw(3p)open(3p)opendir(3p)readdir(3p)rewinddir(3p)seekdir(3p)symlink(3p)telldir(3p)