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DIR(5)                      BSD File Formats Manual                     DIR(5)

NAME
     dir, dirent -- directory file format

SYNOPSIS
     #include <&lt;dirent.h>&gt;

DESCRIPTION
     Directories provide a convenient hierarchical method of grouping files
     while obscuring the underlying details of the storage medium.  A direc-
     tory file is differentiated from a plain file by a flag in its inode(5)
     entry.  It consists of records (directory entries) each of which contains
     information about a file and a pointer to the file itself.  Directory
     entries may contain other directories as well as plain files; such nested
     directories are referred to as subdirectories.  A hierarchy of directo-
     ries and files is formed in this manner and is called a file system (or
     referred to as a file system tree).

     Each directory file contains two special directory entries; one is a
     pointer to the directory itself called dot (``.'') and the other a
     pointer to its parent directory called dot-dot (``..'').  Dot and dot-dot
     are valid pathnames, however, the system root directory (``/''), has no
     parent and dot-dot points to itself like dot.

     File system nodes are ordinary directory files on which has been grafted
     a file system object, such as a physical disk or a partitioned area of
     such a disk (see mount(8)).

     The directory entry format is defined in the file <dirent.h>:

     /*
      * A directory entry has a struct dirent at the front of it, containing
      * its inode number, the length of the entry, and the length of the name
      * contained in the entry.  These are followed by the name padded to some
      * alignment (currently 8 bytes) with NUL bytes.  All names are guaranteed
      * NUL terminated.  The maximum length of a name in a directory is MAXNAMLEN.
      */

     struct dirent {
             ino_t           d_fileno;       /* file number of entry */
             off_t           d_off;          /* offset of next entry */
             u_int16_t       d_reclen;       /* length of this record */
             u_int8_t        d_type;         /* file type, see below */
             u_int8_t        d_namlen;       /* length of string in d_name */
     #define MAXNAMLEN       255
             char    d_name[MAXNAMLEN + 1];  /* maximum name length */
     };

     #define d_ino           d_fileno        /* backward compatibility */

     /*
      * File types
      */
     #define DT_UNKNOWN      0
     #define DT_FIFO         1
     #define DT_CHR          2
     #define DT_DIR          4
     #define DT_BLK          6
     #define DT_REG          8
     #define DT_LNK          10
     #define DT_SOCK         12

SEE ALSO
     getdents(2), fs(5), inode(5)

HISTORY
     A dir file format appeared in Version 7 AT&T UNIX.  The d_off member was
     added in OpenBSD 5.5.

BSD                              May 23, 2017                              BSD