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@(#)dir.5 8.4 (Berkeley) 5/3/95
.Dd $Mdocdate: September 10 2015 $ .Dt DIR 5 .Os .Sh NAME .Nm dir , .Nm dirent .Nd directory file format .Sh SYNOPSIS n dirent.h .Sh DESCRIPTION Directories provide a convenient hierarchical method of grouping files while obscuring the underlying details of the storage medium. A directory file is differentiated from a plain file by a flag in its .Xr 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 directories and files is formed in this manner and is called a file system (or referred to as a file system tree). An entry in this tree,
nested or not nested,
is a pathname.
p Each directory file contains two special directory entries; one is a pointer to the directory itself called dot
q Dq . and the other a pointer to its parent directory called dot-dot
q Dq .. . Dot and dot-dot are valid pathnames, however, the system root directory
q Dq / , has no parent and dot-dot points to itself like dot.
p 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 .Xr mount 8 ) .
p The directory entry format is defined in the file n dirent.h : d -literal /* * 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 .Ed .Sh SEE ALSO .Xr getdents 2 , .Xr fs 5 , .Xr inode 5 .Sh HISTORY A .Nm dir file format appeared in .At v1 . A predecessor .Vt struct direct first appeared in .At v7 . The .Vt dirent structure first appeared in x 4.3 Reno . The .Fa d_off member was added in .Ox 5.5 .