PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

sys_stat.h(0P)            POSIX Programmer's Manual           sys_stat.h(0P)

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

       sys/stat.h — data returned by the stat() function

SYNOPSIS         top

       #include <sys/stat.h>

DESCRIPTION         top

       The <sys/stat.h> header shall define the structure of the data
       returned by the fstat(), lstat(), and stat() functions.

       The <sys/stat.h> header shall define the stat structure, which shall
       include at least the following members:

           dev_t st_dev            Device ID of device containing file.
           ino_t st_ino            File serial number.
           mode_t st_mode          Mode of file (see below).
           nlink_t st_nlink        Number of hard links to the file.
           uid_t st_uid            User ID of file.
           gid_t st_gid            Group ID of file.
           dev_t st_rdev           Device ID (if file is character or block special).
           off_t st_size           For regular files, the file size in bytes.
                                   For symbolic links, the length in bytes of the
                                   pathname contained in the symbolic link.
                                   For a shared memory object, the length in bytes.
                                   For a typed memory object, the length in bytes.
                                   For other file types, the use of this field is
                                   unspecified.
           struct timespec st_atim Last data access timestamp.
           struct timespec st_mtim Last data modification timestamp.
           struct timespec st_ctim Last file status change timestamp.
           blksize_t st_blksize    A file system-specific preferred I/O block size
                                   for this object. In some file system types, this
                                   may vary from file to file.
           blkcnt_t st_blocks      Number of blocks allocated for this object.

       The st_ino and st_dev fields taken together uniquely identify the
       file within the system.

       The <sys/stat.h> header shall define the blkcnt_t, blksize_t, dev_t,
       ino_t, mode_t, nlink_t, uid_t, gid_t, off_t, and time_t types as
       described in <sys/types.h>.

       The <sys/stat.h> header shall define the timespec structure as
       described in <time.h>.  Times shall be given in seconds since the
       Epoch.

       Which structure members have meaningful values depends on the type of
       file. For further information, see the descriptions of fstat(),
       lstat(), and stat() in the System Interfaces volume of POSIX.1‐2008.

       For compatibility with earlier versions of this standard, the
       st_atime macro shall be defined with the value st_atim.tv_sec.
       Similarly, st_ctime and st_mtime shall be defined as macros with the
       values st_ctim.tv_sec and st_mtim.tv_sec, respectively.

       The <sys/stat.h> header shall define the following symbolic constants
       for the file types encoded in type mode_t.  The values shall be
       suitable for use in #if preprocessing directives:

       S_IFMT      Type of file.

                   S_IFBLK     Block special.

                   S_IFCHR     Character special.

                   S_IFIFO     FIFO special.

                   S_IFREG     Regular.

                   S_IFDIR     Directory.

                   S_IFLNK     Symbolic link.

                   S_IFSOCK    Socket.

       The <sys/stat.h> header shall define the following symbolic constants
       for the file mode bits encoded in type mode_t, with the indicated
       numeric values. These macros shall expand to an expression which has
       a type that allows them to be used, either singly or OR'ed together,
       as the third argument to open() without the need for a mode_t cast.
       The values shall be suitable for use in #if preprocessing directives.

      ┌────────┬───────────────┬──────────────────────────────────────────────┐
      │ Name   Numeric Value Description                  │
      ├────────┼───────────────┼──────────────────────────────────────────────┤
      │S_IRWXU │      0700     │ Read, write, execute/search by owner.        │
      │S_IRUSR │      0400     │ Read permission, owner.                      │
      │S_IWUSR │      0200     │ Write permission, owner.                     │
      │S_IXUSR │      0100     │ Execute/search permission, owner.            │
      ├────────┼───────────────┼──────────────────────────────────────────────┤
      │S_IRWXG │       070     │ Read, write, execute/search by group.        │
      │S_IRGRP │       040     │ Read permission, group.                      │
      │S_IWGRP │       020     │ Write permission, group.                     │
      │S_IXGRP │       010     │ Execute/search permission, group.            │
      ├────────┼───────────────┼──────────────────────────────────────────────┤
      │S_IRWXO │        07     │ Read, write, execute/search by others.       │
      │S_IROTH │        04     │ Read permission, others.                     │
      │S_IWOTH │        02     │ Write permission, others.                    │
      │S_IXOTH │        01     │ Execute/search permission, others.           │
      ├────────┼───────────────┼──────────────────────────────────────────────┤
      │S_ISUID │     04000     │ Set-user-ID on execution.                    │
      │S_ISGID │     02000     │ Set-group-ID on execution.                   │
      │S_ISVTX │     01000     │ On directories, restricted deletion flag.    │
      └────────┴───────────────┴──────────────────────────────────────────────┘
       The following macros shall be provided to test whether a file is of
       the specified type. The value m supplied to the macros is the value
       of st_mode from a stat structure. The macro shall evaluate to a non-
       zero value if the test is true; 0 if the test is false.

       S_ISBLK(m)    Test for a block special file.

       S_ISCHR(m)    Test for a character special file.

       S_ISDIR(m)    Test for a directory.

       S_ISFIFO(m)   Test for a pipe or FIFO special file.

       S_ISREG(m)    Test for a regular file.

       S_ISLNK(m)    Test for a symbolic link.

       S_ISSOCK(m)   Test for a socket.

       The implementation may implement message queues, semaphores, or
       shared memory objects as distinct file types. The following macros
       shall be provided to test whether a file is of the specified type.
       The value of the buf argument supplied to the macros is a pointer to
       a stat structure. The macro shall evaluate to a non-zero value if the
       specified object is implemented as a distinct file type and the
       specified file type is contained in the stat structure referenced by
       buf.  Otherwise, the macro shall evaluate to zero.

       S_TYPEISMQ(buf)
                     Test for a message queue.

       S_TYPEISSEM(buf)
                     Test for a semaphore.

       S_TYPEISSHM(buf)
                     Test for a shared memory object.

       The implementation may implement typed memory objects as distinct
       file types, and the following macro shall test whether a file is of
       the specified type. The value of the buf argument supplied to the
       macros is a pointer to a stat structure. The macro shall evaluate to
       a non-zero value if the specified object is implemented as a distinct
       file type and the specified file type is contained in the stat
       structure referenced by buf.  Otherwise, the macro shall evaluate to
       zero.

       S_TYPEISTMO(buf)
                     Test macro for a typed memory object.

       The <sys/stat.h> header shall define the following symbolic constants
       as distinct integer values outside of the range [0,999999999], for
       use with the futimens() and utimensat() functions: UTIME_NOW
       UTIME_OMIT

       The following shall be declared as functions and may also be defined
       as macros. Function prototypes shall be provided.

           int    chmod(const char *, mode_t);
           int    fchmod(int, mode_t);
           int    fchmodat(int, const char *, mode_t, int);
           int    fstat(int, struct stat *);
           int    fstatat(int, const char *restrict, struct stat *restrict, int);
           int    futimens(int, const struct timespec [2]);
           int    lstat(const char *restrict, struct stat *restrict);
           int    mkdir(const char *, mode_t);
           int    mkdirat(int, const char *, mode_t);
           int    mkfifo(const char *, mode_t);
           int    mkfifoat(int, const char *, mode_t);
           int    mknod(const char *, mode_t, dev_t);
           int    mknodat(int, const char *, mode_t, dev_t);
           int    stat(const char *restrict, struct stat *restrict);
           mode_t umask(mode_t);
           int    utimensat(int, const char *, const struct timespec [2], int);

       The following sections are informative.

APPLICATION USAGE         top

       Use of the macros is recommended for determining the type of a file.

RATIONALE         top

       A conforming C-language application must include <sys/stat.h> for
       functions that have arguments or return values of type mode_t, so
       that symbolic values for that type can be used. An alternative would
       be to require that these constants are also defined by including
       <sys/types.h>.

       The S_ISUID and S_ISGID bits may be cleared on any write, not just on
       open(), as some historical implementations do.

       System calls that update the time entry fields in the stat structure
       must be documented by the implementors. POSIX-conforming systems
       should not update the time entry fields for functions listed in the
       System Interfaces volume of POSIX.1‐2008 unless the standard requires
       that they do, except in the case of documented extensions to the
       standard.

       Upon assignment, file timestamps are immediately converted to the
       resolution of the file system by truncation (i.e., the recorded time
       can be older than the actual time). For example, if the file system
       resolution is 1 microsecond, then a conforming stat() must always
       return an st_mtim.tv_nsec that is a multiple of 1000. Some older
       implementations returned higher-resolution timestamps while the inode
       information was cached, and then spontaneously truncated the tv_nsec
       fields when they were stored to and retrieved from disk, but this
       behavior does not conform.

       Note that st_dev must be unique within a Local Area Network (LAN) in
       a ``system'' made up of multiple computers' file systems connected by
       a LAN.

       Networked implementations of a POSIX-conforming system must guarantee
       that all files visible within the file tree (including parts of the
       tree that may be remotely mounted from other machines on the network)
       on each individual processor are uniquely identified by the
       combination of the st_ino and st_dev fields.

       The unit for the st_blocks member of the stat structure is not
       defined within POSIX.1‐2008. In some implementations it is 512 bytes.
       It may differ on a file system basis. There is no correlation between
       values of the st_blocks and st_blksize, and the f_bsize (from
       <sys/statvfs.h>) structure members.

       Traditionally, some implementations defined the multiplier for
       st_blocks in <sys/param.h> as the symbol DEV_BSIZE.

       Some earlier versions of this standard did not specify values for the
       file mode bit macros. The expectation was that some implementors
       might choose to use a different encoding for these bits than the
       traditional one, and that new applications would use symbolic file
       modes instead of numeric. This version of the standard specifies the
       traditional encoding, in recognition that nearly 20 years after the
       first publication of this standard numeric file modes are still in
       widespread use by application developers, and that all conforming
       implementations still use the traditional encoding.

FUTURE DIRECTIONS         top

       No new S_IFMT symbolic names for the file type values of mode_t will
       be defined by POSIX.1‐2008; if new file types are required, they will
       only be testable through S_ISxx() or S_TYPEISxxx() macros instead.

SEE ALSO         top

       sys_statvfs.h(0p), sys_types.h(0p), time.h(0p)

       The System Interfaces volume of POSIX.1‐2008, chmod(3p), fchmod(3p),
       fstat(3p), fstatat(3p), futimens(3p), mkdir(3p), mkfifo(3p),
       mknod(3p), umask(3p)

COPYRIGHT         top

       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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                      sys_stat.h(0P)