sys_stat.h(0P) POSIX Programmer's Manual sys_stat.h(0P)
PROLOG
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
sys/stat.h — data returned by the stat() function
SYNOPSIS
#include <sys/stat.h>
DESCRIPTION
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.1‐2017.
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);
Inclusion of the <sys/stat.h> header may make visible all symbols from
the <time.h> header.
The following sections are informative.
APPLICATION USAGE
Use of the macros is recommended for determining the type of a file.
RATIONALE
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.1‐2017 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
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
<sys_statvfs.h>, <sys_types.h>, <time.h>
The System Interfaces volume of POSIX.1‐2017, chmod(), fchmod(),
fstat(), fstatat(), futimens(), mkdir(), mkfifo(), mknod(), umask()
COPYRIGHT
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 sys_stat.h(0P)
sys/stat.h