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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 .