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PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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sys_stat.h(0P) POSIX Programmer's Manual sys_stat.h(0P)
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.
sys/stat.h — data returned by the stat() function
#include <sys/stat.h>
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.
Use of the macros is recommended for determining the type of a
file.
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.
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.
sys_statvfs.h(0p), sys_types.h(0p), time.h(0p)
The System Interfaces volume of POSIX.1‐2017, chmod(3p),
fchmod(3p), fstat(3p), fstatat(3p), futimens(3p), mkdir(3p),
mkfifo(3p), mknod(3p), umask(3p)
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)
Pages that refer to this page: fcntl.h(0p), ftw.h(0p), utime.h(0p), ls(1p), touch(1p), chmod(3p), creat(3p), fchmod(3p), fstat(3p), fstatat(3p), ftw(3p), futimens(3p), mkdir(3p), mkfifo(3p), mknod(3p), open(3p), umask(3p), utime(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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