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STAT(2) Linux Programmer's Manual STAT(2)
NAME
stat, fstat, lstat, fstatat - get file status
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int stat(const char *pathname, struct stat *buf);
int fstat(int fd, struct stat *buf);
int lstat(const char *pathname, struct stat *buf);
#include <fcntl.h> /* Definition of AT_* constants */
#include <sys/stat.h>
int fstatat(int dirfd, const char *pathname, struct stat *buf,
int flags);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
lstat():
/* glibc 2.19 and earlier */ _BSD_SOURCE ||
/* Since glibc 2.20 */_DEFAULT_SOURCE ||
_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200112L
fstatat():
Since glibc 2.10:
_XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_ATFILE_SOURCE
DESCRIPTION
These functions return information about a file, in the buffer pointed
to by stat. No permissions are required on the file itself, but--in
the case of stat(), fstatat(), and lstat()--execute (search) permission
is required on all of the directories in pathname that lead to the
file.
stat() and fstatat() retrieve information about the file pointed to by
pathname; the differences for fstatat() are described below.
lstat() is identical to stat(), except that if pathname is a symbolic
link, then it returns information about the link itself, not the file
that it refers to.
fstat() is identical to stat(), except that the file about which infor-
mation is to be retrieved is specified by the file descriptor fd.
All of these system calls return a stat structure, which contains the
following fields:
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
mode_t st_mode; /* protection */
nlink_t st_nlink; /* number of hard links */
uid_t st_uid; /* user ID of owner */
gid_t st_gid; /* group ID of owner */
dev_t st_rdev; /* device ID (if special file) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of 512B blocks allocated */
/* Since Linux 2.6, the kernel supports nanosecond
precision for the following timestamp fields.
For the details before Linux 2.6, see NOTES. */
struct timespec st_atim; /* time of last access */
struct timespec st_mtim; /* time of last modification */
struct timespec st_ctim; /* time of last status change */
#define st_atime st_atim.tv_sec /* Backward compatibility */
#define st_mtime st_mtim.tv_sec
#define st_ctime st_ctim.tv_sec
};
Note: the order of fields in the stat structure varies somewhat across
architectures. In addition, the definition above does not show the
padding bytes that may be present between some fields on various archi-
tectures. Consult the the glibc and kernel source code if you need to
know the details.
The st_dev field describes the device on which this file resides. (The
major(3) and minor(3) macros may be useful to decompose the device ID
in this field.)
The st_rdev field describes the device that this file (inode) repre-
sents.
The st_size field gives the size of the file (if it is a regular file
or a symbolic link) in bytes. The size of a symbolic link is the
length of the pathname it contains, without a terminating null byte.
The st_blocks field indicates the number of blocks allocated to the
file, 512-byte units. (This may be smaller than st_size/512 when the
file has holes.)
The st_blksize field gives the "preferred" blocksize for efficient
filesystem I/O. (Writing to a file in smaller chunks may cause an
inefficient read-modify-rewrite.)
Not all of the Linux filesystems implement all of the time fields.
Some filesystem types allow mounting in such a way that file and/or
directory accesses do not cause an update of the st_atime field. (See
noatime, nodiratime, and relatime in mount(8), and related information
in mount(2).) In addition, st_atime is not updated if a file is opened
with the O_NOATIME; see open(2).
The field st_atime is changed by file accesses, for example, by
execve(2), mknod(2), pipe(2), utime(2) and read(2) (of more than zero
bytes). Other routines, like mmap(2), may or may not update st_atime.
The field st_mtime is changed by file modifications, for example, by
mknod(2), truncate(2), utime(2) and write(2) (of more than zero bytes).
Moreover, st_mtime of a directory is changed by the creation or dele-
tion of files in that directory. The st_mtime field is not changed for
changes in owner, group, hard link count, or mode.
The field st_ctime is changed by writing or by setting inode informa-
tion (i.e., owner, group, link count, mode, etc.).
The following mask values are defined for the file type component of
the st_mode field:
S_IFMT 0170000 bit mask for the file type bit fields
S_IFSOCK 0140000 socket
S_IFLNK 0120000 symbolic link
S_IFREG 0100000 regular file
S_IFBLK 0060000 block device
S_IFDIR 0040000 directory
S_IFCHR 0020000 character device
S_IFIFO 0010000 FIFO
Thus, to test for a regular file (for example), one could write:
stat(pathname, &sb);
if ((sb.st_mode & S_IFMT) == S_IFREG) {
/* Handle regular file */
}
Because tests of the above form are common, additional macros are
defined by POSIX to allow the test of the file type in st_mode to be
written more concisely:
S_ISREG(m) is it a regular file?
S_ISDIR(m) directory?
S_ISCHR(m) character device?
S_ISBLK(m) block device?
S_ISFIFO(m) FIFO (named pipe)?
S_ISLNK(m) symbolic link? (Not in POSIX.1-1996.)
S_ISSOCK(m) socket? (Not in POSIX.1-1996.)
The preceding code snippet could thus be rewritten as:
stat(pathname, &sb);
if (S_ISREG(sb.st_mode)) {
/* Handle regular file */
}
The definitions of most of the above file type test macros are provided
if any of the following feature test macros are defined: _BSD_SOURCE
(in glibc 2.19 and earlier), _SVID_SOURCE (in glibc 2.19 and earlier),
or _DEFAULT_SOURCE (in glibc 2.20 and later). In addition, definitions
of all of the above macros except S_IFSOCK and S_ISSOCK() are provided
if _XOPEN_SOURCE is defined. The definition of S_IFSOCK can also be
exposed by defining _XOPEN_SOURCE with a value of 500 or greater.
The definition of S_ISSOCK() is exposed if any of the following feature
test macros is defined: _BSD_SOURCE (in glibc 2.19 and earlier),
_DEFAULT_SOURCE (in glibc 2.20 and later), _XOPEN_SOURCE with a value
of 500 or greater, or _POSIX_C_SOURCE with a value of 200112L or
greater.
The following mask values are defined for the file permissions compo-
nent of the st_mode field:
S_ISUID 0004000 set-user-ID bit
S_ISGID 0002000 set-group-ID bit (see below)
S_ISVTX 0001000 sticky bit (see below)
S_IRWXU 00700 mask for file owner permissions
S_IRUSR 00400 owner has read permission
S_IWUSR 00200 owner has write permission
S_IXUSR 00100 owner has execute permission
S_IRWXG 00070 mask for group permissions
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 mask for permissions for others
(not in group)
S_IROTH 00004 others have read permission
S_IWOTH 00002 others have write permission
S_IXOTH 00001 others have execute permission
The set-group-ID bit (S_ISGID) has several special uses. For a direc-
tory, it indicates that BSD semantics is to be used for that directory:
files created there inherit their group ID from the directory, not from
the effective group ID of the creating process, and directories created
there will also get the S_ISGID bit set. For a file that does not have
the group execution bit (S_IXGRP) set, the set-group-ID bit indicates
mandatory file/record locking.
The sticky bit (S_ISVTX) on a directory means that a file in that
directory can be renamed or deleted only by the owner of the file, by
the owner of the directory, and by a privileged process.
fstatat()
The fstatat() system call operates in exactly the same way as stat(),
except for the differences described here.
If the pathname given in pathname is relative, then it is interpreted
relative to the directory referred to by the file descriptor dirfd
(rather than relative to the current working directory of the calling
process, as is done by stat() for a relative pathname).
If pathname is relative and dirfd is the special value AT_FDCWD, then
pathname is interpreted relative to the current working directory of
the calling process (like stat()).
If pathname is absolute, then dirfd is ignored.
flags can either be 0, or include one or more of the following flags
ORed:
AT_EMPTY_PATH (since Linux 2.6.39)
If pathname is an empty string, operate on the file referred to
by dirfd (which may have been obtained using the open(2) O_PATH
flag). If dirfd is AT_FDCWD, the call operates on the current
working directory. In this case, dirfd can refer to any type of
file, not just a directory. This flag is Linux-specific; define
_GNU_SOURCE to obtain its definition.
AT_NO_AUTOMOUNT (since Linux 2.6.38)
Don't automount the terminal ("basename") component of pathname
if it is a directory that is an automount point. This allows
the caller to gather attributes of an automount point (rather
than the location it would mount). This flag can be used in
tools that scan directories to prevent mass-automounting of a
directory of automount points. The AT_NO_AUTOMOUNT flag has no
effect if the mount point has already been mounted over. This
flag is Linux-specific; define _GNU_SOURCE to obtain its defini-
tion.
AT_SYMLINK_NOFOLLOW
If pathname is a symbolic link, do not dereference it: instead
return information about the link itself, like lstat(). (By
default, fstatat() dereferences symbolic links, like stat().)
See openat(2) for an explanation of the need for fstatat().
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
ERRORS
EACCES Search permission is denied for one of the directories in the
path prefix of pathname. (See also path_resolution(7).)
EBADF fd is bad.
EFAULT Bad address.
ELOOP Too many symbolic links encountered while traversing the path.
ENAMETOOLONG
pathname is too long.
ENOENT A component of pathname does not exist, or pathname is an empty
string.
ENOMEM Out of memory (i.e., kernel memory).
ENOTDIR
A component of the path prefix of pathname is not a directory.
EOVERFLOW
pathname or fd refers to a file whose size, inode number, or
number of blocks cannot be represented in, respectively, the
types off_t, ino_t, or blkcnt_t. This error can occur when, for
example, an application compiled on a 32-bit platform without
-D_FILE_OFFSET_BITS=64 calls stat() on a file whose size exceeds
(1<<31)-1 bytes.
The following additional errors can occur for fstatat():
EBADF dirfd is not a valid file descriptor.
EINVAL Invalid flag specified in flags.
ENOTDIR
pathname is relative and dirfd is a file descriptor referring to
a file other than a directory.
VERSIONS
fstatat() was added to Linux in kernel 2.6.16; library support was
added to glibc in version 2.4.
CONFORMING TO
stat(), fstat(), lstat(): SVr4, 4.3BSD, POSIX.1-2001, POSIX.1.2008.
fstatat(): POSIX.1-2008.
According to POSIX.1-2001, lstat() on a symbolic link need return valid
information only in the st_size field and the file-type component of
the st_mode field of the stat structure. POSIX.1-2008 tightens the
specification, requiring lstat() to return valid information in all
fields except the permission bits in st_mode.
Use of the st_blocks and st_blksize fields may be less portable. (They
were introduced in BSD. The interpretation differs between systems,
and possibly on a single system when NFS mounts are involved.) If you
need to obtain the definition of the blkcnt_t or blksize_t types from
<sys/stat.h>, then define _XOPEN_SOURCE with the value 500 or greater
(before including any header files).
POSIX.1-1990 did not describe the S_IFMT, S_IFSOCK, S_IFLNK, S_IFREG,
S_IFBLK, S_IFDIR, S_IFCHR, S_IFIFO, S_ISVTX constants, but instead
demanded the use of the macros S_ISDIR(), and so on. The S_IF* con-
stants are present in POSIX.1-2001 and later.
The S_ISLNK() and S_ISSOCK() macros are not in POSIX.1-1996, but both
are present in POSIX.1-2001; the former is from SVID 4, the latter from
SUSv2.
UNIX V7 (and later systems) had S_IREAD, S_IWRITE, S_IEXEC, where POSIX
prescribes the synonyms S_IRUSR, S_IWUSR, S_IXUSR.
Other systems
Values that have been (or are) in use on various systems:
hex name ls octal description
f000 S_IFMT 170000 mask for file type
0000 000000 SCO out-of-service inode; BSD
unknown type; SVID-v2 and XPG2 have
both 0 and 0100000 for ordinary file
1000 S_IFIFO p| 010000 FIFO (named pipe)
2000 S_IFCHR c 020000 character special (V7)
3000 S_IFMPC 030000 multiplexed character special (V7)
4000 S_IFDIR d/ 040000 directory (V7)
5000 S_IFNAM 050000 XENIX named special file with two
subtypes, distinguished by st_rdev
values 1, 2
0001 S_INSEM s 000001 XENIX semaphore subtype of IFNAM
0002 S_INSHD m 000002 XENIX shared data subtype of IFNAM
6000 S_IFBLK b 060000 block special (V7)
7000 S_IFMPB 070000 multiplexed block special (V7)
8000 S_IFREG - 100000 regular (V7)
9000 S_IFCMP 110000 VxFS compressed
9000 S_IFNWK n 110000 network special (HP-UX)
a000 S_IFLNK l@ 120000 symbolic link (BSD)
b000 S_IFSHAD 130000 Solaris shadow inode for ACL (not
seen by user space)
c000 S_IFSOCK s= 140000 socket (BSD; also "S_IFSOC" on VxFS)
d000 S_IFDOOR D> 150000 Solaris door
e000 S_IFWHT w% 160000 BSD whiteout (not used for inode)
0200 S_ISVTX 001000 sticky bit: save swapped text even
after use (V7)
reserved (SVID-v2)
On nondirectories: don't cache this
file (SunOS)
On directories: restricted deletion
flag (SVID-v4.2)
0400 S_ISGID 002000 set-group-ID on execution (V7)
for directories: use BSD semantics
for propagation of GID
0400 S_ENFMT 002000 System V file locking enforcement
(shared with S_ISGID)
0800 S_ISUID 004000 set-user-ID on execution (V7)
0800 S_CDF 004000 directory is a context dependent
file (HP-UX)
A sticky command appeared in Version 32V AT&T UNIX.
NOTES
On Linux, lstat() will generally not trigger automounter action,
whereas stat() will (but see fstatat(2)).
For most files under the /proc directory, stat() does not return the
file size in the st_size field; instead the field is returned with the
value 0.
Timestamp fields
Older kernels and older standards did not support nanosecond timestamp
fields. Instead, there were three timestamp fields--st_atime,
st_mtime, and st_ctime--typed as time_t that recorded timestamps with
one-second precision.
Since kernel 2.5.48, the stat structure supports nanosecond resolution
for the three file timestamp fields. The nanosecond components of each
timestamp are available via names of the form st_atim.tv_nsec if the
_BSD_SOURCE or _SVID_SOURCE feature test macro is defined. Nanosecond
timestamps are nowadays standardized, starting with POSIX.1-2008, and,
starting with version 2.12, glibc also exposes the nanosecond component
names if _POSIX_C_SOURCE is defined with the value 200809L or greater,
or _XOPEN_SOURCE is defined with the value 700 or greater. If none of
the aforementioned macros are defined, then the nanosecond values are
exposed with names of the form st_atimensec.
Nanosecond timestamps are supported on XFS, JFS, Btrfs, and ext4 (since
Linux 2.6.23). Nanosecond timestamps are not supported in ext2, ext3,
and Reiserfs. On filesystems that do not support subsecond timestamps,
the nanosecond fields are returned with the value 0.
Underlying kernel interface
Over time, increases in the size of the stat structure have led to
three successive versions of stat(): sys_stat() (slot __NR_oldstat),
sys_newstat() (slot __NR_stat), and sys_stat64() (new in kernel 2.4;
slot __NR_stat64). The glibc stat() wrapper function hides these
details from applications, invoking the most recent version of the sys-
tem call provided by the kernel, and repacking the returned information
if required for old binaries. Similar remarks apply for fstat() and
lstat().
The underlying system call employed by the glibc fstatat() wrapper
function is actually called fstatat64().
EXAMPLE
The following program calls stat() and displays selected fields in the
returned stat structure.
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
struct stat sb;
if (argc != 2) {
fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
exit(EXIT_FAILURE);
}
if (stat(argv[1], &sb) == -1) {
perror("stat");
exit(EXIT_FAILURE);
}
printf("File type: ");
switch (sb.st_mode & S_IFMT) {
case S_IFBLK: printf("block device\n"); break;
case S_IFCHR: printf("character device\n"); break;
case S_IFDIR: printf("directory\n"); break;
case S_IFIFO: printf("FIFO/pipe\n"); break;
case S_IFLNK: printf("symlink\n"); break;
case S_IFREG: printf("regular file\n"); break;
case S_IFSOCK: printf("socket\n"); break;
default: printf("unknown?\n"); break;
}
printf("I-node number: %ld\n", (long) sb.st_ino);
printf("Mode: %lo (octal)\n",
(unsigned long) sb.st_mode);
printf("Link count: %ld\n", (long) sb.st_nlink);
printf("Ownership: UID=%ld GID=%ld\n",
(long) sb.st_uid, (long) sb.st_gid);
printf("Preferred I/O block size: %ld bytes\n",
(long) sb.st_blksize);
printf("File size: %lld bytes\n",
(long long) sb.st_size);
printf("Blocks allocated: %lld\n",
(long long) sb.st_blocks);
printf("Last status change: %s", ctime(&sb.st_ctime));
printf("Last file access: %s", ctime(&sb.st_atime));
printf("Last file modification: %s", ctime(&sb.st_mtime));
exit(EXIT_SUCCESS);
}
SEE ALSO
ls(1), stat(1), access(2), chmod(2), chown(2), readlink(2), utime(2),
capabilities(7), symlink(7)
COLOPHON
This page is part of release 3.69 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
http://www.kernel.org/doc/man-pages/.
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