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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 buf. 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 information 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 architectures. Consult the glibc and kernel source code if you
need to know the details.
Note: For performance and simplicity reasons, different fields in the stat structure may
contain state information from different moments during the execution of the system call.
For example, if st_mode or st_uid is changed by another process by calling chmod(2) or
chown(2), stat() might return the old st_mode together with the new st_uid, or the old
st_uid together with the new st_mode.
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) represents.
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 deletion 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 information (i.e., owner,
group, link count, mode, etc.).
POSIX refers to the st_mode bits corresponding to the mask S_IFMT (see below) as the file
type, the 12 bits corresponding to the mask 07777 as the file mode bits and the least
significant 9 bits (0777) as the file permission bits.
The following mask values are defined for the file type of the st_mode field:
S_IFMT 0170000 bit mask for the file type bit field
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 is 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 mode component of the st_mode field:
S_ISUID 04000 set-user-ID bit
S_ISGID 02000 set-group-ID bit (see below)
S_ISVTX 01000 sticky bit (see below)
S_IRWXU 00700 owner has read, write, and execute permission
S_IRUSR 00400 owner has read permission
S_IWUSR 00200 owner has write permission
S_IXUSR 00100 owner has execute permission
S_IRWXG 00070 group has read, write, and execute permission
S_IRGRP 00040 group has read permission
S_IWGRP 00020 group has write permission
S_IXGRP 00010 group has execute permission
S_IRWXO 00007 others (not in group) have read, write, and
execute permission
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 directory, 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 definition.
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 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 mode 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* constants 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.
C library/kernel differences
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() (slot __NR_stat64) on 32-bit platforms such as i386. The first two versions
were already present in Linux 1.0 (albeit with different names); the last was added in
Linux 2.4. Similar remarks apply for fstat() and lstat().
The kernel-internal versions of the stat structure dealt with by the different versions
are, respectively:
__old_kernel_stat
The original structure, with rather narrow fields, and no padding.
stat Larger st_ino field and padding added to various parts of the structure to
allow for future expansion.
stat64 Even larger st_ino field, larger st_uid and st_gid fields to accommodate the
Linux-2.4 expansion of UIDs and GIDs to 32 bits, and various other enlarged
fields and further padding in the structure. (Various padding bytes were
eventually consumed in Linux 2.6, with the advent of 32-bit device IDs and
nanosecond components for the timestamp fields.)
The glibc stat() wrapper function hides these details from applications, invoking the most
recent version of the system call provided by the kernel, and repacking the returned
information if required for old binaries.
On modern 64-bit systems, life is simpler: there is a single stat() system call and the
kernel deals with a stat structure that contains fields of a sufficient size.
The underlying system call employed by the glibc fstatat() wrapper function is actually
called fstatat64() or, on some architectures, newfstatat().
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
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