newfstatat
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 *statbuf);
int fstat(int fd, struct stat *statbuf);
int lstat(const char *pathname, struct stat *statbuf);
#include <fcntl.h> /* Definition of AT_* constants */
#include <sys/stat.h>
int fstatat(int dirfd, const char *pathname, struct stat *statbuf,
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
|| /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200112L
fstatat():
Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_ATFILE_SOURCE
DESCRIPTION
These functions return information about a file, in the buffer pointed
to by statbuf. 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.
The stat structure
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; /* File type and mode */
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; /* Block size 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 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 fields in the stat structure are as follows:
st_dev This 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.)
st_ino This field contains the file's inode number.
st_mode
This field contains the file type and mode. See inode(7) for
further information.
st_nlink
This field contains the number of hard links to the file.
st_uid This field contains the user ID of the owner of the file.
st_gid This field contains the ID of the group owner of the file.
st_rdev
This field describes the device that this file (inode) repre-
sents.
st_size
This 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.
st_blksize
This field gives the "preferred" block size for efficient
filesystem I/O.
st_blocks
This field indicates the number of blocks allocated to the file,
in 512-byte units. (This may be smaller than st_size/512 when
the file has holes.)
st_atime
This is the file's last access timestamp.
st_mtime
This is the file's last modification timestamp.
st_ctime
This is the file's last status change timestamp.
For further information on the above fields, see inode(7).
fstatat()
The fstatat() system call is a more general interface for accessing
file information which can still provide exactly the behavior of each
of stat(), lstat(), and fstat().
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() and lstat() 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() and lstat()).
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). In this case, dirfd can refer to any type of file, not
just a directory, and the behavior of fstatat() is similar to
that of fstat(). If dirfd is AT_FDCWD, the call operates on the
current working 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). Since Linux 4.14, also don't
instantiate a nonexistent name in an on-demand directory such as
used for automounter indirect maps. 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. Both stat() and lstat() act as though AT_NO_AUTOMOUNT was
set.
AT_SYMLINK_NOFOLLOW
If pathname is a symbolic link, do not dereference it: instead
return information about the link itself, like lstat(). (By de-
fault, 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 not a valid open file descriptor.
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 is a dangling symbolic
link.
ENOENT pathname is an empty string and AT_EMPTY_PATH was not specified
in flags.
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.)
NOTES
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 suit-
able feature test macros are defined. Nanosecond timestamps were stan-
dardized in POSIX.1-2008, and, starting with version 2.12, glibc ex-
poses 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. Up to and including glibc 2.19, the definitions
of the nanoseconds components are also defined if _BSD_SOURCE or
_SVID_SOURCE is defined. If none of the aforementioned macros are de-
fined, then the nanosecond values are exposed with names of the form
st_atimensec.
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 pad-
ding.
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 ac-
commodate 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 applica-
tions, 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 lstat() 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>
#include <sys/sysmacros.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 (lstat(argv[1], &sb) == -1) {
perror("lstat");
exit(EXIT_FAILURE);
}
printf("ID of containing device: [%lx,%lx]\n",
(long) major(sb.st_dev), (long) minor(sb.st_dev));
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), statx(2),
utime(2), capabilities(7), inode(7), symlink(7)
COLOPHON
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