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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 *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 information 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 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 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) represents.
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 definition.
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 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 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 suitable feature test macros are defined. Nanosecond
timestamps were standardized in POSIX.1-2008, and, starting with version 2.12, glibc
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. 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 defined,
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 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 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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