stat, fstat, lstat, fstatat - get file status
#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
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.
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 time of the last access of file data.
- st_mtime
- This is the time of last modification of file data.
- st_ctime
- This is the file's last status change timestamp (time of last change to
the inode).
For further information on the above fields, see
inode(7).
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().
On success, zero is returned. On error, -1 is returned, and
errno is set
appropriately.
- 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.
fstatat() was added to Linux in kernel 2.6.16; library support was added
to glibc in version 2.4.
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.)
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.
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().
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);
}
ls(1),
stat(1),
access(2),
chmod(2),
chown(2),
readlink(2),
statx(2),
utime(2),
capabilities(7),
inode(7),
symlink(7)