stat(2) System Calls Manual stat(2)
NAME
stat, fstat, lstat, fstatat - get file status
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <sys/stat.h>
int stat(const char *restrict pathname,
struct stat *restrict statbuf);
int fstat(int fd, struct stat *statbuf);
int lstat(const char *restrict pathname,
struct stat *restrict statbuf);
#include <fcntl.h> /* Definition of AT_* constants */
#include <sys/stat.h>
int fstatat(int dirfd, const char *restrict pathname,
struct stat *restrict statbuf, int flags);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
lstat():
/* Since glibc 2.20 */ _DEFAULT_SOURCE
|| _XOPEN_SOURCE >= 500
|| /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200112L
|| /* glibc 2.19 and earlier */ _BSD_SOURCE
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 the link 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 (see stat(3type)).
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.
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.
Since Linux 3.1 this flag is ignored. Since Linux 4.11 this
flag is implied.
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 to indicate the error.
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.
EBADF (fstatat()) pathname is relative but dirfd is neither AT_FDCWD
nor a valid file descriptor.
EFAULT Bad address.
EINVAL (fstatat()) Invalid flag specified in flags.
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.
ENOTDIR
(fstatat()) pathname is relative and dirfd is a file descriptor
referring to a file other than 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.
VERSIONS
fstatat() was added in Linux 2.6.16; library support was added in glibc
2.4.
STANDARDS
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
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().
EXAMPLES
The following program calls lstat() and displays selected fields in the
returned stat structure.
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/sysmacros.h>
#include <time.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: [%x,%x]\n",
major(sb.st_dev),
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: %ju\n", (uintmax_t) sb.st_ino);
printf("Mode: %jo (octal)\n",
(uintmax_t) sb.st_mode);
printf("Link count: %ju\n", (uintmax_t) sb.st_nlink);
printf("Ownership: UID=%ju GID=%ju\n",
(uintmax_t) sb.st_uid, (uintmax_t) sb.st_gid);
printf("Preferred I/O block size: %jd bytes\n",
(intmax_t) sb.st_blksize);
printf("File size: %jd bytes\n",
(intmax_t) sb.st_size);
printf("Blocks allocated: %jd\n",
(intmax_t) 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), stat(3type), capabilities(7), inode(7), symlink(7)
Linux man-pages 6.03 2023-02-05 stat(2)
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