получить статус файла (get file status)
Имя (Name)
stat, fstat, lstat, fstatat - get file status
Синопсис (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
Описание (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
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 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).
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 has no effect if the
mount point has already been mounted over.
Both stat() and lstat() act as though AT_NO_AUTOMOUNT was
set.
The AT_NO_AUTOMOUNT can be used in tools that scan
directories to prevent mass-automounting of a directory of
automount points.
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().
Возвращаемое значение (Return value)
On success, zero is returned. On error, -1 is returned, and
errno is set to indicate the error.
Ошибки (Error)
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.
Версии (Versions)
fstatat() was added to Linux in kernel 2.6.16; library support
was added to glibc in version 2.4.
Стандарты (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.)
Примечание (Note)
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().
Примеры (Examples)
The following program calls lstat() and displays selected fields
in the returned stat structure.
#include <sys/types.h>
#include <sys/stat.h>
#include <stdint.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: [%jx,%jx]\n",
(uintmax_t) major(sb.st_dev),
(uintmax_t) 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);
}
Смотри также (See also)
ls(1), stat(1), access(2), chmod(2), chown(2), readlink(2),
statx(2), utime(2), capabilities(7), inode(7), symlink(7)
