| STAT(2) | Linux Programmer's Manual | STAT(2) |
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():
fstatat():
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:
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:
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.
The following additional errors can occur for fstatat():
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:
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), utime(2), capabilities(7), inode(7), symlink(7)
This page is part of release 4.16 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
| 2017-09-15 | Linux |