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)):

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. 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 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().

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

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);
}

ls(1), stat(1), access(2), chmod(2), chown(2), readlink(2), statx(2), utime(2), capabilities(7), inode(7), symlink(7)