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STAT(2) System Calls Manual STAT(2)

stat, lstat, fstatat, fstat, S_ISBLK, S_ISCHR, S_ISDIR, S_ISFIFO, S_ISLNK, S_ISREG, S_ISSOCKget file status

#include <sys/stat.h>

stat(const char *path, struct stat *sb);

lstat(const char *path, struct stat *sb);

fstat(int fd, struct stat *sb);

#include <sys/stat.h>
#include <fcntl.h>

fstatat(int fd, const char *path, struct stat *sb, int flag);

The () function obtains information about the file pointed to by path. Read, write, or execute permission of the named file is not required, but all directories listed in the pathname leading to the file must be searchable.

The () function is identical to stat() except when the named file is a symbolic link, in which case lstat() returns information about the link itself, not the file the link references.

The () function is equivalent to either the stat() or lstat() function depending on the value of flag (see below), except that where path specifies a relative path, the file whose information is returned is determined relative to the directory associated with file descriptor fd instead of the current working directory.

If () is passed the special value AT_FDCWD (defined in <fcntl.h>) in the fd parameter, the current working directory is used and the behavior is identical to a call to stat() or lstat(), depending on whether or not the AT_SYMLINK_NOFOLLOW bit is set in flag.

The flag argument is the bitwise OR of zero or more of the following values:

If path names a symbolic link, then the status of the symbolic link is returned.

The () function obtains the same information about an open file known by the file descriptor fd.

The sb argument is a pointer to a stat structure as defined by <sys/stat.h> (shown below) and into which information is placed concerning the file.

struct stat {
    dev_t      st_dev;    /* inode's device */
    ino_t      st_ino;    /* inode's number */
    mode_t     st_mode;   /* inode protection mode */
    nlink_t    st_nlink;  /* number of hard links */
    uid_t      st_uid;    /* user ID of the file's owner */
    gid_t      st_gid;    /* group ID of the file's group */
    dev_t      st_rdev;   /* device type */
    struct timespec st_atim;  /* time of last access */
    struct timespec st_mtim;  /* time of last data modification */
    struct timespec st_ctim;  /* time of last file status change */
    off_t      st_size;   /* file size, in bytes */
    blkcnt_t   st_blocks; /* blocks allocated for file */
    blksize_t  st_blksize;/* optimal blocksize for I/O */
    u_int32_t  st_flags;  /* user defined flags for file */
    u_int32_t  st_gen;    /* file generation number */

The time-related fields of struct stat are represented in struct timespec format, which has nanosecond precision. However, the actual precision is generally limited by the file system holding the file. The fields are as follows:

Time when file data was last accessed. Set when the file system object was created and updated by the utimes(2) and read(2) system calls.
Time when file data was last modified. Changed by the truncate(2), utimes(2), and write(2) system calls. For directories, changed by any system call that alters which files are in the directory, such as the unlink(2), rename(2), mkdir(2), and symlink(2) system calls.
Time when file status was last changed (inode data modification). Changed by the chmod(2), chown(2), link(2), rename(2), unlink(2), utimes(2), and write(2) system calls.

In addition, all the time fields are set to the current time when a file system object is first created by the mkdir(2), mkfifo(2), mknod(2), open(2), and symlink(2) system calls.

For compatibility with previous standards, st_atime, st_mtime, and st_ctime macros are provided that expand to the tv_secs member of their respective struct timespec member. Deprecated macros are also provided for some transitional names: st_atimensec, st_mtimensec, st_ctimensec, st_atimespec, st_mtimespec, and st_ctimespec.

The size-related fields of the struct stat are as follows:

The optimal I/O block size for the file.
The actual number of blocks allocated for the file in 512-byte units. As short symbolic links are stored in the inode, this number may be zero.

The status information word st_mode has the following bits:

#define S_IFMT   0170000  /* type of file mask */
#define S_IFIFO  0010000  /* named pipe (fifo) */
#define S_IFCHR  0020000  /* character special */
#define S_IFDIR  0040000  /* directory */
#define S_IFBLK  0060000  /* block special */
#define S_IFREG  0100000  /* regular */
#define S_IFLNK  0120000  /* symbolic link */
#define S_IFSOCK 0140000  /* socket */
#define S_ISUID  0004000  /* set-user-ID on execution */
#define S_ISGID  0002000  /* set-group-ID on execution */
#define S_ISVTX  0001000  /* save swapped text even after use */
#define S_IRWXU  0000700  /* RWX mask for owner */
#define S_IRUSR  0000400  /* R for owner */
#define S_IWUSR  0000200  /* W for owner */
#define S_IXUSR  0000100  /* X for owner */
#define S_IRWXG  0000070  /* RWX mask for group */
#define S_IRGRP  0000040  /* R for group */
#define S_IWGRP  0000020  /* W for group */
#define S_IXGRP  0000010  /* X for group */
#define S_IRWXO  0000007  /* RWX mask for other */
#define S_IROTH  0000004  /* R for other */
#define S_IWOTH  0000002  /* W for other */
#define S_IXOTH  0000001  /* X for other */

The following macros test a file's type. If the file is of that type, a non-zero value is returned; otherwise, 0 is returned.

S_ISBLK(st_mode m)  /* block special */
S_ISCHR(st_mode m)  /* char special */
S_ISDIR(st_mode m)  /* directory */
S_ISFIFO(st_mode m) /* fifo */
S_ISLNK(st_mode m)  /* symbolic link */
S_ISREG(st_mode m)  /* regular file */
S_ISSOCK(st_mode m) /* socket */

For a list of access modes, see <sys/stat.h>, access(2), and chmod(2).

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

stat(), lstat(), and fstatat() will fail if:

A component of the path prefix is not a directory.
A component of a pathname exceeded NAME_MAX characters, or an entire pathname (including the terminating NUL) exceeded PATH_MAX bytes.
A component of path does not exist or path is an empty string.
Search permission is denied for a component of the path.
Too many symbolic links were encountered in translating the path.
sb or path points to an invalid address.
An I/O error occurred while reading from or writing to the file system.

Additionally, fstatat() will fail if:

The value of the flag argument was neither zero nor AT_SYMLINK_NOFOLLOW.
The path argument specifies a relative path and the fd argument is neither AT_FDCWD nor a valid file descriptor.
The path argument specifies a relative path and the fd argument is a valid file descriptor but it does not reference a directory.
The path argument specifies a relative path but search permission is denied for the directory which the fd file descriptor references.

fstat() will fail if:

fd is not a valid open file descriptor.
sb points to an invalid address.
An I/O error occurred while reading from the file system.

chmod(2), chown(2), clock_gettime(2), utimes(2), symlink(7)

Previous versions of the system used different types for the st_dev, st_uid, st_gid, st_rdev, st_size, st_blksize, and st_blocks fields.

The fstat(), fstatat(), lstat(), and stat() functions are intended to conform to IEEE Std 1003.1-2008 (“POSIX.1”).

The stat() and fstat() system calls first appeared in Version 1 AT&T UNIX. The <sys/stat.h> header file and the struct stat were introduced in Version 7 AT&T UNIX.

An lstat() function call appeared in 4.2BSD. The fstatat() function appeared in OpenBSD 5.0.

The file generation number, st_gen, is only available to the superuser.

Certain programs written when the timestamps were just of type time_t assumed that the members were consecutive (and could therefore be treated as an array and have their address passed directly to utime(3)). The transition to timestamps of type struct timespec broke them irrevocably.

Applying fstat() to a pipe or socket fails to fill in a unique device and inode number pair. Applying fstat() to a socket also fails to fill in the time fields.

January 3, 2021 OpenBSD-7.0