DESCRIPTION

The lstat() 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 fstatat() 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 fstatat() 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:

The fstat() 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:

st_atim

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.

st_mtim

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.

st_ctim

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:

st_blksize

The optimal I/O block size for the file.

st_blocks

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).