Manual Pages  — STAT

The lstat() system call is like stat() except when the named file is a symbolic link, in which case lstat() returns information about the link, while stat() returns information about the file the link references.

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

The fstatat() system call is equivalent to stat() and lstat() except when the path specifies a relative path. For fstatat() and relative path, the status is retrieved from a file relative to the directory associated with the file descriptor fd instead of the current working directory.

The values for the flag are constructed by a bitwise-inclusive OR of flags from this list, defined in <fcntl.h>:

AT_SYMLINK_NOFOLLOW
	If path names a symbolic link, the status of the symbolic link is returned.
AT_RESOLVE_BENEATH
	Only walk paths below the starting directory. See the description of the O_RESOLVE_BENEATH flag in the open(2) manual page.

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

When fstatat() is called with an absolute path, it ignores the fd argument.

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

The fields of struct stat related to the file system are:

st_dev
	Numeric ID of the device containing the file.
st_ino
	The file's inode number.
st_nlink
	Number of hard links to the file.
st_flags
	Flags enabled for the file. See chflags(2) for the list of flags and their description.

The st_dev and st_ino fields together identify the file uniquely within the system.

The time-related fields of struct stat are:

st_atim
	Time when file data was last accessed. Changed implicitly by syscalls such as read(2) and readv(2), and explicitly by utimes(2).
st_mtim
	Time when file data was last modified. Changed implicitly by syscalls such as truncate(2), write(2), and writev(2), and explicitly by utimes(2). Also, any syscall which modifies directory content changes the st_mtim for the affected directory. For instance, creat(2), mkdir(2), rename(2), link(2), and unlink(2).
st_ctim
	Time when file status was last changed (inode data modification). Changed implicitly by any syscall that affects file metadata, including st_mtim, such as chflags(2), chmod(2), chown(2), truncate(2), utimes(2), and write(2). Also, any syscall which modifies directory content changes the st_ctim for the affected directory. For instance, creat(2), mkdir(2), rename(2), link(2), and unlink(2).
st_birthtim
	Time when the inode was created.

These time-related macros are defined for compatibility:

#define st_atime                st_atim.tv_sec
#define st_mtime                st_mtim.tv_sec
#define st_ctime                st_ctim.tv_sec
#ifndef _POSIX_SOURCE
#define st_birthtime            st_birthtim.tv_sec
#endif

#ifndef _POSIX_SOURCE
#define st_atimespec            st_atim
#define st_mtimespec            st_mtim
#define st_ctimespec            st_ctim
#define st_birthtimespec        st_birthtim
#endif

Size-related fields of the struct stat are:

st_size
	File size in bytes.
st_blksize
	Optimal I/O block size for the file.
st_blocks
	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 access-related fields of struct stat are:

st_uid
	User ID of the file's owner.
st_gid
	Group ID of the file.
st_mode
	Status of the file (see below).

The status information word st_mode has these 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_IFWHT  0160000  /* whiteout */
#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  /* read permission, owner */
#define S_IWUSR  0000200  /* write permission, owner */
#define S_IXUSR  0000100  /* execute/search permission, owner */
#define S_IRWXG  0000070  /* RWX mask for group */
#define S_IRGRP  0000040  /* read permission, group */
#define S_IWGRP  0000020  /* write permission, group */
#define S_IXGRP  0000010  /* execute/search permission, group */
#define S_IRWXO  0000007  /* RWX mask for other */
#define S_IROTH  0000004  /* read permission, other */
#define S_IWOTH  0000002  /* write permission, other */
#define S_IXOTH  0000001  /* execute/search permission, other */