NAME
stat
, lstat
,
fstatat
, fstat
—
get file status
SYNOPSIS
#include
<sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int
stat
(const
char *path, struct stat
*sb);
int
lstat
(const
char *path, struct stat
*sb);
int
fstatat
(int
fd, const char
*path, struct stat
*sb, int flag);
int
fstat
(int
fd, struct stat
*sb);
DESCRIPTION
The
stat
()
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 path name leading to
the file must be searchable.
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.
Unlike other file system objects, symbolic links do not have an owner,
group, access mode, times, etc. Instead, these attributes are taken from the
directory that contains the link. The only attributes returned from an
lstat
() that refer to the symbolic link itself are
the file type (S_IFLNK
), size, blocks, and link
count.
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.
Values for flag are constructed by
bitwise-inclusive ORing flags from the following list defined in
<fcntl.h>
:
AT_SYMLINK_NOFOLLOW
- If path names a symbolic link, then the status of the symbolic link is returned.
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 */ int64_t st_blocks; /* blocks allocated for file */ u_int32_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).
RETURN VALUES
Upon successful completion a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.
ERRORS
stat
(), lstat
(),
and fstatat
() will fail if:
- [
ENOTDIR
] - A component of the path prefix is not a directory.
- [
ENAMETOOLONG
] - A component of a pathname exceeded
NAME_MAX
characters, or an entire path name exceededPATH_MAX
characters. - [
ENOENT
] - The named file does not exist.
- [
EACCES
] - Search permission is denied for a component of the path prefix.
- [
ELOOP
] - Too many symbolic links were encountered in translating the pathname.
- [
EFAULT
] - sb or name points to an invalid address.
- [
EIO
] - An I/O error occurred while reading from or writing to the file system.
Additionally, fstatat
() will fail if:
- [
EBADF
] - The path argument does not specify an absolute path
and the fd argument is neither
AT_FDCWD
nor a valid file descriptor open for reading.
fstat
() will fail if:
- [
EBADF
] - fd is not a valid open file descriptor.
- [
EFAULT
] - sb points to an invalid address.
- [
EIO
] - An I/O error occurred while reading from or writing to the file system.
SEE ALSO
STANDARDS
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 stat
(),
lstat
(), fstatat
(), and
fstat
() function calls are expected to conform to
IEEE Std 1003.1-1988 (“POSIX.1”).
HISTORY
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.
CAVEATS
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 placed directly to
utimes(2)). The transition to timestamps of type
struct timespec
broke them irrevocably.
BUGS
Applying fstat
() to a socket (and thus to
a pipe) returns a zeroed buffer, except for the blocksize field, and a
unique device and inode number.