Originální popis anglicky:
stat, fstat, lstat - get file status
Návod, kniha: Linux Programmer's Manual
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
int stat(const char *file_name, struct stat
*buf);
int fstat(int filedes, struct stat *buf);
int lstat(const char *file_name, struct stat
*buf);
These functions return information about the specified file. You do not need any
access rights to the file to get this information but you need search rights
to all directories named in the path leading to the file.
stat stats the file pointed to by
file_name and fills in
buf.
lstat is identical to
stat, except in the case of a symbolic link,
where the link itself is stat-ed, not the file that it refers to.
fstat is identical to
stat, only the open file pointed to by
filedes (as returned by
open(2)) is stat-ed in place of
file_name.
They all return a
stat structure, which contains the following fields:
struct stat {
dev_t st_dev; /* device */
ino_t st_ino; /* inode */
mode_t st_mode; /* protection */
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 type (if inode device) */
off_t st_size; /* total size, in bytes */
blksize_t st_blksize; /* blocksize for filesystem I/O */
blkcnt_t st_blocks; /* number of blocks allocated */
time_t st_atime; /* time of last access */
time_t st_mtime; /* time of last modification */
time_t st_ctime; /* time of last status change */
};
The value
st_size gives the size of the file (if it is a regular file or
a symlink) in bytes. The size of a symlink is the length of the pathname it
contains, without trailing NUL.
The value
st_blocks gives the size of the file in 512-byte blocks. (This
may be smaller than
st_size/512 e.g. when the file has holes.) The
value
st_blksize gives the "preferred" blocksize for
efficient file system I/O. (Writing to a file in smaller chunks may cause an
inefficient read-modify-rewrite.)
Not all of the Linux filesystems implement all of the time fields. Some file
system types allow mounting in such a way that file accesses do not cause an
update of the
st_atime field. (See `noatime' in
mount(8).)
The field
st_atime is changed by file accesses, e.g. by
execve(2),
mknod(2),
pipe(2),
utime(2) and
read(2) (of more
than zero bytes). Other routines, like
mmap(2), may or may not update
st_atime.
The field
st_mtime is changed by file modifications, e.g. by
mknod(2),
truncate(2),
utime(2) and
write(2) (of
more than zero bytes). Moreover,
st_mtime of a directory is changed by
the creation or deletion of files in that directory. The
st_mtime field
is
not changed for changes in owner, group, hard link count, or mode.
The field
st_ctime is changed by writing or by setting inode information
(i.e., owner, group, link count, mode, etc.).
The following POSIX macros are defined to check the file type:
- S_ISREG(m)
- is it a regular file?
- S_ISDIR(m)
- directory?
- S_ISCHR(m)
- character device?
- S_ISBLK(m)
- block device?
- S_ISFIFO(m)
- fifo?
- S_ISLNK(m)
- symbolic link? (Not in POSIX.1-1996.)
- S_ISSOCK(m)
- socket? (Not in POSIX.1-1996.)
The following flags are defined for the
st_mode field:
| S_IFMT |
0170000 |
bitmask for the file type bitfields |
| S_IFSOCK |
0140000 |
socket |
| S_IFLNK |
0120000 |
symbolic link |
| S_IFREG |
0100000 |
regular file |
| S_IFBLK |
0060000 |
block device |
| S_IFDIR |
0040000 |
directory |
| S_IFCHR |
0020000 |
character device |
| S_IFIFO |
0010000 |
fifo |
| S_ISUID |
0004000 |
set UID bit |
| S_ISGID |
0002000 |
set GID bit (see below) |
| S_ISVTX |
0001000 |
sticky bit (see below) |
| S_IRWXU |
00700 |
mask for file owner permissions |
| S_IRUSR |
00400 |
owner has read permission |
| S_IWUSR |
00200 |
owner has write permission |
| S_IXUSR |
00100 |
owner has execute permission |
| S_IRWXG |
00070 |
mask for group permissions |
| S_IRGRP |
00040 |
group has read permission |
| S_IWGRP |
00020 |
group has write permission |
| S_IXGRP |
00010 |
group has execute permission |
| S_IRWXO |
00007 |
mask for permissions for others (not in group) |
| S_IROTH |
00004 |
others have read permission |
| S_IWOTH |
00002 |
others have write permisson |
| S_IXOTH |
00001 |
others have execute permission |
The set GID bit (S_ISGID) has several special uses: For a directory it indicates
that BSD semantics is to be used for that directory: files created there
inherit their group ID from the directory, not from the effective group ID of
the creating process, and directories created there will also get the S_ISGID
bit set. For a file that does not have the group execution bit (S_IXGRP) set,
it indicates mandatory file/record locking.
The `sticky' bit (S_ISVTX) on a directory means that a file in that directory
can be renamed or deleted only by the owner of the file, by the owner of the
directory, and by a privileged process.
On success, zero is returned. On error, -1 is returned, and
errno is set
appropriately.
- EACCES
- Search permission is denied for one of the directories in
the path prefix of file_name. (See also
path_resolution(2).)
- EBADF
- filedes is bad.
- EFAULT
- Bad address.
- ELOOP
- Too many symbolic links encountered while traversing the
path.
- ENAMETOOLONG
- File name too long.
- ENOENT
- A component of the path file_name does not exist, or
the path is an empty string.
- ENOMEM
- Out of memory (i.e. kernel memory).
- ENOTDIR
- A component of the path is not a directory.
The
stat and
fstat calls conform to SVr4, SVID, POSIX, X/OPEN, BSD
4.3. The
lstat call conforms to 4.3BSD and SVr4. SVr4 documents
additional
fstat error conditions EINTR, ENOLINK, and EOVERFLOW. SVr4
documents additional
stat and
lstat error conditions EINTR,
EMULTIHOP, ENOLINK, and EOVERFLOW. Use of the
st_blocks and
st_blksize fields may be less portable. (They were introduced in BSD.
Are not specified by POSIX. The interpretation differs between systems, and
possibly on a single system when NFS mounts are involved.)
POSIX does not describe the S_IFMT, S_IFSOCK, S_IFLNK, S_IFREG, S_IFBLK,
S_IFDIR, S_IFCHR, S_IFIFO, S_ISVTX bits, but instead demands the use of the
macros S_ISDIR(), etc. The S_ISLNK and S_ISSOCK macros are not in
POSIX.1-1996, but both will be in the next POSIX standard; the former is from
SVID 4v2, the latter from SUSv2.
Unix V7 (and later systems) had S_IREAD, S_IWRITE, S_IEXEC, where POSIX
prescribes the synonyms S_IRUSR, S_IWUSR, S_IXUSR.
Values that have been (or are) in use on various systems:
| hex |
name |
ls |
octal |
description |
| f000 |
S_IFMT |
|
170000 |
mask for file type |
| 0000 |
|
|
000000 |
SCO out-of-service inode, BSD unknown type |
|
|
|
|
SVID-v2 and XPG2 have both 0 and 0100000 for ordinary file |
| 1000 |
S_IFIFO |
p| |
010000 |
fifo (named pipe) |
| 2000 |
S_IFCHR |
c |
020000 |
character special (V7) |
| 3000 |
S_IFMPC |
|
030000 |
multiplexed character special (V7) |
| 4000 |
S_IFDIR |
d/ |
040000 |
directory (V7) |
| 5000 |
S_IFNAM |
|
050000 |
XENIX named special file |
|
|
|
|
with two subtypes, distinguished by st_rdev values 1, 2: |
| 0001 |
S_INSEM |
s |
000001 |
XENIX semaphore subtype of IFNAM |
| 0002 |
S_INSHD |
m |
000002 |
XENIX shared data subtype of IFNAM |
| 6000 |
S_IFBLK |
b |
060000 |
block special (V7) |
| 7000 |
S_IFMPB |
|
070000 |
multiplexed block special (V7) |
| 8000 |
S_IFREG |
- |
100000 |
regular (V7) |
| 9000 |
S_IFCMP |
|
110000 |
VxFS compressed |
| 9000 |
S_IFNWK |
n |
110000 |
network special (HP-UX) |
| a000 |
S_IFLNK |
l@ |
120000 |
symbolic link (BSD) |
| b000 |
S_IFSHAD |
|
130000 |
Solaris shadow inode for ACL (not seen by userspace) |
| c000 |
S_IFSOCK |
s= |
140000 |
socket (BSD; also "S_IFSOC" on VxFS) |
| d000 |
S_IFDOOR |
D> |
150000 |
Solaris door |
| e000 |
S_IFWHT |
w% |
160000 |
BSD whiteout (not used for inode) |
|
|
|
|
|
| 0200 |
S_ISVTX |
|
001000 |
`sticky bit': save swapped text even after use (V7) |
|
|
|
|
reserved (SVID-v2) |
|
|
|
|
On non-directories: don't cache this file (SunOS) |
|
|
|
|
On directories: restricted deletion flag (SVID-v4.2) |
| 0400 |
S_ISGID |
|
002000 |
set group ID on execution (V7) |
|
|
|
|
for directories: use BSD semantics for propagation of gid |
| 0400 |
S_ENFMT |
|
002000 |
SysV file locking enforcement (shared w/ S_ISGID) |
| 0800 |
S_ISUID |
|
004000 |
set user ID on execution (V7) |
| 0800 |
S_CDF |
|
004000 |
directory is a context dependent file (HP-UX) |
A sticky command appeared in Version 32V AT&T UNIX.
chmod(2),
chown(2),
readlink(2),
utime(2),
capabilities(7)
