STAT (2)
get file status
SYNOPSIS
#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 );
DESCRIPTION
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 ,
only the link itself is stated, not the file that is obtained by tracing
the links.
fstat
is identical to stat, only the open file pointed to by
filedes
(as returned by
open (2))
is stated 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 */
unsigned long st_blksize; /* blocksize for filesystem I/O */
unsigned long 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 change */
};
The value
st_blocks
gives the size of the file in 512-byte blocks.
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.
Traditionally,
st_atime
is changed by
mknod (2), utime (2), read (2), write (2), and truncate (2).
Traditionally,
st_mtime
is changed by
mknod (2), utime (2), and write (2).
The
st_mtime
is
not
changed for changes in owner, group, hard link count, or mode.
Traditionally,
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_ISLNK(m)
S_ISREG(m)
S_ISDIR(m)
S_ISCHR(m)
S_ISBLK(m)
S_ISFIFO(m)
S_ISSOCK(m)
The following flags are defined for the
st_mode
field:
l l l.
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 gid 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 root.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and
errno
is set appropriately.
ERRORS
EBADF
ENOENT
A component of the path
file_name
does not exist, or the path is an empty string.
ENOTDIR
A component of the path is not a directory.
ELOOP
Too many symbolic links encountered while traversing the path.
EFAULT
EACCES
ENOMEM
Out of memory (i.e. kernel memory).
ENAMETOOLONG
CONFORMING TO
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 EACCES, 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.
Unix V7 (and later systems) had S_IREAD, S_IWRITE, S_IEXEC, where POSIX
prescribes the synonyms S_IRUSR, S_IWUSR, S_IXUSR.
OTHER SYSTEMS
Values that have been (or are) in use on various systems:
l l l l l.
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.
SEE ALSO
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