stat
NAME
stat, fstat, lstat - get file status
SYNOPSIS
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h> I int stat(const char * path , struct stat * buf );
I int fstat(int filedes , struct stat * buf );
I int lstat(const char * path , struct stat * buf );
#include <sys/stat.h>
#include <unistd.h> I int stat(const char * path , struct stat * buf );
I int fstat(int filedes , struct stat * buf );
I int lstat(const char * path , struct stat * buf );
DESCRIPTION
These functions return information about a file.
No permissions are required on the file itself, but in the case of
R stat ()
and
R lstat ()
execute (search) permission is required on all of the directories in
path
that lead to the file.
R stat ()
stats the file pointed to by
path
and fills in
R buf .
R lstat ()
is identical to
R stat (),
except that if
path
is a symbolic link, then the link itself is stat-ed,
not the file that it refers to.
R fstat ()
is identical to
R stat (),
except that the file to be stat-ed is specified by the file descriptor
R filedes .
All of these system calls return a
stat
structure, which contains the following fields:
struct stat {
dev_t st_dev; /* ID of device containing file */
ino_t st_ino; /* inode number */
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 ID (if special file) */
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
st_dev
field describes the device on which this file resides.
The
st_rdev
field describes the device that this file (inode) represents.
The
st_size
field gives the size of the file (if it is a regular
file or a symbolic link) in bytes.
The size of a symlink is the length of the pathname
it contains, without a trailing null byte.
The
st_blocks
field indicates the number of blocks allocated to the file, 512-byte units.
(This may be smaller than
R st_size /512,
for example, when the file has holes.)
The
R st_blksize
field 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, for example, 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
R st_atime .
The field
st_mtime
is changed by file modifications, for example, 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 using the
st_mode
field:
R S_ISREG (m)
is it a regular file?
R S_ISDIR (m)
directory?
R S_ISCHR (m)
character device?
R S_ISBLK (m)
block device?
R S_ISFIFO (m)
FIFO (named pipe)?
R S_ISLNK (m)
symbolic link? (Not in POSIX.1-1996.)
R S_ISSOCK (m)
socket? (Not in POSIX.1-1996.)
The following flags are defined for the
st_mode
field:
lB 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-group-ID 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 permission
S_IXOTH 00001 others have execute permission
The set-group-ID 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,
the set-group-ID bit 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.
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
EACCES
Search permission is denied for one of the directories
in the path prefix of
R path .
(See also
path_resolution(7).)
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
path
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.
CONFORMING TO
These system calls conform to SVr4, 4.3BSD, POSIX.1-2001.
Use of the
st_blocks
and
st_blksize
fields may be less portable.
(They were introduced in BSD.
The interpretation differs between systems,
and possibly on a single system when NFS mounts are involved.)
POSIX does not describe the
R S_IFMT ,
R S_IFSOCK ,
R S_IFLNK ,
R S_IFREG ,
R S_IFBLK ,
R S_IFDIR ,
R S_IFCHR ,
R S_IFIFO ,
R S_ISVTX
bits, but instead demands the use of
the macros
R S_ISDIR (),
etc.
The
R S_ISLNK ()
and
R S_ISSOCK ()
macros are not in
POSIX.1-1996, but both are present in POSIX.1-2001;
the former is from SVID 4, the latter from SUSv2.
Unix V7 (and later systems) had
R S_IREAD ,
R S_IWRITE ,
R S_IEXEC ,
where POSIX
prescribes the synonyms
R S_IRUSR ,
R S_IWUSR ,
R 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 with 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.NOTES
Linux Notes
Since kernel 2.5.48, the stat structure supports nanosecond resolution for the three file timestamp fields. Glibc exposes the nanosecond component of each field using names either of the form R st_atim.tv_nsec , if the _BSD_SOURCE or _SVID_SOURCE feature test macro is defined, or of the form R st_atimensec , if neither of these macros is defined. On file systems that do not support sub-second timestamps, these nanosecond fields are returned with the value 0. For most files under the /proc directory, R stat () does not return the file size in the st_size field; instead the field is returned with the value 0.EXAMPLE
The following program calls
stat(2)
and displays selected fields in the returned
stat
structure.
#include <sys/types.h>
#include <sys/stat.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
struct stat sb;
if (argc != 2) {
fprintf(stderr, "Usage: %s <pathname>\n", argv[0]);
exit(EXIT_FAILURE);
}
if (stat(argv[1], &sb) == -1) {
perror("stat");
exit(EXIT_SUCCESS);
}
printf("File type: ");
switch (sb.st_mode & S_IFMT) {
case S_IFBLK: printf("block device\n"); break;
case S_IFCHR: printf("character device\n"); break;
case S_IFDIR: printf("directory\n"); break;
case S_IFIFO: printf("FIFO/pipe\n"); break;
case S_IFLNK: printf("symlink\n"); break;
case S_IFREG: printf("regular file\n"); break;
case S_IFSOCK: printf("socket\n"); break;
default: printf("unknown?\n"); break;
}
printf("I-node number: %ld\n", (long) sb.st_ino);
printf("Mode: %lo (octal)\n",
(unsigned long) sb.st_mode);
printf("Link count: %ld\n", (long) sb.st_nlink);
printf("Ownership: UID=%ld GID=%ld\n",
(long) sb.st_uid, (long) sb.st_gid);
printf("Preferred I/O block size: %ld bytes\n",
(long) sb.st_blksize);
printf("File size: %lld bytes\n",
(long long) sb.st_size);
printf("Blocks allocated: %lld\n",
(long long) sb.st_blocks);
printf("Last inode change: %s", ctime(&sb.st_ctime));
printf("Last file access: %s", ctime(&sb.st_atime));
printf("Last file modification: %s", ctime(&sb.st_mtime));
exit(EXIT_SUCCESS);
}
