stat, fstat, lstat — get file status
#include <sys/types.h> #include <sys/stat.h> #include <unistd.h>
int
stat( |
const char * | path, |
| struct stat * | buf); |
int
fstat( |
int | filedes, |
| struct stat * | buf); |
int
lstat( |
const char * | path, |
| struct stat * | buf); |
These functions return information about a file. No
permissions are required on the file itself, but — in
the case of stat() and
lstat() — execute
(search) permission is required on all of the directories in
path that lead to the
file.
stat() stats the file
pointed to by path
and fills in buf.
lstat() is identical to
stat(), except that if
path is a symbolic
link, then the link itself is stat-ed, not the file that it
refers to.
fstat() is identical to
stat(), except that the file to
be stat-ed is specified by the file descriptor 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 st_size/512, for example,
when the file has holes.)
The 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 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:
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 (named pipe)?
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_IFMT0170000 bitmask for the file type bitfields S_IFSOCK0140000 socket S_IFLNK0120000 symbolic link S_IFREG0100000 regular file S_IFBLK0060000 block device S_IFDIR0040000 directory S_IFCHR0020000 character device S_IFIFO0010000 FIFO S_ISUID0004000 set UID bit S_ISGID0002000 set-group-ID bit (see below) S_ISVTX0001000 sticky bit (see below) S_IRWXU00700 mask for file owner permissions S_IRUSR00400 owner has read permission S_IWUSR00200 owner has write permission S_IXUSR00100 owner has execute permission S_IRWXG00070 mask for group permissions S_IRGRP00040 group has read permission S_IWGRP00020 group has write permission S_IXGRP00010 group has execute permission S_IRWXO00007 mask for permissions for others (not in group) S_IROTH00004 others have read permission S_IWOTH00002 others have write permission S_IXOTH00001 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.
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
Search permission is denied for one of the
directories in the path prefix of path. (See also path_resolution(7).)
filedes is
bad.
Bad address.
Too many symbolic links encountered while traversing the path.
File name too long.
A component of the path path does not exist, or
the path is an empty string.
Out of memory (i.e., kernel memory).
A component of the path is not a directory.
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 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 are present in POSIX.1-2001; the former is from SVID
4, 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 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.
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 st_atim.tv_nsec, if the
_BSD_SOURCE or _SVID_SOURCE feature test macro is
defined, or of the form 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, stat() does not return the file size in
the st_size
field; instead the field is returned with the value 0.
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);
}
access(2), chmod(2), chown(2), fstatat(2), readlink(2), utime(2), capabilities(7)
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