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man fstat .....
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STAT(2) System calls STAT(2)
NAME
stat, fstat, lstat - get file status
SYNOPSIS
#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);
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, except in the case of a sym?
bolic 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 stated in place of
file_name.
They all return a stat structure, which contains the fol?
lowing 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_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 trail?
ing NUL.
The value st_blocks gives the size of the file in 512-byte
blocks. The value st_blksize gives the "preferred" block?
size 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( .)
The field st_atime is changed by file accesses, e.g. by
exec(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 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 filedes is bad.
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 travers?
ing the path.
EFAULT Bad address.
EACCES Permission denied.
ENOMEM Out of memory (i.e. kernel memory).
ENAMETOOLONG
File name too long.
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_blk?
size fields may be less portable. (They were introduced in
BSD. Are not specified by POSIX. The interpretation dif?
fers 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.
OTHER SYSTEMS
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.
SEE ALSO
chmod(2), chown(2), readlink(2), utime(2)
Linux May 13, 1998 |
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发表于 2004-02-24 16:44
