path: root/man2/stat.2

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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\" Modified by Michael Haardt <michael@moria.de>
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1995-05-18 by Todd Larason <jtl@molehill.org>
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.\" 
.TH STAT 2 2004-06-23 "Linux 2.6.7" "Linux Programmer's Manual"
.SH NAME
stat, fstat, lstat \- get file status
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/stat.h>
.br
.B #include <unistd.h>
.sp
.BI "int stat(const char *" file_name ", struct stat *" buf );
.br
.BI "int fstat(int " filedes ", struct stat *" buf );
.br
.BI "int lstat(const char *" file_name ", struct stat *" buf );
.SH DESCRIPTION
.PP
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.
.PP
.B stat
stats the file pointed to by 
.I file_name
and fills in
.IR buf .

.B lstat
is identical to
.BR stat ,
except in the case of a symbolic link, where the link itself is stat-ed,
not the file that it refers to.

.B fstat
is identical to
.BR stat ,
only the open file pointed to by 
.I filedes
(as returned by
.BR open (2))
is stat-ed in place of 
.IR file_name .

.PP
They all return a
.I stat
structure, which contains the following fields:
.PP
.RS
.nf
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 */
};
.fi
.RE
.PP
The value
.I 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
.I st_blocks
gives the size of the file in 512-byte blocks.
(This may be smaller than
.IR st_size /512
e.g. when the file has holes.)
The value
.IR 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.)
.PP
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
.I st_atime
field. (See `noatime' in
.BR mount (8).)

The field
.I st_atime
is changed by file accesses, e.g. by
.BR execve (2),
.BR mknod (2),
.BR pipe (2),
.BR utime (2)
and
.BR read (2)
(of more than zero bytes). Other routines, like
.BR mmap (2),
may or may not update
.IR st_atime .

The field
.I st_mtime
is changed by file modifications, e.g. by
.BR mknod (2),
.BR truncate (2),
.BR utime (2)
and
.BR write (2)
(of more than zero bytes).
Moreover,
.I st_mtime
of a directory is changed by the creation or deletion of files
in that directory.
The
.I st_mtime
field is
.I not
changed for changes in owner, group, hard link count, or mode.

The field
.I st_ctime
is changed by writing or by setting inode information
(i.e., owner, group, link count, mode, etc.).
.PP
The following POSIX macros are defined to check the file type:
.RS
.TP 1.2i
S_ISREG(m)
is it a regular file?
.TP
S_ISDIR(m)
directory?
.TP
S_ISCHR(m)
character device?
.TP
S_ISBLK(m)
block device?
.TP
S_ISFIFO(m)
fifo?
.TP
S_ISLNK(m)
symbolic link? (Not in POSIX.1-1996.)
.TP
S_ISSOCK(m)
socket? (Not in POSIX.1-1996.)
.RE
.PP
The following flags are defined for the
.I st_mode
field:
.P
.TS
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
.TE
.P
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.
.P
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.
.SH "RETURN VALUE"
On success, zero is returned.  On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
Search permission is denied for one of the directories
in the path prefix of
.IR file_name .
(See also
.BR path_resolution (2).)
.TP
.B EBADF
.I filedes
is bad.
.TP
.B EFAULT
Bad address.
.TP
.B ELOOP
Too many symbolic links encountered while traversing the path.
.TP
.B ENAMETOOLONG
File name too long.
.TP
.B ENOENT
A component of the path
.I file_name
does not exist, or the path is an empty string.
.TP
.B ENOMEM
Out of memory (i.e. kernel memory).
.TP
.B ENOTDIR
A component of the path is not a directory.
.SH "CONFORMING TO"
The
.B stat
and
.B fstat
calls conform to SVr4, SVID, POSIX, X/OPEN, BSD 4.3.  The
.B lstat
call conforms to 4.3BSD and SVr4.
SVr4 documents additional
.B fstat
error conditions EINTR, ENOLINK, and EOVERFLOW.  SVr4
documents additional
.B stat
and
.B lstat
error conditions EINTR, EMULTIHOP, ENOLINK, and EOVERFLOW.
Use of the
.I st_blocks
and
.I 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.)
.LP
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.
.LP
Unix V7 (and later systems) had S_IREAD, S_IWRITE, S_IEXEC, where POSIX
prescribes the synonyms S_IRUSR, S_IWUSR, S_IXUSR.
.SH "OTHER SYSTEMS"
Values that have been (or are) in use on various systems:
.P
.TS
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)
.TE

A sticky command appeared in Version 32V AT&T UNIX.

.SH "SEE ALSO"
.BR chmod (2),
.BR chown (2),
.BR readlink (2),
.BR utime (2),
.BR capabilities (7)