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[thirdparty/man-pages.git] / man2 / stat.2

'\" t
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.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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.\" and Copyright (c) 2007 Michael Kerrisk <mtk-manpages@gmx.net>
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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>
.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1995-01-09 by Richard Kettlewell <richard@greenend.org.uk>
.\" Modified 1998-05-13 by Michael Haardt <michael@cantor.informatik.rwth-aachen.de>
.\" Modified 1999-07-06 by aeb & Albert Cahalan
.\" Modified 2000-01-07 by aeb
.\" Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
.\" 2007-06-08 mtk: Added example program
.\" 2007-07-05 mtk: Added details on underlying system call interfaces
.\"
.TH STAT 2 2007-07-26 "Linux" "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 *" path ", struct stat *" buf );
.br
.BI "int fstat(int " filedes ", struct stat *" buf );
.br
.BI "int lstat(const char *" path ", struct stat *" buf );
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR lstat ():
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.SH DESCRIPTION
.PP
These functions return information about a file.
No permissions are required on the file itself, but \(em in the case of
.BR stat ()
and
.BR lstat ()
\(em
execute (search) permission is required on all of the directories in
.I path
that lead to the file.
.PP
.BR stat ()
stats the file pointed to by
.I path
and fills in
.IR buf .

.BR lstat ()
is identical to
.BR stat (),
except that if
.I path
is a symbolic link, then the link itself is stat-ed,
not the file that it refers to.

.BR fstat ()
is identical to
.BR stat (),
except that the file to be stat-ed is specified by the file descriptor
.IR filedes .
.PP
All of these system calls return a
.I stat
structure, which contains the following fields:
.PP
.RS 0.25i
.nf
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 */
};
.fi
.RE
.PP
The
.I st_dev
field describes the device on which this file resides.

The
.I st_rdev
field describes the device that this file (inode) represents.

The
.I 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
.I st_blocks
field indicates the number of blocks allocated to the file, 512-byte units.
(This may be smaller than
.IR st_size /512
when the file has holes.)

The
.IR 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.)
.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, for example, 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, for example, 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 using the
.I st_mode
field:
.RS
.TP 1.2i
.BR S_ISREG (m)
is it a regular file?
.TP
.BR S_ISDIR (m)
directory?
.TP
.BR S_ISCHR (m)
character device?
.TP
.BR S_ISBLK (m)
block device?
.TP
.BR S_ISFIFO (m)
FIFO (named pipe)?
.TP
.BR S_ISLNK (m)
symbolic link? (Not in POSIX.1-1996.)
.TP
.BR S_ISSOCK (m)
socket? (Not in POSIX.1-1996.)
.RE
.PP
The following flags are defined for the
.I st_mode
field:
.RS
.TS
lB l l.
S_IFMT	0170000	bit mask for the file type bit fields
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
.TE
.RE
.P
The set-group-ID bit
.RB ( 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
.B S_ISGID
bit set.
For a file that does not have the group execution bit
.RB ( S_IXGRP )
set,
the set-group-ID bit indicates mandatory file/record locking.
.P
The `sticky' bit
.RB ( 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 path .
(See also
.BR path_resolution (7).)
.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 path
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"
These system calls conform to SVr4, 4.3BSD, POSIX.1-2001.
.\" SVr4 documents additional
.\" .BR fstat ()
.\" error conditions EINTR, ENOLINK, and EOVERFLOW.  SVr4
.\" documents additional
.\" .BR stat ()
.\" and
.\" .BR 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.
The interpretation differs between systems,
and possibly on a single system when NFS mounts are involved.)
.LP
POSIX does not describe the
.BR S_IFMT ,
.BR S_IFSOCK ,
.BR S_IFLNK ,
.BR S_IFREG ,
.BR S_IFBLK ,
.BR S_IFDIR ,
.BR S_IFCHR ,
.BR S_IFIFO ,
.BR S_ISVTX
bits, but instead demands the use of
the macros
.BR S_ISDIR (),
etc.
The
.BR S_ISLNK ()
and
.BR 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.
.LP
Unix V7 (and later systems) had
.BR S_IREAD ,
.BR S_IWRITE ,
.BR S_IEXEC ,
where POSIX
prescribes the synonyms
.BR S_IRUSR ,
.BR S_IWUSR ,
.BR S_IXUSR .
.SS "Other Systems"
Values that have been (or are) in use on various systems:
.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 \fIst_rdev\fP 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)
.TE

A sticky command appeared in Version 32V AT&T UNIX.
.SH NOTES
.SS Linux Notes
Since kernel 2.5.48, the
.I 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
.IR st_atim.tv_nsec ,
if the
.B _BSD_SOURCE
or
.B _SVID_SOURCE
feature test macro is defined,
or of the form
.IR 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
.I /proc
directory,
.BR stat ()
does not return the file size in the
.I st_size
field; instead the field is returned with the value 0.
.SS Underlying kernel interface
Over time, increases in the size of the
.I stat
structure have led to three successive versions of
.BR stat ():
.IR sys_stat ()
(slot
.IR __NR_oldstat ),
.IR sys_newstat ()
(slot
.IR __NR_stat ),
and
.IR sys_stat64()
(new in kernel 2.4; slot
.IR __NR_stat64 ).
The glibc
.BR stat ()
wrapper function hides these details from applications,
invoking the most recent version of the system call provided by the kernel,
and repacking the returned information if required for old binaries.
Similar remarks apply for
.BR fstat (2)
and
.BR lstat (2).
.\"
.\" A note from Andries Brouwer, July 2007
.\"
.\" > Is the story not rather more complicated for some calls like
.\" > stat(2)?
.\"
.\" Yes and no, mostly no. See /usr/include/sys/stat.h .
.\"
.\" The idea is here not so much that syscalls change, but that
.\" the definitions of struct stat and of the types dev_t and mode_t change.
.\" This means that libc (even if it does not call the kernel
.\" but only calls some internal function) must know what the
.\" format of dev_t or of struct stat is.
.\" The communication between the application and libc goes via
.\" the include file <sys/stat.h> that defines a _STAT_VER and
.\" _MKNOD_VER describing the layout of the data that user space
.\" uses. Each (almost each) occurrence of stat() is replaced by
.\" an occurrence of xstat() where the first parameter of xstat()
.\" is this version number _STAT_VER.
.\"
.\" Now, also the definitions used by the kernel change.
.\" But glibc copes with this in the standard way, and the
.\" struct stat as returned by the kernel is repacked into
.\" the struct stat as expected by the application.
.\" Thus, _STAT_VER and this setup cater for the application-libc
.\" interface, rather than the libc-kernel interface.
.\"
.\" (Note that the details depend on gcc being used as c compiler.)
.SH EXAMPLE
The following program calls
.BR stat (2)
and displays selected fields in the returned
.I stat
structure.
.nf

#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);
}
.fi
.SH "SEE ALSO"
.BR access (2),
.BR chmod (2),
.BR chown (2),
.BR fstatat (2),
.BR readlink (2),
.BR utime (2),
.BR capabilities (7)