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

.\" Copyright (c) 1983, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)readlink.2	6.8 (Berkeley) 3/10/91
.\"
.\" Modified Sat Jul 24 00:10:21 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Tue Jul  9 23:55:17 1996 by aeb
.\" Modified Fri Jan 24 00:26:00 1997 by aeb
.\"
.TH READLINK 2 2007-07-26 "Linux" "Linux Programmer's Manual"
.SH NAME
readlink \- read value of a symbolic link
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "ssize_t readlink(const char *" path ", char *" buf ", size_t " bufsiz );
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR readlink ():
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _POSIX_C_SOURCE\ >=\ 200112L
.ad b
.SH DESCRIPTION
.BR readlink ()
places the contents of the symbolic link
.I path
in the buffer
.IR buf ,
which has size
.IR bufsiz .
.BR readlink ()
does not append a null byte to
.IR buf .
It will truncate the contents (to a length of
.I bufsiz
characters), in case the buffer is too small to hold all of the contents.
.SH "RETURN VALUE"
On success,
.BR readlink ()
returns the number of bytes placed in
.IR buf .
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EACCES
Search permission is denied for a component of the path prefix.
(See also
.BR path_resolution (7).)
.TP
.B EFAULT
.I buf
extends outside the process's allocated address space.
.TP
.B EINVAL
.I bufsiz
is not positive.
.\" At the glibc level, bufsiz is unsigned, so this error can only occur
.\" if bufsiz==0.  However, the in the kernel syscall, bufsiz is signed,
.\" and this error can also occur if bufsiz < 0.
.\" See: http://thread.gmane.org/gmane.linux.man/380
.\" Subject: [patch 0/3] [RFC] kernel/glibc mismatch of "readlink" syscall?
.TP
.B EINVAL
The named file is not a symbolic link.
.TP
.B EIO
An I/O error occurred while reading from the file system.
.TP
.B ELOOP
Too many symbolic links were encountered in translating the pathname.
.TP
.B ENAMETOOLONG
A pathname, or a component of a pathname, was too long.
.TP
.B ENOENT
The named file does not exist.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.SH "CONFORMING TO"
4.4BSD (the
.BR readlink ()
function call appeared in 4.2BSD),
POSIX.1-2001.
.SH NOTES
In versions of glibc up to and including glibc 2.4, the return type of
.BR readlink ()
was declared as
.IR int .
Nowadays, the return type is declared as
.IR ssize_t ,
as (newly) required in POSIX.1-2001.
.SH "SEE ALSO"
.BR lstat (2),
.BR readlinkat (2),
.BR stat (2),
.BR symlink (2),
.BR path_resolution (7),
.BR symlink (7)
Commit	Line	Data
fea681da MK	1	.\" Copyright (c) 1983, 1991 The Regents of the University of California.
	2	.\" All rights reserved.
	3	.\"
	4	.\" Redistribution and use in source and binary forms, with or without
	5	.\" modification, are permitted provided that the following conditions
	6	.\" are met:
	7	.\" 1. Redistributions of source code must retain the above copyright
	8	.\" notice, this list of conditions and the following disclaimer.
	9	.\" 2. Redistributions in binary form must reproduce the above copyright
	10	.\" notice, this list of conditions and the following disclaimer in the
	11	.\" documentation and/or other materials provided with the distribution.
	12	.\" 3. All advertising materials mentioning features or use of this software
	13	.\" must display the following acknowledgement:
	14	.\" This product includes software developed by the University of
	15	.\" California, Berkeley and its contributors.
	16	.\" 4. Neither the name of the University nor the names of its contributors
	17	.\" may be used to endorse or promote products derived from this software
	18	.\" without specific prior written permission.
	19	.\"
	20	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	21	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	22	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	23	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	24	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	25	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	26	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	27	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	28	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	29	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	30	.\" SUCH DAMAGE.
	31	.\"
	32	.\" @(#)readlink.2 6.8 (Berkeley) 3/10/91
	33	.\"
	34	.\" Modified Sat Jul 24 00:10:21 1993 by Rik Faith (faith@cs.unc.edu)
	35	.\" Modified Tue Jul 9 23:55:17 1996 by aeb
	36	.\" Modified Fri Jan 24 00:26:00 1997 by aeb
	37	.\"
cc4615cc	38	.TH READLINK 2 2007-07-26 "Linux" "Linux Programmer's Manual"
fea681da MK	39	.SH NAME
	40	readlink \- read value of a symbolic link
	41	.SH SYNOPSIS
	42	.B #include <unistd.h>
	43	.sp
4595d739	44	.BI "ssize_t readlink(const char " path ", char " buf ", size_t " bufsiz );
cc4615cc MK	45	.sp
	46	.in -4n
	47	Feature Test Macro Requirements for glibc (see
	48	.BR feature_test_macros (7)):
	49	.in
	50	.sp
	51	.ad l
	52	.BR readlink ():
	53	_BSD_SOURCE \|\| _XOPEN_SOURCE\ >=\ 500 \|\| _POSIX_C_SOURCE\ >=\ 200112L
	54	.ad b
fea681da	55	.SH DESCRIPTION
e511ffb6	56	.BR readlink ()
fea681da MK	57	places the contents of the symbolic link
	58	.I path
	59	in the buffer
	60	.IR buf ,
	61	which has size
	62	.IR bufsiz .
e511ffb6	63	.BR readlink ()
28d88c17	64	does not append a null byte to
fea681da MK	65	.IR buf .
	66	It will truncate the contents (to a length of
	67	.I bufsiz
	68	characters), in case the buffer is too small to hold all of the contents.
	69	.SH "RETURN VALUE"
64aae2b1 MK	70	On success,
	71	.BR readlink ()
	72	returns the number of bytes placed in
	73	.IR buf .
	74	On error, \-1 is returned and
	75	.I errno
	76	is set to indicate the error.
fea681da MK	77	.SH ERRORS
	78	.TP
	79	.B EACCES
	80	Search permission is denied for a component of the path prefix.
	81	(See also
ad7cc990	82	.BR path_resolution (7).)
fea681da MK	83	.TP
	84	.B EFAULT
	85	.I buf
	86	extends outside the process's allocated address space.
	87	.TP
	88	.B EINVAL
	89	.I bufsiz
	90	is not positive.
89cb804a MK	91	.\" At the glibc level, bufsiz is unsigned, so this error can only occur
	92	.\" if bufsiz==0. However, the in the kernel syscall, bufsiz is signed,
	93	.\" and this error can also occur if bufsiz < 0.
	94	.\" See: http://thread.gmane.org/gmane.linux.man/380
	95	.\" Subject: [patch 0/3] [RFC] kernel/glibc mismatch of "readlink" syscall?
fea681da MK	96	.TP
	97	.B EINVAL
	98	The named file is not a symbolic link.
	99	.TP
	100	.B EIO
	101	An I/O error occurred while reading from the file system.
	102	.TP
	103	.B ELOOP
	104	Too many symbolic links were encountered in translating the pathname.
	105	.TP
	106	.B ENAMETOOLONG
	107	A pathname, or a component of a pathname, was too long.
	108	.TP
	109	.B ENOENT
	110	The named file does not exist.
	111	.TP
	112	.B ENOMEM
	113	Insufficient kernel memory was available.
	114	.TP
	115	.B ENOTDIR
	116	A component of the path prefix is not a directory.
	117	.SH "CONFORMING TO"
97c1eac8	118	4.4BSD (the
e511ffb6	119	.BR readlink ()
97c1eac8 MK	120	function call appeared in 4.2BSD),
97c1eac8 MK	121	POSIX.1-2001.
889829be	122	.SH NOTES
4595d739 MK	123	In versions of glibc up to and including glibc 2.4, the return type of
	124	.BR readlink ()
	125	was declared as
	126	.IR int .
	127	Nowadays, the return type is declared as
	128	.IR ssize_t ,
	129	as (newly) required in POSIX.1-2001.
fea681da MK	130	.SH "SEE ALSO"
fea681da MK	131	.BR lstat (2),
591f90f7	132	.BR readlinkat (2),
fea681da	133	.BR stat (2),
ad7cc990	134	.BR symlink (2),
a9cfde1d	135	.BR path_resolution (7),
ad22ad55	136	.BR symlink (7)