[apple/xnu.git] / bsd / man / man2 / access.2

.\"	$NetBSD: access.2,v 1.7 1995/02/27 12:31:44 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\"	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.
.\"
.\"     @(#)access.2	8.2 (Berkeley) 4/1/94
.\"
.Dd April 1, 1994
.Dt ACCESS 2
.Os BSD 4
.Sh NAME
.Nm access ,
.Nm faccessat
.Nd check access permissions of a file or pathname
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fo access
.Fa "const char *path"
.Fa "int amode"
.Fc
.Ft int
.Fn faccessat "int fd" "const char *path" "int mode" "int flag"
.Sh DESCRIPTION
The
.Fn access
function checks the accessibility of the
file named by
.Fa path
for the access permissions indicated by
.Fa amode .
The value of
.Fa amode
is the bitwise inclusive OR of the access permissions to be
checked
.Pf ( Dv R_OK
for read permission,
.Dv W_OK
for write permission and
.Dv X_OK
for execute/search permission) or the existence test,
.Dv F_OK .
All components of the pathname
.Fa path
are checked for access permissions (including
.Dv F_OK ) .
.Pp
The real user ID is used in place of the effective user ID
and the real group access list
(including the real group ID) are
used in place of the effective ID for verifying permission.
.Pp
The
.Fn faccessat
system call is equivalent to
.Fn access
except in the case where
.Fa path
specifies a relative path.
In this case the file whose accessibility is to be determined is
located relative to the directory associated with the file descriptor
.Fa fd
instead of the current working directory.
If
.Fn faccessat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used and the behavior is
identical to a call to
.Fn access .
Values for
.Fa flag
are constructed by a bitwise-inclusive OR of flags from the following
list, defined in
.In fcntl.h :
.Bl -tag -width indent
.It Dv AT_EACCESS
The checks for accessibility are performed using the effective user and group
IDs instead of the real user and group ID as required in a call to
.Fn access .
.El
.Pp
Even if a process has appropriate privileges and indicates success for
.Dv X_OK ,
the file may not actually have execute permission bits set.
Likewise for
.Dv R_OK
and
.Dv W_OK .
.Sh RETURN VALUES
If
.Fa path
cannot be found
or if any of the desired access modes would not be granted,
then a -1 value is returned and the global integer variable
.Va errno
is set to indicate the error.
Otherwise, a 0 value is returned.
.Sh ERRORS
Access to the file is denied if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EACCES
Permission bits of the file mode do not permit the requested access,
or search permission is denied on a component of the path prefix.
.Pp
The owner of a file has permission checked
with respect to the ``owner'' read, write, and execute mode bits,
members of the file's group other than the owner have permission checked
with respect to the ``group'' mode bits,
and all others have permissions checked
with respect to the ``other'' mode bits.
.\" 
.\" ==========
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.It Bq Er EINVAL
An invalid value was specified for
.Ar amode .
.\" ==========
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.\" ==========
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.\" ==========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 
.Dv {NAME_MAX}
characters, or an entire path name exceeded 
.Dv {PATH_MAX}
characters.
.\" ==========
.It Bq Er ENOENT
The named file does not exist.
.\" ==========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ==========
.It Bq Er EROFS
Write access is requested for a file on a read-only file system.
.\" ==========
.It Bq Er ETXTBSY
Write access is requested for a pure procedure (shared text)
file that is presently being executed.
.El
.Pp
Also, the
.Fn faccessat
system call may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is
neither
.Dv AT_FDCWD
nor a valid file descriptor.
.It Bq Er EINVAL
The value of the
.Fa flag
argument is not valid.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr stat 2
.Sh STANDARDS
The
.Fn access
function conforms to 
.St -p1003.1-90 .
The
.Fn faccessat
system call is expected to conform to POSIX.1-2008 .
.Sh CAVEAT
.Fn access
is a potential security hole and
should never be used.
Commit	Line	Data
9bccf70c A	1	.\" $NetBSD: access.2,v 1.7 1995/02/27 12:31:44 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)access.2 8.2 (Berkeley) 4/1/94
	35	.\"
	36	.Dd April 1, 1994
	37	.Dt ACCESS 2
	38	.Os BSD 4
	39	.Sh NAME
fe8ab488 A	40	.Nm access ,
fe8ab488 A	41	.Nm faccessat
9bccf70c A	42	.Nd check access permissions of a file or pathname
	43	.Sh SYNOPSIS
	44	.Fd #include <unistd.h>
	45	.Ft int
2d21ac55 A	46	.Fo access
	47	.Fa "const char *path"
	48	.Fa "int amode"
	49	.Fc
fe8ab488 A	50	.Ft int
fe8ab488 A	51	.Fn faccessat "int fd" "const char *path" "int mode" "int flag"
9bccf70c A	52	.Sh DESCRIPTION
	53	The
	54	.Fn access
	55	function checks the accessibility of the
	56	file named by
	57	.Fa path
	58	for the access permissions indicated by
2d21ac55	59	.Fa amode .
9bccf70c	60	The value of
2d21ac55	61	.Fa amode
9bccf70c A	62	is the bitwise inclusive OR of the access permissions to be
	63	checked
	64	.Pf ( Dv R_OK
	65	for read permission,
	66	.Dv W_OK
	67	for write permission and
	68	.Dv X_OK
	69	for execute/search permission) or the existence test,
	70	.Dv F_OK .
	71	All components of the pathname
	72	.Fa path
	73	are checked for access permissions (including
	74	.Dv F_OK ) .
	75	.Pp
	76	The real user ID is used in place of the effective user ID
	77	and the real group access list
	78	(including the real group ID) are
	79	used in place of the effective ID for verifying permission.
	80	.Pp
fe8ab488 A	81	The
	82	.Fn faccessat
	83	system call is equivalent to
	84	.Fn access
	85	except in the case where
	86	.Fa path
	87	specifies a relative path.
	88	In this case the file whose accessibility is to be determined is
	89	located relative to the directory associated with the file descriptor
	90	.Fa fd
	91	instead of the current working directory.
	92	If
	93	.Fn faccessat
	94	is passed the special value
	95	.Dv AT_FDCWD
	96	in the
	97	.Fa fd
	98	parameter, the current working directory is used and the behavior is
	99	identical to a call to
	100	.Fn access .
	101	Values for
	102	.Fa flag
	103	are constructed by a bitwise-inclusive OR of flags from the following
	104	list, defined in
	105	.In fcntl.h :
	106	.Bl -tag -width indent
	107	.It Dv AT_EACCESS
	108	The checks for accessibility are performed using the effective user and group
	109	IDs instead of the real user and group ID as required in a call to
	110	.Fn access .
	111	.El
	112	.Pp
9bccf70c A	113	Even if a process has appropriate privileges and indicates success for
	114	.Dv X_OK ,
	115	the file may not actually have execute permission bits set.
	116	Likewise for
	117	.Dv R_OK
	118	and
	119	.Dv W_OK .
	120	.Sh RETURN VALUES
	121	If
	122	.Fa path
2d21ac55 A	123	cannot be found
	124	or if any of the desired access modes would not be granted,
	125	then a -1 value is returned and the global integer variable
	126	.Va errno
	127	is set to indicate the error.
	128	Otherwise, a 0 value is returned.
9bccf70c A	129	.Sh ERRORS
	130	Access to the file is denied if:
	131	.Bl -tag -width Er
2d21ac55 A	132	.\" ==========
	133	.It Bq Er EACCES
	134	Permission bits of the file mode do not permit the requested access,
	135	or search permission is denied on a component of the path prefix.
	136	.Pp
	137	The owner of a file has permission checked
	138	with respect to the ``owner'' read, write, and execute mode bits,
	139	members of the file's group other than the owner have permission checked
	140	with respect to the ``group'' mode bits,
	141	and all others have permissions checked
	142	with respect to the ``other'' mode bits.
	143	.\"
	144	.\" ==========
	145	.It Bq Er EFAULT
	146	.Fa Path
	147	points outside the process's allocated address space.
	148	.It Bq Er EINVAL
	149	An invalid value was specified for
	150	.Ar amode .
	151	.\" ==========
	152	.It Bq Er EIO
	153	An I/O error occurred while reading from or writing to the file system.
	154	.\" ==========
	155	.It Bq Er ELOOP
	156	Too many symbolic links were encountered in translating the pathname.
	157	.\" ==========
9bccf70c A	158	.It Bq Er ENAMETOOLONG
	159	A component of a pathname exceeded
	160	.Dv {NAME_MAX}
	161	characters, or an entire path name exceeded
	162	.Dv {PATH_MAX}
	163	characters.
2d21ac55	164	.\" ==========
9bccf70c A	165	.It Bq Er ENOENT
9bccf70c A	166	The named file does not exist.
2d21ac55 A	167	.\" ==========
	168	.It Bq Er ENOTDIR
	169	A component of the path prefix is not a directory.
	170	.\" ==========
9bccf70c A	171	.It Bq Er EROFS
9bccf70c A	172	Write access is requested for a file on a read-only file system.
2d21ac55	173	.\" ==========
9bccf70c A	174	.It Bq Er ETXTBSY
9bccf70c A	175	Write access is requested for a pure procedure (shared text)
2d21ac55	176	file that is presently being executed.
9bccf70c	177	.El
fe8ab488 A	178	.Pp
	179	Also, the
	180	.Fn faccessat
	181	system call may fail if:
	182	.Bl -tag -width Er
	183	.It Bq Er EBADF
	184	The
	185	.Fa path
	186	argument does not specify an absolute path and the
	187	.Fa fd
	188	argument is
	189	neither
	190	.Dv AT_FDCWD
	191	nor a valid file descriptor.
	192	.It Bq Er EINVAL
	193	The value of the
	194	.Fa flag
	195	argument is not valid.
	196	.It Bq Er ENOTDIR
	197	The
	198	.Fa path
	199	argument is not an absolute path and
	200	.Fa fd
	201	is neither
	202	.Dv AT_FDCWD
	203	nor a file descriptor associated with a directory.
	204	.El
9bccf70c A	205	.Sh SEE ALSO
	206	.Xr chmod 2 ,
	207	.Xr stat 2
	208	.Sh STANDARDS
	209	The
	210	.Fn access
	211	function conforms to
	212	.St -p1003.1-90 .
fe8ab488 A	213	The
	214	.Fn faccessat
	215	system call is expected to conform to POSIX.1-2008 .
9bccf70c	216	.Sh CAVEAT
fe8ab488	217	.Fn access
9bccf70c A	218	is a potential security hole and
9bccf70c A	219	should never be used.