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

.\"
.\" Copyright (c) 2010 Apple Inc.  All rights reserved.
.\"
.\" @APPLE_LICENSE_HEADER_START@
.\" 
.\" This file contains Original Code and/or Modifications of Original Code
.\" as defined in and that are subject to the Apple Public Source License
.\" Version 2.0 (the 'License'). You may not use this file except in
.\" compliance with the License. Please obtain a copy of the License at
.\" http://www.opensource.apple.com/apsl/ and read it before using this
.\" file.
.\" 
.\" The Original Code and all software distributed under the License are
.\" distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
.\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
.\" Please see the License for the specific language governing rights and
.\" limitations under the License.
.\" 
.\" @APPLE_LICENSE_HEADER_END@
.\"
.\"
.\"	$NetBSD: open.2,v 1.8 1995/02/27 12:35:14 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.
.\"
.\"     @(#)open.2	8.2 (Berkeley) 11/16/93
.\"
.Dd November 10, 2010
.Dt OPEN 2
.Os BSD 4
.Sh NAME
.Nm open
.Nd open or create a file for reading or writing
.Sh SYNOPSIS
.\" OH??? .Fd #include <sys/stat.h>
.Fd #include <fcntl.h>
.Ft int
.Fo open
.Fa "const char *path"
.Fa "int oflag"
.Fa "..."
.Fc
.Sh DESCRIPTION
The file name specified by
.Fa path
is opened
for reading and/or writing,
as specified by the argument
.Fa oflag ;
the file descriptor is returned to the calling process.
.Pp
The
.Fa oflag
argument may indicate that the file is to be
created if it does not exist (by specifying the
.Dv O_CREAT
flag).  In this case,
.Nm
requires a third argument
.Fa "mode_t mode" ;
the file is created with mode
.Fa mode
as described in
.Xr chmod 2
and modified by the process' umask value (see
.Xr umask 2 ) .
.Pp
The flags specified are formed by
.Em or Ns 'ing
the following values:
.Pp
.Bd -literal -offset indent -compact
O_RDONLY	open for reading only
O_WRONLY	open for writing only
O_RDWR		open for reading and writing
O_NONBLOCK	do not block on open or for data to become available
O_APPEND	append on each write
O_CREAT		create file if it does not exist
O_TRUNC		truncate size to 0
O_EXCL		error if O_CREAT and the file exists
O_SHLOCK	atomically obtain a shared lock
O_EXLOCK	atomically obtain an exclusive lock
O_NOFOLLOW	do not follow symlinks
O_SYMLINK	allow open of symlinks
O_EVTONLY	descriptor requested for event notifications only
O_CLOEXEC	mark as close-on-exec
.Ed
.Pp
Opening a file with
.Dv O_APPEND
set causes each write on the file to be appended to the end.  If
.Dv O_TRUNC
is specified and the
file exists, the file is truncated to zero length.
If
.Dv O_EXCL
is set with
.Dv O_CREAT
and the file already
exists,
.Fn open
returns an error.
This may be used to implement a simple exclusive-access locking mechanism.
If
.Dv O_EXCL
is set with
.Dv O_CREAT
and the last component of the pathname is a symbolic link,
.Fn open
will fail even if the symbolic link points to a non-existent name.
.Pp
If the
.Dv O_NONBLOCK
flag is specified, do not wait for the device or file
to be ready or available.  If the
.Fn open
call would result
in the process being blocked for some reason
(e.g., waiting for carrier on a dialup line),
.Fn open
returns immediately.
This flag also has the effect of making all subsequent I/O
on the open file non-blocking.
.Pp
When opening a file, a lock with
.Xr flock 2
semantics can be obtained by setting
.Dv O_SHLOCK
for a shared lock, or
.Dv O_EXLOCK
for an exclusive lock.
If creating a file with
.Dv O_CREAT ,
the request for the lock will never fail
(provided that the underlying filesystem supports locking).
.Pp
If
.Dv O_NOFOLLOW
is used in the mask and the target file passed to
.Fn open
is a symbolic link then the
.Fn open
will fail.
.Pp
If
.Dv O_SYMLINK
is used in the mask and the target file passed to
.Fn open
is a symbolic link then the
.Fn open
will be for the symbolic link itself, not what it links to.
.Pp
The
.Dv O_EVTONLY
flag is only intended for monitoring a file for changes (e.g. kqueue). Note: when 
this flag is used, the opened file will not prevent an unmount 
of the volume that contains the file.
.Pp
The
.Dv O_CLOEXEC
flag causes the file descriptor to be marked as close-on-exec,
setting the
.Dv FD_CLOEXEC
flag.  The state of the file descriptor flags can be inspected
using the F_GETFD fcntl.  See
.Xr fcntl 2 .
.Pp
If successful,
.Fn open
returns a non-negative integer, termed a file descriptor.
It returns -1 on failure.
The file pointer (used to mark the current position within the file)
is set to the beginning of the file.
.Pp
When a new file is created,
it is given the group of the directory which contains it.
.Pp
The new descriptor is set to remain open across
.Xr execve
system calls; see
.Xr close 2
and
.Xr fcntl 2 .
.Pp
The system imposes a limit on the number of file descriptors
that can be held open simultaneously by one process.
.Xr Getdtablesize 2
returns the current system limit.
.Sh RETURN VALUES
If successful,
.Fn open
returns a non-negative integer, termed a file descriptor.
It returns -1 on failure, and sets
.Va errno
to indicate the error.
.Sh ERRORS
The named file is opened unless:
.Bl -tag -width Er
.\" ===========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ===========
.It Bq Er EACCES
The required permissions (for reading and/or writing)
are denied for the given flags.
.\" ===========
.It Bq Er EACCES
.Dv O_CREAT
is specified,
the file does not exist,
and the directory in which it is to be created
does not permit writing.
.\" ===========
.It Bq Er EACCES
.Dv O_TRUNC
is specified and write permission is denied.
.\" ===========
.It Bq Er EAGAIN
.Fa path
specifies the slave side of a locked pseudo-terminal device.
.\" ===========
.It Bq Er EDQUOT
.Dv O_CREAT
is specified,
the file does not exist,
and the directory in which the entry for the new file
is being placed cannot be extended because the
user's quota of disk blocks on the file system
containing the directory has been exhausted.
.\" ===========
.It Bq Er EDQUOT
.Dv O_CREAT
is specified,
the file does not exist,
and the user's quota of inodes on the file system
on which the file is being created has been exhausted.
.\" ===========
.It Bq Er EEXIST
.Dv O_CREAT
and
.Dv O_EXCL
are specified and the file exists.
.\" ===========
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.\" ===========
.It Bq Er EINTR
The
.Fn open
operation is interrupted by a signal.
.\" ===========
.It Bq Er EINVAL
The value of
.Fa oflag
is not valid.
.\" ===========
.It Bq Er EIO
An I/O error occurs while making the directory entry or
allocating the inode for
.Dv O_CREAT .
.\" ===========
.It Bq Er EISDIR
The named file is a directory, and the arguments specify
that it is to be opened for writing.
.\" ===========
.It Bq Er ELOOP
Too many symbolic links are encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ===========
.It Bq Er EMFILE
The process has already reached its limit for open file descriptors.
.\" ===========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeds
.Dv {NAME_MAX}
characters, or an entire path name exceeded 
.Dv {PATH_MAX}
characters.
.\" ===========
.It Bq Er ENFILE
The system file table is full.
.\" ===========
.It Bq Er ELOOP
.Dv O_NOFOLLOW
was specified and the target is a symbolic link.
.\" ===========
.It Bq Er ENOENT
.Dv O_CREAT
is not set and the named file does not exist.
.\" ===========
.It Bq Er ENOENT
A component of the path name that must exist does not exist.
.\" ===========
.It Bq Er ENOSPC
.Dv O_CREAT
is specified,
the file does not exist,
and the directory in which the entry for the new file is being placed
cannot be extended because there is no space left on the file
system containing the directory.
.\" ===========
.It Bq Er ENOSPC
.Dv O_CREAT
is specified,
the file does not exist,
and there are no free inodes on the file system on which the
file is being created.
.\" ===========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ===========
.It Bq Er ENXIO
The named file is a character-special or block-special file
and the device associated with this special file does not exist.
.\" ===========
.It Bq Er ENXIO
O_NONBLOCK and O_WRONLY are set, the file is a FIFO,
and no process has it open for reading.
.\" ===========
.It Bq Er EOPNOTSUPP
.Dv O_SHLOCK
or
.Dv O_EXLOCK
is specified, but the underlying filesystem does not support locking.
.\" ===========
.It Bq Er EOPNOTSUPP
An attempt is made to open a socket (not currently implemented).
.\" ===========
.It Bq Er EOVERFLOW
The named file is a regular file
and its size does not fit in an object of type off_t.
.\" ===========
.It Bq Er EROFS
The named file resides on a read-only file system,
and the file is to be modified.
.\" ===========
.It Bq Er ETXTBSY
The file is a pure procedure (shared text) file that is being
executed and the
.Fn open
call requests write access.
.El
.Sh COMPATIBILITY
.Fn open
on a terminal device (i.e., /dev/console)
will now make that device a controlling terminal for the process.
Use the O_NOCTTY flag to open a terminal device
without changing your controlling terminal.
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr close 2 ,
.Xr dup 2 ,
.Xr getdtablesize 2 ,
.Xr lseek 2 ,
.Xr read 2 ,
.Xr umask 2 ,
.Xr write 2
.Sh HISTORY
An
.Fn open
function call appeared in 
.At v6 .
Commit	Line	Data
b0d623f7	1	.\"
6d2010ae	2	.\" Copyright (c) 2010 Apple Inc. All rights reserved.
b0d623f7 A	3	.\"
	4	.\" @APPLE_LICENSE_HEADER_START@
	5	.\"
	6	.\" This file contains Original Code and/or Modifications of Original Code
	7	.\" as defined in and that are subject to the Apple Public Source License
	8	.\" Version 2.0 (the 'License'). You may not use this file except in
	9	.\" compliance with the License. Please obtain a copy of the License at
	10	.\" http://www.opensource.apple.com/apsl/ and read it before using this
	11	.\" file.
	12	.\"
	13	.\" The Original Code and all software distributed under the License are
	14	.\" distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
	15	.\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
	16	.\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
	17	.\" FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
	18	.\" Please see the License for the specific language governing rights and
	19	.\" limitations under the License.
	20	.\"
	21	.\" @APPLE_LICENSE_HEADER_END@
	22	.\"
	23	.\"
9bccf70c A	24	.\" $NetBSD: open.2,v 1.8 1995/02/27 12:35:14 cgd Exp $
	25	.\"
	26	.\" Copyright (c) 1980, 1991, 1993
	27	.\" The Regents of the University of California. All rights reserved.
	28	.\"
	29	.\" Redistribution and use in source and binary forms, with or without
	30	.\" modification, are permitted provided that the following conditions
	31	.\" are met:
	32	.\" 1. Redistributions of source code must retain the above copyright
	33	.\" notice, this list of conditions and the following disclaimer.
	34	.\" 2. Redistributions in binary form must reproduce the above copyright
	35	.\" notice, this list of conditions and the following disclaimer in the
	36	.\" documentation and/or other materials provided with the distribution.
	37	.\" 3. All advertising materials mentioning features or use of this software
	38	.\" must display the following acknowledgement:
	39	.\" This product includes software developed by the University of
	40	.\" California, Berkeley and its contributors.
	41	.\" 4. Neither the name of the University nor the names of its contributors
	42	.\" may be used to endorse or promote products derived from this software
	43	.\" without specific prior written permission.
	44	.\"
	45	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	46	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	47	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	48	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	49	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	50	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	51	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	52	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	53	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	54	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	55	.\" SUCH DAMAGE.
	56	.\"
	57	.\" @(#)open.2 8.2 (Berkeley) 11/16/93
	58	.\"
6d2010ae	59	.Dd November 10, 2010
9bccf70c A	60	.Dt OPEN 2
	61	.Os BSD 4
	62	.Sh NAME
	63	.Nm open
	64	.Nd open or create a file for reading or writing
	65	.Sh SYNOPSIS
2d21ac55	66	.\" OH??? .Fd #include <sys/stat.h>
9bccf70c A	67	.Fd #include <fcntl.h>
9bccf70c A	68	.Ft int
2d21ac55 A	69	.Fo open
	70	.Fa "const char *path"
	71	.Fa "int oflag"
	72	.Fa "..."
	73	.Fc
9bccf70c A	74	.Sh DESCRIPTION
	75	The file name specified by
	76	.Fa path
	77	is opened
2d21ac55 A	78	for reading and/or writing,
	79	as specified by the argument
	80	.Fa oflag ;
	81	the file descriptor is returned to the calling process.
	82	.Pp
9bccf70c	83	The
2d21ac55 A	84	.Fa oflag
2d21ac55 A	85	argument may indicate that the file is to be
9bccf70c A	86	created if it does not exist (by specifying the
9bccf70c A	87	.Dv O_CREAT
2d21ac55 A	88	flag). In this case,
	89	.Nm
	90	requires a third argument
	91	.Fa "mode_t mode" ;
	92	the file is created with mode
9bccf70c A	93	.Fa mode
	94	as described in
	95	.Xr chmod 2
	96	and modified by the process' umask value (see
	97	.Xr umask 2 ) .
	98	.Pp
	99	The flags specified are formed by
	100	.Em or Ns 'ing
2d21ac55	101	the following values:
9bccf70c A	102	.Pp
	103	.Bd -literal -offset indent -compact
	104	O_RDONLY open for reading only
	105	O_WRONLY open for writing only
	106	O_RDWR open for reading and writing
	107	O_NONBLOCK do not block on open or for data to become available
	108	O_APPEND append on each write
	109	O_CREAT create file if it does not exist
	110	O_TRUNC truncate size to 0
2d21ac55	111	O_EXCL error if O_CREAT and the file exists
9bccf70c A	112	O_SHLOCK atomically obtain a shared lock
9bccf70c A	113	O_EXLOCK atomically obtain an exclusive lock
2d21ac55 A	114	O_NOFOLLOW do not follow symlinks
2d21ac55 A	115	O_SYMLINK allow open of symlinks
b0d623f7	116	O_EVTONLY descriptor requested for event notifications only
6d2010ae	117	O_CLOEXEC mark as close-on-exec
9bccf70c A	118	.Ed
	119	.Pp
	120	Opening a file with
	121	.Dv O_APPEND
2d21ac55	122	set causes each write on the file to be appended to the end. If
9bccf70c A	123	.Dv O_TRUNC
	124	is specified and the
	125	file exists, the file is truncated to zero length.
	126	If
	127	.Dv O_EXCL
	128	is set with
	129	.Dv O_CREAT
	130	and the file already
	131	exists,
	132	.Fn open
2d21ac55 A	133	returns an error.
2d21ac55 A	134	This may be used to implement a simple exclusive-access locking mechanism.
9bccf70c A	135	If
9bccf70c A	136	.Dv O_EXCL
6d2010ae A	137	is set with
	138	.Dv O_CREAT
	139	and the last component of the pathname is a symbolic link,
9bccf70c	140	.Fn open
2d21ac55 A	141	will fail even if the symbolic link points to a non-existent name.
2d21ac55 A	142	.Pp
9bccf70c A	143	If the
9bccf70c A	144	.Dv O_NONBLOCK
2d21ac55 A	145	flag is specified, do not wait for the device or file
2d21ac55 A	146	to be ready or available. If the
9bccf70c A	147	.Fn open
9bccf70c A	148	call would result
2d21ac55 A	149	in the process being blocked for some reason
2d21ac55 A	150	(e.g., waiting for carrier on a dialup line),
9bccf70c A	151	.Fn open
9bccf70c A	152	returns immediately.
2d21ac55 A	153	This flag also has the effect of making all subsequent I/O
2d21ac55 A	154	on the open file non-blocking.
9bccf70c A	155	.Pp
	156	When opening a file, a lock with
	157	.Xr flock 2
	158	semantics can be obtained by setting
	159	.Dv O_SHLOCK
	160	for a shared lock, or
	161	.Dv O_EXLOCK
	162	for an exclusive lock.
	163	If creating a file with
	164	.Dv O_CREAT ,
	165	the request for the lock will never fail
	166	(provided that the underlying filesystem supports locking).
	167	.Pp
2d21ac55 A	168	If
	169	.Dv O_NOFOLLOW
	170	is used in the mask and the target file passed to
	171	.Fn open
	172	is a symbolic link then the
	173	.Fn open
	174	will fail.
	175	.Pp
	176	If
	177	.Dv O_SYMLINK
	178	is used in the mask and the target file passed to
	179	.Fn open
	180	is a symbolic link then the
	181	.Fn open
	182	will be for the symbolic link itself, not what it links to.
	183	.Pp
b0d623f7 A	184	The
	185	.Dv O_EVTONLY
	186	flag is only intended for monitoring a file for changes (e.g. kqueue). Note: when
	187	this flag is used, the opened file will not prevent an unmount
	188	of the volume that contains the file.
	189	.Pp
6d2010ae A	190	The
	191	.Dv O_CLOEXEC
	192	flag causes the file descriptor to be marked as close-on-exec,
	193	setting the
	194	.Dv FD_CLOEXEC
	195	flag. The state of the file descriptor flags can be inspected
	196	using the F_GETFD fcntl. See
	197	.Xr fcntl 2 .
	198	.Pp
9bccf70c A	199	If successful,
	200	.Fn open
	201	returns a non-negative integer, termed a file descriptor.
	202	It returns -1 on failure.
2d21ac55 A	203	The file pointer (used to mark the current position within the file)
2d21ac55 A	204	is set to the beginning of the file.
9bccf70c	205	.Pp
2d21ac55 A	206	When a new file is created,
2d21ac55 A	207	it is given the group of the directory which contains it.
9bccf70c A	208	.Pp
	209	The new descriptor is set to remain open across
	210	.Xr execve
	211	system calls; see
	212	.Xr close 2
	213	and
	214	.Xr fcntl 2 .
	215	.Pp
	216	The system imposes a limit on the number of file descriptors
2d21ac55	217	that can be held open simultaneously by one process.
9bccf70c A	218	.Xr Getdtablesize 2
9bccf70c A	219	returns the current system limit.
2d21ac55 A	220	.Sh RETURN VALUES
	221	If successful,
	222	.Fn open
	223	returns a non-negative integer, termed a file descriptor.
	224	It returns -1 on failure, and sets
	225	.Va errno
	226	to indicate the error.
9bccf70c A	227	.Sh ERRORS
	228	The named file is opened unless:
	229	.Bl -tag -width Er
2d21ac55	230	.\" ===========
9bccf70c A	231	.It Bq Er EACCES
9bccf70c A	232	Search permission is denied for a component of the path prefix.
2d21ac55	233	.\" ===========
9bccf70c A	234	.It Bq Er EACCES
	235	The required permissions (for reading and/or writing)
	236	are denied for the given flags.
2d21ac55	237	.\" ===========
9bccf70c A	238	.It Bq Er EACCES
	239	.Dv O_CREAT
	240	is specified,
	241	the file does not exist,
	242	and the directory in which it is to be created
	243	does not permit writing.
2d21ac55 A	244	.\" ===========
	245	.It Bq Er EACCES
	246	.Dv O_TRUNC
	247	is specified and write permission is denied.
	248	.\" ===========
	249	.It Bq Er EAGAIN
	250	.Fa path
	251	specifies the slave side of a locked pseudo-terminal device.
	252	.\" ===========
	253	.It Bq Er EDQUOT
	254	.Dv O_CREAT
	255	is specified,
	256	the file does not exist,
	257	and the directory in which the entry for the new file
	258	is being placed cannot be extended because the
	259	user's quota of disk blocks on the file system
	260	containing the directory has been exhausted.
	261	.\" ===========
	262	.It Bq Er EDQUOT
	263	.Dv O_CREAT
	264	is specified,
	265	the file does not exist,
	266	and the user's quota of inodes on the file system
	267	on which the file is being created has been exhausted.
	268	.\" ===========
	269	.It Bq Er EEXIST
	270	.Dv O_CREAT
	271	and
	272	.Dv O_EXCL
	273	are specified and the file exists.
	274	.\" ===========
	275	.It Bq Er EFAULT
	276	.Fa Path
	277	points outside the process's allocated address space.
	278	.\" ===========
	279	.It Bq Er EINTR
	280	The
	281	.Fn open
	282	operation is interrupted by a signal.
	283	.\" ===========
	284	.It Bq Er EINVAL
	285	The value of
	286	.Fa oflag
	287	is not valid.
	288	.\" ===========
	289	.It Bq Er EIO
	290	An I/O error occurs while making the directory entry or
	291	allocating the inode for
	292	.Dv O_CREAT .
	293	.\" ===========
9bccf70c A	294	.It Bq Er EISDIR
9bccf70c A	295	The named file is a directory, and the arguments specify
2d21ac55 A	296	that it is to be opened for writing.
	297	.\" ===========
	298	.It Bq Er ELOOP
	299	Too many symbolic links are encountered in translating the pathname.
	300	This is taken to be indicative of a looping symbolic link.
	301	.\" ===========
9bccf70c A	302	.It Bq Er EMFILE
9bccf70c A	303	The process has already reached its limit for open file descriptors.
2d21ac55 A	304	.\" ===========
	305	.It Bq Er ENAMETOOLONG
	306	A component of a pathname exceeds
	307	.Dv {NAME_MAX}
	308	characters, or an entire path name exceeded
	309	.Dv {PATH_MAX}
	310	characters.
	311	.\" ===========
9bccf70c A	312	.It Bq Er ENFILE
9bccf70c A	313	The system file table is full.
2d21ac55 A	314	.\" ===========
	315	.It Bq Er ELOOP
	316	.Dv O_NOFOLLOW
	317	was specified and the target is a symbolic link.
	318	.\" ===========
	319	.It Bq Er ENOENT
	320	.Dv O_CREAT
	321	is not set and the named file does not exist.
	322	.\" ===========
	323	.It Bq Er ENOENT
	324	A component of the path name that must exist does not exist.
	325	.\" ===========
9bccf70c A	326	.It Bq Er ENOSPC
	327	.Dv O_CREAT
	328	is specified,
	329	the file does not exist,
	330	and the directory in which the entry for the new file is being placed
	331	cannot be extended because there is no space left on the file
	332	system containing the directory.
2d21ac55	333	.\" ===========
9bccf70c A	334	.It Bq Er ENOSPC
	335	.Dv O_CREAT
	336	is specified,
	337	the file does not exist,
	338	and there are no free inodes on the file system on which the
	339	file is being created.
2d21ac55 A	340	.\" ===========
	341	.It Bq Er ENOTDIR
	342	A component of the path prefix is not a directory.
	343	.\" ===========
	344	.It Bq Er ENXIO
	345	The named file is a character-special or block-special file
	346	and the device associated with this special file does not exist.
	347	.\" ===========
	348	.It Bq Er ENXIO
	349	O_NONBLOCK and O_WRONLY are set, the file is a FIFO,
	350	and no process has it open for reading.
	351	.\" ===========
	352	.It Bq Er EOPNOTSUPP
	353	.Dv O_SHLOCK
	354	or
	355	.Dv O_EXLOCK
	356	is specified, but the underlying filesystem does not support locking.
	357	.\" ===========
	358	.It Bq Er EOPNOTSUPP
	359	An attempt is made to open a socket (not currently implemented).
	360	.\" ===========
	361	.It Bq Er EOVERFLOW
	362	The named file is a regular file
	363	and its size does not fit in an object of type off_t.
	364	.\" ===========
	365	.It Bq Er EROFS
	366	The named file resides on a read-only file system,
	367	and the file is to be modified.
	368	.\" ===========
9bccf70c A	369	.It Bq Er ETXTBSY
	370	The file is a pure procedure (shared text) file that is being
	371	executed and the
	372	.Fn open
	373	call requests write access.
9bccf70c	374	.El
2d21ac55 A	375	.Sh COMPATIBILITY
	376	.Fn open
	377	on a terminal device (i.e., /dev/console)
	378	will now make that device a controlling terminal for the process.
	379	Use the O_NOCTTY flag to open a terminal device
	380	without changing your controlling terminal.
9bccf70c A	381	.Sh SEE ALSO
	382	.Xr chmod 2 ,
	383	.Xr close 2 ,
	384	.Xr dup 2 ,
	385	.Xr getdtablesize 2 ,
	386	.Xr lseek 2 ,
	387	.Xr read 2 ,
2d21ac55 A	388	.Xr umask 2 ,
2d21ac55 A	389	.Xr write 2
9bccf70c A	390	.Sh HISTORY
	391	An
	392	.Fn open
	393	function call appeared in
	394	.At v6 .