[dragonfly.git] / lib / libc / sys / open.2

.\" 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
.\" $FreeBSD: src/lib/libc/sys/open.2,v 1.11.2.9 2001/12/14 18:34:01 ru Exp $
.\" $DragonFly: src/lib/libc/sys/open.2,v 1.3 2005/07/29 23:16:04 hsu Exp $
.\"
.Dd July 31, 2012
.Dt OPEN 2
.Os
.Sh NAME
.Nm open , openat
.Nd open or create a file for reading or writing
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In fcntl.h
.Ft int
.Fn open "const char *path" "int flags" "..."
.Ft int
.Fn openat "int fd" "const char *path" "int flags" "..."
.Sh DESCRIPTION
The file name specified by
.Fa path
is opened
for reading and/or writing as specified by the
argument
.Fa flags
and the lowest unused file descriptor in the process' file descriptor table
is returned.
The
.Fa flags
argument may indicate the file is to be
created if it does not exist (by specifying the
.Dv O_CREAT
flag).
In this case
.Fn open
and
.Fn openat
require a third argument
.Fa "mode_t mode" ,
and 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
.Fn openat
function is equivalent to the
.Fn open
function except in the case where the
.Fa path
specifies a relative path.
In this case the file to be opened is determined relative to the directory
associated with the file descriptor
.Fa fd
instead of the current working directory.
The
.Fa flag
parameter and the optional fourth parameter correspond exactly to
the parameters of
.Fn open .
If
.Fn openat
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 open .
.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
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 create and file exists
O_SHLOCK	atomically obtain a shared lock
O_EXLOCK	atomically obtain an exclusive lock
O_DIRECT	eliminate or reduce cache effects
O_FSYNC		synchronous writes
O_NOFOLLOW	do not follow symlinks
O_DIRECTORY	error if file is not a directory
O_CLOEXEC	set FD_CLOEXEC upon open
.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 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.
If the
.Dv O_NONBLOCK
flag is specified and 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.
The first time the process attempts to perform I/O on the open
file it will block (not currently implemented).
.Pp
If
.Dv O_FSYNC
is used in the mask, all writes will
immediately be written to disk,
the kernel will not cache written data
and all writes on the descriptor will not return until
the data to be written completes.
.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
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
.Dv O_DIRECT
may be used to minimize or eliminate the cache effects of reading and writing.
The system will attempt to avoid caching the data you read or write.
If it cannot avoid caching the data,
it will minimize the impact the data has on the cache.
Use of this flag can drastically reduce performance if not used with care.
.Pp
.Dv O_DIRECTORY
may be used to ensure the resulting file descriptor refers to a directory.
This flag can be used to prevent applications with elevated privileges
from opening files which are even unsafe to open with
.Dv O_RDONLY ,
such as device nodes.
.Pp
.Dv O_CLOEXEC
may be used to atomically set the
.Dv FD_CLOEXEC
flag for the newly returned file descriptor.
.Pp
If successful,
.Fn open
and
.Fn openat
return 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
Unless
.Dv O_CLOEXEC
was specified, the new descriptor is set to remain open across
.Xr execve 2
system calls; see
.Xr close 2 ,
.Xr fcntl 2
and
.Dv O_CLOEXEC
description.
.Pp
The system imposes a limit on the number of file descriptors
open simultaneously by one process.
.Xr Getdtablesize 2
returns the current system limit.
.Sh RETURN VALUES
If successful,
.Fn open
and
.Fn openat
return a non-negative integer, termed a file descriptor.
They return -1 on failure, and set
.Va errno
to indicate the error.
.Sh ERRORS
The named file is opened unless:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory or the
.Fa path
argument is not an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory or
.Dv O_DIRECTORY
is specified and the file is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.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 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 ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EISDIR
The named file is a directory, and the arguments specify
it is to be opened for writing.
.It Bq Er EROFS
The named file resides on a read-only file system,
and the file is to be modified.
.It Bq Er EMFILE
The process has already reached its limit for open file descriptors.
.It Bq Er ENFILE
The system file table is full.
.It Bq Er EMLINK
.Dv O_NOFOLLOW
was specified and the target is a symbolic link.
.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
The named file is a fifo, no process has
it open for reading, and the arguments specify it is
to be opened for writing.
.It Bq Er EINTR
The
.Fn open
operation was interrupted by a signal.
.It Bq Er EOPNOTSUPP
.Dv O_SHLOCK
or
.Dv O_EXLOCK
is specified but the underlying filesystem does not support locking.
.It Bq Er EWOULDBLOCK
.Dv O_NONBLOCK
and one of
.Dv O_SHLOCK
or
.Dv O_EXLOCK
is specified and the file is locked.
.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 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 EIO
An I/O error occurred while making the directory entry or
allocating the inode for
.Dv O_CREAT .
.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.
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.It Bq Er EEXIST
.Dv O_CREAT
and
.Dv O_EXCL
were specified and the file exists.
.It Bq Er EOPNOTSUPP
An attempt was made to open a socket (not currently implemented).
.It Bq Er EINVAL
An attempt was made to open a descriptor with an illegal combination
of
.Dv O_RDONLY ,
.Dv O_WRONLY ,
and
.Dv O_RDWR .
.El
.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 .
An
.Fn openat
function call appeared first in Solaris and was ported to
.Dx 2.3 .
.Sh BUGS
The Open Group Extended API Set 2 specification requires that the test
for
.Fa fd Ap s
searchability is based on whether it is open for searching,
and not whether the underlying directory currently permits searches.
The present implementation of
.Fn openat
checks the current permissions of directory instead.
Commit	Line	Data
984263bc MD	1	.\" Copyright (c) 1980, 1991, 1993
	2	.\" The Regents of the University of California. 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	.\" @(#)open.2 8.2 (Berkeley) 11/16/93
	33	.\" $FreeBSD: src/lib/libc/sys/open.2,v 1.11.2.9 2001/12/14 18:34:01 ru Exp $
3a0c0554	34	.\" $DragonFly: src/lib/libc/sys/open.2,v 1.3 2005/07/29 23:16:04 hsu Exp $
984263bc	35	.\"
f3b0543f	36	.Dd July 31, 2012
984263bc MD	37	.Dt OPEN 2
	38	.Os
	39	.Sh NAME
95c2ffe9	40	.Nm open , openat
984263bc MD	41	.Nd open or create a file for reading or writing
	42	.Sh LIBRARY
	43	.Lb libc
	44	.Sh SYNOPSIS
	45	.In fcntl.h
	46	.Ft int
	47	.Fn open "const char *path" "int flags" "..."
95c2ffe9 NT	48	.Ft int
95c2ffe9 NT	49	.Fn openat "int fd" "const char *path" "int flags" "..."
984263bc MD	50	.Sh DESCRIPTION
	51	The file name specified by
	52	.Fa path
	53	is opened
	54	for reading and/or writing as specified by the
	55	argument
	56	.Fa flags
3a0c0554 JH	57	and the lowest unused file descriptor in the process' file descriptor table
3a0c0554 JH	58	is returned.
984263bc MD	59	The
	60	.Fa flags
	61	argument may indicate the file is to be
	62	created if it does not exist (by specifying the
	63	.Dv O_CREAT
	64	flag).
	65	In this case
95c2ffe9 NT	66	.Fn open
	67	and
	68	.Fn openat
	69	require a third argument
984263bc MD	70	.Fa "mode_t mode" ,
	71	and the file is created with mode
	72	.Fa mode
	73	as described in
	74	.Xr chmod 2
	75	and modified by the process' umask value (see
	76	.Xr umask 2 ) .
	77	.Pp
95c2ffe9 NT	78	The
	79	.Fn openat
	80	function is equivalent to the
	81	.Fn open
	82	function except in the case where the
	83	.Fa path
	84	specifies a relative path.
	85	In this case the file to be opened is determined relative to the directory
	86	associated with the file descriptor
	87	.Fa fd
	88	instead of the current working directory.
	89	The
	90	.Fa flag
	91	parameter and the optional fourth parameter correspond exactly to
	92	the parameters of
	93	.Fn open .
	94	If
	95	.Fn openat
	96	is passed the special value
	97	.Dv AT_FDCWD
	98	in the
	99	.Fa fd
	100	parameter, the current working directory is used
	101	and the behavior is identical to a call to
	102	.Fn open .
	103	.Pp
984263bc MD	104	The flags specified are formed by
	105	.Em or Ns 'ing
	106	the following values
	107	.Pp
	108	.Bd -literal -offset indent -compact
	109	O_RDONLY open for reading only
	110	O_WRONLY open for writing only
	111	O_RDWR open for reading and writing
	112	O_NONBLOCK do not block on open
	113	O_APPEND append on each write
	114	O_CREAT create file if it does not exist
	115	O_TRUNC truncate size to 0
	116	O_EXCL error if create and file exists
	117	O_SHLOCK atomically obtain a shared lock
	118	O_EXLOCK atomically obtain an exclusive lock
	119	O_DIRECT eliminate or reduce cache effects
	120	O_FSYNC synchronous writes
	121	O_NOFOLLOW do not follow symlinks
f3b0543f	122	O_DIRECTORY error if file is not a directory
6e4ea98e	123	O_CLOEXEC set FD_CLOEXEC upon open
984263bc MD	124	.Ed
	125	.Pp
	126	Opening a file with
	127	.Dv O_APPEND
	128	set causes each write on the file
	129	to be appended to the end.
	130	If
	131	.Dv O_TRUNC
	132	is specified and the
	133	file exists, the file is truncated to zero length.
	134	If
	135	.Dv O_EXCL
	136	is set with
	137	.Dv O_CREAT
	138	and the file already
	139	exists,
	140	.Fn open
	141	returns an error.
	142	This may be used to
	143	implement a simple exclusive access locking mechanism.
	144	If
	145	.Dv O_EXCL
	146	is set and the last component of the pathname is
	147	a symbolic link,
	148	.Fn open
	149	will fail even if the symbolic
	150	link points to a non-existent name.
	151	If the
	152	.Dv O_NONBLOCK
	153	flag is specified and the
	154	.Fn open
	155	call would result
	156	in the process being blocked for some reason (e.g., waiting for
	157	carrier on a dialup line),
	158	.Fn open
	159	returns immediately.
	160	The first time the process attempts to perform I/O on the open
	161	file it will block (not currently implemented).
	162	.Pp
	163	If
	164	.Dv O_FSYNC
	165	is used in the mask, all writes will
	166	immediately be written to disk,
	167	the kernel will not cache written data
	168	and all writes on the descriptor will not return until
	169	the data to be written completes.
	170	.Pp
	171	If
	172	.Dv O_NOFOLLOW
	173	is used in the mask and the target file passed to
	174	.Fn open
	175	is a symbolic link then the
	176	.Fn open
	177	will fail.
	178	.Pp
	179	When opening a file, a lock with
	180	.Xr flock 2
	181	semantics can be obtained by setting
	182	.Dv O_SHLOCK
	183	for a shared lock, or
	184	.Dv O_EXLOCK
	185	for an exclusive lock.
	186	If creating a file with
	187	.Dv O_CREAT ,
188	the request for the lock will never fail
189	(provided that the underlying filesystem supports locking).
190	.Pp
191	.Dv O_DIRECT
192	may be used to minimize or eliminate the cache effects of reading and writing.
193	The system will attempt to avoid caching the data you read or write.
194	If it cannot avoid caching the data,
195	it will minimize the impact the data has on the cache.
196	Use of this flag can drastically reduce performance if not used with care.
197	.Pp
f3b0543f AH	198	.Dv O_DIRECTORY
	199	may be used to ensure the resulting file descriptor refers to a directory.
	200	This flag can be used to prevent applications with elevated privileges
	201	from opening files which are even unsafe to open with
	202	.Dv O_RDONLY ,
	203	such as device nodes.
	204	.Pp
6e4ea98e FT	205	.Dv O_CLOEXEC
	206	may be used to atomically set the
	207	.Dv FD_CLOEXEC
	208	flag for the newly returned file descriptor.
	209	.Pp
984263bc MD	210	If successful,
984263bc MD	211	.Fn open
95c2ffe9 NT	212	and
	213	.Fn openat
	214	return a non-negative integer, termed a file descriptor.
984263bc MD	215	It returns -1 on failure.
	216	The file pointer used to mark the current position within the
	217	file is set to the beginning of the file.
	218	.Pp
	219	When a new file is created it is given the group of the directory
	220	which contains it.
	221	.Pp
6e4ea98e	222	Unless
d0217aec SW	223	.Dv O_CLOEXEC
d0217aec SW	224	was specified, the new descriptor is set to remain open across
984263bc MD	225	.Xr execve 2
984263bc MD	226	system calls; see
6e4ea98e FT	227	.Xr close 2 ,
6e4ea98e FT	228	.Xr fcntl 2
984263bc	229	and
6e4ea98e FT	230	.Dv O_CLOEXEC
6e4ea98e FT	231	description.
984263bc MD	232	.Pp
	233	The system imposes a limit on the number of file descriptors
	234	open simultaneously by one process.
	235	.Xr Getdtablesize 2
	236	returns the current system limit.
	237	.Sh RETURN VALUES
	238	If successful,
	239	.Fn open
95c2ffe9 NT	240	and
	241	.Fn openat
	242	return a non-negative integer, termed a file descriptor.
	243	They return -1 on failure, and set
984263bc MD	244	.Va errno
	245	to indicate the error.
	246	.Sh ERRORS
	247	The named file is opened unless:
	248	.Bl -tag -width Er
	249	.It Bq Er ENOTDIR
95c2ffe9 NT	250	A component of the path prefix is not a directory or the
	251	.Fa path
	252	argument is not an absolute path and the
	253	.Fa fd
5212f0c1	254	argument is neither
95c2ffe9	255	.Dv AT_FDCWD
f3b0543f AH	256	nor a file descriptor associated with a directory or
	257	.Dv O_DIRECTORY
	258	is specified and the file is not a directory.
984263bc MD	259	.It Bq Er ENAMETOOLONG
	260	A component of a pathname exceeded 255 characters,
	261	or an entire path name exceeded 1023 characters.
	262	.It Bq Er ENOENT
	263	.Dv O_CREAT
	264	is not set and the named file does not exist.
	265	.It Bq Er ENOENT
	266	A component of the path name that must exist does not exist.
	267	.It Bq Er EACCES
	268	Search permission is denied for a component of the path prefix.
	269	.It Bq Er EACCES
	270	The required permissions (for reading and/or writing)
	271	are denied for the given flags.
	272	.It Bq Er EACCES
	273	.Dv O_CREAT
	274	is specified,
	275	the file does not exist,
	276	and the directory in which it is to be created
	277	does not permit writing.
	278	.It Bq Er ELOOP
	279	Too many symbolic links were encountered in translating the pathname.
	280	.It Bq Er EISDIR
	281	The named file is a directory, and the arguments specify
	282	it is to be opened for writing.
	283	.It Bq Er EROFS
	284	The named file resides on a read-only file system,
	285	and the file is to be modified.
	286	.It Bq Er EMFILE
	287	The process has already reached its limit for open file descriptors.
	288	.It Bq Er ENFILE
	289	The system file table is full.
	290	.It Bq Er EMLINK
	291	.Dv O_NOFOLLOW
	292	was specified and the target is a symbolic link.
	293	.It Bq Er ENXIO
	294	The named file is a character special or block
	295	special file, and the device associated with this special file
	296	does not exist.
	297	.It Bq Er ENXIO
	298	The named file is a fifo, no process has
	299	it open for reading, and the arguments specify it is
	300	to be opened for writing.
	301	.It Bq Er EINTR
	302	The
	303	.Fn open
	304	operation was interrupted by a signal.
	305	.It Bq Er EOPNOTSUPP
	306	.Dv O_SHLOCK
	307	or
	308	.Dv O_EXLOCK
	309	is specified but the underlying filesystem does not support locking.
	310	.It Bq Er EWOULDBLOCK
	311	.Dv O_NONBLOCK
	312	and one of
	313	.Dv O_SHLOCK
	314	or
	315	.Dv O_EXLOCK
	316	is specified and the file is locked.
	317	.It Bq Er ENOSPC
	318	.Dv O_CREAT
	319	is specified,
	320	the file does not exist,
	321	and the directory in which the entry for the new file is being placed
	322	cannot be extended because there is no space left on the file
323	system containing the directory.
324	.It Bq Er ENOSPC
325	.Dv O_CREAT
326	is specified,
327	the file does not exist,
328	and there are no free inodes on the file system on which the
329	file is being created.
330	.It Bq Er EDQUOT
331	.Dv O_CREAT
332	is specified,
333	the file does not exist,
334	and the directory in which the entry for the new file
335	is being placed cannot be extended because the
336	user's quota of disk blocks on the file system
337	containing the directory has been exhausted.
338	.It Bq Er EDQUOT
339	.Dv O_CREAT
340	is specified,
341	the file does not exist,
342	and the user's quota of inodes on the file system on
343	which the file is being created has been exhausted.
344	.It Bq Er EIO
345	An I/O error occurred while making the directory entry or
346	allocating the inode for
347	.Dv O_CREAT .
348	.It Bq Er ETXTBSY
349	The file is a pure procedure (shared text) file that is being
350	executed and the
351	.Fn open
352	call requests write access.
353	.It Bq Er EFAULT
354	.Fa Path
355	points outside the process's allocated address space.
356	.It Bq Er EEXIST
357	.Dv O_CREAT
358	and
359	.Dv O_EXCL
360	were specified and the file exists.
361	.It Bq Er EOPNOTSUPP
362	An attempt was made to open a socket (not currently implemented).
363	.It Bq Er EINVAL
364	An attempt was made to open a descriptor with an illegal combination
365	of
366	.Dv O_RDONLY ,
367	.Dv O_WRONLY ,
368	and
369	.Dv O_RDWR .
370	.El
371	.Sh SEE ALSO
372	.Xr chmod 2 ,
373	.Xr close 2 ,
374	.Xr dup 2 ,
375	.Xr getdtablesize 2 ,
376	.Xr lseek 2 ,
377	.Xr read 2 ,
378	.Xr umask 2 ,
379	.Xr write 2
380	.Sh HISTORY
381	An
382	.Fn open
383	function call appeared in
384	.At v6 .
95c2ffe9 NT	385	An
95c2ffe9 NT	386	.Fn openat
1badc694	387	function call appeared first in Solaris and was ported to
95c2ffe9 NT	388	.Dx 2.3 .
	389	.Sh BUGS
	390	The Open Group Extended API Set 2 specification requires that the test
5212f0c1 SW	391	for
	392	.Fa fd Ap s
	393	searchability is based on whether it is open for searching,
	394	and not whether the underlying directory currently permits searches.
	395	The present implementation of
	396	.Fn openat
95c2ffe9	397	checks the current permissions of directory instead.