1 .\" Copyright (c) 1980, 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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.
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
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 $
34 .\" $DragonFly: src/lib/libc/sys/open.2,v 1.3 2005/07/29 23:16:04 hsu Exp $
41 .Nd open or create a file for reading or writing
47 .Fn open "const char *path" "int flags" "..."
49 .Fn openat "int fd" "const char *path" "int flags" "..."
51 The file name specified by
54 for reading and/or writing as specified by the
57 and the lowest unused file descriptor in the process' file descriptor table
61 argument may indicate the file is to be
62 created if it does not exist (by specifying the
69 require a third argument
71 and the file is created with mode
75 and modified by the process' umask value (see
80 function is equivalent to the
82 function except in the case where the
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
88 instead of the current working directory.
91 parameter and the optional fourth parameter correspond exactly to
96 is passed the special value
100 parameter, the current working directory is used
101 and the behavior is identical to a call to
104 The flags specified are formed by
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
122 O_DIRECTORY error if file is not a directory
127 set causes each write on the file
128 to be appended to the end.
132 file exists, the file is truncated to zero length.
142 implement a simple exclusive access locking mechanism.
145 is set and the last component of the pathname is
148 will fail even if the symbolic
149 link points to a non-existent name.
152 flag is specified and the
155 in the process being blocked for some reason (e.g., waiting for
156 carrier on a dialup line),
159 The first time the process attempts to perform I/O on the open
160 file it will block (not currently implemented).
164 is used in the mask, all writes will
165 immediately be written to disk,
166 the kernel will not cache written data
167 and all writes on the descriptor will not return until
168 the data to be written completes.
172 is used in the mask and the target file passed to
174 is a symbolic link then the
178 When opening a file, a lock with
180 semantics can be obtained by setting
182 for a shared lock, or
184 for an exclusive lock.
185 If creating a file with
187 the request for the lock will never fail
188 (provided that the underlying filesystem supports locking).
191 may be used to minimize or eliminate the cache effects of reading and writing.
192 The system will attempt to avoid caching the data you read or write.
193 If it cannot avoid caching the data,
194 it will minimize the impact the data has on the cache.
195 Use of this flag can drastically reduce performance if not used with care.
198 may be used to ensure the resulting file descriptor refers to a directory.
199 This flag can be used to prevent applications with elevated privileges
200 from opening files which are even unsafe to open with
202 such as device nodes.
208 return a non-negative integer, termed a file descriptor.
209 It returns -1 on failure.
210 The file pointer used to mark the current position within the
211 file is set to the beginning of the file.
213 When a new file is created it is given the group of the directory
216 The new descriptor is set to remain open across
223 The system imposes a limit on the number of file descriptors
224 open simultaneously by one process.
226 returns the current system limit.
232 return a non-negative integer, termed a file descriptor.
233 They return -1 on failure, and set
235 to indicate the error.
237 The named file is opened unless:
240 A component of the path prefix is not a directory or the
242 argument is not an absolute path and the
246 nor a file descriptor associated with a directory or
248 is specified and the file is not a directory.
249 .It Bq Er ENAMETOOLONG
250 A component of a pathname exceeded 255 characters,
251 or an entire path name exceeded 1023 characters.
254 is not set and the named file does not exist.
256 A component of the path name that must exist does not exist.
258 Search permission is denied for a component of the path prefix.
260 The required permissions (for reading and/or writing)
261 are denied for the given flags.
265 the file does not exist,
266 and the directory in which it is to be created
267 does not permit writing.
269 Too many symbolic links were encountered in translating the pathname.
271 The named file is a directory, and the arguments specify
272 it is to be opened for writing.
274 The named file resides on a read-only file system,
275 and the file is to be modified.
277 The process has already reached its limit for open file descriptors.
279 The system file table is full.
282 was specified and the target is a symbolic link.
284 The named file is a character special or block
285 special file, and the device associated with this special file
288 The named file is a fifo, no process has
289 it open for reading, and the arguments specify it is
290 to be opened for writing.
294 operation was interrupted by a signal.
299 is specified but the underlying filesystem does not support locking.
300 .It Bq Er EWOULDBLOCK
306 is specified and the file is locked.
310 the file does not exist,
311 and the directory in which the entry for the new file is being placed
312 cannot be extended because there is no space left on the file
313 system containing the directory.
317 the file does not exist,
318 and there are no free inodes on the file system on which the
319 file is being created.
323 the file does not exist,
324 and the directory in which the entry for the new file
325 is being placed cannot be extended because the
326 user's quota of disk blocks on the file system
327 containing the directory has been exhausted.
331 the file does not exist,
332 and the user's quota of inodes on the file system on
333 which the file is being created has been exhausted.
335 An I/O error occurred while making the directory entry or
336 allocating the inode for
339 The file is a pure procedure (shared text) file that is being
342 call requests write access.
345 points outside the process's allocated address space.
350 were specified and the file exists.
352 An attempt was made to open a socket (not currently implemented).
354 An attempt was made to open a descriptor with an illegal combination
365 .Xr getdtablesize 2 ,
373 function call appeared in
377 function call appeared first in Solaris and was ported to
380 The Open Group Extended API Set 2 specification requires that the test
383 searchability is based on whether it is open for searching,
384 and not whether the underlying directory currently permits searches.
385 The present implementation of
387 checks the current permissions of directory instead.