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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
126 set causes each write on the file
127 to be appended to the end.
131 file exists, the file is truncated to zero length.
141 implement a simple exclusive access locking mechanism.
144 is set and the last component of the pathname is
147 will fail even if the symbolic
148 link points to a non-existent name.
151 flag is specified and the
154 in the process being blocked for some reason (e.g., waiting for
155 carrier on a dialup line),
158 The first time the process attempts to perform I/O on the open
159 file it will block (not currently implemented).
163 is used in the mask, all writes will
164 immediately be written to disk,
165 the kernel will not cache written data
166 and all writes on the descriptor will not return until
167 the data to be written completes.
171 is used in the mask and the target file passed to
173 is a symbolic link then the
177 When opening a file, a lock with
179 semantics can be obtained by setting
181 for a shared lock, or
183 for an exclusive lock.
184 If creating a file with
186 the request for the lock will never fail
187 (provided that the underlying filesystem supports locking).
190 may be used to minimize or eliminate the cache effects of reading and writing.
191 The system will attempt to avoid caching the data you read or write.
192 If it cannot avoid caching the data,
193 it will minimize the impact the data has on the cache.
194 Use of this flag can drastically reduce performance if not used with care.
200 return a non-negative integer, termed a file descriptor.
201 It returns -1 on failure.
202 The file pointer used to mark the current position within the
203 file is set to the beginning of the file.
205 When a new file is created it is given the group of the directory
208 The new descriptor is set to remain open across
215 The system imposes a limit on the number of file descriptors
216 open simultaneously by one process.
218 returns the current system limit.
224 return a non-negative integer, termed a file descriptor.
225 They return -1 on failure, and set
227 to indicate the error.
229 The named file is opened unless:
232 A component of the path prefix is not a directory or the
234 argument is not an absolute path and the
238 nor a file descriptor associated with a directory.
239 .It Bq Er ENAMETOOLONG
240 A component of a pathname exceeded 255 characters,
241 or an entire path name exceeded 1023 characters.
244 is not set and the named file does not exist.
246 A component of the path name that must exist does not exist.
248 Search permission is denied for a component of the path prefix.
250 The required permissions (for reading and/or writing)
251 are denied for the given flags.
255 the file does not exist,
256 and the directory in which it is to be created
257 does not permit writing.
259 Too many symbolic links were encountered in translating the pathname.
261 The named file is a directory, and the arguments specify
262 it is to be opened for writing.
264 The named file resides on a read-only file system,
265 and the file is to be modified.
267 The process has already reached its limit for open file descriptors.
269 The system file table is full.
272 was specified and the target is a symbolic link.
274 The named file is a character special or block
275 special file, and the device associated with this special file
278 The named file is a fifo, no process has
279 it open for reading, and the arguments specify it is
280 to be opened for writing.
284 operation was interrupted by a signal.
289 is specified but the underlying filesystem does not support locking.
290 .It Bq Er EWOULDBLOCK
296 is specified and the file is locked.
300 the file does not exist,
301 and the directory in which the entry for the new file is being placed
302 cannot be extended because there is no space left on the file
303 system containing the directory.
307 the file does not exist,
308 and there are no free inodes on the file system on which the
309 file is being created.
313 the file does not exist,
314 and the directory in which the entry for the new file
315 is being placed cannot be extended because the
316 user's quota of disk blocks on the file system
317 containing the directory has been exhausted.
321 the file does not exist,
322 and the user's quota of inodes on the file system on
323 which the file is being created has been exhausted.
325 An I/O error occurred while making the directory entry or
326 allocating the inode for
329 The file is a pure procedure (shared text) file that is being
332 call requests write access.
335 points outside the process's allocated address space.
340 were specified and the file exists.
342 An attempt was made to open a socket (not currently implemented).
344 An attempt was made to open a descriptor with an illegal combination
355 .Xr getdtablesize 2 ,
363 function call appeared in
367 function call appeared first in Solaris and was ported to
370 The Open Group Extended API Set 2 specification requires that the test
373 searchability is based on whether it is open for searching,
374 and not whether the underlying directory currently permits searches.
375 The present implementation of
377 checks the current permissions of directory instead.