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28 .\" @(#)open.2 8.2 (Berkeley) 11/16/93
36 .Nd open or create a file for reading, writing or executing
42 .Fn open "const char *path" "int flags" "..."
44 .Fn openat "int fd" "const char *path" "int flags" "..."
46 The file name specified by
49 for either execution or reading and/or writing as specified by the
52 and the file descriptor returned to the calling process.
55 argument may indicate the file is to be
56 created if it does not exist (by specifying the
63 require an additional argument
65 and the file is created with mode
69 and modified by the process' umask value (see
74 function is equivalent to the
76 function except in the case where the
78 specifies a relative path.
79 In this case the file to be opened is determined relative to the directory
80 associated with the file descriptor
82 instead of the current working directory.
85 parameter and the optional fourth parameter correspond exactly to
90 is passed the special value
94 parameter, the current working directory is used
95 and the behavior is identical to a call to
98 The flags specified are formed by
102 .Bd -literal -offset indent -compact
103 O_RDONLY open for reading only
104 O_WRONLY open for writing only
105 O_RDWR open for reading and writing
106 O_EXEC open for execute only
107 O_NONBLOCK do not block on open
108 O_APPEND append on each write
109 O_CREAT create file if it does not exist
110 O_TRUNC truncate size to 0
111 O_EXCL error if create and file exists
112 O_SHLOCK atomically obtain a shared lock
113 O_EXLOCK atomically obtain an exclusive lock
114 O_DIRECT eliminate or reduce cache effects
115 O_FSYNC synchronous writes
116 O_SYNC synchronous writes
117 O_NOFOLLOW do not follow symlinks
118 O_NOCTTY don't assign controlling terminal
119 O_TTY_INIT restore default terminal attributes
120 O_DIRECTORY error if file is not a directory
121 O_CLOEXEC set FD_CLOEXEC upon open
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
153 system call would result
154 in the process being blocked for some reason (e.g., waiting for
155 carrier on a dialup line),
158 The descriptor remains in non-blocking mode for subsequent operations.
162 is used in the mask, all writes will
163 immediately be written to disk,
164 the kernel will not cache written data
165 and all writes on the descriptor will not return until
166 the data to be written completes.
176 is used in the mask and the target file passed to
178 is a symbolic link then the
182 When opening a file, a lock with
184 semantics can be obtained by setting
186 for a shared lock, or
188 for an exclusive lock.
189 If creating a file with
191 the request for the lock will never fail
192 (provided that the underlying file system supports locking).
195 may be used to minimize or eliminate the cache effects of reading and writing.
196 The system will attempt to avoid caching the data you read or write.
197 If it cannot avoid caching the data,
198 it will minimize the impact the data has on the cache.
199 Use of this flag can drastically reduce performance if not used with care.
202 may be used to ensure the OS does not assign this file as the
203 controlling terminal when it opens a tty device.
204 This is the default on
211 system call will not assign controlling terminals on
215 may be used to ensure the OS restores the terminal attributes when
216 initially opening a TTY.
217 This is the default on
224 on a TTY will always restore default terminal attributes on
228 may be used to ensure the resulting file descriptor refers to a
230 This flag can be used to prevent applications with elevated privileges
231 from opening files which are even unsafe to open with
233 such as device nodes.
238 flag for the newly returned file descriptor.
242 returns a non-negative integer, termed a file descriptor.
243 It returns \-1 on failure.
244 The file pointer used to mark the current position within the
245 file is set to the beginning of the file.
247 When a new file is created it is given the group of the directory
253 the new descriptor is set to remain open across
262 The system imposes a limit on the number of file descriptors
263 open simultaneously by one process.
266 system call returns the current system limit.
272 return a non-negative integer, termed a file descriptor.
273 They return \-1 on failure, and set
275 to indicate the error.
277 The named file is opened unless:
280 A component of the path prefix is not a directory.
281 .It Bq Er ENAMETOOLONG
282 A component of a pathname exceeded 255 characters,
283 or an entire path name exceeded 1023 characters.
286 is not set and the named file does not exist.
288 A component of the path name that must exist does not exist.
290 Search permission is denied for a component of the path prefix.
292 The required permissions (for reading and/or writing)
293 are denied for the given flags.
296 is specified and write permission is denied.
300 the file does not exist,
301 and the directory in which it is to be created
302 does not permit writing.
305 is specified, the file does not exist, and the directory in which it is to be
306 created has its immutable flag set, see the
308 manual page for more information.
310 The named file has its immutable flag set and the file is to be modified.
312 The named file has its append-only flag set, the file is to be modified, and
318 Too many symbolic links were encountered in translating the pathname.
320 The named file is a directory, and the arguments specify
321 it is to be modified.
323 The named file resides on a read-only file system,
324 and the file is to be modified.
327 is specified and the named file would reside on a read-only file system.
329 The process has already reached its limit for open file descriptors.
331 The system file table is full.
334 was specified and the target is a symbolic link.
336 The named file is a character special or block
337 special file, and the device associated with this special file
341 is set, the named file is a fifo,
343 is set, and no process has the file open for reading.
347 operation was interrupted by a signal.
352 is specified but the underlying file system does not support locking.
354 The named file is a special file mounted through a file system that
355 does not support access to it (e.g.\& NFS).
356 .It Bq Er EWOULDBLOCK
362 is specified and the file is locked.
366 the file does not exist,
367 and the directory in which the entry for the new file is being placed
368 cannot be extended because there is no space left on the file
369 system containing the directory.
373 the file does not exist,
374 and there are no free inodes on the file system on which the
375 file is being created.
379 the file does not exist,
380 and the directory in which the entry for the new file
381 is being placed cannot be extended because the
382 user's quota of disk blocks on the file system
383 containing the directory has been exhausted.
387 the file does not exist,
388 and the user's quota of inodes on the file system on
389 which the file is being created has been exhausted.
391 An I/O error occurred while making the directory entry or
392 allocating the inode for
395 The file is a pure procedure (shared text) file that is being
398 system call requests write access.
403 points outside the process's allocated address space.
408 were specified and the file exists.
410 An attempt was made to open a socket (not currently implemented).
412 An attempt was made to open a descriptor with an illegal combination
422 argument does not specify an absolute path and the
427 nor a valid file descriptor open for searching.
431 argument is not an absolute path and
435 nor a file descriptor associated with a directory.
438 is specified and the file is not a directory.
446 .Xr getdtablesize 2 ,
461 function was introduced in
464 The Open Group Extended API Set 2 specification requires that the test
467 is searchable is based on whether
469 is open for searching, not whether the underlying directory currently
471 The present implementation of the
473 checks the current permissions of directory instead.