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28 .\" @(#)open.2 8.2 (Berkeley) 11/16/93
31 .Dd September 30, 2016
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
107 must be strictly relative to a file descriptor
110 .Pa sys/kern/vfs_lookup.c .
112 must not be an absolute path and must not contain ".." components.
113 Additionally, no symbolic link in
115 may contain ".." components either.
120 The flags specified are formed by
124 .Bd -literal -offset indent -compact
125 O_RDONLY open for reading only
126 O_WRONLY open for writing only
127 O_RDWR open for reading and writing
128 O_EXEC open for execute only
129 O_NONBLOCK do not block on open
130 O_APPEND append on each write
131 O_CREAT create file if it does not exist
132 O_TRUNC truncate size to 0
133 O_EXCL error if create and file exists
134 O_SHLOCK atomically obtain a shared lock
135 O_EXLOCK atomically obtain an exclusive lock
136 O_DIRECT eliminate or reduce cache effects
137 O_FSYNC synchronous writes
138 O_SYNC synchronous writes
139 O_NOFOLLOW do not follow symlinks
142 O_DIRECTORY error if file is not a directory
143 O_CLOEXEC set FD_CLOEXEC upon open
148 set causes each write on the file
149 to be appended to the end.
153 file exists, the file is truncated to zero length.
163 implement a simple exclusive access locking mechanism.
166 is set and the last component of the pathname is
169 will fail even if the symbolic
170 link points to a non-existent name.
173 flag is specified and the
175 system call would result
176 in the process being blocked for some reason (e.g., waiting for
177 carrier on a dialup line),
180 The descriptor remains in non-blocking mode for subsequent operations.
184 is used in the mask, all writes will
185 immediately be written to disk,
186 the kernel will not cache written data
187 and all writes on the descriptor will not return until
188 the data to be written completes.
198 is used in the mask and the target file passed to
200 is a symbolic link then the
204 When opening a file, a lock with
206 semantics can be obtained by setting
208 for a shared lock, or
210 for an exclusive lock.
211 If creating a file with
213 the request for the lock will never fail
214 (provided that the underlying file system supports locking).
217 may be used to minimize or eliminate the cache effects of reading and writing.
218 The system will attempt to avoid caching the data you read or write.
219 If it cannot avoid caching the data,
220 it will minimize the impact the data has on the cache.
221 Use of this flag can drastically reduce performance if not used with care.
224 may be used to ensure the OS does not assign this file as the
225 controlling terminal when it opens a tty device.
226 This is the default on
233 system call will not assign controlling terminals on
237 may be used to ensure the OS restores the terminal attributes when
238 initially opening a TTY.
239 This is the default on
246 on a TTY will always restore default terminal attributes on
250 may be used to ensure the resulting file descriptor refers to a
252 This flag can be used to prevent applications with elevated privileges
253 from opening files which are even unsafe to open with
255 such as device nodes.
260 flag for the newly returned file descriptor.
264 returns a non-negative integer, termed a file descriptor.
265 It returns \-1 on failure.
266 The file pointer used to mark the current position within the
267 file is set to the beginning of the file.
269 If a sleeping open of a device node from
271 is interrupted by a signal, the call always fails with
275 flag is set for the signal.
276 A sleeping open of a fifo (see
278 is restarted as normal.
280 When a new file is created it is given the group of the directory
286 the new descriptor is set to remain open across
295 The system imposes a limit on the number of file descriptors
296 open simultaneously by one process.
299 system call returns the current system limit.
305 return a non-negative integer, termed a file descriptor.
306 They return \-1 on failure, and set
308 to indicate the error.
310 The named file is opened unless:
313 A component of the path prefix is not a directory.
314 .It Bq Er ENAMETOOLONG
315 A component of a pathname exceeded 255 characters,
316 or an entire path name exceeded 1023 characters.
319 is not set and the named file does not exist.
321 A component of the path name that must exist does not exist.
323 Search permission is denied for a component of the path prefix.
325 The required permissions (for reading and/or writing)
326 are denied for the given flags.
329 is specified and write permission is denied.
333 the file does not exist,
334 and the directory in which it is to be created
335 does not permit writing.
338 is specified, the file does not exist, and the directory in which it is to be
339 created has its immutable flag set, see the
341 manual page for more information.
343 The named file has its immutable flag set and the file is to be modified.
345 The named file has its append-only flag set, the file is to be modified, and
351 Too many symbolic links were encountered in translating the pathname.
353 The named file is a directory, and the arguments specify
354 it is to be modified.
356 The named file resides on a read-only file system,
357 and the file is to be modified.
360 is specified and the named file would reside on a read-only file system.
362 The process has already reached its limit for open file descriptors.
364 The system file table is full.
367 was specified and the target is a symbolic link.
369 The named file is a character special or block
370 special file, and the device associated with this special file
374 is set, the named file is a fifo,
376 is set, and no process has the file open for reading.
380 operation was interrupted by a signal.
385 is specified but the underlying file system does not support locking.
387 The named file is a special file mounted through a file system that
388 does not support access to it (e.g.\& NFS).
389 .It Bq Er EWOULDBLOCK
395 is specified and the file is locked.
399 the file does not exist,
400 and the directory in which the entry for the new file is being placed
401 cannot be extended because there is no space left on the file
402 system containing the directory.
406 the file does not exist,
407 and there are no free inodes on the file system on which the
408 file is being created.
412 the file does not exist,
413 and the directory in which the entry for the new file
414 is being placed cannot be extended because the
415 user's quota of disk blocks on the file system
416 containing the directory has been exhausted.
420 the file does not exist,
421 and the user's quota of inodes on the file system on
422 which the file is being created has been exhausted.
424 An I/O error occurred while making the directory entry or
425 allocating the inode for
428 The file is a pure procedure (shared text) file that is being
431 system call requests write access.
436 points outside the process's allocated address space.
441 were specified and the file exists.
443 An attempt was made to open a socket (not currently implemented).
445 An attempt was made to open a descriptor with an illegal combination
455 argument does not specify an absolute path and the
460 nor a valid file descriptor open for searching.
464 argument is not an absolute path and
468 nor a file descriptor associated with a directory.
471 is specified and the file is not a directory.
474 is specified and the process is in capability mode.
477 was called and the process is in capability mode.
478 .It Bq Er ENOTCAPABLE
480 is an absolute path or contained "..".
489 .Xr getdtablesize 2 ,
504 function was introduced in
507 The Open Group Extended API Set 2 specification requires that the test
510 is searchable is based on whether
512 is open for searching, not whether the underlying directory currently
514 The present implementation of the
516 checks the current permissions of directory instead.