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28 .\" @(#)open.2 8.2 (Berkeley) 11/16/93
31 .Dd September 15, 2017
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
144 O_VERIFY verify the contents of the file
149 set causes each write on the file
150 to be appended to the end.
154 file exists, the file is truncated to zero length.
164 implement a simple exclusive access locking mechanism.
167 is set and the last component of the pathname is
170 will fail even if the symbolic
171 link points to a non-existent name.
174 flag is specified and the
176 system call would result
177 in the process being blocked for some reason (e.g., waiting for
178 carrier on a dialup line),
181 The descriptor remains in non-blocking mode for subsequent operations.
185 is used in the mask, all writes will
186 immediately be written to disk,
187 the kernel will not cache written data
188 and all writes on the descriptor will not return until
189 the data to be written completes.
199 is used in the mask and the target file passed to
201 is a symbolic link then the
205 When opening a file, a lock with
207 semantics can be obtained by setting
209 for a shared lock, or
211 for an exclusive lock.
212 If creating a file with
214 the request for the lock will never fail
215 (provided that the underlying file system supports locking).
218 may be used to minimize or eliminate the cache effects of reading and writing.
219 The system will attempt to avoid caching the data you read or write.
220 If it cannot avoid caching the data,
221 it will minimize the impact the data has on the cache.
222 Use of this flag can drastically reduce performance if not used with care.
225 may be used to ensure the OS does not assign this file as the
226 controlling terminal when it opens a tty device.
227 This is the default on
234 system call will not assign controlling terminals on
238 may be used to ensure the OS restores the terminal attributes when
239 initially opening a TTY.
240 This is the default on
247 on a TTY will always restore default terminal attributes on
251 may be used to ensure the resulting file descriptor refers to a
253 This flag can be used to prevent applications with elevated privileges
254 from opening files which are even unsafe to open with
256 such as device nodes.
261 flag for the newly returned file descriptor.
264 may be used to indicate to the kernel that the contents of the file should
265 be verified before allowing the open to proceed.
268 means is implementation specific.
269 The run-time linker (rtld) uses this flag to ensure shared objects have
270 been verified before operating on them.
274 returns a non-negative integer, termed a file descriptor.
275 It returns \-1 on failure.
276 The file pointer used to mark the current position within the
277 file is set to the beginning of the file.
279 If a sleeping open of a device node from
281 is interrupted by a signal, the call always fails with
285 flag is set for the signal.
286 A sleeping open of a fifo (see
288 is restarted as normal.
290 When a new file is created it is given the group of the directory
296 the new descriptor is set to remain open across
305 The system imposes a limit on the number of file descriptors
306 open simultaneously by one process.
309 system call returns the current system limit.
315 return a non-negative integer, termed a file descriptor.
316 They return \-1 on failure, and set
318 to indicate the error.
320 The named file is opened unless:
323 A component of the path prefix is not a directory.
324 .It Bq Er ENAMETOOLONG
325 A component of a pathname exceeded 255 characters,
326 or an entire path name exceeded 1023 characters.
329 is not set and the named file does not exist.
331 A component of the path name that must exist does not exist.
333 Search permission is denied for a component of the path prefix.
335 The required permissions (for reading and/or writing)
336 are denied for the given flags.
339 is specified and write permission is denied.
343 the file does not exist,
344 and the directory in which it is to be created
345 does not permit writing.
348 is specified, the file does not exist, and the directory in which it is to be
349 created has its immutable flag set, see the
351 manual page for more information.
353 The named file has its immutable flag set and the file is to be modified.
355 The named file has its append-only flag set, the file is to be modified, and
361 Too many symbolic links were encountered in translating the pathname.
363 The named file is a directory, and the arguments specify
364 it is to be modified.
366 The named file resides on a read-only file system,
367 and the file is to be modified.
370 is specified and the named file would reside on a read-only file system.
372 The process has already reached its limit for open file descriptors.
374 The system file table is full.
377 was specified and the target is a symbolic link.
379 The named file is a character special or block
380 special file, and the device associated with this special file
384 is set, the named file is a fifo,
386 is set, and no process has the file open for reading.
390 operation was interrupted by a signal.
395 is specified but the underlying file system does not support locking.
397 The named file is a special file mounted through a file system that
398 does not support access to it (e.g.\& NFS).
399 .It Bq Er EWOULDBLOCK
405 is specified and the file is locked.
409 the file does not exist,
410 and the directory in which the entry for the new file is being placed
411 cannot be extended because there is no space left on the file
412 system containing the directory.
416 the file does not exist,
417 and there are no free inodes on the file system on which the
418 file is being created.
422 the file does not exist,
423 and the directory in which the entry for the new file
424 is being placed cannot be extended because the
425 user's quota of disk blocks on the file system
426 containing the directory has been exhausted.
430 the file does not exist,
431 and the user's quota of inodes on the file system on
432 which the file is being created has been exhausted.
434 An I/O error occurred while making the directory entry or
435 allocating the inode for
438 The file is a pure procedure (shared text) file that is being
441 system call requests write access.
446 points outside the process's allocated address space.
451 were specified and the file exists.
453 An attempt was made to open a socket (not currently implemented).
455 An attempt was made to open a descriptor with an illegal combination
465 argument does not specify an absolute path and the
470 nor a valid file descriptor open for searching.
474 argument is not an absolute path and
478 nor a file descriptor associated with a directory.
481 is specified and the file is not a directory.
484 is specified and the process is in capability mode.
487 was called and the process is in capability mode.
488 .It Bq Er ENOTCAPABLE
490 is an absolute path or contained a ".." component leading to a
491 directory outside of the directory hierarchy specified by
500 .Xr getdtablesize 2 ,
510 These functions are specified by
516 .Er EMLINK instead of
522 is set in flags and the final component of pathname is a symbolic link
523 to distinguish it from the case of too many symbolic link traversals
524 in one of its non-final components.
532 function was introduced in
535 The Open Group Extended API Set 2 specification requires that the test
538 is searchable is based on whether
540 is open for searching, not whether the underlying directory currently
542 The present implementation of the
544 checks the current permissions of directory instead.