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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.
83 the file to be opened is determined relative to the directory
84 associated with the file descriptor
86 instead of the current working directory.
89 parameter and the optional fourth parameter correspond exactly to
94 is passed the special value
98 parameter, the current working directory is used
99 and the behavior is identical to a call to
104 is called with an absolute
119 must be strictly relative to a file descriptor
122 must not be an absolute path and must not contain ".." components
123 which cause the path resolution to escape the directory hierarchy
126 Additionally, no symbolic link in
128 may target absolute path or contain escaping ".." components.
134 .Dv vfs.lookup_cap_dotdot
136 MIB is set to zero, ".." components in the paths,
137 used in capability mode,
138 are completely disabled.
140 .Dv vfs.lookup_cap_dotdot_nonlocal
141 MIB is set to zero, ".." is not allowed if found on non-local filesystem.
143 The flags specified are formed by
147 .Bd -literal -offset indent -compact
148 O_RDONLY open for reading only
149 O_WRONLY open for writing only
150 O_RDWR open for reading and writing
151 O_EXEC open for execute only
152 O_SEARCH open for search only, an alias for O_EXEC
153 O_NONBLOCK do not block on open
154 O_APPEND append on each write
155 O_CREAT create file if it does not exist
156 O_TRUNC truncate size to 0
157 O_EXCL error if create and file exists
158 O_SHLOCK atomically obtain a shared lock
159 O_EXLOCK atomically obtain an exclusive lock
160 O_DIRECT eliminate or reduce cache effects
161 O_FSYNC synchronous writes (historical synonym for O_SYNC)
162 O_SYNC synchronous writes
163 O_DSYNC synchronous data writes
164 O_NOFOLLOW do not follow symlinks
167 O_DIRECTORY error if file is not a directory
168 O_CLOEXEC set FD_CLOEXEC upon open
169 O_VERIFY verify the contents of the file
170 O_RESOLVE_BENEATH path resolution must not cross the fd directory
171 O_PATH record only the target path in the opened descriptor
176 set causes each write on the file
177 to be appended to the end.
181 file exists, the file is truncated to zero length.
191 implement a simple exclusive access locking mechanism.
194 is set and the last component of the pathname is
197 will fail even if the symbolic
198 link points to a non-existent name.
201 flag is specified and the
203 system call would result
204 in the process being blocked for some reason (e.g., waiting for
205 carrier on a dialup line),
208 The descriptor remains in non-blocking mode for subsequent operations.
212 is used in the mask, all writes will
213 immediately and synchronously be written to disk.
215 is an historical synonym for
220 is used in the mask, all data and metadata required to read the data will be
221 synchronously written to disk, but changes to metadata such as file access and
222 modification timestamps may be written later.
226 is used in the mask and the target file passed to
228 is a symbolic link then the
232 When opening a file, a lock with
234 semantics can be obtained by setting
236 for a shared lock, or
238 for an exclusive lock.
239 If creating a file with
241 the request for the lock will never fail
242 (provided that the underlying file system supports locking).
245 may be used to minimize or eliminate the cache effects of reading and writing.
246 The system will attempt to avoid caching the data you read or write.
247 If it cannot avoid caching the data,
248 it will minimize the impact the data has on the cache.
249 Use of this flag can drastically reduce performance if not used with care.
252 may be used to ensure the OS does not assign this file as the
253 controlling terminal when it opens a tty device.
254 This is the default on
261 system call will not assign controlling terminals on
265 may be used to ensure the OS restores the terminal attributes when
266 initially opening a TTY.
267 This is the default on
274 on a TTY will always restore default terminal attributes on
278 may be used to ensure the resulting file descriptor refers to a
280 This flag can be used to prevent applications with elevated privileges
281 from opening files which are even unsafe to open with
283 such as device nodes.
288 flag for the newly returned file descriptor.
291 may be used to indicate to the kernel that the contents of the file should
292 be verified before allowing the open to proceed.
295 means is implementation specific.
296 The run-time linker (rtld) uses this flag to ensure shared objects have
297 been verified before operating on them.
299 .Dv O_RESOLVE_BENEATH
302 if any intermediate component of the specified relative path does not
303 reside in the directory hierarchy beneath the starting directory.
304 Absolute paths or even the temporal escape from beneath of the starting
305 directory is not allowed.
311 execute permissions are checked at open time.
314 may not be used for any read operations like
315 .Xr getdirentries 2 .
316 The primary use for this descriptor will be as the lookup descriptor for the
321 returns a file descriptor that can be used as a directory file descriptor for
323 and other system calls taking a file descriptor argument, like
326 The other functionality of the returned file descriptor is limited to
327 the descriptor-level operations.
329 .Bl -tag -width SCM_RIGHTS -offset indent -compact
331 but advisory locking is not allowed
338 was also specified at open time
349 and any other that operate on file and not on file descriptor (except
354 flag does not prevent non-forced unmount of the volume it belongs to.
355 See also the description of
359 and related syscalls.
363 returns a non-negative integer, termed a file descriptor.
364 It returns \-1 on failure.
365 The file pointer used to mark the current position within the
366 file is set to the beginning of the file.
368 If a sleeping open of a device node from
370 is interrupted by a signal, the call always fails with
374 flag is set for the signal.
375 A sleeping open of a fifo (see
377 is restarted as normal.
379 When a new file is created it is given the group of the directory
385 the new descriptor is set to remain open across
394 The system imposes a limit on the number of file descriptors
395 open simultaneously by one process.
398 system call returns the current system limit.
404 return a non-negative integer, termed a file descriptor.
405 They return \-1 on failure, and set
407 to indicate the error.
409 The named file is opened unless:
412 A component of the path prefix is not a directory.
413 .It Bq Er ENAMETOOLONG
414 A component of a pathname exceeded 255 characters,
415 or an entire path name exceeded 1023 characters.
418 is not set and the named file does not exist.
420 A component of the path name that must exist does not exist.
422 Search permission is denied for a component of the path prefix.
424 The required permissions (for reading and/or writing)
425 are denied for the given flags.
428 is specified and write permission is denied.
432 the file does not exist,
433 and the directory in which it is to be created
434 does not permit writing.
437 is specified, the file does not exist, and the directory in which it is to be
438 created has its immutable flag set, see the
440 manual page for more information.
442 The named file has its immutable flag set and the file is to be modified.
444 The named file has its append-only flag set, the file is to be modified, and
450 Too many symbolic links were encountered in translating the pathname.
452 The named file is a directory, and the arguments specify
453 it is to be modified.
455 The named file is a directory, and the flags specified
460 The named file resides on a read-only file system,
461 and the file is to be modified.
464 is specified and the named file would reside on a read-only file system.
466 The process has already reached its limit for open file descriptors.
468 The system file table is full.
471 was specified and the target is a symbolic link.
473 The named file is a character special or block
474 special file, and the device associated with this special file
478 is set, the named file is a fifo,
480 is set, and no process has the file open for reading.
484 operation was interrupted by a signal.
489 is specified but the underlying file system does not support locking.
491 The named file is a special file mounted through a file system that
492 does not support access to it (e.g.\& NFS).
493 .It Bq Er EWOULDBLOCK
499 is specified and the file is locked.
503 the file does not exist,
504 and the directory in which the entry for the new file is being placed
505 cannot be extended because there is no space left on the file
506 system containing the directory.
510 the file does not exist,
511 and there are no free inodes on the file system on which the
512 file is being created.
516 the file does not exist,
517 and the directory in which the entry for the new file
518 is being placed cannot be extended because the
519 user's quota of disk blocks on the file system
520 containing the directory has been exhausted.
524 the file does not exist,
525 and the user's quota of inodes on the file system on
526 which the file is being created has been exhausted.
528 An I/O error occurred while making the directory entry or
529 allocating the inode for
532 Corrupted data was detected while reading from the file system.
534 The file is a pure procedure (shared text) file that is being
537 system call requests write access.
542 points outside the process's allocated address space.
547 were specified and the file exists.
549 An attempt was made to open a socket (not currently implemented).
551 An attempt was made to open a descriptor with an illegal combination
563 .Dv O_RESOLVE_BENEATH
564 flag is specified and
570 argument does not specify an absolute path and the
575 nor a valid file descriptor open for searching.
579 argument is not an absolute path and
583 nor a file descriptor associated with a directory.
586 is specified and the file is not a directory.
589 is specified and the process is in capability mode.
592 was called and the process is in capability mode.
593 .It Bq Er ENOTCAPABLE
596 or contained a ".." component leading to a
597 directory outside of the directory hierarchy specified by
599 and the process is in capability mode.
600 .It Bq Er ENOTCAPABLE
602 .Dv O_RESOLVE_BENEATH
603 flag was provided, and the relative
615 .Xr getdtablesize 2 ,
625 These functions are specified by
631 .Er EMLINK instead of
637 is set in flags and the final component of pathname is a symbolic link
638 to distinguish it from the case of too many symbolic link traversals
639 in one of its non-final components.
647 function was introduced in
652 The Open Group Extended API Set 2 specification requires that the test
655 is searchable is based on whether
657 is open for searching, not whether the underlying directory currently
659 The present implementation of the
661 checks the current permissions of directory instead.
665 argument is variadic and may result in different calling conventions
666 than might otherwise be expected.