1 .\" Copyright (c) 1980, 1991, 1993
2 .\" The Regents of the University of California. All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
7 .\" 1. Redistributions of source code must retain the above copyright
8 .\" notice, this list of conditions and the following disclaimer.
9 .\" 2. Redistributions in binary form must reproduce the above copyright
10 .\" notice, this list of conditions and the following disclaimer in the
11 .\" documentation and/or other materials provided with the distribution.
12 .\" 3. Neither the name of the University nor the names of its contributors
13 .\" may be used to endorse or promote products derived from this software
14 .\" without specific prior written permission.
16 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
17 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
20 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28 .\" @(#)open.2 8.2 (Berkeley) 11/16/93
31 .Dd September 28, 2019
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, or the
85 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
106 is called with an absolute
115 is specified with an absolute
117 a directory passed by the
119 argument is used as the topping point for the resolution.
120 See the definition of the
133 must be strictly relative to a file descriptor
136 .Pa sys/kern/vfs_lookup.c .
138 must not be an absolute path and must not contain ".." components
139 which cause the path resolution to escape the directory hierarchy
142 Additionally, no symbolic link in
144 may target absolute path or contain escaping ".." components.
150 .Dv vfs.lookup_cap_dotdot
152 MIB is set to zero, ".." components in the paths,
153 used in capability mode, or with the
155 flag, are completely disabled.
157 .Dv vfs.lookup_cap_dotdot_nonlocal
158 MIB is set to zero, ".." is not allowed if found on non-local filesystem.
160 The flags specified are formed by
164 .Bd -literal -offset indent -compact
165 O_RDONLY open for reading only
166 O_WRONLY open for writing only
167 O_RDWR open for reading and writing
168 O_EXEC open for execute only
169 O_NONBLOCK do not block on open
170 O_APPEND append on each write
171 O_CREAT create file if it does not exist
172 O_TRUNC truncate size to 0
173 O_EXCL error if create and file exists
174 O_SHLOCK atomically obtain a shared lock
175 O_EXLOCK atomically obtain an exclusive lock
176 O_DIRECT eliminate or reduce cache effects
177 O_FSYNC synchronous writes
178 O_SYNC synchronous writes
179 O_NOFOLLOW do not follow symlinks
182 O_DIRECTORY error if file is not a directory
183 O_CLOEXEC set FD_CLOEXEC upon open
184 O_VERIFY verify the contents of the file
185 O_BENEATH require path to be strictly relative to topping directory
190 set causes each write on the file
191 to be appended to the end.
195 file exists, the file is truncated to zero length.
205 implement a simple exclusive access locking mechanism.
208 is set and the last component of the pathname is
211 will fail even if the symbolic
212 link points to a non-existent name.
215 flag is specified and the
217 system call would result
218 in the process being blocked for some reason (e.g., waiting for
219 carrier on a dialup line),
222 The descriptor remains in non-blocking mode for subsequent operations.
226 is used in the mask, all writes will
227 immediately and synchronously be written to disk.
237 is used in the mask and the target file passed to
239 is a symbolic link then the
243 When opening a file, a lock with
245 semantics can be obtained by setting
247 for a shared lock, or
249 for an exclusive lock.
250 If creating a file with
252 the request for the lock will never fail
253 (provided that the underlying file system supports locking).
256 may be used to minimize or eliminate the cache effects of reading and writing.
257 The system will attempt to avoid caching the data you read or write.
258 If it cannot avoid caching the data,
259 it will minimize the impact the data has on the cache.
260 Use of this flag can drastically reduce performance if not used with care.
263 may be used to ensure the OS does not assign this file as the
264 controlling terminal when it opens a tty device.
265 This is the default on
272 system call will not assign controlling terminals on
276 may be used to ensure the OS restores the terminal attributes when
277 initially opening a TTY.
278 This is the default on
285 on a TTY will always restore default terminal attributes on
289 may be used to ensure the resulting file descriptor refers to a
291 This flag can be used to prevent applications with elevated privileges
292 from opening files which are even unsafe to open with
294 such as device nodes.
299 flag for the newly returned file descriptor.
302 may be used to indicate to the kernel that the contents of the file should
303 be verified before allowing the open to proceed.
306 means is implementation specific.
307 The run-time linker (rtld) uses this flag to ensure shared objects have
308 been verified before operating on them.
313 if the specified relative path, after resolving all symlinks and ".."
314 references, does not reside in the directory hierarchy of
315 children beneath the topping directory.
316 Topping directory is the process current directory if relative
320 and the directory referenced by the
324 If the specified path is absolute,
326 allows arbitrary prefix that ends up at the topping directory,
327 after which all further resolved components must be under it.
331 returns a non-negative integer, termed a file descriptor.
332 It returns \-1 on failure.
333 The file pointer used to mark the current position within the
334 file is set to the beginning of the file.
336 If a sleeping open of a device node from
338 is interrupted by a signal, the call always fails with
342 flag is set for the signal.
343 A sleeping open of a fifo (see
345 is restarted as normal.
347 When a new file is created it is given the group of the directory
353 the new descriptor is set to remain open across
362 The system imposes a limit on the number of file descriptors
363 open simultaneously by one process.
366 system call returns the current system limit.
372 return a non-negative integer, termed a file descriptor.
373 They return \-1 on failure, and set
375 to indicate the error.
377 The named file is opened unless:
380 A component of the path prefix is not a directory.
381 .It Bq Er ENAMETOOLONG
382 A component of a pathname exceeded 255 characters,
383 or an entire path name exceeded 1023 characters.
386 is not set and the named file does not exist.
388 A component of the path name that must exist does not exist.
390 Search permission is denied for a component of the path prefix.
392 The required permissions (for reading and/or writing)
393 are denied for the given flags.
396 is specified and write permission is denied.
400 the file does not exist,
401 and the directory in which it is to be created
402 does not permit writing.
405 is specified, the file does not exist, and the directory in which it is to be
406 created has its immutable flag set, see the
408 manual page for more information.
410 The named file has its immutable flag set and the file is to be modified.
412 The named file has its append-only flag set, the file is to be modified, and
418 Too many symbolic links were encountered in translating the pathname.
420 The named file is a directory, and the arguments specify
421 it is to be modified.
423 The named file is a directory, and the flags specified
428 The named file resides on a read-only file system,
429 and the file is to be modified.
432 is specified and the named file would reside on a read-only file system.
434 The process has already reached its limit for open file descriptors.
436 The system file table is full.
439 was specified and the target is a symbolic link.
441 The named file is a character special or block
442 special file, and the device associated with this special file
446 is set, the named file is a fifo,
448 is set, and no process has the file open for reading.
452 operation was interrupted by a signal.
457 is specified but the underlying file system does not support locking.
459 The named file is a special file mounted through a file system that
460 does not support access to it (e.g.\& NFS).
461 .It Bq Er EWOULDBLOCK
467 is specified and the file is locked.
471 the file does not exist,
472 and the directory in which the entry for the new file is being placed
473 cannot be extended because there is no space left on the file
474 system containing the directory.
478 the file does not exist,
479 and there are no free inodes on the file system on which the
480 file is being created.
484 the file does not exist,
485 and the directory in which the entry for the new file
486 is being placed cannot be extended because the
487 user's quota of disk blocks on the file system
488 containing the directory has been exhausted.
492 the file does not exist,
493 and the user's quota of inodes on the file system on
494 which the file is being created has been exhausted.
496 An I/O error occurred while making the directory entry or
497 allocating the inode for
500 The file is a pure procedure (shared text) file that is being
503 system call requests write access.
508 points outside the process's allocated address space.
513 were specified and the file exists.
515 An attempt was made to open a socket (not currently implemented).
517 An attempt was made to open a descriptor with an illegal combination
527 argument does not specify an absolute path and the
532 nor a valid file descriptor open for searching.
536 argument is not an absolute path and
540 nor a file descriptor associated with a directory.
543 is specified and the file is not a directory.
546 is specified and the process is in capability mode.
549 was called and the process is in capability mode.
550 .It Bq Er ENOTCAPABLE
553 or contained a ".." component leading to a
554 directory outside of the directory hierarchy specified by
556 and the process is in capability mode.
557 .It Bq Er ENOTCAPABLE
560 flag was provided, and the absolute
562 does not have its tail fully contained under the topping directory,
573 .Xr getdtablesize 2 ,
583 These functions are specified by
589 .Er EMLINK instead of
595 is set in flags and the final component of pathname is a symbolic link
596 to distinguish it from the case of too many symbolic link traversals
597 in one of its non-final components.
605 function was introduced in
608 The Open Group Extended API Set 2 specification requires that the test
611 is searchable is based on whether
613 is open for searching, not whether the underlying directory currently
615 The present implementation of the
617 checks the current permissions of directory instead.
621 argument is variadic and may result in different calling conventions
622 than might otherwise be expected.