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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
120 O_DIRECTORY error if file is not a directory
121 O_CLOEXEC set FD_CLOEXEC upon open
122 O_VERIFY verify the contents of the file
127 set causes each write on the file
128 to be appended to the end.
132 file exists, the file is truncated to zero length.
142 implement a simple exclusive access locking mechanism.
145 is set and the last component of the pathname is
148 will fail even if the symbolic
149 link points to a non-existent name.
152 flag is specified and the
154 system call would result
155 in the process being blocked for some reason (e.g., waiting for
156 carrier on a dialup line),
159 The descriptor remains in non-blocking mode for subsequent operations.
163 is used in the mask, all writes will
164 immediately be written to disk,
165 the kernel will not cache written data
166 and all writes on the descriptor will not return until
167 the data to be written completes.
177 is used in the mask and the target file passed to
179 is a symbolic link then the
183 When opening a file, a lock with
185 semantics can be obtained by setting
187 for a shared lock, or
189 for an exclusive lock.
190 If creating a file with
192 the request for the lock will never fail
193 (provided that the underlying file system supports locking).
196 may be used to minimize or eliminate the cache effects of reading and writing.
197 The system will attempt to avoid caching the data you read or write.
198 If it cannot avoid caching the data,
199 it will minimize the impact the data has on the cache.
200 Use of this flag can drastically reduce performance if not used with care.
203 may be used to ensure the OS does not assign this file as the
204 controlling terminal when it opens a tty device.
205 This is the default on
212 system call will not assign controlling terminals on
216 may be used to ensure the OS restores the terminal attributes when
217 initially opening a TTY.
218 This is the default on
225 on a TTY will always restore default terminal attributes on
229 may be used to ensure the resulting file descriptor refers to a
231 This flag can be used to prevent applications with elevated privileges
232 from opening files which are even unsafe to open with
234 such as device nodes.
239 flag for the newly returned file descriptor.
242 may be used to indicate to the kernel that the contents of the file should
243 be verified before allowing the open to proceed.
246 means is implementation specific.
247 The run-time linker (rtld) uses this flag to ensure shared objects have
248 been verified before operating on them.
252 returns a non-negative integer, termed a file descriptor.
253 It returns \-1 on failure.
254 The file pointer used to mark the current position within the
255 file is set to the beginning of the file.
257 If a sleeping open of a device node from
259 is interrupted by a signal, the call always fails with
263 flag is set for the signal.
264 A sleeping open of a fifo (see
266 is restarted as normal.
268 When a new file is created it is given the group of the directory
274 the new descriptor is set to remain open across
283 The system imposes a limit on the number of file descriptors
284 open simultaneously by one process.
287 system call returns the current system limit.
293 return a non-negative integer, termed a file descriptor.
294 They return \-1 on failure, and set
296 to indicate the error.
298 The named file is opened unless:
301 A component of the path prefix is not a directory.
302 .It Bq Er ENAMETOOLONG
303 A component of a pathname exceeded 255 characters,
304 or an entire path name exceeded 1023 characters.
307 is not set and the named file does not exist.
309 A component of the path name that must exist does not exist.
311 Search permission is denied for a component of the path prefix.
313 The required permissions (for reading and/or writing)
314 are denied for the given flags.
317 is specified and write permission is denied.
321 the file does not exist,
322 and the directory in which it is to be created
323 does not permit writing.
326 is specified, the file does not exist, and the directory in which it is to be
327 created has its immutable flag set, see the
329 manual page for more information.
331 The named file has its immutable flag set and the file is to be modified.
333 The named file has its append-only flag set, the file is to be modified, and
339 Too many symbolic links were encountered in translating the pathname.
341 The named file is a directory, and the arguments specify
342 it is to be modified.
344 The named file resides on a read-only file system,
345 and the file is to be modified.
348 is specified and the named file would reside on a read-only file system.
350 The process has already reached its limit for open file descriptors.
352 The system file table is full.
355 was specified and the target is a symbolic link.
357 The named file is a character special or block
358 special file, and the device associated with this special file
362 is set, the named file is a fifo,
364 is set, and no process has the file open for reading.
368 operation was interrupted by a signal.
373 is specified but the underlying file system does not support locking.
375 The named file is a special file mounted through a file system that
376 does not support access to it (e.g.\& NFS).
377 .It Bq Er EWOULDBLOCK
383 is specified and the file is locked.
387 the file does not exist,
388 and the directory in which the entry for the new file is being placed
389 cannot be extended because there is no space left on the file
390 system containing the directory.
394 the file does not exist,
395 and there are no free inodes on the file system on which the
396 file is being created.
400 the file does not exist,
401 and the directory in which the entry for the new file
402 is being placed cannot be extended because the
403 user's quota of disk blocks on the file system
404 containing the directory has been exhausted.
408 the file does not exist,
409 and the user's quota of inodes on the file system on
410 which the file is being created has been exhausted.
412 An I/O error occurred while making the directory entry or
413 allocating the inode for
416 The file is a pure procedure (shared text) file that is being
419 system call requests write access.
424 points outside the process's allocated address space.
429 were specified and the file exists.
431 An attempt was made to open a socket (not currently implemented).
433 An attempt was made to open a descriptor with an illegal combination
443 argument does not specify an absolute path and the
448 nor a valid file descriptor open for searching.
452 argument is not an absolute path and
456 nor a file descriptor associated with a directory.
459 is specified and the file is not a directory.
467 .Xr getdtablesize 2 ,
482 function was introduced in
485 These functions are specified by
491 .Er EMLINK instead of
497 is set in flags and the final component of pathname is a symbolic link
498 to distinguish it from the case of too many symbolic link traversals
499 in one of its non-final components.
501 The Open Group Extended API Set 2 specification requires that the test
504 is searchable is based on whether
506 is open for searching, not whether the underlying directory currently
508 The present implementation of the
510 checks the current permissions of directory instead.