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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
118 O_NOCTTY don't assign controlling terminal
119 O_TTY_INIT restore default terminal attributes
120 O_DIRECTORY error if file is not a directory
121 O_CLOEXEC set FD_CLOEXEC upon open
126 set causes each write on the file
127 to be appended to the end.
131 file exists, the file is truncated to zero length.
141 implement a simple exclusive access locking mechanism.
144 is set and the last component of the pathname is
147 will fail even if the symbolic
148 link points to a non-existent name.
151 flag is specified and the
153 system call would result
154 in the process being blocked for some reason (e.g., waiting for
155 carrier on a dialup line),
158 The descriptor remains in non-blocking mode for subsequent operations.
162 is used in the mask, all writes will
163 immediately be written to disk,
164 the kernel will not cache written data
165 and all writes on the descriptor will not return until
166 the data to be written completes.
176 is used in the mask and the target file passed to
178 is a symbolic link then the
182 When opening a file, a lock with
184 semantics can be obtained by setting
186 for a shared lock, or
188 for an exclusive lock.
189 If creating a file with
191 the request for the lock will never fail
192 (provided that the underlying file system supports locking).
195 may be used to minimize or eliminate the cache effects of reading and writing.
196 The system will attempt to avoid caching the data you read or write.
197 If it cannot avoid caching the data,
198 it will minimize the impact the data has on the cache.
199 Use of this flag can drastically reduce performance if not used with care.
202 may be used to ensure the OS does not assign this file as the
203 controlling terminal when it opens a tty device.
204 This is the default on
211 system call will not assign controlling terminals on
215 may be used to ensure the OS restores the terminal attributes when
216 initially opening a TTY.
217 This is the default on
224 on a TTY will always restore default terminal attributes on
228 may be used to ensure the resulting file descriptor refers to a
230 This flag can be used to prevent applications with elevated privileges
231 from opening files which are even unsafe to open with
233 such as device nodes.
238 flag for the newly returned file descriptor.
242 returns a non-negative integer, termed a file descriptor.
243 It returns \-1 on failure.
244 The file pointer used to mark the current position within the
245 file is set to the beginning of the file.
247 If a sleeping open of a device node from
249 is interrupted by a signal, the call always fails with
253 flag is set for the signal.
254 A sleeping open of a fifo (see
256 is restarted as normal.
258 When a new file is created it is given the group of the directory
264 the new descriptor is set to remain open across
273 The system imposes a limit on the number of file descriptors
274 open simultaneously by one process.
277 system call returns the current system limit.
283 return a non-negative integer, termed a file descriptor.
284 They return \-1 on failure, and set
286 to indicate the error.
288 The named file is opened unless:
291 A component of the path prefix is not a directory.
292 .It Bq Er ENAMETOOLONG
293 A component of a pathname exceeded 255 characters,
294 or an entire path name exceeded 1023 characters.
297 is not set and the named file does not exist.
299 A component of the path name that must exist does not exist.
301 Search permission is denied for a component of the path prefix.
303 The required permissions (for reading and/or writing)
304 are denied for the given flags.
307 is specified and write permission is denied.
311 the file does not exist,
312 and the directory in which it is to be created
313 does not permit writing.
316 is specified, the file does not exist, and the directory in which it is to be
317 created has its immutable flag set, see the
319 manual page for more information.
321 The named file has its immutable flag set and the file is to be modified.
323 The named file has its append-only flag set, the file is to be modified, and
329 Too many symbolic links were encountered in translating the pathname.
331 The named file is a directory, and the arguments specify
332 it is to be modified.
334 The named file resides on a read-only file system,
335 and the file is to be modified.
338 is specified and the named file would reside on a read-only file system.
340 The process has already reached its limit for open file descriptors.
342 The system file table is full.
345 was specified and the target is a symbolic link.
347 The named file is a character special or block
348 special file, and the device associated with this special file
352 is set, the named file is a fifo,
354 is set, and no process has the file open for reading.
358 operation was interrupted by a signal.
363 is specified but the underlying file system does not support locking.
365 The named file is a special file mounted through a file system that
366 does not support access to it (e.g.\& NFS).
367 .It Bq Er EWOULDBLOCK
373 is specified and the file is locked.
377 the file does not exist,
378 and the directory in which the entry for the new file is being placed
379 cannot be extended because there is no space left on the file
380 system containing the directory.
384 the file does not exist,
385 and there are no free inodes on the file system on which the
386 file is being created.
390 the file does not exist,
391 and the directory in which the entry for the new file
392 is being placed cannot be extended because the
393 user's quota of disk blocks on the file system
394 containing the directory has been exhausted.
398 the file does not exist,
399 and the user's quota of inodes on the file system on
400 which the file is being created has been exhausted.
402 An I/O error occurred while making the directory entry or
403 allocating the inode for
406 The file is a pure procedure (shared text) file that is being
409 system call requests write access.
414 points outside the process's allocated address space.
419 were specified and the file exists.
421 An attempt was made to open a socket (not currently implemented).
423 An attempt was made to open a descriptor with an illegal combination
433 argument does not specify an absolute path and the
438 nor a valid file descriptor open for searching.
442 argument is not an absolute path and
446 nor a file descriptor associated with a directory.
449 is specified and the file is not a directory.
457 .Xr getdtablesize 2 ,
472 function was introduced in
475 The Open Group Extended API Set 2 specification requires that the test
478 is searchable is based on whether
480 is open for searching, not whether the underlying directory currently
482 The present implementation of the
484 checks the current permissions of directory instead.