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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
124 set causes each write on the file
125 to be appended to the end.
129 file exists, the file is truncated to zero length.
139 implement a simple exclusive access locking mechanism.
142 is set and the last component of the pathname is
145 will fail even if the symbolic
146 link points to a non-existent name.
149 flag is specified and the
151 system call would result
152 in the process being blocked for some reason (e.g., waiting for
153 carrier on a dialup line),
156 The descriptor remains in non-blocking mode for subsequent operations.
160 is used in the mask, all writes will
161 immediately be written to disk,
162 the kernel will not cache written data
163 and all writes on the descriptor will not return until
164 the data to be written completes.
174 is used in the mask and the target file passed to
176 is a symbolic link then the
180 When opening a file, a lock with
182 semantics can be obtained by setting
184 for a shared lock, or
186 for an exclusive lock.
187 If creating a file with
189 the request for the lock will never fail
190 (provided that the underlying file system supports locking).
193 may be used to minimize or eliminate the cache effects of reading and writing.
194 The system will attempt to avoid caching the data you read or write.
195 If it cannot avoid caching the data,
196 it will minimize the impact the data has on the cache.
197 Use of this flag can drastically reduce performance if not used with care.
200 may be used to ensure the OS does not assign this file as the
201 controlling terminal when it opens a tty device.
202 This is the default on
209 system call will not assign controlling terminals on
213 may be used to ensure the OS restores the terminal attributes when
214 initially opening a TTY.
215 This is the default on
222 on a TTY will always restore default terminal attributes on
227 returns a non-negative integer, termed a file descriptor.
228 It returns \-1 on failure.
229 The file pointer used to mark the current position within the
230 file is set to the beginning of the file.
232 When a new file is created it is given the group of the directory
235 The new descriptor is set to remain open across
242 The system imposes a limit on the number of file descriptors
243 open simultaneously by one process.
246 system call returns the current system limit.
252 return a non-negative integer, termed a file descriptor.
253 They return \-1 on failure, and set
255 to indicate the error.
257 The named file is opened unless:
260 A component of the path prefix is not a directory.
261 .It Bq Er ENAMETOOLONG
262 A component of a pathname exceeded 255 characters,
263 or an entire path name exceeded 1023 characters.
266 is not set and the named file does not exist.
268 A component of the path name that must exist does not exist.
270 Search permission is denied for a component of the path prefix.
272 The required permissions (for reading and/or writing)
273 are denied for the given flags.
276 is specified and write permission is denied.
280 the file does not exist,
281 and the directory in which it is to be created
282 does not permit writing.
285 is specified, the file does not exist, and the directory in which it is to be
286 created has its immutable flag set, see the
288 manual page for more information.
290 .Dv The named file has its immutable flag set and the file is to be modified.
292 .Dv The named file has its append-only flag set, the file is to be modified, and
298 Too many symbolic links were encountered in translating the pathname.
300 The named file is a directory, and the arguments specify
301 it is to be modified.
303 The named file resides on a read-only file system,
304 and the file is to be modified.
307 is specified and the named file would reside on a read-only file system.
309 The process has already reached its limit for open file descriptors.
311 The system file table is full.
314 was specified and the target is a symbolic link.
316 The named file is a character special or block
317 special file, and the device associated with this special file
321 is set, the named file is a fifo,
323 is set, and no process has the file open for reading.
327 operation was interrupted by a signal.
332 is specified but the underlying file system does not support locking.
334 The named file is a special file mounted through a file system that
335 does not support access to it (e.g.\& NFS).
336 .It Bq Er EWOULDBLOCK
342 is specified and the file is locked.
346 the file does not exist,
347 and the directory in which the entry for the new file is being placed
348 cannot be extended because there is no space left on the file
349 system containing the directory.
353 the file does not exist,
354 and there are no free inodes on the file system on which the
355 file is being created.
359 the file does not exist,
360 and the directory in which the entry for the new file
361 is being placed cannot be extended because the
362 user's quota of disk blocks on the file system
363 containing the directory has been exhausted.
367 the file does not exist,
368 and the user's quota of inodes on the file system on
369 which the file is being created has been exhausted.
371 An I/O error occurred while making the directory entry or
372 allocating the inode for
375 The file is a pure procedure (shared text) file that is being
378 system call requests write access.
383 points outside the process's allocated address space.
388 were specified and the file exists.
390 An attempt was made to open a socket (not currently implemented).
392 An attempt was made to open a descriptor with an illegal combination
402 argument does not specify an absolute path and the
407 nor a valid file descriptor open for searching.
411 argument is not an absolute path and
415 nor a file descriptor associated with a directory.
423 .Xr getdtablesize 2 ,
438 function was introduced in
441 The Open Group Extended API Set 2 specification requires that the test
444 is searchable is based on whether
446 is open for searching, not whether the underlying directory currently
448 The present implementation of the
450 checks the current permissions of directory instead.