Use standard bool instead of our own Boolean type.
[dragonfly.git] / lib / libc / sys / open.2
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32.\" @(#)open.2 8.2 (Berkeley) 11/16/93
33.\" $FreeBSD: src/lib/libc/sys/open.2,v 1.11.2.9 2001/12/14 18:34:01 ru Exp $
1de703da 34.\" $DragonFly: src/lib/libc/sys/open.2,v 1.2 2003/06/17 04:26:47 dillon Exp $
984263bc
MD
35.\"
36.Dd November 16, 1993
37.Dt OPEN 2
38.Os
39.Sh NAME
40.Nm open
41.Nd open or create a file for reading or writing
42.Sh LIBRARY
43.Lb libc
44.Sh SYNOPSIS
45.In fcntl.h
46.Ft int
47.Fn open "const char *path" "int flags" "..."
48.Sh DESCRIPTION
49The file name specified by
50.Fa path
51is opened
52for reading and/or writing as specified by the
53argument
54.Fa flags
55and the file descriptor returned to the calling process.
56The
57.Fa flags
58argument may indicate the file is to be
59created if it does not exist (by specifying the
60.Dv O_CREAT
61flag).
62In this case
63.Nm
64requires a third argument
65.Fa "mode_t mode" ,
66and the file is created with mode
67.Fa mode
68as described in
69.Xr chmod 2
70and modified by the process' umask value (see
71.Xr umask 2 ) .
72.Pp
73The flags specified are formed by
74.Em or Ns 'ing
75the following values
76.Pp
77.Bd -literal -offset indent -compact
78O_RDONLY open for reading only
79O_WRONLY open for writing only
80O_RDWR open for reading and writing
81O_NONBLOCK do not block on open
82O_APPEND append on each write
83O_CREAT create file if it does not exist
84O_TRUNC truncate size to 0
85O_EXCL error if create and file exists
86O_SHLOCK atomically obtain a shared lock
87O_EXLOCK atomically obtain an exclusive lock
88O_DIRECT eliminate or reduce cache effects
89O_FSYNC synchronous writes
90O_NOFOLLOW do not follow symlinks
91.Ed
92.Pp
93Opening a file with
94.Dv O_APPEND
95set causes each write on the file
96to be appended to the end.
97If
98.Dv O_TRUNC
99is specified and the
100file exists, the file is truncated to zero length.
101If
102.Dv O_EXCL
103is set with
104.Dv O_CREAT
105and the file already
106exists,
107.Fn open
108returns an error.
109This may be used to
110implement a simple exclusive access locking mechanism.
111If
112.Dv O_EXCL
113is set and the last component of the pathname is
114a symbolic link,
115.Fn open
116will fail even if the symbolic
117link points to a non-existent name.
118If the
119.Dv O_NONBLOCK
120flag is specified and the
121.Fn open
122call would result
123in the process being blocked for some reason (e.g., waiting for
124carrier on a dialup line),
125.Fn open
126returns immediately.
127The first time the process attempts to perform I/O on the open
128file it will block (not currently implemented).
129.Pp
130If
131.Dv O_FSYNC
132is used in the mask, all writes will
133immediately be written to disk,
134the kernel will not cache written data
135and all writes on the descriptor will not return until
136the data to be written completes.
137.Pp
138If
139.Dv O_NOFOLLOW
140is used in the mask and the target file passed to
141.Fn open
142is a symbolic link then the
143.Fn open
144will fail.
145.Pp
146When opening a file, a lock with
147.Xr flock 2
148semantics can be obtained by setting
149.Dv O_SHLOCK
150for a shared lock, or
151.Dv O_EXLOCK
152for an exclusive lock.
153If creating a file with
154.Dv O_CREAT ,
155the request for the lock will never fail
156(provided that the underlying filesystem supports locking).
157.Pp
158.Dv O_DIRECT
159may be used to minimize or eliminate the cache effects of reading and writing.
160The system will attempt to avoid caching the data you read or write.
161If it cannot avoid caching the data,
162it will minimize the impact the data has on the cache.
163Use of this flag can drastically reduce performance if not used with care.
164.Pp
165If successful,
166.Fn open
167returns a non-negative integer, termed a file descriptor.
168It returns -1 on failure.
169The file pointer used to mark the current position within the
170file is set to the beginning of the file.
171.Pp
172When a new file is created it is given the group of the directory
173which contains it.
174.Pp
175The new descriptor is set to remain open across
176.Xr execve 2
177system calls; see
178.Xr close 2
179and
180.Xr fcntl 2 .
181.Pp
182The system imposes a limit on the number of file descriptors
183open simultaneously by one process.
184.Xr Getdtablesize 2
185returns the current system limit.
186.Sh RETURN VALUES
187If successful,
188.Fn open
189returns a non-negative integer, termed a file descriptor.
190It returns -1 on failure, and sets
191.Va errno
192to indicate the error.
193.Sh ERRORS
194The named file is opened unless:
195.Bl -tag -width Er
196.It Bq Er ENOTDIR
197A component of the path prefix is not a directory.
198.It Bq Er ENAMETOOLONG
199A component of a pathname exceeded 255 characters,
200or an entire path name exceeded 1023 characters.
201.It Bq Er ENOENT
202.Dv O_CREAT
203is not set and the named file does not exist.
204.It Bq Er ENOENT
205A component of the path name that must exist does not exist.
206.It Bq Er EACCES
207Search permission is denied for a component of the path prefix.
208.It Bq Er EACCES
209The required permissions (for reading and/or writing)
210are denied for the given flags.
211.It Bq Er EACCES
212.Dv O_CREAT
213is specified,
214the file does not exist,
215and the directory in which it is to be created
216does not permit writing.
217.It Bq Er ELOOP
218Too many symbolic links were encountered in translating the pathname.
219.It Bq Er EISDIR
220The named file is a directory, and the arguments specify
221it is to be opened for writing.
222.It Bq Er EROFS
223The named file resides on a read-only file system,
224and the file is to be modified.
225.It Bq Er EMFILE
226The process has already reached its limit for open file descriptors.
227.It Bq Er ENFILE
228The system file table is full.
229.It Bq Er EMLINK
230.Dv O_NOFOLLOW
231was specified and the target is a symbolic link.
232.It Bq Er ENXIO
233The named file is a character special or block
234special file, and the device associated with this special file
235does not exist.
236.It Bq Er ENXIO
237The named file is a fifo, no process has
238it open for reading, and the arguments specify it is
239to be opened for writing.
240.It Bq Er EINTR
241The
242.Fn open
243operation was interrupted by a signal.
244.It Bq Er EOPNOTSUPP
245.Dv O_SHLOCK
246or
247.Dv O_EXLOCK
248is specified but the underlying filesystem does not support locking.
249.It Bq Er EWOULDBLOCK
250.Dv O_NONBLOCK
251and one of
252.Dv O_SHLOCK
253or
254.Dv O_EXLOCK
255is specified and the file is locked.
256.It Bq Er ENOSPC
257.Dv O_CREAT
258is specified,
259the file does not exist,
260and the directory in which the entry for the new file is being placed
261cannot be extended because there is no space left on the file
262system containing the directory.
263.It Bq Er ENOSPC
264.Dv O_CREAT
265is specified,
266the file does not exist,
267and there are no free inodes on the file system on which the
268file is being created.
269.It Bq Er EDQUOT
270.Dv O_CREAT
271is specified,
272the file does not exist,
273and the directory in which the entry for the new file
274is being placed cannot be extended because the
275user's quota of disk blocks on the file system
276containing the directory has been exhausted.
277.It Bq Er EDQUOT
278.Dv O_CREAT
279is specified,
280the file does not exist,
281and the user's quota of inodes on the file system on
282which the file is being created has been exhausted.
283.It Bq Er EIO
284An I/O error occurred while making the directory entry or
285allocating the inode for
286.Dv O_CREAT .
287.It Bq Er ETXTBSY
288The file is a pure procedure (shared text) file that is being
289executed and the
290.Fn open
291call requests write access.
292.It Bq Er EFAULT
293.Fa Path
294points outside the process's allocated address space.
295.It Bq Er EEXIST
296.Dv O_CREAT
297and
298.Dv O_EXCL
299were specified and the file exists.
300.It Bq Er EOPNOTSUPP
301An attempt was made to open a socket (not currently implemented).
302.It Bq Er EINVAL
303An attempt was made to open a descriptor with an illegal combination
304of
305.Dv O_RDONLY ,
306.Dv O_WRONLY ,
307and
308.Dv O_RDWR .
309.El
310.Sh SEE ALSO
311.Xr chmod 2 ,
312.Xr close 2 ,
313.Xr dup 2 ,
314.Xr getdtablesize 2 ,
315.Xr lseek 2 ,
316.Xr read 2 ,
317.Xr umask 2 ,
318.Xr write 2
319.Sh HISTORY
320An
321.Fn open
322function call appeared in
323.At v6 .