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1.1 root 1: .\" Copyright (c) 1980 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)open.2 6.5 (Berkeley) 8/12/88
6: .\"
7: .TH OPEN 2 "August 12, 1988"
8: .UC 4
9: .SH NAME
10: open \- open a file for reading or writing, or create a new file
11: .SH SYNOPSIS
12: .nf
13: .ft B
14: #include <sys/file.h>
15: .PP
16: .ft B
17: open(path, flags, mode)
18: char *path;
19: int flags, mode;
20: .fi
21: .SH DESCRIPTION
22: .I Open
23: opens the file
24: .I path
25: for reading and/or writing, as specified by the
26: .I flags
27: argument and returns a descriptor for that file.
28: The
29: .I flags
30: argument may indicate the file is to be
31: created if it does not already exist (by specifying the
32: O_CREAT flag), in which case the file is created with mode
33: .I mode
34: as described in
35: .IR chmod (2)
36: and modified by the process' umask value (see
37: .IR umask (2)).
38: .PP
39: .I Path
40: is the address of a string of ASCII characters representing
41: a path name, terminated by a null character.
42: The flags specified are formed by
43: .IR or 'ing
44: the following values
45: .PP
46: .RS
47: O_RDONLY open for reading only
48: O_WRONLY open for writing only
49: O_RDWR open for reading and writing
50: O_NDELAY do not block on open
51: O_APPEND append on each write
52: O_CREAT create file if it does not exist
53: O_TRUNC truncate size to 0
54: O_EXCL error if create and file exists
55: .RE
56: .PP
57: Opening a file with O_APPEND set causes each write on the file
58: to be appended to the end. If O_TRUNC is specified and the
59: file exists, the file is truncated to zero length.
60: If O_EXCL is set with O_CREAT, then if the file already
61: exists, the open returns an error. This can be used to
62: implement a simple exclusive access locking mechanism.
63: If O_EXCL is set and the last component of the pathname is
64: a symbolic link, the open will fail even if the symbolic
65: link points to a non-existent name.
66: If the O_NDELAY flag is specified and the open call would result
67: in the process being blocked for some reason (e.g. waiting for
68: carrier on a dialup line), the open returns immediately.
69: The first time the process attempts to perform i/o on the open
70: file it will block (not currently implemented).
71: .PP
72: If successful, \fIopen\fP returns a non-negative integer, termed a
73: file descriptor. It returns -1 on failure.
74: The file pointer used to mark the current position within the
75: file is set to the beginning of the file.
76: .PP
77: The new descriptor is set to remain open across
78: .IR execve
79: system calls; see
80: .IR close (2).
81: .PP
82: The system imposes a limit on the number of file descriptors
83: open simultaneously by one process.
84: .IR Getdtablesize (2)
85: returns the current system limit.
86: .SH "ERRORS
87: The named file is opened unless one or more of the
88: following are true:
89: .TP 15
90: [ENOTDIR]
91: A component of the path prefix is not a directory.
92: .TP 15
93: [EINVAL]
94: The pathname contains a character with the high-order bit set.
95: .TP 15
96: [ENAMETOOLONG]
97: A component of a pathname exceeded 255 characters,
98: or an entire path name exceeded 1023 characters.
99: .TP 15
100: [ENOENT]
101: O_CREAT is not set and the named file does not exist.
102: .TP 15
103: [ENOENT]
104: A component of the path name that must exist does not exist.
105: .TP 15
106: [EACCES]
107: Search permission is denied for a component of the path prefix.
108: .TP 15
109: [EACCES]
110: The required permissions (for reading and/or writing)
111: are denied for the named flag.
112: .TP 15
113: [EACCES]
114: O_CREAT is specified,
115: the file does not exist,
116: and the directory in which it is to be created
117: does not permit writing.
118: .TP 15
119: [ELOOP]
120: Too many symbolic links were encountered in translating the pathname.
121: .TP 15
122: [EISDIR]
123: The named file is a directory, and the arguments specify
124: it is to be opened for writting.
125: .TP 15
126: [EROFS]
127: The named file resides on a read-only file system,
128: and the file is to be modified.
129: .TP 15
130: [EMFILE]
131: The system limit for open file descriptors per process has already been reached.
132: .TP 15
133: [ENFILE]
134: The system file table is full.
135: .TP 15
136: [ENXIO]
137: The named file is a character special or block
138: special file, and the device associated with this special file
139: does not exist.
140: .TP 15
141: [ENOSPC]
142: O_CREAT is specified,
143: the file does not exist,
144: and the directory in which the entry for the new file is being placed
145: cannot be extended because there is no space left on the file
146: system containing the directory.
147: .TP 15
148: [ENOSPC]
149: O_CREAT is specified,
150: the file does not exist,
151: and there are no free inodes on the file system on which the
152: file is being created.
153: .TP 15
154: [EDQUOT]
155: O_CREAT is specified,
156: the file does not exist,
157: and the directory in which the entry for the new fie
158: is being placed cannot be extended because the
159: user's quota of disk blocks on the file system
160: containing the directory has been exhausted.
161: .TP 15
162: [EDQUOT]
163: O_CREAT is specified,
164: the file does not exist,
165: and the user's quota of inodes on the file system on
166: which the file is being created has been exhausted.
167: .TP 15
168: [EIO]
169: An I/O error occurred while making the directory entry or
170: allocating the inode for O_CREAT.
171: .TP 15
172: [ETXTBSY]
173: The file is a pure procedure (shared text) file that is being
174: executed and the \fIopen\fP call requests write access.
175: .TP 15
176: [EFAULT]
177: .I Path
178: points outside the process's allocated address space.
179: .TP 15
180: [EEXIST]
181: O_CREAT and O_EXCL were specified and the file exists.
182: .TP 15
183: [EOPNOTSUPP]
184: An attempt was made to open a socket (not currently implemented).
185: .SH "SEE ALSO"
186: chmod(2), close(2), dup(2), getdtablesize(2),
187: lseek(2), read(2), write(2), umask(2)
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