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1.1 root 1: .TH OPEN 2 "2 July 1983"
2: .UC 4
3: .SH NAME
4: open \- open a file for reading or writing, or create a new file
5: .SH SYNOPSIS
6: .nf
7: .ft B
8: #include <sys/file.h>
9: .PP
10: .ft B
11: open(path, flags, mode)
12: char *path;
13: int flags, mode;
14: .fi
15: .SH DESCRIPTION
16: .I Open
17: opens the file
18: .I path
19: for reading and/or writing, as specified by the
20: .I flags
21: argument and returns a descriptor for that file.
22: The
23: .I flags
24: argument may indicate the file is to be
25: created if it does not already exist (by specifying the
26: O_CREAT flag), in which case the file is created with mode
27: .I mode
28: as described in
29: .IR chmod (2)
30: and modified by the process' umask value (see
31: .IR umask (2)).
32: .PP
33: .I Path
34: is the address of a string of ASCII characters representing
35: a path name, terminated by a null character.
36: The flags specified are formed by
37: .IR or 'ing
38: the following values
39: .PP
40: .RS
41: O_RDONLY open for reading only
42: O_WRONLY open for writing only
43: O_RDWR open for reading and writing
44: O_NDELAY do not block on open
45: O_APPEND append on each write
46: O_CREAT create file if it does not exist
47: O_TRUNC truncate size to 0
48: O_EXCL error if create and file exists
49: .RE
50: .PP
51: Opening a file with O_APPEND set causes each write on the file
52: to be appended to the end. If O_TRUNC is specified and the
53: file exists, the file is truncated to zero length.
54: If O_EXCL is set with O_CREAT, then if the file already
55: exists, the open returns an error. This can be used to
56: implement a simple exclusive access locking mechanism.
57: If the O_NDELAY flag is specified and the open call would result
58: in the process being blocked for some reason (e.g. waiting for
59: carrier on a dialup line), the open returns immediately.
60: The first time the process attempts to perform i/o on the open
61: file it will block (not currently implemented).
62: .PP
63: Upon successful completion a non-negative integer termed a
64: file descriptor is returned.
65: The file pointer used to mark the current position within the
66: file is set to the beginning of the file.
67: .PP
68: The new descriptor is set to remain open across
69: .IR execve
70: system calls; see
71: .IR close (2).
72: .PP
73: No process may have more than {OPEN_MAX} file descriptors open
74: simultaneously.
75: .SH "ERRORS
76: The named file is opened unless one or more of the
77: following are true:
78: .TP 15
79: [EPERM]
80: The pathname contains a character with the high-order bit set.
81: .TP 15
82: [ENOTDIR]
83: A component of the path prefix is not a directory.
84: .TP 15
85: [ENOENT]
86: O_CREAT is not set and the named file does not exist.
87: .TP 15
88: [EACCES]
89: A component of the path prefix denies search permission.
90: .TP 15
91: [EACCES]
92: The required permissions (for reading and/or writing)
93: are denied for the named flag.
94: .TP 15
95: [EISDIR]
96: The named file is a directory, and the arguments specify
97: it is to be opened for writting.
98: .TP 15
99: [EROFS]
100: The named file resides on a read-only file system,
101: and the file is to be modified.
102: .TP 15
103: [EMFILE]
104: {OPEN_MAX} file descriptors are currently open.
105: .TP 15
106: [ENXIO]
107: The named file is a character special or block
108: special file, and the device associated with this special file
109: does not exist.
110: .TP 15
111: [ETXTBSY]
112: The file is a pure procedure (shared text) file that is being
113: executed and the \fIopen\fP call requests write access.
114: .TP 15
115: [EFAULT]
116: .I Path
117: points outside the process's allocated address space.
118: .TP 15
119: [ELOOP]
120: Too many symbolic links were encountered in translating the pathname.
121: .TP 15
122: [EEXIST]
123: O_EXCL was specified and the file exists.
124: .TP 15
125: [ENXIO]
126: The O_NDELAY flag is given, and the file is a communications device
127: on which their is no carrier present.
128: .TP 15
129: [EOPNOTSUPP]
130: An attempt was made to open a socket (not currently implemented).
131: .SH "SEE ALSO"
132: chmod(2), close(2), dup(2), lseek(2), read(2), write(2), umask(2)
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