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1.1 root 1: .\" Copyright (c) 1983 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: .\" @(#)getsockopt.2 6.4 (Berkeley) 5/23/86
6: .\"
7: .TH GETSOCKOPT 2 "May 23, 1986"
8: .UC 5
9: .SH NAME
10: getsockopt, setsockopt \- get and set options on sockets
11: .SH SYNOPSIS
12: .nf
13: .ft B
14: #include <sys/types.h>
15: #include <sys/socket.h>
16: .PP
17: .ft B
18: getsockopt(s, level, optname, optval, optlen)
19: int s, level, optname;
20: char *optval;
21: int *optlen;
22: .sp
23: setsockopt(s, level, optname, optval, optlen)
24: int s, level, optname;
25: char *optval;
26: int optlen;
27: .fi
28: .SH DESCRIPTION
29: .I Getsockopt
30: and
31: .I setsockopt
32: manipulate
33: .I options
34: associated with a socket. Options may exist at multiple
35: protocol levels; they are always present at the uppermost
36: ``socket'' level.
37: .PP
38: When manipulating socket options the level at which the
39: option resides and the name of the option must be specified.
40: To manipulate options at the ``socket'' level,
41: .I level
42: is specified as SOL_SOCKET. To manipulate options at any
43: other level the protocol number of the appropriate protocol
44: controlling the option is supplied. For example,
45: to indicate that an option is to be interpreted by the TCP protocol,
46: .I level
47: should be set to the protocol number of TCP; see
48: .IR getprotoent (3N).
49: .PP
50: The parameters
51: .I optval
52: and
53: .I optlen
54: are used to access option values for
55: .IR setsockopt .
56: For
57: .I getsockopt
58: they identify a buffer in which the value for the
59: requested option(s) are to be returned. For
60: .IR getsockopt ,
61: .I optlen
62: is a value-result parameter, initially containing the
63: size of the buffer pointed to by
64: .IR optval ,
65: and modified on return to indicate the actual size of
66: the value returned. If no option value is
67: to be supplied or returned,
68: .I optval
69: may be supplied as 0.
70: .PP
71: .I Optname
72: and any specified options are passed uninterpreted to the appropriate
73: protocol module for interpretation.
74: The include file
75: .RI < sys/socket.h >
76: contains definitions for ``socket'' level options, described below.
77: Options at other protocol levels vary in format and
78: name; consult the appropriate entries in section (4P).
79: .PP
80: Most socket-level options take an
81: .I int
82: parameter for
83: .IR optval .
84: For
85: .IR setsockopt ,
86: the parameter should non-zero to enable a boolean option,
87: or zero if the option is to be disabled.
88: SO_LINGER uses a
89: .I struct linger
90: parameter, defined in
91: .RI < sys/socket.h >,
92: which specifies the desired state of the option and the
93: linger interval (see below).
94: .PP
95: The following options are recognized at the socket level.
96: Except as noted, each may be examined with
97: .I getsockopt
98: and set with
99: .IR setsockopt .
100: .PP
101: .RS
102: .ta \w'SO_BROADCAST\ \ \ \ 'u
103: .nf
104: SO_DEBUG toggle recording of debugging information
105: SO_REUSEADDR toggle local address reuse
106: SO_KEEPALIVE toggle keep connections alive
107: SO_DONTROUTE toggle routing bypass for outgoing messages
108: SO_LINGER linger on close if data present
109: SO_BROADCAST toggle permission to transmit broadcast messages
110: SO_OOBINLINE toggle reception of out-of-band data in band
111: SO_SNDBUF set buffer size for output
112: SO_RCVBUF set buffer size for input
113: SO_TYPE get the type of the socket (get only)
114: SO_ERROR get and clear error on the socket (get only)
115: .fi
116: .RE
117: .PP
118: SO_DEBUG enables debugging in the underlying protocol modules.
119: SO_REUSEADDR indicates that the rules used in validating addresses supplied
120: in a
121: .IR bind (2)
122: call should allow reuse of local addresses. SO_KEEPALIVE enables the
123: periodic transmission of messages on a connected socket. Should the
124: connected party fail to respond to these messages, the connection is
125: considered broken and processes using the socket are notified via a
126: SIGPIPE signal. SO_DONTROUTE indicates that outgoing messages should
127: bypass the standard routing facilities. Instead, messages are directed
128: to the appropriate network interface according to the network portion
129: of the destination address.
130: .PP
131: SO_LINGER controls the action taken when unsent messags
132: are queued on socket and a
133: .IR close (2)
134: is performed.
135: If the socket promises reliable delivery of data and SO_LINGER is set,
136: the system will block the process on the
137: .I close
138: attempt until it is able to transmit the data or until it decides it
139: is unable to deliver the information (a timeout period, termed the
140: linger interval, is specified in the
141: .IR setsockopt
142: call when SO_LINGER is requested).
143: If SO_LINGER is disabled and a
144: .I close
145: is issued, the system will process the close in a manner that allows
146: the process to continue as quickly as possible.
147: .PP
148: The option SO_BROADCAST requests permission to send broadcast datagrams
149: on the socket.
150: Broadcast was a privileged operation in earlier versions of the system.
151: With protocols that support out-of-band data, the SO_OOBINLINE option
152: requests that out-of-band data be placed in the normal data input queue
153: as received; it will then be accessible with
154: .I recv
155: or
156: .I read
157: calls without the MSG_OOB flag.
158: SO_SNDBUF and SO_RCVBUF are options to adjust the normal
159: buffer sizes allocated for output and input buffers, respectively.
160: The buffer size may be increased for high-volume connections,
161: or may be decreased to limit the possible backlog of incoming data.
162: The system places an absolute limit on these values.
163: Finally, SO_TYPE and SO_ERROR are options used only with
164: .IR setsockopt .
165: SO_TYPE returns the type of the socket, such as SOCK_STREAM;
166: it is useful for servers that inherit sockets on startup.
167: SO_ERROR returns any pending error on the socket and clears
168: the error status.
169: It may be used to check for asynchronous errors on connected
170: datagram sockets or for other asynchronous errors.
171: .SH "RETURN VALUE"
172: A 0 is returned if the call succeeds, \-1 if it fails.
173: .SH ERRORS
174: The call succeeds unless:
175: .TP 20
176: [EBADF]
177: The argument \fIs\fP is not a valid descriptor.
178: .TP 20
179: [ENOTSOCK]
180: The argument \fIs\fP is a file, not a socket.
181: .TP 20
182: [ENOPROTOOPT]
183: The option is unknown at the level indicated.
184: .TP 20
185: [EFAULT]
186: The address pointed to by
187: .I optval
188: is not in a valid part of the process address space.
189: For
190: .IR getsockopt ,
191: this error may also be returned if
192: .I optlen
193: is not in a valid part of the process address space.
194: .SH "SEE ALSO"
195: ioctl(2), socket(2), getprotoent(3N)
196: .SH BUGS
197: Several of the socket options should be handled at lower levels of the system.
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