1GETSOCKOPT(2) System Calls Manual GETSOCKOPT(2)
2
6 getsockopt, setsockopt - get and set options on sockets
7
9 #include <sys/types.h>
10 #include <sys/socket.h>
11 getsockopt(s, level, optname, optval, optlen)
13 int s, level, optname;
14 char *optval;
15 int *optlen;
16 setsockopt(s, level, optname, optval, optlen)
18 int s, level, optname;
19 char *optval;
20 int optlen;
21
23 Getsockopt and setsockopt manipulate options associated with a socket.
24 Options may exist at multiple protocol levels; they are always present
25 at the uppermost ``socket'' level.
26 When manipulating socket options the level at which the option resides
28 and the name of the option must be specified. To manipulate options at
29 the ``socket'' level, level is specified as SOL_SOCKET. To manipulate
30 options at any other level the protocol number of the appropriate pro‐
31 tocol controlling the option is supplied. For example, to indicate
32 that an option is to be interpreted by the TCP protocol, level should
33 be set to the protocol number of TCP; see getprotoent(3N).
34 The parameters optval and optlen are used to access option values for
36 setsockopt. For getsockopt they identify a buffer in which the value
37 for the requested option(s) are to be returned. For getsockopt, optlen
38 is a value-result parameter, initially containing the size of the buf‐
39 fer pointed to by optval, and modified on return to indicate the actual
40 size of the value returned. If no option value is to be supplied or
41 returned, optval may be supplied as 0.
42 Optname and any specified options are passed uninterpreted to the
44 appropriate protocol module for interpretation. The include file
45 <sys/socket.h> contains definitions for ``socket'' level options,
46 described below. Options at other protocol levels vary in format and
47 name; consult the appropriate entries in section (4P).
48 Most socket-level options take an int parameter for optval. For set‐
50 sockopt, the parameter should non-zero to enable a boolean option, or
51 zero if the option is to be disabled. SO_LINGER uses a struct linger
52 parameter, defined in <sys/socket.h>, which specifies the desired state
53 of the option and the linger interval (see below).
54 The following options are recognized at the socket level. Except as
56 noted, each may be examined with getsockopt and set with setsockopt.
57 SO_DEBUG toggle recording of debugging information
59 SO_REUSEADDR toggle local address reuse
60 SO_KEEPALIVE toggle keep connections alive
61 SO_DONTROUTE toggle routing bypass for outgoing messages
62 SO_LINGER linger on close if data present
63 SO_BROADCAST toggle permission to transmit broadcast messages
64 SO_OOBINLINE toggle reception of out-of-band data in band
65 SO_SNDBUF set buffer size for output
66 SO_RCVBUF set buffer size for input
67 SO_TYPE get the type of the socket (get only)
68 SO_ERROR get and clear error on the socket (get only)
69 SO_DEBUG enables debugging in the underlying protocol modules.
71 SO_REUSEADDR indicates that the rules used in validating addresses sup‐
72 plied in a bind(2) call should allow reuse of local addresses.
73 SO_KEEPALIVE enables the periodic transmission of messages on a con‐
74 nected socket. Should the connected party fail to respond to these
75 messages, the connection is considered broken and processes using the
76 socket are notified via a SIGPIPE signal. SO_DONTROUTE indicates that
77 outgoing messages should bypass the standard routing facilities.
78 Instead, messages are directed to the appropriate network interface
79 according to the network portion of the destination address.
80 SO_LINGER controls the action taken when unsent messags are queued on
82 socket and a close(2) is performed. If the socket promises reliable
83 delivery of data and SO_LINGER is set, the system will block the
84 process on the close attempt until it is able to transmit the data or
85 until it decides it is unable to deliver the information (a timeout
86 period, termed the linger interval, is specified in the setsockopt call
87 when SO_LINGER is requested). If SO_LINGER is disabled and a close is
88 issued, the system will process the close in a manner that allows the
89 process to continue as quickly as possible.
90 The option SO_BROADCAST requests permission to send broadcast datagrams
92 on the socket. Broadcast was a privileged operation in earlier ver‐
93 sions of the system. With protocols that support out-of-band data, the
94 SO_OOBINLINE option requests that out-of-band data be placed in the
95 normal data input queue as received; it will then be accessible with
96 recv or read calls without the MSG_OOB flag. SO_SNDBUF and SO_RCVBUF
97 are options to adjust the normal buffer sizes allocated for output and
98 input buffers, respectively. The buffer size may be increased for
99 high-volume connections, or may be decreased to limit the possible
100 backlog of incoming data. The system places an absolute limit on these
101 values. Finally, SO_TYPE and SO_ERROR are options used only with set‐
102 sockopt. SO_TYPE returns the type of the socket, such as SOCK_STREAM;
103 it is useful for servers that inherit sockets on startup. SO_ERROR
104 returns any pending error on the socket and clears the error status.
105 It may be used to check for asynchronous errors on connected datagram
106 sockets or for other asynchronous errors.
107
109 A 0 is returned if the call succeeds, -1 if it fails.
110
112 The call succeeds unless:
113 [EBADF] The argument s is not a valid descriptor.
115 [ENOTSOCK] The argument s is a file, not a socket.
117 [ENOPROTOOPT] The option is unknown at the level indicated.
119 [EFAULT] The address pointed to by optval is not in a valid
121 part of the process address space. For getsockopt,
122 this error may also be returned if optlen is not in
123 a valid part of the process address space.
124
126 ioctl(2), socket(2), getprotoent(3N)
127
129 Several of the socket options should be handled at lower levels of the
130 system.
1314.2 Berkeley Distribution May 23, 1986 GETSOCKOPT(2)