.\" Copyright (c) 1983 The Regents of the University of California.
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.\" @(#)getsockopt.2 6.5 (Berkeley) %G%
getsockopt, setsockopt \- get and set options on sockets
getsockopt(s, level, optname, optval, optlen)
setsockopt(s, level, optname, optval, optlen)
associated with a socket. Options may exist at multiple
protocol levels; they are always present at the uppermost
When manipulating socket options the level at which the
option resides and the name of the option must be specified.
To manipulate options at the ``socket'' level,
is specified as SOL_SOCKET. To manipulate options at any
other level the protocol number of the appropriate protocol
controlling the option is supplied. For example,
to indicate that an option is to be interpreted by the TCP protocol,
should be set to the protocol number of TCP; see
are used to access option values for
they identify a buffer in which the value for the
requested option(s) are to be returned. For
is a value-result parameter, initially containing the
size of the buffer pointed to by
and modified on return to indicate the actual size of
the value returned. If no option value is
to be supplied or returned,
and any specified options are passed uninterpreted to the appropriate
protocol module for interpretation.
contains definitions for ``socket'' level options, described below.
Options at other protocol levels vary in format and
name; consult the appropriate entries in section (4P).
Most socket-level options take an
the parameter should non-zero to enable a boolean option,
or zero if the option is to be disabled.
which specifies the desired state of the option and the
linger interval (see below).
The following options are recognized at the socket level.
Except as noted, each may be examined with
.ta \w'SO_BROADCAST\ \ \ \ 'u
SO_DEBUG toggle recording of debugging information
SO_REUSEADDR toggle local address reuse
SO_KEEPALIVE toggle keep connections alive
SO_DONTROUTE toggle routing bypass for outgoing messages
SO_LINGER linger on close if data present
SO_BROADCAST toggle permission to transmit broadcast messages
SO_OOBINLINE toggle reception of out-of-band data in band
SO_SNDBUF set buffer size for output
SO_RCVBUF set buffer size for input
SO_TYPE get the type of the socket (get only)
SO_ERROR get and clear error on the socket (get only)
SO_DEBUG enables debugging in the underlying protocol modules.
SO_REUSEADDR indicates that the rules used in validating addresses supplied
call should allow reuse of local addresses. SO_KEEPALIVE enables the
periodic transmission of messages on a connected socket. Should the
connected party fail to respond to these messages, the connection is
considered broken and processes using the socket are notified via a
SIGPIPE signal. SO_DONTROUTE indicates that outgoing messages should
bypass the standard routing facilities. Instead, messages are directed
to the appropriate network interface according to the network portion
of the destination address.
SO_LINGER controls the action taken when unsent messags
are queued on socket and a
If the socket promises reliable delivery of data and SO_LINGER is set,
the system will block the process on the
attempt until it is able to transmit the data or until it decides it
is unable to deliver the information (a timeout period, termed the
linger interval, is specified in the
call when SO_LINGER is requested).
If SO_LINGER is disabled and a
is issued, the system will process the close in a manner that allows
the process to continue as quickly as possible.
The option SO_BROADCAST requests permission to send broadcast datagrams
Broadcast was a privileged operation in earlier versions of the system.
With protocols that support out-of-band data, the SO_OOBINLINE option
requests that out-of-band data be placed in the normal data input queue
as received; it will then be accessible with
calls without the MSG_OOB flag.
SO_SNDBUF and SO_RCVBUF are options to adjust the normal
buffer sizes allocated for output and input buffers, respectively.
The buffer size may be increased for high-volume connections,
or may be decreased to limit the possible backlog of incoming data.
The system places an absolute limit on these values.
Finally, SO_TYPE and SO_ERROR are options used only with
SO_TYPE returns the type of the socket, such as SOCK_STREAM;
it is useful for servers that inherit sockets on startup.
SO_ERROR returns any pending error on the socket and clears
It may be used to check for asynchronous errors on connected
datagram sockets or for other asynchronous errors.
A 0 is returned if the call succeeds, \-1 if it fails.
The call succeeds unless:
The argument \fIs\fP is not a valid descriptor.
The argument \fIs\fP is a file, not a socket.
The option is unknown at the level indicated.
The address pointed to by
is not in a valid part of the process address space.
this error may also be returned if
is not in a valid part of the process address space.
ioctl(2), socket(2), getprotoent(3N)
Several of the socket options should be handled at lower levels of the system.