4.3BSD/usr/man/man2/getsockopt.2

.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)getsockopt.2	6.4 (Berkeley) 5/23/86
.\"
.TH GETSOCKOPT 2 "May 23, 1986"
.UC 5
.SH NAME
getsockopt, setsockopt \- get and set options on sockets
.SH SYNOPSIS
.nf
.ft B
#include <sys/types.h>
#include <sys/socket.h>
.PP
.ft B
getsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char *optval;
int *optlen;
.sp
setsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char *optval;
int optlen;
.fi
.SH DESCRIPTION
.I Getsockopt
and
.I setsockopt
manipulate
.I options
associated with a socket.  Options may exist at multiple
protocol levels; they are always present at the uppermost
``socket'' level.
.PP
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,
.I 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,
.I level
should be set to the protocol number of TCP; see
.IR getprotoent (3N).
.PP
The parameters
.I optval
and
.I optlen
are used to access option values for
.IR setsockopt .
For
.I getsockopt
they identify a buffer in which the value for the
requested option(s) are to be returned.  For
.IR getsockopt ,
.I optlen
is a value-result parameter, initially containing the
size of the buffer pointed to by
.IR optval ,
and modified on return to indicate the actual size of
the value returned.  If no option value is
to be supplied or returned,
.I optval
may be supplied as 0.
.PP
.I Optname
and any specified options are passed uninterpreted to the appropriate
protocol module for interpretation.
The include file
.RI < sys/socket.h >
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).
.PP
Most socket-level options take an
.I int
parameter for
.IR optval .
For
.IR setsockopt ,
the parameter should non-zero to enable a boolean option,
or zero if the option is to be disabled.
SO_LINGER uses a
.I struct linger
parameter, defined in
.RI < sys/socket.h >,
which specifies the desired state of the option and the
linger interval (see below).
.PP
The following options are recognized at the socket level.
Except as noted, each may be examined with
.I getsockopt
and set with
.IR setsockopt .
.PP
.RS
.ta \w'SO_BROADCAST\ \ \ \ 'u
.nf
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)
.fi
.RE
.PP
SO_DEBUG enables debugging in the underlying protocol modules.
SO_REUSEADDR indicates that the rules used in validating addresses supplied
in a
.IR bind (2)
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.
.PP
SO_LINGER controls the action taken when unsent messags
are queued on socket and a 
.IR close (2)
is performed.
If the socket promises reliable delivery of data and SO_LINGER is set,
the system will block the process on the 
.I close
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
.IR setsockopt 
call when SO_LINGER is requested). 
If SO_LINGER is disabled and a 
.I close
is issued, the system will process the close in a manner that allows
the process to continue as quickly as possible.
.PP
The option SO_BROADCAST requests permission to send broadcast datagrams
on the socket.
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
.I recv
or
.I read
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
.IR setsockopt .
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
the error status.
It may be used to check for asynchronous errors on connected
datagram sockets or for other asynchronous errors.
.SH "RETURN VALUE"
A 0 is returned if the call succeeds, \-1 if it fails.
.SH ERRORS
The call succeeds unless:
.TP 20
[EBADF]
The argument \fIs\fP is not a valid descriptor.
.TP 20
[ENOTSOCK]
The argument \fIs\fP is a file, not a socket.
.TP 20
[ENOPROTOOPT]
The option is unknown at the level indicated.
.TP 20
[EFAULT]
The address pointed to by 
.I optval
is not in a valid part of the process address space.
For
.IR getsockopt ,
this error may also be returned if
.I optlen
is not in a valid part of the process address space.
.SH "SEE ALSO"
ioctl(2), socket(2), getprotoent(3N)
.SH BUGS
Several of the socket options should be handled at lower levels of the system.