4.2BSD/usr/man/man2/getsockopt.2

.TH GETSOCKOPT 2 "7 July 1983"
.UC 4
.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 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; see
.IR socket (2).
Options at other protocol levels vary in format and
name, consult the appropriate entries in (4P).  
.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.
.TP 20
[EFAULT]
The options are not in a valid part of the
process address space.
.SH "SEE ALSO"
socket(2), getprotoent(3N)