GETSOCKOPT(2) — SYSTEM CALLS

NAME

getsockopt, setsockopt − get and set options on sockets

SYNOPSIS

#include <sys/types.h>
#include <sys/socket.h>

getsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char ∗optval;
int ∗optlen;
setsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char ∗optval;
int optlen;

DESCRIPTION

getsockopt and setsockopt manipulate options associated with a socket. Options may exist at multiple protocol levels; they are always present at the uppermost “socket” level.

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, 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, level should be set to the protocol number of TCP; see getprotoent(3N).

The parameters optval and optlen are used to access option values for setsockopt. For getsockopt they identify a buffer in which the value for the requested option(s) are to be returned. For getsockopt, optlen is a value-result parameter, initially containing the size of the buffer pointed to by optval, and modified on return to indicate the actual size of the value returned. If no option value is to be supplied or returned, optval may be supplied as 0.

optname and any specified options are passed uninterpreted to the appropriate protocol module for interpretation. The include file <sys/socket.h> contains definitions for “socket” level options; see socket(2). Options at other protocol levels vary in format and name, consult the appropriate entries in (4P).

RETURN VALUE

A 0 is returned if the call succeeds, −1 if it fails.

ERRORS

The call succeeds unless:

EBADF The argument s is not a valid descriptor.

ENOTSOCK The argument s is a file, not a socket.

ENOPROTOOPT The option is unknown.

EFAULT The address pointed to by optval is not in a valid part of the process address space. For getsockopt, this error may also be returned if optlen is not in a valid part of the process address space.

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