getsockopt(2)

Name

getsockopt, setsockopt − get or set options on sockets

Syntax

#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

The getsockopt and setsockopt system calls manipulate options associated with a socket. Options can 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 must be 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. For further information, see getprotoent(.).

The parameters optval and optlen are used to access option values for setsockopt. For getsockopt, they identify a buffer in which the values for the requested options 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 can be supplied as 0.

The optname parameter 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. For further information, see socket(.). Options at other protocol levels vary in format and name. Consult the arp(,), ip(,), tcp() or udp() reference pages for details.

Return Values

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

Diagnostics

The getsockopt call fails under the following conditions:

[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 can also be returned if optlen is not in a valid part of the process address space.

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