GETSOCKOPT(2)

NAME
getsockopt, setsockopt - get and set options on sockets

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

int getsockopt(int s, int level, int optname, void *optval, socklen_t *optlen);

int setsockopt(int s, int level, int optname, const void *optval, socklen_t optlen);

DESCRIPTION
Getsockopt and setsockopt() manipulate the 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 that an option is to be interpreted by the TCP protocol, level should be set to the protocol number of TCP; see getprotoent(3).

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 NULL.

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, described below. Options at other protocol levels vary in format and name; consult the appropriate entries in section 4 of the manual.

Most socket-level options utilize an int parameter for optval. For setsockopt(), the parameter should be non-zero to enable a boolean option, or zero if the option is to be disabled.

For a description of the available socket options see socket(7) and the appropriate protocol man pages.

RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

ERRORS

EBADF
    The argument s is not a valid descriptor.

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.

EINVAL
    optlen invalid in setsockopt().

ENOPROTOOPT
    The option is unknown at the level indicated.

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

CONFORMING TO
SVr4, 4.4BSD (these system calls first appeared in 4.2BSD). SVr4 documents additional ENOMEM and ENOSR error codes, but does not document the SO_SNDLOWAT, SO_RCVLOWAT, SO_SNDTIMEO, SO_RCVTIMEO options

NOTE
The fifth argument of getsockopt and setsockopt is in reality an int [*] (and this is what 4.x BSD and libc4 and libc5 have). Some POSIX confusion resulted in the present socklen_t, also used by glibc. See also accept(2).

BUGS
Several of the socket options should be handled at lower levels of the system.

SEE ALSO
ioctl(2), socket(2), getprotoent(3), protocols(5), socket(7), tcp(7), unix(7)