GETSOCKOPT(2)
NAME
getsockopt, setsockopt − get/set options on sockets
USAGE
#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 socket s. 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(3N).
The parameters optval and optlen are used to access option values for setsockopt. For getsockopt, optval and optlen identify a buffer in which the value for the requested option(s) is 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 designated as zero.
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).
RETURN VALUE
A successful call returns zero. A failed call returns -1 and sets errno as indicated below.
ERRORS
These calls succeed 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] Options are not in a valid part of process address space.