getsockopt(3SOCKET) Sockets Library Functions getsockopt(3SOCKET)
NAME
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS
cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int s, int level, int optname, void *optval, int *optlen);
int setsockopt(int s, int level, int optname, const void *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, level is the protocol number of the pro-
tocol that controls the option. For example, to indicate that an option is to be interpreted by the TCP protocol, level is set to the TCP
protocol number . See getprotobyname(3SOCKET).
The parameters optval and optlen are used to access option values for setsockopt(). For getsockopt(), they identify a buffer in which the
value(s) 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. Use a 0 optval if no
option value is to be supplied or returned.
optname and any specified options are passed uninterpreted to the appropriate protocol module for interpretation. The include file
<sys/socket.h> contains definitions for the socket-level options described below. Options at other protocol levels vary in format and name.
Most socket-level options take an int for optval. For setsockopt(), the optval parameter should be non-zero to enable a boolean option, or
zero if the option is to be disabled. SO_LINGER uses a struct linger parameter that specifies the desired state of the option and the
linger interval. struct linger is defined in <sys/socket.h>. struct linger contains the following members:
l_onoff on = 1/off = 0
l_linger linger time, in seconds
The following options are recognized at the socket level. Except as noted, each may be examined with getsockopt() and set with setsock-
opt().
SO_DEBUG enable/disable recording of debugging information
SO_REUSEADDR enable/disable local address reuse
SO_KEEPALIVE enable/disable keep connections alive
SO_DONTROUTE enable/disable routing bypass for outgoing messages
SO_LINGER linger on close if data is present
SO_BROADCAST enable/disable permission to transmit broadcast messages
SO_OOBINLINE enable/disable reception of out-of-band data in band
SO_SNDBUF set buffer size for output
SO_RCVBUF set buffer size for input
SO_DGRAM_ERRIND application wants delayed error
SO_TYPE get the type of the socket (get only)
SO_ERROR get and clear error on the socket (get only)
SO_DEBUG enables debugging in the underlying protocol modules. SO_REUSEADDR indicates that the rules used in validating addresses supplied
in a bind(3SOCKET) call should allow reuse of local addresses. SO_KEEPALIVE enables the periodic transmission of messages on a connected
socket. If the connected party fails to respond to these messages, the connection is considered broken and threads using the socket are
notified using a SIGPIPE signal. SO_DONTROUTE indicates that outgoing messages should bypass the standard routing facilities. Instead, mes-
sages are directed to the appropriate network interface according to the network portion of the destination address.
SO_LINGER controls the action taken when unsent messages are queued on a socket and a close(2) is performed. If the socket promises reli-
able delivery of data and SO_LINGER is set, the system will block the thread on the close() attempt until it is able to transmit the data
or until it decides it is unable to deliver the information (a timeout period, termed the linger interval, is specified in the setsockopt()
call when SO_LINGER is requested). If SO_LINGER is disabled and a close() is issued, the system will process the close() in a manner that
allows the thread to continue as quickly as possible.
The option SO_BROADCAST requests permission to send broadcast datagrams on the socket. With protocols that support out-of-band data, the
SO_OOBINLINE option requests that out-of-band data be placed in the normal data input queue as received; it will then be accessible with
recv() or read() calls without the MSG_OOB flag.
SO_SNDBUF and SO_RCVBUF are options that adjust the normal buffer sizes allocated for output and input buffers, respectively. The buffer
size may be increased for high-volume connections or may be decreased to limit the possible backlog of incoming data. The maximum buffer
size for UDP is determined by the value of the ndd variable udp_max_buf. The maximum buffer size for TCP is determined the value of
the ndd variable tcp_max_buf. Use the ndd(1M) utility to determine the current default values. See the Solaris Tunable Parameters Refer-
ence Manual for information on setting the values of udp_max_buf and tcp_max_buf.
By default, delayed errors (such as ICMP port unreachable packets) are returned only for connected datagram sockets. SO_DGRAM_ERRIND makes
it possible to receive errors for datagram sockets that are not connected. When this option is set, certain delayed errors received after
completion of a sendto() or sendmsg() operation will cause a subsequent sendto() or sendmsg() operation using the same destination address
(to parameter) to fail with the appropriate error. See send(3SOCKET).
Finally, SO_TYPE and SO_ERROR are options used only with getsockopt(). SO_TYPE returns the type of the socket, for example, SOCK_STREAM.
It is useful for servers that inherit sockets on startup. SO_ERROR returns any pending error on the socket and clears the error status. It
may be used to check for asynchronous errors on connected datagram sockets or for other asynchronous errors.
RETURN VALUES
If successful, getsockopt() and setsockopt() return 0; otherwise, the functions return -1 and set errno to indicate the error.
ERRORS
The getsockopt() and setsockopt() calls succeed unless:
EBADF The argument s is not a valid file descriptor.
ENOMEM There was insufficient memory available for the operation to complete.
ENOPROTOOPT The option is unknown at the level indicated.
ENOSR There were insufficient STREAMS resources available for the operation to complete.
ENOTSOCK The argument s is not a socket.
ENOBUFS SO_SNDBUF or SO_RCVBUF exceeds a system limit.
EINVAL Invalid length for IP_OPTIONS.
EHOSTUNREACH Invalid address for IP_MULTICAST_IF.
EINVAL Not a multicast address for IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP.
EADDRNOTAVAIL Bad interface address for IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP.
EADDRINUSE Address already joined for IP_ADD_MEMBERSHIP.
ENOENT Address not joined for IP_DROP_MEMBERSHIP.
EPERM No permissions.
EINVAL The specified option is invalid at the specified socket level, or the socket has been shut down.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|MT-Level |Safe |
+-----------------------------+-----------------------------+
SEE ALSO
ndd(1M), close(2), ioctl(2), read(2), bind(3SOCKET), getprotobyname(3SOCKET), recv(3SOCKET), send(3SOCKET), socket(3SOCKET), attributes(5)
Solaris Tunable Parameters Reference Manual
SunOS 5.10 1 Nov 2003 getsockopt(3SOCKET)