getsockopt, setsockopt - get and set options on sockets

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);

The getsockopt() and setsockopt() functions manipulate options associated with a socket. Options may exist at multiple protocol levels; they are always present at the uppermost "socket" level.

The level argument specifies the protocol level at which the option resides. To manipulate options at the socket level, specify the level argument as SOL_SOCKET. To manipulate options at the protocol level, supply the appropriate protocol number for the protocol controlling the option. For example, to indicate that an option will be interpreted by the TCP, set level to the protocol number of TCP, as defined in the <netinet/in.h> header, or as determined by using getprotobyname(3SOCKET). Some socket protocol families may also define additional levels, such as SOL_ROUTE. Only socket-level options are described here.

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.

The 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:


on = 1/off = 0


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 setsockopt().


enable/disable recording of debugging information


enable/disable local address reuse


enable/disable keep connections alive


enable/disable routing bypass for outgoing messages


linger on close if data is present


enable/disable permission to transmit broadcast messages


enable/disable reception of out-of-band data in band


set buffer size for output


set buffer size for input


application wants delayed error


enable/disable reception of timestamp with datagrams


enable/disable exclusive binding of the socket


get the type of the socket (get only)


get and clear error on the socket (get only)


get or set mandatory access control on the socket. This option is available only when the system is configured with Trusted Extensions.


bypass zone boundaries (privileged).


get the domain used in the socket (get only)


for socket in domains PF_INET and PF_INET6, get the underlying protocol number used in the socket. For socket in domain PF_ROUTE, get the address family used in the socket.

The SO_DEBUG option enables debugging in the underlying protocol modules. The SO_REUSEADDR option indicates that the rules used in validating addresses supplied in a bind(3SOCKET) call should allow reuse of local addresses. The SO_KEEPALIVE option 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. The SO_DONTROUTE option indicates that outgoing messages should bypass the standard routing facilities. Instead, messages are directed to the appropriate network interface according to the network portion of the destination address.

The SO_LINGER option controls the action taken when unsent messages are queued on a socket and a close(2) is performed. If the socket promises reliable 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.

The SO_SNDBUF and SO_RCVBUF options 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(8) utility to determine the current default values. See the Solaris Tunable Parameters Reference Manual for information on setting the values of udp_max_buf and tcp_max_buf. At present, lowering SO_RCVBUF on a TCP connection after it has been established has no effect.

By default, delayed errors (such as ICMP port unreachable packets) are returned only for connected datagram sockets. The SO_DGRAM_ERRIND option 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).

If the SO_TIMESTAMP option is enabled on a SO_DGRAM or a SO_RAW socket, the recvmsg(3XNET) call will return a timestamp in the native data format, corresponding to when the datagram was received.

The SO_EXCLBIND option is used to enable or disable the exclusive binding of a socket. It overrides the use of the SO_REUSEADDR option to reuse an address on bind(3SOCKET). The actual semantics of the SO_EXCLBIND option depend on the underlying protocol. See tcp(4P) or udp(4P) for more information.

The SO_TYPE and SO_ERROR options are used only with getsockopt(). The SO_TYPE option returns the type of the socket, for example, SOCK_STREAM. It is useful for servers that inherit sockets on startup. The SO_ERROR option 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.

The SO_MAC_EXEMPT option is used to toggle socket behavior with unlabeled peers. A socket that has this option enabled can communicate with an unlabeled peer if it is in the global zone or has a label that dominates the default label of the peer. Otherwise, the socket must have a label that is equal to the default label of the unlabeled peer. Calling setsockopt() with this option returns an EACCES error if the process lacks the NET_MAC_AWARE privilege or if the socket is bound. The SO_MAC_EXEMPT option is available only when the system is configured with Trusted Extensions.

The SO_ALLZONES option can be used to bypass zone boundaries between shared-IP zones. Normally, the system prevents a socket from being bound to an address that is not assigned to the current zone. It also prevents a socket that is bound to a wildcard address from receiving traffic for other zones. However, some daemons which run in the global zone might need to send and receive traffic using addresses that belong to other shared-IP zones. If set before a socket is bound, SO_ALLZONES causes the socket to ignore zone boundaries between shared-IP zones and permits the socket to be bound to any address assigned to the shared-IP zones. If the socket is bound to a wildcard address, it receives traffic intended for all shared-IP zones and behaves as if an equivalent socket were bound in each active shared-IP zone. Applications that use the SO_ALLZONES option to initiate connections or send datagram traffic should specify the source address for outbound traffic by binding to a specific address. There is no effect from setting this option in an exclusive-IP zone. Setting this option requires the sys_net_config privilege. See zones(7).

If successful, getsockopt() and setsockopt() return 0. Otherwise, the functions return −1 and set errno to indicate the error.

The getsockopt() and setsockopt() calls succeed unless:


The argument s is not a valid file descriptor.


There was insufficient memory available for the operation to complete.


The option is unknown at the level indicated.


There were insufficient STREAMS resources available for the operation to complete.


The argument s is not a socket.


SO_SNDBUF or SO_RCVBUF exceeds a system limit.


Invalid length for a given socket option.


Invalid address for IP_MULTICAST_IF.


Not a multicast address for IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP.


Bad interface address for IP_ADD_MEMBERSHIP and IP_DROP_MEMBERSHIP.


Address already joined for IP_ADD_MEMBERSHIP.


Address not joined for IP_DROP_MEMBERSHIP.


No permissions.


Permission denied.


The specified option is invalid at the specified socket level, or the socket has been shut down.

See attributes(7) for descriptions of the following attributes:

MT-Level Safe

close(2), ioctl(2), read(2), socket.h(3HEAD), bind(3SOCKET), getprotobyname(3SOCKET), recv(3SOCKET), send(3SOCKET), socket(3SOCKET), recvmsg(3XNET), tcp(4P), udp(4P), attributes(7), zones(7), ndd(8)

Solaris Tunable Parameters Reference Manual

January 27, 2009 OmniOS