getsockopt, setsockopt - get and set options on sockets
cc [ flag ... ] file ... -lsocket-lnsl [ library ... ]
int getsockopt(int s, int level, int optname, void *optval,
int setsockopt(int s, int level, int optname, const void *optval,
The getsockopt() and setsockopt() functions manipulate options associ‐
ated 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 getprotoby‐
name(3SOCKET). Some socket protocol families may also define additional
levels, such as SOL_ROUTE. Only socket-level options are described
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 getsock‐
opt(), 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
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 parame‐
ter 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 setsock‐
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 mes‐
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 mod‐
ules. The SO_REUSEADDR option indicates that the rules used in vali‐
dating addresses supplied in a bind(3SOCKET) call should allow reuse of
local addresses. The SO_KEEPALIVE option enables the periodic transmis‐
sion 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
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(1M) utility to determine the current default
values. See the Solaris Tunable Parameters Reference Manual for infor‐
mation 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 des‐
tination address (to parameter) to fail with the appropriate error.
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 for‐
mat, corresponding to when the datagram was received.
The SO_EXCLBIND option is used to enable or disable the exclusive bind‐
ing of a socket. It overrides the use of the SO_REUSEADDR option to re‐
use an address on bind(3SOCKET). The actual semantics of the
SO_EXCLBIND option depend on the underlying protocol. See tcp(7P) or
udp(7P) 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 unla‐
beled 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 domi‐
nates 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 traf‐
fic 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(5).
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 opera‐
tion 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
Bad interface address for IP_ADD_MEMBERSHIP and
Address already joined for IP_ADD_MEMBERSHIP.
Address not joined for IP_DROP_MEMBERSHIP.
The specified option is invalid at the specified
socket level, or the socket has been shut down.
See attributes(5) for descriptions of the following attributes:
│ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│MT-Level │ Safe │
SEE ALSOndd(1M), close(2), ioctl(2), read(2), bind(3SOCKET), getprotoby‐
name(3SOCKET), recv(3SOCKET), recvmsg(3XNET), send(3SOCKET),
socket(3SOCKET), socket.h(3HEAD), attributes(5), zones(5), tcp(7P),
Solaris Tunable Parameters Reference Manual
Jan 27, 2009 GETSOCKOPT(3SOCKET)