getsockopt(3N) getsockopt(3N)
NAME
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS
cc [options] file -lsocket -lnsl
#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int s, int level, int optname, void *optval,
size_t *optlen);
int setsockopt(int s, int level, int optname, const void *optval,
size_t 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 protocol 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 getprotoent(3N)].
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. If no option value is to be supplied or
returned, a 0 optval may be supplied.
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 (see
Copyright 1994 Novell, Inc. Page 1
getsockopt(3N) getsockopt(3N)
below). struct linger is defined in
/usr/include/sys/socket.h.
The following options are recognized at the socket level.
Except as noted, each may be examined with getsockopt and set
with setsockopt.
SO_DEBUG toggle recording of debugging information
SO_REUSEADDR toggle local address reuse
SO_KEEPALIVE toggle keep connections alive
SO_DONTROUTE toggle routing bypass for outgoing messages
SO_LINGER linger on close if data is present
SO_BROADCAST toggle permission to transmit broadcast
messages
SO_OOBINLINE toggle reception of out-of-band data in band
SO_SNDBUF set buffer size for output
SO_RCVBUF set buffer size for input
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 call should allow reuse of local
addresses.
SO_KEEPALIVE comes into play when a connection has had no
traffic on it for two hours. At that point either side of the
connection that has SO_KEEPALIVE set will send a special
packet guaranteed to elict a response from a properly
implemented TCP/IP product. If a response is not received,
(after several short-interval timeouts), the connection is
declared down and processes using the socket are notified by
sending a SIGPIPE signal.
SO_DONTROUTE 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.
SO_LINGER controls the action taken when unsent messages are
queued on a socket and a close is performed. If the socket
promises reliable delivery of data and SO_LINGER is set, the
system will block the process 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
Copyright 1994 Novell, Inc. Page 2
getsockopt(3N) getsockopt(3N)
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 process to continue as quickly as possible.
SO_BROADCAST requests permission to send broadcast datagrams
on the socket.
SO_OOBINLINE works with protocols that support out-of-band
data to request that out-of-band data be placed in the normal
data input queue as received. The data will then be
accessible with recv or read calls without the MSG_OOB flag.
SO_SNDBUF and SO_RCVBUF 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 system places an absolute limit on these values.
SO_TYPE and SO_ERROR are 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.
Files
/usr/lib/locale/locale/LC_MESSAGES/uxns1
Return Values
A 0 is returned if the call succeeds, -1 if it fails.
ERRORS
The call succeeds 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 at the level
indicated.
ENOMEM There was insufficient user memory available
for the operation to complete.
ENOSR There were insufficient STREAMS resources
available for the operation to complete.
Copyright 1994 Novell, Inc. Page 3
getsockopt(3N) getsockopt(3N)
REFERENCES
close(2), getprotoent(3N), ioctl(2), read(2), socket(3N)
Copyright 1994 Novell, Inc. Page 4