getsockopt(3N) LIBRARY FUNCTIONS getsockopt(3N)
NAME
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char *optval;
int *optlen;
int setsockopt(s, level, optname, optval, optlen)
int s, level, optname;
char *optval;
int optlen;
DESCRIPTION
getsockopt() and setsockopt() manipulate options associated
with a socket. Options may exist at multiple protocol lev-
els; 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 speci-
fied 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 /usr/include/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 set-
sockopt(), 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
below). struct linger is defined in
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getsockopt(3N) LIBRARY FUNCTIONS getsockopt(3N)
/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(3N) 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 processes using the
socket are notified using 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 por-
tion 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 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 interval, is specified in the set-
sockopt() 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.
The option SO_BROADCAST requests permission to send broad-
cast datagrams on the socket. With protocols that support
out-of-band data, the SO_OOBINLINE option requests that
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getsockopt(3N) LIBRARY FUNCTIONS getsockopt(3N)
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 system
places an absolute limit on these values. 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 VALUE
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 descrip-
tor.
ENOTSOCK The argument s is a file, not a socket.
ENOPROTOOPT The option is unknown at the level indi-
cated.
ENOMEM There was insufficient user memory
available for the operation to complete.
ENOSR There were insufficient STREAMS
resources available for the operation to
complete.
SEE ALSO
ioctl(2), socket(3N), getprotoent(3N).
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