getsockopt(3N) 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 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 SOLSOCKET. 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 setsockopt(),
the optval parameter should be non-zero to enable a boolean option,
or zero if the option is to be disabled. SOLINGER uses a struct
linger parameter that specifies the desired state of the option and
the linger interval (see below). struct linger is defined in
/usr/include/sys/socket.h.
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getsockopt(3N) getsockopt(3N)
The following options are recognized at the socket level. Except as
noted, each may be examined with getsockopt() and set with
setsockopt().
SODEBUG toggle recording of debugging information
SOREUSEADDR toggle local address reuse
SOKEEPALIVE toggle keep connections alive
SODONTROUTE toggle routing bypass for outgoing messages
SOLINGER linger on close if data is present
SOBROADCAST toggle permission to transmit broadcast
messages
SOOOBINLINE toggle reception of out-of-band data in
band
SOSNDBUF set buffer size for output
SORCVBUF set buffer size for input
SOTYPE get the type of the socket(get only)
SOERROR get and clear error on the socket(get only)
SODEBUG enables debugging in the underlying protocol modules.
SOREUSEADDR indicates that the rules used in validating addresses
supplied in a bind(3N) call should allow reuse of local addresses.
SOKEEPALIVE 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. SODONTROUTE 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.
SOLINGER 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 SOLINGER 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
setsockopt() call when SOLINGER is requested). If SOLINGER 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 SOBROADCAST requests permission to send broadcast
datagrams on the socket. With protocols that support out-of-band
data, the SOOOBINLINE 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 MSGOOB flag.
SOSNDBUF and SORCVBUF 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, SOTYPE and
SOERROR are options used only with getsockopt(). SOTYPE returns
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getsockopt(3N) getsockopt(3N)
the type of the socket (for example, SOCKSTREAM). It is useful for
servers that inherit sockets on startup. SOERROR 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 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.
SEE ALSO
ioctl(2), socket(3N), getprotoent(3N).
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