getsockopt(3N) getsockopt(3N)
NAME
getsockopt, setsockopt - query and set options on sockets
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int s, int level, int optname,
char *optval, int *optlen);
int setsockopt(int s, int level, int 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 SOLSOCKET 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. With SOLINGER, optval points to
a structure struct linger which specifies the desired state of the
option and the linger interval (see below). struct linger is defined
in /usr/include/sys/socket.h.
The following options are possible at the socket level. Except as
noted, each may be queried with getsockopt() and set with
setsockopt().
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getsockopt(3N) getsockopt(3N)
SODEBUG record debugging information
SOREUSEADDR reuse local address
SOKEEPALIVE examine connections via which no further data
traffic is being transported
SODONTROUTE toggle routing bypass for outgoing messages
SOLINGER linger on close if data is present
SOBROADCAST permission to transmit broadcast messages
SOOOBINLINE handle out-of-band data in the entry
SOSNDBUF buffer size for output
SORCVBUF buffer size for input
SOTYPE identify the type of the socket (get only)
SOERROR identify and clear error states on the socket (get
only)
SODEBUG enables debugging in the underlying protocol modules.
SOREUSEADDR enables local addresses to be reused in the bind(3N)
call.
SOKEEPALIVE monitors the connection. If the connection is idle for a
certain length of time (i.e. if no messages are exchanged between
partners), then messages are sent periodically to the relevant
partner. If the connected partner fails to respond to these messages
for any reason, the connection is considered broken and processes
using the socket are notified using a SIGPIPE signal.
SODONTROUTE instructs the system to bypass the standard routing algo-
rithm. In this case, packets are sent directly via the interface where
the network number in the interface address matches the network number
of the recipient's address in the packet.
SOLINGER controls the action taken when unsent messages are queued on
a socket while a close(2) is performed. If the socket guarantees reli-
able delivery of data (socket type SOCKSTREAM) 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 discovers it is unable to
deliver the data - because, for example, the maximum linger interval
specified in the setsockopt() call when SOLINGER was requested has
expired. If SOLINGER is disabled and a close() is issued while there
is still data to be sent, the close() call is rejected after a short
interval and the system attempts to send the outstanding data in the
background.
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getsockopt(3N) getsockopt(3N)
The option SOBROADCAST requests permission to send broadcast data-
grams 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 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.
DIAGNOSTICS
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), ip(7).
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