SunOS man pages : getsockopt (3)
Sockets Library Functions getsockopt(3SOCKET)
NAME
getsockopt, setsockopt - get and set options on sockets
SYNOPSIS
cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>
int getsockopt(int s, int level, int optname, void *optval,
int *optlen);
int setsockopt(int s, int level, int optname, const void
*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 getprotobyname(3SOCKET).
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. Use a 0 optval if no
option value is to be supplied or returned.
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 pro-
tocol 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. struct
linger is defined in <<sys/socket.h>. struct linger contains
the following members:
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Sockets Library Functions getsockopt(3SOCKET)
l_onoff
on = 1/off = 0
l_linger
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 setsockopt().
SO_DEBUG
enable/disable recording of debugging information
SO_REUSEADDR
enable/disable local address reuse
SO_KEEPALIVE
enable/disable keep connections alive
SO_DONTROUTE
enable/disable routing bypass for outgoing messages
SO_LINGER
linger on close if data is present
SO_BROADCAST
enable/disable permission to transmit broadcast mes-
sages
SO_OOBINLINE
enable/disable reception of out-of-band data in band
SO_SNDBUF
set buffer size for output
SO_RCVBUF
set buffer size for input
SO_DGRAM_ERRIND
application wants delayed error
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 vali-
dating addresses supplied in a bind(3SOCKET) call should
allow reuse of local addresses. SO_KEEPALIVE enables the
periodic transmission of messages on a connected socket. If
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Sockets Library Functions getsockopt(3SOCKET)
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
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, respec-
tively. The buffer size may be increased for high-volume
connections or may be decreased to limit the possible back-
log 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 Tun-
able Parameters Reference Manual for information on setting
the values of udp_max_buf and tcp_max_buf.
By default, delayed errors (such as ICMP port unreachable
packets) are returned only for connected datagram sockets.
SO_DGRAM_ERRIND 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 destination
address (to parameter) to fail with the appropriate error.
See send(3SOCKET).
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
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Sockets Library Functions getsockopt(3SOCKET)
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 VALUES
If successful, getsockopt() returns 0; otherwise, it returns
-1 and sets errno to indicate the error.
ERRORS
The call succeeds unless:
EBADF The argument s is not a valid file descriptor.
ENOMEM
There was insufficient memory available for the opera-
tion to complete.
ENOPROTOOPT
The option is unknown at the level indicated.
ENOSR There were insufficient STREAMS resources available
for the operation to complete.
ENOTSOCK
The argument s is not a socket.
ENOBUFS
SO_SNDBUF or SO_RCVBUF exceeds a system limit.
EINVAL
Invalid length for IP_OPTIONS.
EHOSTUNREACH
Invalid address for IP_MULTICAST_IF.
EINVAL
Not a multicast address for IP_ADD_MEMBERSHIP and
IP_DROP_MEMBERSHIP.
EADDRNOTAVAIL
Bad interface address for IP_ADD_MEMBERSHIP and
IP_DROP_MEMBERSHIP.
EADDRINUSE
Address already joined for IP_ADD_MEMBERSHIP.
ENOENT
Address not joined for IP_DROP_MEMBERSHIP.
EPERM No permissions.
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Sockets Library Functions getsockopt(3SOCKET)
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| MT-Level | Safe |
|_____________________________|_____________________________|
SEE ALSO
ndd(1M), close(2), ioctl(2), read(2), bind(3SOCKET),
getprotobyname(3SOCKET), recv(3SOCKET), send(3SOCKET),
socket(3SOCKET), attributes(5)
Solaris Tunable Parameters Reference Manual
SunOS 5.8 Last change: 24 Aug 2001 5
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