SETSOCKOPT(3P) POSIX Programmer's Manual SETSOCKOPT(3P)
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This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
NAME
setsockopt - set the socket options
SYNOPSIS
#include <sys/socket.h>
int setsockopt(int socket, int level, int option_name,
const void *option_value, socklen_t option_len);
DESCRIPTION
The setsockopt() function shall set the option specified by the
option_name argument, at the protocol level specified by the level
argument, to the value pointed to by the option_value argument for the
socket associated with the file descriptor specified by the socket
argument.
The level argument specifies the protocol level at which the option
resides. To set options at the socket level, specify the level argument
as SOL_SOCKET. To set options at other levels, supply the appropriate
level identifier for the protocol controlling the option. For example,
to indicate that an option is interpreted by the TCP (Transport Control
Protocol), set level to IPPROTO_TCP as defined in the <netinet/in.h>
header.
The option_name argument specifies a single option to set. The
option_name argument and any specified options are passed uninterpreted
to the appropriate protocol module for interpretations. The
<sys/socket.h> header defines the socket-level options. The options
are as follows:
SO_DEBUG
Turns on recording of debugging information. This option enables
or disables debugging in the underlying protocol modules. This
option takes an int value. This is a Boolean option.
SO_BROADCAST
Permits sending of broadcast messages, if this is supported by
the protocol. This option takes an int value. This is a Boolean
option.
SO_REUSEADDR
Specifies that the rules used in validating addresses supplied
to bind() should allow reuse of local addresses, if this is sup-
ported by the protocol. This option takes an int value. This is
a Boolean option.
SO_KEEPALIVE
Keeps connections active by enabling the periodic transmission
of messages, if this is supported by the protocol. This option
takes an int value.
If the connected socket fails to respond to these messages, the connec-
tion is broken and threads writing to that socket are notified with a
SIGPIPE signal. This is a Boolean option.
SO_LINGER
Lingers on a close() if data is present. This option controls
the action taken when unsent messages queue on a socket and
close() is performed. If SO_LINGER is set, the system shall
block the process during close() until it can transmit the data
or until the time expires. If SO_LINGER is not specified, and
close() is issued, the system handles the call in a way that
allows the process to continue as quickly as possible. This
option takes a linger structure, as defined in the
<sys/socket.h> header, to specify the state of the option and
linger interval.
SO_OOBINLINE
Leaves received out-of-band data (data marked urgent) inline.
This option takes an int value. This is a Boolean option.
SO_SNDBUF
Sets send buffer size. This option takes an int value.
SO_RCVBUF
Sets receive buffer size. This option takes an int value.
SO_DONTROUTE
Requests that outgoing messages bypass the standard routing
facilities. The destination shall be on a directly-connected
network, and messages are directed to the appropriate network
interface according to the destination address. The effect, if
any, of this option depends on what protocol is in use. This
option takes an int value. This is a Boolean option.
SO_RCVLOWAT
Sets the minimum number of bytes to process for socket input
operations. The default value for SO_RCVLOWAT is 1. If
SO_RCVLOWAT is set to a larger value, blocking receive calls
normally wait until they have received the smaller of the low
water mark value or the requested amount. (They may return less
than the low water mark if an error occurs, a signal is caught,
or the type of data next in the receive queue is different from
that returned; for example, out-of-band data.) This option takes
an int value. Note that not all implementations allow this
option to be set.
SO_RCVTIMEO
Sets the timeout value that specifies the maximum amount of time
an input function waits until it completes. It accepts a timeval
structure with the number of seconds and microseconds specifying
the limit on how long to wait for an input operation to com-
plete. If a receive operation has blocked for this much time
without receiving additional data, it shall return with a par-
tial count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data
is received. The default for this option is zero, which indi-
cates that a receive operation shall not time out. This option
takes a timeval structure. Note that not all implementations
allow this option to be set.
SO_SNDLOWAT
Sets the minimum number of bytes to process for socket output
operations. Non-blocking output operations shall process no
data if flow control does not allow the smaller of the send low
water mark value or the entire request to be processed. This
option takes an int value. Note that not all implementations
allow this option to be set.
SO_SNDTIMEO
Sets the timeout value specifying the amount of time that an
output function blocks because flow control prevents data from
being sent. If a send operation has blocked for this time, it
shall return with a partial count or with errno set to [EAGAIN]
or [EWOULDBLOCK] if no data is sent. The default for this option
is zero, which indicates that a send operation shall not time
out. This option stores a timeval structure. Note that not all
implementations allow this option to be set.
For Boolean options, 0 indicates that the option is disabled and 1
indicates that the option is enabled.
Options at other protocol levels vary in format and name.
RETURN VALUE
Upon successful completion, setsockopt() shall return 0. Otherwise, -1
shall be returned and errno set to indicate the error.
ERRORS
The setsockopt() function shall fail if:
EBADF The socket argument is not a valid file descriptor.
EDOM The send and receive timeout values are too big to fit into the
timeout fields in the socket structure.
EINVAL The specified option is invalid at the specified socket level or
the socket has been shut down.
EISCONN
The socket is already connected, and a specified option cannot
be set while the socket is connected.
ENOPROTOOPT
The option is not supported by the protocol.
ENOTSOCK
The socket argument does not refer to a socket.
The setsockopt() function may fail if:
ENOMEM There was insufficient memory available for the operation to
complete.
ENOBUFS
Insufficient resources are available in the system to complete
the call.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
The setsockopt() function provides an application program with the
means to control socket behavior. An application program can use set-
sockopt() to allocate buffer space, control timeouts, or permit socket
data broadcasts. The <sys/socket.h> header defines the socket-level
options available to setsockopt().
Options may exist at multiple protocol levels. The SO_ options are
always present at the uppermost socket level.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Sockets, bind(), endprotoent(), getsockopt(), socket(), the Base Defi-
nitions volume of IEEE Std 1003.1-2001, <netinet/in.h>, <sys/socket.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SETSOCKOPT(3P)
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