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SETSOCKOPT(3P) POSIX Programmer's Manual SETSOCKOPT(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult 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 descrip-
tor 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 proto-
col controlling the option. For example, to indicate that an option is interpreted by the TCP (Transport Control Proto-
col), 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 supported 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 connection 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 complete. If a receive operation has blocked for this much time without receiving addi-
tional data, it shall return with a partial count or errno set to [EAGAIN] or [EWOULDBLOCK] if no data is
received. The default for this option is zero, which indicates 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 implementa-
tions 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 pro-
gram can use setsockopt() 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 Definitions 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, Copy-
right (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.open-
group.org/unix/online.html .
IEEE/The Open Group 2003 SETSOCKOPT(3P)
