.\" Copyright (c) 1983, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\" %sccs.include.redist.man%
.\" @(#)getsockopt.2 8.2 (Berkeley) %G%
.Nd get and set options on sockets
.Fd #include <sys/types.h>
.Fd #include <sys/socket.h>
.Fn getsockopt "int s" "int level" "int optname" "void *optval" "int *optlen"
.Fn setsockopt "int s" "int level" "int optname" "const void *optval" "int optlen"
associated with a socket. Options may exist at multiple
protocol levels; they are always present at the uppermost
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,
To manipulate options at any
other level the protocol number of the appropriate protocol
controlling the option is supplied. For example,
to indicate that an option is to be interpreted by the
should be set to the protocol number of
are used to access option values for
they identify a buffer in which the value for the
requested option(s) are to be returned. For
is a value-result parameter, initially containing the
size of the buffer pointed to by
and modified on return to indicate the actual size of
the value returned. If no option value is
to be supplied or returned,
and any specified options are passed uninterpreted to the appropriate
protocol module for interpretation.
socket level options, described below.
Options at other protocol levels vary in format and
name; consult the appropriate entries in
Most socket-level options utilize an
the parameter should be non-zero to enable a boolean option,
or zero if the option is to be disabled.
which specifies the desired state of the option and the
linger interval (see below).
The following options are recognized at the socket level.
Except as noted, each may be examined with
.Bl -column SO_OOBINLINE -offset indent
.It Dv SO_DEBUG Ta "enables recording of debugging information"
.It Dv SO_REUSEADDR Ta "enables local address reuse"
.It Dv SO_REUSEPORT Ta "enables duplicate address and port bindings"
.It Dv SO_KEEPALIVE Ta "enables keep connections alive"
.It Dv SO_DONTROUTE Ta "enables routing bypass for outgoing messages"
.It Dv SO_LINGER Ta "linger on close if data present"
.It Dv SO_BROADCAST Ta "enables permission to transmit broadcast messages"
.It Dv SO_OOBINLINE Ta "enables reception of out-of-band data in band"
.It Dv SO_SNDBUF Ta "set buffer size for output"
.It Dv SO_RCVBUF Ta "set buffer size for input"
.It Dv SO_SNDLOWAT Ta "set minimum count for output"
.It Dv SO_RCVLOWAT Ta "set minimum count for input"
.It Dv SO_SNDTIMEO Ta "set timeout value for output"
.It Dv SO_RCVTIMEO Ta "set timeout value for input"
.It Dv SO_TYPE Ta "get the type of the socket (get only)"
.It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
enables debugging in the underlying protocol modules.
indicates that the rules used in validating addresses supplied
call should allow reuse of local addresses.
allows completely duplicate bindings by multiple processes
This option permits multiple instances of a program to each
receive UDP/IP multicast or broadcast datagrams destined for the bound port.
periodic transmission of messages on a connected socket. Should the
connected party fail to respond to these messages, the connection is
considered broken and processes using the socket are notified via a
signal when attempting to send data.
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.
controls the action taken when unsent messags
are queued on socket and a
If the socket promises reliable delivery of data and
the system will block the process on the
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
is issued, the system will process the close in a manner that allows
the process to continue as quickly as possible.
requests permission to send broadcast datagrams
Broadcast was a privileged operation in earlier versions of the system.
With protocols that support out-of-band data, the
requests that out-of-band data be placed in the normal data input queue
as received; it will then be accessible with
Some protocols always behave as if this option is set.
are options to 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.
is an option to set the minimum count for output operations.
Most output operations process all of the data supplied
by the call, delivering data to the protocol for transmission
and blocking as necessary for flow control.
Nonblocking output operations will process as much data as permitted
subject to flow control without blocking, but will process no data
if flow control does not allow the smaller of the low water mark value
or the entire request to be processed.
operation testing the ability to write to a socket will return true
only if the low water mark amount could be processed.
is set to a convenient size for network efficiency, often 1024.
is an option to set the minimum count for input operations.
In general, receive calls will block until any (non-zero) amount of data
is received, then return with the smaller of the amount available or the amount
is set to a larger value, blocking receive calls normally
wait until they have received the smaller of the low water mark value
Receive calls may still 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 than that returned.
is an option to set a timeout value for output operations.
parameter with the number of seconds and microseconds
used to limit waits for output operations to complete.
If a send operation has blocked for this much time,
it returns with a partial count
In the current implementation, this timer is restarted each time additional
data are delivered to the protocol,
implying that the limit applies to output portions ranging in size
from the low water mark to the high water mark for output.
is an option to set a timeout value for input operations.
parameter with the number of seconds and microseconds
used to limit waits for input operations to complete.
In the current implementation, this timer is restarted each time additional
data are received by the protocol,
and thus the limit is in effect an inactivity timer.
If a receive operation has been blocked for this much time without
receiving additional data, it returns with a short count
if no data were received.
are options used only with
returns the type of the socket, such as
it is useful for servers that inherit sockets on startup.
returns any pending error on the socket and clears
It may be used to check for asynchronous errors on connected
datagram sockets or for other asynchronous errors.
A 0 is returned if the call succeeds, -1 if it fails.
The call succeeds unless:
.Bl -tag -width ENOPROTOOPTAA
is not a valid descriptor.
The option is unknown at the level indicated.
The address pointed to by
is not in a valid part of the process address space.
this error may also be returned if
is not in a valid part of the process address space.
Several of the socket options should be handled at lower levels of the system.