NAME
getsockopt, setsockopt - get and set options on sockets

and manipulate the associated with a socket. Options may exist at multiple protocol levels; they are always present at the uppermost 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, is specified as 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 protocol, should be set to the protocol number of see The parameters and are used to access option values for 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, may be NULL. and any specified options are passed uninterpreted to the appropriate protocol module for interpretation. The include file contains definitions for socket level options, described below. Options at other protocol levels vary in format and name; consult the appropriate entries in section 4 of the manual. Most socket-level options utilize an parameter for For the parameter should be non-zero to enable a boolean option, or zero if the option is to be disabled. uses a parameter, defined in which specifies the desired state of the option and the linger interval (see below). and use a parameter, defined in The following options are recognized at the socket level. Except as noted, each may be examined with and set with SO_DEBUG enables recording of debugging information SO_REUSEADDR enables local address reuse SO_KEEPALIVE enables keep connections alive SO_DONTROUTE enables routing bypass for outgoing messages SO_LINGER linger on close if data present SO_BROADCAST enables permission to transmit broadcast messages SO_OOBINLINE enables reception of out-of-band data in band SO_SNDBUF set buffer size for output SO_RCVBUF set buffer size for input SO_SNDLOWAT set minimum count for output SO_RCVLOWAT set minimum count for input SO_SNDTIMEO set timeout value for output SO_RCVTIMEO set timeout value for input SO_TYPE get the type of the socket (get only) SO_ERROR 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 in a call should allow reuse of local addresses. enables the 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 messages are queued on socket and a is performed. 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 call when is requested). If is disabled and a is issued, the system will process the close in a manner that allows the process to continue as quickly as possible. The option requests permission to send broadcast datagrams on the socket. Broadcast was a privileged operation in earlier versions of the system. With protocols that support out-of-band data, the option requests that out-of-band data be placed in the normal data input queue as received; it will then be accessible with or calls without the flag. Some protocols always behave as if this option is set. and 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. A operation testing the ability to write to a socket will return true only if the low water mark amount could be processed. The default value for 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 smaller of the amount available or the amount requested. The default value for is 1. If 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. 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. It accepts a 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 or with the error if no data were sent. 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. It accepts a 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 or with the error if no data were received. Finally, and 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 the error status. It may be used to check for asynchronous errors on connected datagram sockets or for other asynchronous errors. On success, zero is returned. On error, -1 is returned, and is set appropriately.

ERRORS
The argument is not a valid descriptor. The argument is a file, not a socket. The option is unknown at the level indicated. The address pointed to by is not in a valid part of the process address space. For this error may also be returned if is not in a valid part of the process address space. These system calls appeared in BSD 4.2. Several of the socket options should be handled at lower levels of the system.