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getsockopt(2) System Calls Manual getsockopt(2) NAME getsockopt(), setsockopt() - get and set options on sockets SYNOPSIS _XOPEN_SOURCE_EXTENDED Only (UNIX 98) Obsolescent _XOPEN_SOURCE_EXTENDED Only (UNIX 95) DESCRIPTION The and system calls manipulate options associated with a socket. The socket is identified by the socket descriptor s. Options can exist at multiple protocol levels, and they are always present at the uppermost "socket" level (see socket(2)). When manipulating socket options, the level at which the option resides (level) and the name of the option (optname) must be specified. To ma- nipulate options at the "socket" level, level is specified as To spec- ify options at another level, level should be the protocol number spec- ified in (for example, The parameters optval and optlen specify the value of the option. opt- val is the address of the data structure that contains the option value, and optlen is the length of the data structure. The type and value of the data structure that optval points to depends on the op- tion. For "boolean" options, the value may be zero (not set) or non- zero (set). The value of other options depends on the purpose of the option. Usually, neither optval nor optlen may be the NULL address or zero; see individual protocol manual entries for any exceptions, such as tcp(7P) and ip(7P). For optval and optlen are used to pass information from the application to the system. optval is the address of a location in memory that con- tains the option information to be passed to the system. The parameter optlen is an integer value that specifies the size, in bytes, of the data structure pointed to by optval. For optval and optlen are used to pass information from the system to the application. The parameter optlen is the address of a variable. Before calling the application should set the value of the variable to the maximum size, in bytes, of the data structure pointed to by optval. Normally, upon return, the variable pointed to by optlen is set to the actual size the data returned in the structure pointed to by optval, if returns without error. The following ``socket'' level option names (optname) are defined in The type of the variable pointed to by optval is indicated in parenthe- ses. Options for other protocol levels are described in the individual protocol manual pages, such as tcp(7P) and ip(7P). boolean ) Returns a non-zero value if socket lis- tening is enabled, otherwise returns a zero value. boolean; SOCK_DGRAM sockets only) Allows the application to send messages to a broadcast address. disallowed. Note, the actual effect of this option is communication domain dependent. In AF_INET domain, broadcasts are always allowed regardless of the value set for this option. In AF_UNIX domain, broad- casts are not supported. For validity in other domains, see individual prod- uct manual. boolean; AF_INET SOCK_STREAM sockets only) Enables or disables the recording of internal debug information. disabled. boolean; AF_INET sockets only) Causes outbound messages to bypass nor- mal routing facilities. Instead, mes- sages are sent through the appropriate network interface based on the network portion of the destination address. disabled. Returns any pending error on the socket, and clears the error status. The value re- turned by would be the value of after the next socket data transfer system call. boolean; AF_INET SOCK_STREAM sockets only) If enabled, keeps an otherwise idle TCP connection active. disabled. AF_INET SOCK_STREAM sockets only) Controls whether or not an application "lingers" (waits) if there are untrans- mitted data in the send socket buffer when the socket is closed. The data type is defined in disabled, as if had been set to zero. (See details below.) boolean; AF_INET SOCK_STREAM sockets only) If enabled, specifies that out-of-band data (TCP "urgent data") should be left "in-line" among the normal data stream. Otherwise, one byte of out-of-band data is pulled out of the data stream, and it is accessible only by setting MSG_OOB in the flags parameter when the application reads the data (see recv(2)). disabled. Specifies the maximum size, in bytes, of the receive socket buffer. For SOCK_DGRAM sockets, the receive buffer size may limit the maxi- mum size of messages that the socket can receive. protocol-dependent; see individual protocol manual entries, such as tcp(7P) (default buffer size: 32768 bytes; maximum buffer size: 1073725440 bytes; maximum buffer size can be lowered using the ndd variable tcp_recv_hiwater_max) and udp(7P) (de- fault buffer size: 2147483647 bytes; maximum buffer size: 2147483647 bytes; udp maximum receive buffer size can be lowered using the ndd parameter udp_recv_hiwater_max). boolean; AF_INET sockets only) If enabled, allows a local address to be reused in subsequent calls to disal- lowed. boolean; AF_INET sockets only) If enabled, allows a local address and port to be reused in subsequent calls to disallowed. Specifies the maximum size, in bytes, of the send socket buffer. For SOCK_STREAM sockets, the send buffer size limits how much data can be queued for transmission before the application is blocked. For SOCK_DGRAM sockets, the send buffer size may limit the maximum size of mes- sages that the application can send through the socket. protocol-depen- dent; see individual protocol manual entries, such as tcp(7P) (default send buffer size: 32768 bytes; maximum send buffer size: 2147483647 bytes; maximum buffer size can be lowered using the ndd variable tcp_xmit_hiwater_max) and udp(7P) (default send buffer size: 65535 bytes; maximum send buffer size: 2147483647 bytes). Returns the socket type. boolean) Not used internally; provided only for compatibility. Setting the option allows the application to send messages through the SOCK_DGRAM socket to a broadcast destination address. If is set, the system does not use the network routing tables when de- termining which interface to use to send an outbound message. Instead, the system sends the message through the interface whose network ad- dress matches the network portion of the destination address. If is not set (default), the system uses the network routing tables. If is disabled (default), a TCP connection may remain idle until the connection is released at the protocol layer. If is enabled and the connection has been idle for two hours, TCP sends a packet to the re- mote socket, expecting the remote TCP to acknowledge that the connec- tion is still active. If the remote TCP does not respond in a timely manner, TCP continues to send keepalive packets according to the normal retransmission algorithm. If the remote TCP does not respond within a particular time limit, TCP drops the connection. The next socket system call (for example, returns an error, and is set to ETIMEDOUT. controls the actions to be taken when there are untransmitted data in a SOCK_STREAM send socket buffer when the socket is closed, either due to an explicit call to or because the application terminates normally or abnormally. The action is determined by the values of members of the data structure pointed to by optval in a call to The data type is de- fined in If is zero (the default action), returns immediately, but the system tries to transmit any unsent data and release the protocol con- nection gracefully. If is non-zero and is zero, returns immediately, any unsent data is discarded, and the protocol connection is aborted. If both and are non-zero, does not return until the system has tried to transmit all unsent data and release the connection gracefully. In that case, can return an error, and may be set to ETIMEDOUT, if the system is unable to transmit the data after a protocol-defined time limit. Note that the value of is treated simply as a boolean; a non- zero value is interpreted as a time limit( see below). does not affect the actions taken when the function is called. If is set, out-of-band data (TCP "urgent data") is left "in-line" among the normal data stream. In that case, the SIOCATMARK request must be used to determine if the inbound data stream has been read up to the point where the out-of-band data begins. If multiple transmissions of out-of-band data are received before the application reads them, all of the data is left in-line; however, SIOCATMARK indicates the location of only the last transmission of out-of-band data. If is not set (de- fault), only one byte of out-of-band is saved. This byte is pulled out of the normal data stream, and it is accessible only by setting MSG_OOB in the flags parameter when the application reads the data (see recv(2)). In that case, if multiple transmissions of out-of-band data are received before the application reads them, previous bytes of out- of-band data are lost. Setting the option allows the local socket address to be reused in sub- sequent calls to This permits multiple SOCK_STREAM sockets to be bound to the same local address, as long as all existing sockets with the de- sired local address are in a connected state before is called for a new socket. For SOCK_DGRAM sockets, allows multiple sockets to receive UDP multicast datagrams addressed to the bound port number. For all SOCK_DGRAM sockets bound to the same local address, must be set before calling Setting the option allows multiple SOCK_DGRAM sockets to share the same address and port. Each one of those sockets, including the first one to use that port, must specify this option before calling and specify the maximum number of bytes that the system may allocate, as needed, for the receive and send buffers, respectively. These lim- its are merely approximate because of the way in which memory is allo- cated. For example, a large number of small transmissions may require more memory than the sum of the number of data bytes sent. The default receive and send buffer sizes are protocol-specific. For more informa- tion, see the appropriate manual entries, such as tcp(7P) and udp(7P). For SOCK_STREAM sockets, larger buffer sizes can improve performance. An application can increase the size of the receive buffer at any time; however, it can decrease the receive buffer size only prior to calling or An application can increase or decrease the send buffer at any time. For SOCK_DGRAM sockets, the size of the receive and send buffers limits the size of the maximum datagram that can be received and sent, respec- tively. These limits include socket buffer space that is also used to save the sender's socket address which is associated with each datagram transmission. The sender's socket address can be returned in the from parameter when is called (see recv(2)). AF_CCITT and are the only options supported for sockets of the AF_CCITT address family. _XOPEN_SOURCE_EXTENDED Only The value of in the linger structure is interpreted as a time limit in seconds. RETURN VALUE and return the following values: Successful completion. Failure. is set to indicate the error. ERRORS If or fails, is set to one of the following values: [EBADF] The argument s is not a valid descriptor. [EFAULT] The optval or optlen address is not valid. [EINVAL] The level or optlen value is not valid; or optval is the NULL address; or the protocol connection has been released. [ENOBUFS] Insufficient memory is available for internal sys- tem data structures. [ENOPROTOOPT] The option is not recognized at the specified op- tion level. [ENOTSOCK] The argument s is not a socket descriptor. [EOPNOTSUPP] The option is not supported by the socket family or socket type. OBSOLESCENCE Currently, the and types are the same size. This is compatible with both the UNIX 95 and UNIX 98 profiles. However, in a future release, might be a different size. In that case, passing a pointer will evoke compile-time warnings, which must be corrected in order for the appli- cation to behave correctly. Applications that use now, where appropri- ate, will avoid such migration problems. On the other hand, applica- tions that need to be portable to the UNIX 95 profile should follow the X/Open specification (see xopen_networking(7)). FUTURE DIRECTION Currently, the default behavior is the however, it might be changed to in a future release. At that time, any behavior that is incompatible with might be obsoleted. Applications that conform to the X/Open spec- ification now will avoid migration problems (see xopen_networking(7)). AUTHOR and were developed by HP and the University of California, Berkeley. SEE ALSO socket(2), getprotoent(3N), thread_safety(5), tcp(7P), udp(7P), unix(7P), xopen_networking(7). STANDARDS CONFORMANCE getsockopt(2)
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | OBSOLESCENCE | FUTURE DIRECTION | AUTHOR | SEE ALSO | STANDARDS CONFORMANCE
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