getsockopt(SSC) 6 January 1993 getsockopt(SSC) Name getsockopt, setsockopt - get and set options on sockets Syntax #include <sys/types.h> #include <sys/socket.h> int getsockopt(s, level, optname, optval, optlen) int s, level, optname; char *optval; int *optlen; int setsockopt(s, level, optname, optval, optlen) int s, level, optname; char *optval; int optlen; Description Getsockopt and setsockopt manipulate options associated with a socket. Options may exist at multiple protocol levels; they are always present at the uppermost ``socket'' 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, level is specified as SOLSOCKET. To manipulate options at any other level, the protocol number of the appropriate proto- col controlling the option is supplied. For example, to indicate that an option is to be interpreted by the TCP protocol, level should be set to the protocol number of TCP. See getprotoent(SLIB) for more information. The parameters optval and optlen are used to access option values for setsockopt. For getsockopt, they identify a buffer in which the value for the requested option(s) are to be returned. For getsockopt, optlen is a value-result parameter, initially containing the size of the buffer pointed to by optval, and modified on return to indicate the actual size of the value returned. If no option value is to be supplied or returned, optval may be supplied as 0. Optname and any specified options are passed uninterpreted to the appropriate protocol module for interpretation. The include file <sys/socket.h> contains definitions for ``socket'' level options, described below. Options at other protocol levels vary in format and name; consult the appropriate entries in the (SFF) man page section. Most socket-level options take an int parameter for optval. For set- sockopt, the parameter should be non-zero to enable a boolean option, or zero if the option is to be disabled. SOLINGER uses a structlinger parameter, defined in <sys/socket.h>, 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 getsockopt and set with setsockopt. SODEBUG toggle recording of debugging information SOREUSEADDR toggle local address reuse SOKEEPALIVE toggle keep connections alive SODONTROUTE toggle routing bypass for outgoing messages SOLINGER linger on close if data present SOBROADCAST toggle permission to transmit broadcast messages SOOOBINLINE toggle reception of out-of-band data in band SOSNDBUF set buffer size for output - not currently supported SORCVBUF set buffer size for input - not currently supported SOTYPE get the type of the socket (get only) SOERROR get and clear error on the socket (get only) SOPROTOTYPE get/set the protocol number associated with the stream SODEBUG enables debugging in the underlying protocol modules. SOREUSEADDR indicates that the rules used in validating addresses sup- plied in a bind(SSC) call should allow reuse of local addresses. SOKEEPALIVE 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 SIGPIPE signal. SODONTROUTE 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. SOLINGER controls the action taken when unsent messages are queued on socket and a close(S) is performed. If the socket promises reliable delivery of data and SOLINGER is set, the system will block the process on the close 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 setsockopt call when SOLINGER is requested. If SOLINGER is disabled and a close is issued, the system will process the close in a manner that allows the process to continue as quickly as possible. SOBROADCAST 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, SOOOBINLINE requests that out-of-band data be placed in the normal data input queue as received; it will then be accessible with recv or read calls without the MSGOOB flag. SOSNDBUF and SORCVBUF 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 abso- lute limit on these values. SOTYPE and SOERROR are options used only with setsockopt. SOTYPE returns the type of the socket, such as SOCKSTREAM; it is useful for servers that inherit sockets on startup. SOERROR 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 asyn- chronous errors. SOPROTOTYPE binds a protocol number to the socket. This option is necessary to support raw IP sockets (for example) and, as such, is used primarily by the BSD compatibility module. Return value A return value of zero indicates that the call succeeded. A return value of -1 indicates that an error occurred, and in this case an error code is stored in the global variable errno. Errors The call fails if: [EBADF] The argument s is not a valid descriptor. [ENOTSOCK] The argument s is a file, not a socket. [ENOPROTOOPT] The option is unknown at the level indicated. [EFAULT] The address pointed to by optval is not in a valid part of the process address space. For getsockopt, this error may also be returned if optlen is not in a valid part of the process address space. Notes Several of the socket options should be handled at lower levels of the system. See also ioctl(S), socket(SSC) and getprotoent(SLIB).