GETSOCKOPT(2) GETSOCKOPT(2) NAME getsockopt, setsockopt - get and set options on sockets SYNOPSIS #include #include getsockopt(s, level, optname, optval, optlen) int s, level, optname; char *optval; int *optlen; setsockopt(s, level, optname, optval, optlen) int s, level, optname; char *optval; int optlen; DESCRIPTION _G_e_t_s_o_c_k_o_p_t and _s_e_t_s_o_c_k_o_p_t manipulate _o_p_t_i_o_n_s 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, _l_e_v_e_l is specified as SOL_SOCKET. To manipulate options at any other level the protocol number of the appropriate pro‐ tocol controlling the option is supplied. For example, to indicate that an option is to be interpreted by the TCP protocol, _l_e_v_e_l should be set to the protocol number of TCP; see _g_e_t_p_r_o_t_o_e_n_t(3N). The parameters _o_p_t_v_a_l and _o_p_t_l_e_n are used to access option values for _s_e_t_s_o_c_k_o_p_t. For _g_e_t_s_o_c_k_o_p_t they identify a buffer in which the value for the requested option(s) are to be returned. For _g_e_t_s_o_c_k_o_p_t, _o_p_t_l_e_n is a value-result parameter, initially containing the size of the buffer pointed to by _o_p_t_v_a_l, and modified on return to indicate the actual size of the value returned. If no option value is to be sup‐ plied or returned, _o_p_t_v_a_l may be supplied as 0. _O_p_t_n_a_m_e and any specified options are passed uninterpreted to the appropriate protocol module for interpretation. The include file <_s_y_s_/_s_o_c_k_e_t_._h> contains definitions for ‘‘socket’’ level options, described below. Options at other protocol levels vary in format and name; consult the appropriate entries in section (4P). Most socket-level options take an _i_n_t parameter for _o_p_t_v_a_l. For _s_e_t_‐ _s_o_c_k_o_p_t, the parameter should non-zero to enable a boolean option, or zero if the option is to be disabled. SO_LINGER uses a _s_t_r_u_c_t _l_i_n_g_e_r parameter, defined in <_s_y_s_/_s_o_c_k_e_t_._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 _g_e_t_s_o_c_k_o_p_t and set with _s_e_t_s_o_c_k_o_p_t. SO_DEBUG toggle recording of debugging information SO_REUSEADDR toggle local address reuse SO_KEEPALIVE toggle keep connections alive SO_DONTROUTE toggle routing bypass for outgoing messages SO_LINGER linger on close if data present SO_BROADCAST toggle permission to transmit broadcast messages SO_OOBINLINE toggle reception of out-of-band data in band SO_SNDBUF set buffer size for output SO_RCVBUF set buffer size for input SO_TYPE get the type of the socket (get only) SO_ERROR get and clear error on the socket (get only) SO_DEBUG enables debugging in the underlying protocol modules. SO_REUSEADDR indicates that the rules used in validating addresses sup‐ plied in a _b_i_n_d(2) call should allow reuse of local addresses. SO_KEEPALIVE enables the periodic transmission of messages on a con‐ nected 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. SO_DONTROUTE 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. SO_LINGER controls the action taken when unsent messags are queued on socket and a _c_l_o_s_e(2) is performed. If the socket promises reliable delivery of data and SO_LINGER is set, the system will block the pro‐ cess on the _c_l_o_s_e 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 _s_e_t_s_o_c_k_o_p_t call when SO_LINGER is requested). If SO_LINGER is disabled and a _c_l_o_s_e is issued, the system will process the close in a manner that allows the process to continue as quickly as possible. The option SO_BROADCAST requests permission to send broadcast datagrams on the socket. Broadcast was a privileged operation in earlier ver‐ sions of the system. With protocols that support out-of-band data, the SO_OOBINLINE option requests that out-of-band data be placed in the normal data input queue as received; it will then be accessible with _r_e_c_v or _r_e_a_d calls without the MSG_OOB flag. SO_SNDBUF and SO_RCVBUF 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. Finally, SO_TYPE and SO_ERROR are options used only with _s_e_t_‐ _s_o_c_k_o_p_t. SO_TYPE returns the type of the socket, such as SOCK_STREAM; it is useful for servers that inherit sockets on startup. SO_ERROR 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. RETURN VALUE A 0 is returned if the call succeeds, -1 if it fails. ERRORS The call succeeds unless: [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 _o_p_t_v_a_l is not in a valid part of the process address space. For _g_e_t_s_o_c_k_o_p_t, this error may also be returned if _o_p_t_l_e_n is not in a valid part of the process address space. SEE ALSO ioctl(2), socket(2), getprotoent(3N) BUGS Several of the socket options should be handled at lower levels of the system. 4.2 Berkeley Distribution May 23, 1986 GETSOCKOPT(2)