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getsockopt(2) System Calls Manual getsockopt(2) NAME getsockopt - Gets socket options SYNOPSIS #include <sys/socket.h> int getsockopt ( int socket, int level, int option_nam, void *op- tion_value, size_t *option_len ); [Digital] The following definition of the getsockopt() function does not conform to current standards and is supported only for backward compatibility (see standards(5)): int getsockopt ( int socket, int level, int option_nam, char *op- tion_value, int *option_len ); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: getsockopt(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies the unique socket name. Specifies the protocol level at which the option resides. To retrieve options at the socket level, specify the level parameter as SOL_SOCKET. To retrieve options at other levels, supply the appropriate protocol number for the protocol controlling the option. For example, to indicate that an option will be interpreted by the TCP protocol, set level to the protocol number of TCP, as defined in the netinet/in.h header file, or as determined by using the getprotobyname() function. Specifies a single option to be retrieved. The socket level options can be enabled or disabled by the setsockopt() function. The getsockopt() function retrieves information about the following options: Reports whether debugging information is being recorded. This option returns an int value. Reports whether socket listening is enabled. This option returns an int value. Re- ports whether transmission of broadcast messages is supported. This option returns an int value. Reports whether the rules used in vali- dating addresses supplied by a bind() function should allow reuse of local addresses. This option returns an int value. Reports whether connections are kept active with periodic transmission of messages. If the connected socket fails to respond to these messages, the connection is broken and processes using that socket are notified with a SIGPIPE signal. This option returns an int value. Reports whether outgoing messages should bypass the standard routing facilities. (Not recom- mended, for debugging purposes only.) This option returns an int value. Only valid for routing sockets. Reports whether the sender re- ceives a copy of each message. This option returns an int value. Re- ports whether the socket lingers on a close() function if data is present. If SO_LINGER is set, the system blocks the process during the close() function until it can transmit the data or until the time ex- pires. If SO_LINGER is not specified, and a close() function is is- sued, the system handles the call in a way that allows the process to continue as quickly as possible. This option returns an struct linger value. Reports whether the socket leaves received out-of-band data (data marked urgent) in line. This option returns an int value. Re- ports send buffer size information. This option returns an int value. Reports receive buffer size information. This option returns an int value. [Digital] Reports send low-water mark information. This option returns an int value. [Digital] Reports receive low-water mark infor- mation. This option returns an int value. [Digital] Reports send time-out information. This option returns a struct timeval value. [Digital] Reports receive time-out information. This option returns a struct timeval value. Reports information about error status and clear. This option returns an int value. Reports the socket type. This option returns an int value. [Digital] Options at other protocol levels vary in format and name. See the tcp(7) and ip(7) reference pages for more information on option names relevant for TCP and IP options respectively. Note [Digital] The default values for socket level options like SO_SENDBUF, SO_RCVBUF, SO_SNDLOWAT, and SO_RCVLOWAT are not con- stant across different protocols and implementations. Use the getsockopt(2) routine to obtain the default values programmati- cally. The address of a buffer. Specifies the length of buffer pointed to by option_value. The option_len parameter initially contains the size of the buffer pointed to by the option_value parameter. On return, the option_len parameter is modified to indicate the actual size of the value returned. If no option value is sup- plied or returned, the option_value parameter can be 0 (zero). Options at other protocol levels vary in format and name. DESCRIPTION The getsockopt() function allows an application program to query socket options. The calling program specifies the name of the socket, the name of the option, and a place to store the requested information. The operating system gets the socket option information from its inter- nal data structures and passes the requested information back to the calling program. Options may exist at multiple protocol levels. They are always present at the uppermost socket level. When retrieving socket options, specify the level at which the option resides and the name of the option. RETURN VALUES Upon successful completion, the getsockopt() function returns a value of 0 (zero). Otherwise, a value of -1 is returned, and errno is set to indicate the error. ERRORS If the getsockopt() function fails, errno may be set to one of the fol- lowing values: The socket parameter is not valid. The address pointed to by the option_value parameter is not in a valid (writable) part of the process space, or the option_len parameter is not in a valid part of the process address space. The socket has been shut down. The op- tion is unknown. The socket parameter refers to a file, not a socket. The operation is not supported by the socket protocol. RELATED INFORMATION Functions: bind(2), close(2), endprotoent(3), getprotobynumber(3), get- protoent(3), setprotoent(3), setsockopt(2), socket(2) Network Information: ip(7), tcp(7) Standards: standards(5) delim off getsockopt(2)