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 *option_value, socklen_t *option_len );
[XNS4.0] The definition of the getsockopt() function in XNS4.0 uses a size_t data type instead of a socklen_t data type as specified in
XNS5.0 (the previous definition).
[Tru64 UNIX] The following definition of the getsockopt() function does not conform to current standards and is supported only for back-
ward compatibility (see standards(5)):
int getsockopt (
int socket, int level, int option_nam, char *option_value, int *option_len );
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
getsockopt(): XNS5.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies the file descriptor for the socket. 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 pro-
tocol 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 socket listening is enabled. This option returns an int value. Reports
whether transmission of broadcast messages is supported. This option returns an int value. [Tru64 UNIX] In a cluster, reports whether
the socket will use the default cluster alias as its source address. [Tru64 UNIX] In a cluster, reports whether the socket can only
receive packets addressed to this cluster member. [Tru64 UNIX] In a cluster, reports whether the socket must receive packets addressed to
a cluster alias and will drop any packets that are not addressed to a cluster alias. Reports whether debugging information is being
recorded. This option returns an int value. Reports whether outgoing messages should bypass the standard routing facilities. The desti-
nation must be on a directly-connected network; messages are directed to the appropriate network interface. The protocol in use determines
the effect of this option. (Not recommended, for debugging purposes only.) This option returns an int value. Reports information about
error status and clears it. 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 noti-
fied with a SIGPIPE signal. This option returns an int value. Reports 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
expires. If SO_LINGER is not specified, and a close() function is issued, 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. Reports receive buffer size information. This option returns an int
value. Reports the minimum number of bytes (low-water mark) for socket receive operations. The default value is 1. If the value is set
to a larger value, blocking receive calls wait until they receive either the low water mark value or the requested value (whichever is
smaller). The calls might return less than the water mark if an error occurs, a signal is received, or type of data in the receive queue
is different than that returned. This option returns an int value. Reports receive time-out information. This option returns a struct
timeval value that specifies the amount of time to wait for a receive operation to complete. If a receive operation has blocked for the
specified amount of time without receiving additional data, it returns with a partial error count or errno set to [EAGAIN] or [EWOULD-
BLOCK]. The default is 0 (zero), which indicates that a receive operation will not time out. [Tru64 UNIX] In a cluster, reports whether
an attempt to bind the socket to a port in the reserved range (512-1024) will fail if the port is marked static. Reports whether the rules
used in validating addresses supplied by a bind() function should allow reuse of local addresses. This option returns an int value.
[Tru64 UNIX] In a cluster, reports whether the socket can reuse a locked cluster alias port. Reports send buffer size information. This
option returns an int value. Reports the minimum number of bytes (low-water mark) for socket transmit operations. Non-blocking transmit
operations process no data if flow control does not allow either the send low water mark value or the entire request (whichever is smaller)
to be processed. This option returns an int value. Reports send time-out information. This option returns a struct timeval value that
specifies the amount of time a transmit function blocks when flow control prevents the transmission of data. If a transmit operation
blocks for this amount of time without transmitting data, it returns with a partial error count or errno set to [EAGAIN] or [EWOULDBLOCK].
The default is 0 (zero), which indicates that a transmit operation will not time out. Reports the socket type. This option returns an int
value. Only valid for routing sockets. Reports whether the sender receives a copy of each message. This option returns an int value.
[Tru64 UNIX] 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
[Tru64 UNIX] 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 programmatically.
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 supplied 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
internal 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 following values: The calling process does not have appropriate permis-
sions. The socket parameter is not valid. [POSIX] The send and receive timeout values are too large to fit in the timeout fields of the
socket structure. 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 option_value or option_len parameter is invalid; or the
socket is shut down. Insufficient resources are available in the system to complete the call. The option is unknown. The available
STREAMS resources were insufficient for the operation to complete. The socket parameter refers to a file, not a socket. [XNS4.0] The
operation is not supported by the socket protocol.
RELATED INFORMATION
Functions: bind(2), close(2), endprotoent(3), getprotobynumber(3), getprotoent(3), setprotoent(3), setsockopt(2), socket(2).
Network Information: ip(7), tcp(7).
Standards: standards(5). delim off
getsockopt(2)