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getsockopt(2)
NAME
getsockopt - Gets socket options
SYNOPSIS
#include <sys/socket.h>
int getsockopt (
int socket,
int level,
int option_nam,
void *option_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 *option_value,
int *option_len );
STANDARDS
Interfaces documented on this reference page conform to industry standards
as follows:
getsockopt(): XPG4-UNIX
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
socket Specifies the unique socket name.
level 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.
option_nam
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:
SO_DEBUG Reports whether debugging information is being
recorded. This option returns an int value.
SO_ACCEPTCONN
Reports whether socket listening is enabled. This
option returns an int value.
SO_BROADCAST
Reports whether transmission of broadcast messages is
supported. This option returns an int value.
SO_REUSEADDR
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.
SO_KEEPALIVE
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.
SO_DONTROUTE
Reports whether outgoing messages should bypass the
standard routing facilities. (Not recommended, for
debugging purposes only.) This option returns an int
value.
SO_USELOOPBACK
Only valid for routing sockets. Reports whether the
sender receives a copy of each message. This option
returns an int value.
SO_LINGER 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.
SO_OOBINLINE
Reports whether the socket leaves received out-of-band
data (data marked urgent) in line. This option returns
an int value.
SO_SNDBUF Reports send buffer size information. This option
returns an int value.
SO_RCVBUF Reports receive buffer size information. This option
returns an int value.
SO_SNDLOWAT
[Digital] Reports send low-water mark information.
This option returns an int value.
SO_RCVLOWAT
[Digital] Reports receive low-water mark information.
This option returns an int value.
SO_SNDTIMEO
[Digital] Reports send time-out information. This
option returns a struct timeval value.
SO_RCVTIMEO
[Digital] Reports receive time-out information. This
option returns a struct timeval value.
SO_ERROR Reports information about error status and clear. This
option returns an int value.
SO_TYPE 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 constant
across different protocols and implementations. Use the getsockopt(2)
routine to obtain the default values programmatically.
option_value
The address of a buffer.
option_len
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:
[EBADF] The socket parameter is not valid.
[EFAULT] 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.
[EINVAL] The socket has been shut down.
[ENOPROTOOPT]
The option is unknown.
[ENOTSOCK]
The socket parameter refers to a file, not a socket.
[EOPNOTSUPP]
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)