getsockopt

SYNOPSIS
       #include <sys/socket.h>

       int getsockopt(int socket, int level, int option_name,
              void *restrict option_value, socklen_t *restrict option_len);


DESCRIPTION
       The getsockopt() function manipulates options associated with a socket.

       The getsockopt() function shall retrieve the value for the option spec-
       ified by the option_name argument  for  the  socket  specified  by  the
       socket  argument.  If  the  size  of  the  option value is greater than
       option_len,  the  value  stored  in  the  object  pointed  to  by   the
       option_value  argument  shall  be  silently  truncated.  Otherwise, the
       object pointed to by the option_len argument shall be modified to indi-
       cate the actual length of the value.

       The  level  argument  specifies  the protocol level at which the option
       resides. To retrieve options at the socket  level,  specify  the  level
       argument as SOL_SOCKET. To retrieve options at other levels, supply the
       appropriate level identifier for the protocol controlling  the  option.
       For  example,  to  indicate  that  an  option is interpreted by the TCP
       (Transmission Control Protocol), set level to IPPROTO_TCP as defined in
       the <netinet/in.h> header.

       The  socket  in  use may require the process to have appropriate privi-
       leges to use the getsockopt() function.

       The option_name argument specifies a single option to be retrieved.  It
       can be one of the following values defined in <sys/socket.h>:

       SO_DEBUG
              Reports  whether  debugging  information is being recorded. This
              option shall store an int value. This is a Boolean option.

       SO_ACCEPTCONN
              Reports whether socket listening is enabled. This  option  shall
              store an int value. This is a Boolean option.

       SO_BROADCAST
              Reports whether transmission of broadcast messages is supported,
              if this is supported by the protocol. This option shall store an
              int value. This is a Boolean option.

       SO_REUSEADDR
              Reports  whether the rules used in validating addresses supplied
              to bind() should allow reuse of local addresses, if this is sup-
              ported  by  the protocol.  This option shall store an int value.
              This is a Boolean option.

       SO_KEEPALIVE
              Reports whether connections are kept active with periodic trans-
              comes first. If SO_LINGER  is  not  specified,  and  close()  is
              issued,  the  system  handles  the call in a way that allows the
              process to continue as quickly as possible.  This  option  shall
              store a linger structure.

       SO_OOBINLINE
              Reports  whether  the  socket  leaves  received out-of-band data
              (data marked urgent) inline. This  option  shall  store  an  int
              value. This is a Boolean option.

       SO_SNDBUF
              Reports send buffer size information. This option shall store an
              int value.

       SO_RCVBUF
              Reports receive buffer size information. This option shall store
              an int value.

       SO_ERROR
              Reports  information  about  error  status  and  clears it. This
              option shall store an int value.

       SO_TYPE
              Reports the socket type. This option shall store an  int  value.
              Socket types are described in Socket Types .

       SO_DONTROUTE
              Reports  whether  outgoing  messages bypass the standard routing
              facilities.  The destination shall be  on  a  directly-connected
              network,  and  messages  are directed to the appropriate network
              interface according to the destination address. The  effect,  if
              any,  of  this  option  depends on what protocol is in use. This
              option shall store an int value. This is a Boolean option.

       SO_RCVLOWAT
              Reports the minimum number of bytes to process for socket  input
              operations.    The  default  value  for  SO_RCVLOWAT  is  1.  If
              SO_RCVLOWAT is set to a larger  value,  blocking  receive  calls
              normally  wait  until  they have received the smaller of the low
              water mark value or the requested amount. (They may return  less
              than  the low water mark if an error occurs, a signal is caught,
              or the type of data next in the receive queue is different  from
              that returned; for example, out-of-band data.) This option shall
              store an int value. Note that not all implementations allow this
              option to be retrieved.

       SO_RCVTIMEO
              Reports  the  timeout  value  for  input operations. This option
              shall store a timeval structure with the number of  seconds  and
              microseconds  specifying  the  limit  on how long to wait for an
              input operation to complete. If a receive operation has  blocked
              for  this  much time without receiving additional data, it shall
              return with a partial count or errno set to [EAGAIN] or [EWOULD-
              BLOCK]  if  no data was received. The default for this option is

       SO_SNDTIMEO
              Reports  the timeout value specifying the amount of time that an
              output function blocks because flow control prevents  data  from
              being  sent.  If  a send operation has blocked for this time, it
              shall return with a partial count or with errno set to  [EAGAIN]
              or  [EWOULDBLOCK]  if  no  data  was  sent. The default for this
              option is zero, which indicates that a send operation shall  not
              time  out. The option shall store a timeval structure. Note that
              not all implementations allow this option to be retrieved.


       For Boolean options, a zero value indicates that the option is disabled
       and a non-zero value indicates that the option is enabled.

RETURN VALUE
       Upon  successful completion, getsockopt() shall return 0; otherwise, -1
       shall be returned and errno set to indicate the error.

ERRORS
       The getsockopt() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.

       EINVAL The specified option is invalid at the specified socket level.

       ENOPROTOOPT

              The option is not supported by the protocol.

       ENOTSOCK
              The socket argument does not refer to a socket.


       The getsockopt() function may fail if:

       EACCES The calling process does not have the appropriate privileges.

       EINVAL The socket has been shut down.

       ENOBUFS
              Insufficient resources are available in the system  to  complete
              the function.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                        GETSOCKOPT(P)