Man Pages

getsockopt(3p) - phpMan getsockopt(3p) - phpMan

Command: man perldoc info search(apropos)  


GETSOCKOPT(3P)             POSIX Programmer's Manual            GETSOCKOPT(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       getsockopt - get the socket options

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 specified 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 indicate 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  inter-
       preted  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 privileges 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  supported  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 transmission of messages, if this is supported
              by the protocol.

       If  the connected socket fails to respond to these messages, the connection shall be broken and threads writing
       to that socket shall be notified with a SIGPIPE signal. This option shall store an int value. This is a Boolean
       option.

       SO_LINGER
              Reports  whether  the  socket  lingers  on  close() if data is present.  If SO_LINGER is set, the system
              blocks the process during close() until it can transmit the data  or  until  the  end  of  the  interval
              indicated  by  the l_linger member, whichever 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 [EWOULDBLOCK] if no data was received. The
              default  for this option is zero, which indicates that a receive operation shall not time out. Note that
              not all implementations allow this option to be retrieved.

       SO_SNDLOWAT
              Reports the minimum number of bytes to process for socket output operations.  Non-blocking output opera-
              tions  shall process no data if flow control does not allow the smaller of the send low water mark value
              or the entire request to be processed. This option shall store an int value. Note that not all implemen-
              tations allow this option to be retrieved.

       SO_SNDTIMEO
              Reports the timeout value specifying the amount of time that an output function blocks because flow con-
              trol 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 indi-
       cate 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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       bind(),  close(),  endprotoent(),  setsockopt(), socket(), the Base Definitions volume of IEEE Std 1003.1-2001,
       <sys/socket.h>, <netinet/in.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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(3P)