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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 differ (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 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 socket-level options defined  in  <sys_socket.h>  and
       described in Section 2.10.16, Use of Options.
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 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
       Section  2.10.16,  Use of Options, bind(), close(), endprotoent(), set-
       sockopt(), socket()
       The  Base   Definitions   volume   of   POSIX.1-2008,   <sys_socket.h>,
       <netinet_in.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  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.unix.org/online.html .
       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,  see  https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                       GETSOCKOPT(3P)