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 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 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 privileges 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(), setsockopt(), 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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .