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 .