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



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

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.1-2017, <sys_socket.h>,
       <netinet_in.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .



IEEE/The Open Group                  2017                        GETSOCKOPT(3)
