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

       setsockopt — set the socket options

SYNOPSIS

       #include <sys/socket.h>

       int setsockopt(int socket, int level, int option_name,
           const void *option_value, socklen_t option_len);

DESCRIPTION

       The  setsockopt()  function shall set the option specified by the option_name argument, at
       the protocol level specified by the level  argument,  to  the  value  pointed  to  by  the
       option_value  argument for the socket associated with the file descriptor specified by the
       socket argument.

       The level argument specifies the protocol level  at  which  the  option  resides.  To  set
       options  at  the socket level, specify the level argument as SOL_SOCKET. To set 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 (Transport
       Control Protocol), set level to IPPROTO_TCP as defined in the <netinet/in.h> header.

       The option_name argument specifies a single option to set. It can be one  of  the  socket-
       level  options defined in <sys_socket.h> and described in Section 2.10.16, Use of Options.
       If option_name is equal to SO_RCVTIMEO or  SO_SNDTIMEO  and  the  implementation  supports
       setting  the  option,  it  is  unspecified  whether  the  struct  timeval  pointed  to  by
       option_value is stored as provided by this function or is rounded up  to  align  with  the
       resolution  of  the  clock being used. If setsockopt() is called with option_name equal to
       SO_ACCEPTCONN, SO_ERROR, or SO_TYPE, the behavior is unspecified.

RETURN VALUE

       Upon successful completion, setsockopt() shall return 0. Otherwise, -1 shall  be  returned
       and errno set to indicate the error.

ERRORS

       The setsockopt() function shall fail if:

       EBADF  The socket argument is not a valid file descriptor.

       EDOM   The  send  and receive timeout values are too big to fit into the timeout fields in
              the socket structure.

       EINVAL The specified option is invalid at the specified socket level  or  the  socket  has
              been shut down.

       EISCONN
              The  socket  is  already  connected, and a specified option cannot be set while the
              socket is connected.

       ENOPROTOOPT
              The option is not supported by the protocol.

       ENOTSOCK
              The socket argument does not refer to a socket.

       The setsockopt() function may fail if:

       ENOMEM There was insufficient memory available for the operation to complete.

       ENOBUFS
              Insufficient resources are available in the system to complete the call.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       The setsockopt() function provides an application program with the means to control socket
       behavior.  An  application  program can use setsockopt() to allocate buffer space, control
       timeouts, or permit socket data broadcasts. The <sys/socket.h> header defines the  socket-
       level options available to setsockopt().

       Options  may  exist at multiple protocol levels. The SO_ options are always present at the
       uppermost socket level.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.10, Sockets, bind(), endprotoent(), getsockopt(), socket()

       The Base Definitions volume of POSIX.1‐2017, <netinet_in.h>, <sys_socket.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 .