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NAME

       getsockopt, setsockopt - get and set options on sockets

SYNOPSIS

       #include <sys/types.h>          /* See NOTES */
       #include <sys/socket.h>

       int getsockopt(int s, int level, int optname,
                      void *optval, socklen_t *optlen);
       int setsockopt(int s, int level, int optname,
                      const void *optval, socklen_t optlen);

DESCRIPTION

       getsockopt()  and setsockopt() manipulate the options associated with a
       socket.  Options may exist at multiple protocol levels; they are always
       present at the uppermost socket level.

       When  manipulating socket options the level at which the option resides
       and the name of the option must be specified.  To manipulate options at
       the  socket  level,  level  is  specified as SOL_SOCKET.  To manipulate
       options at any other level  the  protocol  number  of  the  appropriate
       protocol  controlling the option is supplied.  For example, to indicate
       that an option is to be interpreted by the TCP protocol,  level  should
       be set to the protocol number of TCP; see getprotoent(3).

       The  parameters  optval and optlen are used to access option values for
       setsockopt().  For getsockopt() they identify a  buffer  in  which  the
       value   for   the   requested   option(s)  are  to  be  returned.   For
       getsockopt(), optlen is a value-result parameter, initially  containing
       the  size of the buffer pointed to by optval, and modified on return to
       indicate the actual size of the value returned.  If no option value  is
       to be supplied or returned, optval may be NULL.

       Optname  and  any  specified  options  are  passed uninterpreted to the
       appropriate protocol  module  for  interpretation.   The  include  file
       <sys/socket.h> contains definitions for socket level options, described
       below.  Options at other protocol  levels  vary  in  format  and  name;
       consult the appropriate entries in section 4 of the manual.

       Most  socket-level  options  utilize  an int parameter for optval.  For
       setsockopt(), the parameter should  be  nonzero  to  enable  a  boolean
       option, or zero if the option is to be disabled.

       For a description of the available socket options see socket(7) and the
       appropriate protocol man pages.

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.

ERRORS

       EBADF     The argument s is not a valid descriptor.

       EFAULT    The  address  pointed  to by optval is not in a valid part of
                 the process address space.  For getsockopt(), this error  may
                 also  be  returned  if  optlen  is not in a valid part of the
                 process address space.

       EINVAL    optlen invalid in setsockopt().

       ENOPROTOOPT
                 The option is unknown at the level indicated.

       ENOTSOCK  The argument s is a file, not a socket.

CONFORMING TO

       SVr4,  4.4BSD  (these  system  calls   first   appeared   in   4.2BSD),
       POSIX.1-2001.

NOTES

       POSIX.1-2001  does not require the inclusion of <sys/types.h>, and this
       header file is not required on Linux.  However, some  historical  (BSD)
       implementations  required  this  header file, and portable applications
       are probably wise to include it.

       The optlen argument of getsockopt() and setsockopt() is in  reality  an
       int  [*]  (and  this  is  what 4.x BSD and libc4 and libc5 have).  Some
       POSIX confusion resulted in the present socklen_t, also used by  glibc.
       See also accept(2).

BUGS

       Several  of the socket options should be handled at lower levels of the
       system.

SEE ALSO

       ioctl(2), socket(2), getprotoent(3), protocols(5),  socket(7),  tcp(7),
       unix(7)

COLOPHON

       This  page  is  part of release 2.77 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.