GETSOCKOPT(2)              Linux Programmer's Manual             GETSOCKOPT(2)

       getsockopt, setsockopt - get and set options on sockets

       #include <sys/types.h>
       #include <sys/socket.h>

       int  getsockopt(int  s, int level, int optname, void *optval, socklen_t

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

       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  pro-
       tocol  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  sup-
       plied 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;  con-
       sult 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  non-zero  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.

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

       EBADF  The argument s is not a valid descriptor.

              The argument s is a file, not a socket.

              The option is unknown at the level indicated.

       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

       SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).  SVr4 docu-
       ments  additional  ENOMEM  and ENOSR error codes, but does not document

       The fifth argument of getsockopt and setsockopt is in  reality  an  int
       [*]  (and  this  is what BSD 4.* and libc4 and libc5 have).  Some POSIX
       confusion resulted in the present socklen_t.  The  draft  standard  has
       not  been  adopted  yet,  but  glibc2  already  follows it and also has
       socklen_t [*]. See also accept(2).

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

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

Linux Man Page                    1999-05-24                     GETSOCKOPT(2)