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getsockopt(2) - getsockopt, setsockopt, getsockopt, setsockopt - get and set options on sockets - man 2 getsockopt

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



NAME
       getsockopt, setsockopt - get and set(7,n,1 builtins) options on sockets

SYNOPSIS
       #include <sys/types.h>
       #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(2,7,n) level.

       When  manipulating socket(2,7,n) options the level at which the option resides
       and the name of the option must be specified.  To manipulate options at
       the  socket(2,7,n)  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(7,n,1 builtins) to the protocol number of TCP; see getprotoent(3).

       The  parameters  optval and optlen are used to access(2,5) option values for
       setsockopt.  For getsockopt they identify a buffer in(1,8) 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(1,n)
       <sys/socket.h> contains definitions for socket(2,7,n) level options, described
       below.  Options at other protocol levels vary in(1,8) format and name;  con-
       sult the appropriate entries in(1,8) 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(3,n) the option is to be disabled.


       For a description of the available socket(2,7,n) options see socket(2,7,n)(7) and the
       appropriate protocol man(1,5,7) pages.


RETURN VALUE
       On success, zero is returned.  On error(8,n), -1 is returned, and  errno  is
       set(7,n,1 builtins) appropriately.

ERRORS
       EBADF     The argument s is not a valid descriptor.

       EFAULT    The  address  pointed  to by optval is not in(1,8) a valid part of
                 the process address space.  For getsockopt,  this  error(8,n)  may
                 also  be  returned  if(3,n)  optlen  is not in(1,8) a valid part of the
                 process address space.

       EINVAL    optlen invalid in(1,8) setsockopt

       ENOPROTOOPT
                 The option is unknown at the level indicated.

       ENOTSOCK  The argument s is a file(1,n), not a socket.

CONFORMING TO
       SVr4, 4.4BSD (these system calls first appeared in(1,8) 4.2BSD).  SVr4 docu-
       ments  additional  ENOMEM  and ENOSR error(8,n) codes, but does not document
       the SO_SNDLOWAT, SO_RCVLOWAT, SO_SNDTIMEO, SO_RCVTIMEO options

NOTE
       The fifth argument of getsockopt and setsockopt is in(1,8)  reality  an  int
       [*]  (and  this  is what BSD 4.* and libc4 and libc5 have).  Some POSIX
       confusion resulted in(1,8) the present socklen_t, also used by  glibc.   See
       also accept(2,8)(2).

BUGS
       Several  of the socket(2,7,n) options should be handled at lower levels of the
       system.

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



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

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