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

NAME
       getsockopt, setsockopt -	get and	set 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 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 op-
       tions at	any other level	the protocol number of the appropriate	proto-
       col  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  buf-
       fer 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 ap-
       propriate  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  op-
       tion, 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.

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

       ENOPROTOOPT
	      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
	      space.

CONFORMING TO
       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 SO_SNDLOWAT,	SO_RCVLOWAT, SO_SNDTIMEO, SO_RCVTIMEO options

NOTE
       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).

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), unix(7),
       tcp(7)

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

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTE | BUGS | SEE ALSO

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