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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
       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 getsock-
       opt(), 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;  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.


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 pro-
		 cess 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.

NOTE
       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)



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