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
       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 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;
       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  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.

       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 documents 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)