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

NAME

       getsockopt, setsockopt - get and set options on sockets

SYNOPSIS

       #include <sys/types.h>	       /* See NOTES */
       #include <sys/socket.h>

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

DESCRIPTION

       getsockopt()  and  setsockopt() manipulate options for the socket referred to by the file descriptor sockfd.  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  sockets API 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  arguments  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 argument, 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;
       consult the appropriate entries in section 4 of the manual.

       Most socket-level options utilize an int argument for optval.  For setsockopt(), the argument should be nonzero 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 sockfd 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 process address space.

       EINVAL	 optlen invalid in setsockopt().  In some cases this error can	also  occur  for  an  invalid  value  in  optval  (e.g.,  for  the
		 IP_ADD_MEMBERSHIP option described in ip(7)).

       ENOPROTOOPT
		 The option is unknown at the level indicated.

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

CONFORMING TO

       SVr4, 4.4BSD (these system calls first appeared in 4.2BSD), POSIX.1-2001.

NOTES

       POSIX.1-2001  does  not	require  the  inclusion of <sys/types.h>, and this header file is not required on Linux.  However, some historical
       (BSD) implementations required this header file, and portable applications are probably wise to include it.

       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)

COLOPHON

       This  page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-12-03							     GETSOCKOPT(2)