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Linux 2.6 - man page for setsockopt (linux section 2)

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

       getsockopt, setsockopt - get and set options on sockets

       #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);

       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 proto-
       col 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 argu-
       ment  should  be  nonzero  to enable a boolean option, or zero if the option is to be dis-

       For a description of the available socket options see socket(7) and the appropriate proto-
       col man pages.

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

       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

		 The option is unknown at the level indicated.

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

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

       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).

       Several of the socket options should be handled at lower levels of the system.

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

       This  page  is  part of release 3.55 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at

Linux					    2008-12-03				    GETSOCKOPT(2)

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