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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  for  the  standard options.  On error, -1 is returned, and errno is set
       appropriately.

       Netfilter allows the programmer to define custom  socket  options  with  associated  handlers;  for  such
       options, the return value on success is the value returned by the handler.

ERRORS

       EBADF     The argument sockfd is not a valid file 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 file descriptor sockfd does not refer to a socket.

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD (these system calls first appeared in 4.2BSD).

NOTES

       POSIX.1 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.

       For background on the socklen_t type, see 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), ip(7), packet(7), socket(7), tcp(7), udp(7), unix(7)

COLOPHON

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