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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 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 pro-
       tocol module for interpretation.  The include file <sys/socket.h> contains  defini-
       tions  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  man-

       Most  socket-level  options  utilize an int argument for optval.  For setsockopt(),
       the argument 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.

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

       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)).

                 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 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-

Linux                             2008-12-03                     GETSOCKOPT(2)

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