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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 iden-
       tify 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  interpreta-
       tion.  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  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 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 getsock-
                 opt(), 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 opt-
                 val (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 proba-
       bly 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

       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  informa-
       tion about reporting bugs, can be found at

Linux                             2008-12-03                     GETSOCKOPT(2)