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 buf-
       fer in which the value for the requested option(s) are to be returned.  For getsockopt(), optlen is a value-result  argu-
       ment,  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)