4.3BSD-UWisc/man/cat2/getsockopt.2

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



NAME
     getsockopt, setsockopt - get and set options on sockets

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>

     getsockopt(s, level, optname, optval, optlen)
     int s, level, optname;
     char *optval;
     int *optlen;

     setsockopt(s, level, optname, optval, optlen)
     int s, level, optname;
     char *optval;
     int optlen;

DESCRIPTION
     _G_e_t_s_o_c_k_o_p_t and _s_e_t_s_o_c_k_o_p_t manipulate _o_p_t_i_o_n_s associated with
     a socket.  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 ``socket'' level, _l_e_v_e_l is
     specified as SOL_SOCKET.  To manipulate options at any other
     level the protocol number of the appropriate protocol con-
     trolling the option is supplied.  For example, to indicate
     that an option is to be interpreted by the TCP protocol,
     _l_e_v_e_l should be set to the protocol number of TCP; see
     _g_e_t_p_r_o_t_o_e_n_t(3N).

     The parameters _o_p_t_v_a_l and _o_p_t_l_e_n are used to access option
     values for _s_e_t_s_o_c_k_o_p_t.  For _g_e_t_s_o_c_k_o_p_t they identify a
     buffer in which the value for the requested option(s) are to
     be returned.  For _g_e_t_s_o_c_k_o_p_t, _o_p_t_l_e_n is a value-result
     parameter, initially containing the size of the buffer
     pointed to by _o_p_t_v_a_l, and modified on return to indicate the
     actual size of the value returned.  If no option value is to
     be supplied or returned, _o_p_t_v_a_l may be supplied as 0.

     _O_p_t_n_a_m_e and any specified options are passed uninterpreted
     to the appropriate protocol module for interpretation.  The
     include file <_s_y_s/_s_o_c_k_e_t._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 (4P).

     Most socket-level options take an _i_n_t parameter for _o_p_t_v_a_l.
     For _s_e_t_s_o_c_k_o_p_t, the parameter should non-zero to enable a
     boolean option, or zero if the option is to be disabled.
     SO_LINGER uses a _s_t_r_u_c_t _l_i_n_g_e_r parameter, defined in



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



     <_s_y_s/_s_o_c_k_e_t._h>, which specifies the desired state of the
     option and the linger interval (see below).

     The following options are recognized at the socket level.
     Except as noted, each may be examined with _g_e_t_s_o_c_k_o_p_t and
     set with _s_e_t_s_o_c_k_o_p_t.

          SO_DEBUG        toggle recording of debugging information
          SO_REUSEADDR    toggle local address reuse
          SO_KEEPALIVE    toggle keep connections alive
          SO_DONTROUTE    toggle routing bypass for outgoing messages
          SO_LINGER       linger on close if data present
          SO_BROADCAST    toggle permission to transmit broadcast messages
          SO_OOBINLINE    toggle reception of out-of-band data in band
          SO_SNDBUF       set buffer size for output
          SO_RCVBUF       set buffer size for input
          SO_TYPE         get the type of the socket (get only)
          SO_ERROR        get and clear error on the socket (get only)

     SO_DEBUG enables debugging in the underlying protocol
     modules.  SO_REUSEADDR indicates that the rules used in
     validating addresses supplied in a _b_i_n_d(2) call should allow
     reuse of local addresses.  SO_KEEPALIVE enables the periodic
     transmission of messages on a connected socket.  Should the
     connected party fail to respond to these messages, the con-
     nection is considered broken and processes using the socket
     are notified via a SIGPIPE signal.  SO_DONTROUTE indicates
     that outgoing messages should bypass the standard routing
     facilities.  Instead, messages are directed to the appropri-
     ate network interface according to the network portion of
     the destination address.

     SO_LINGER controls the action taken when unsent messags are
     queued on socket and a _c_l_o_s_e(2) is performed.  If the socket
     promises reliable delivery of data and SO_LINGER is set, the
     system will block the process on the _c_l_o_s_e attempt until it
     is able to transmit the data or until it decides it is
     unable to deliver the information (a timeout period, termed
     the linger interval, is specified in the _s_e_t_s_o_c_k_o_p_t call
     when SO_LINGER is requested). If SO_LINGER is disabled and a
     _c_l_o_s_e is issued, the system will process the close in a
     manner that allows the process to continue as quickly as
     possible.

     The option SO_BROADCAST requests permission to send broad-
     cast datagrams on the socket.  Broadcast was a privileged
     operation in earlier versions of the system.  With protocols
     that support out-of-band data, the SO_OOBINLINE option
     requests that out-of-band data be placed in the normal data
     input queue as received; it will then be accessible with
     _r_e_c_v or _r_e_a_d calls without the MSG_OOB flag.  SO_SNDBUF and
     SO_RCVBUF are options to adjust the normal buffer sizes



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



     allocated for output and input buffers, respectively.  The
     buffer size may be increased for high-volume connections, or
     may be decreased to limit the possible backlog of incoming
     data.  The system places an absolute limit on these values.
     Finally, SO_TYPE and SO_ERROR are options used only with
     _s_e_t_s_o_c_k_o_p_t.  SO_TYPE returns the type of the socket, such as
     SOCK_STREAM; it is useful for servers that inherit sockets
     on startup.  SO_ERROR returns any pending error on the
     socket and clears the error status.  It may be used to check
     for asynchronous errors on connected datagram sockets or for
     other asynchronous errors.

RETURN VALUE
     A 0 is returned if the call succeeds, -1 if it fails.

ERRORS
     The call succeeds unless:

     [EBADF]             The argument _s is not a valid descrip-
                         tor.

     [ENOTSOCK]          The argument _s is a file, not a socket.

     [ENOPROTOOPT]       The option is unknown at the level indi-
                         cated.

     [EFAULT]            The address pointed to by _o_p_t_v_a_l is not
                         in a valid part of the process address
                         space.  For _g_e_t_s_o_c_k_o_p_t, this error may
                         also be returned if _o_p_t_l_e_n is not in a
                         valid part of the process address space.

SEE ALSO
     ioctl(2), socket(2), getprotoent(3N)

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

















Printed 12/27/86          May 23, 1986                          3