Provided by: rwhod_0.17-11_i386 bug

NAME

     rwhod - system status server

SYNOPSIS

     rwhod [-bpaf] [-i <if>...] [-u user]

DESCRIPTION

     Rwhod is the server which maintains the database used by the rwho(1) and
     ruptime(1) programs.  Its operation is predicated on the ability to
     broadcast messages on a network.

     Rwhod operates as both a producer and consumer of status information.  As
     a producer of information it periodically queries the state of the system
     and constructs status messages which are broadcast on a network.  As a
     consumer of information, it listens for other rwhod servers’ status
     messages, validating them, then recording them in a collection of files
     located in the directory /var/spool/rwho.

     The server transmits and receives messages at the port indicated in the
     ‘‘rwho’’ service specification; see services(5).

     The messages sent and received, are of the form:

           struct  outmp {
                   char    out_line[8];            /* tty name */
                   char    out_name[8];            /* user id */
                   long    out_time;               /* time on */
           };

           struct  whod {
                   char    wd_vers;
                   char    wd_type;
                   char    wd_fill[2];
                   int     wd_sendtime;
                   int     wd_recvtime;
                   char    wd_hostname[32];
                   int     wd_loadav[3];
                   int     wd_boottime;
                   struct  whoent {
                           struct  outmp we_utmp;
                           int     we_idle;
                   } wd_we[1024 / sizeof (struct whoent)];
           };

     All fields are converted to network byte order prior to transmission.
     The load averages are as calculated by the w(1) program, and represent
     load averages over the 5, 10, and 15 minute intervals prior to a server’s
     transmission; they are multiplied by 100 for representation in an
     integer.  The host name included is that returned by the gethostname(2)
     system call, with any trailing domain name omitted.  The array at the end
     of the message contains information about the users logged in to the
     sending machine.  This information includes the contents of the utmp(5)
     entry for each non-idle terminal line and a value indicating the time in
     seconds since a character was last received on the terminal line.

     Messages received by the rwho server are discarded unless they originated
     at an rwho server’s port.  In addition, if the host’s name, as specified
     in the message, contains any unprintable ASCII characters, the message is
     discarded.  Valid messages received by rwhod are placed in files named
     whod.hostname in the directory /var/spool/rwho.  These files contain only
     the most recent message, in the format described above.

     Status messages are generated approximately once every 3 minutes.  Rwhod
     recomputes the system boot time every 30 minutes because on some (non-
     Linux) systems it is not a totally reliable process.

FLAGS

     If the -b flag is supplied, only broadcast interfaces, such as ethernets,
     will be used.  If the -p flag is supplied, only point-to-point interfaces
     will be used. If the -a flag is supplied, or no flags are supplied, all
     interfaces will be used.

     Alternately, you may specify interfaces by name by providing one or more
     -i options followed by the interface name.

     If the -u flag is supplied, rwhod will run as the specified user instead
     of as rwhod. The initial user until the daemon drops privileges is root.

     Rwhod can also forward packets between interfaces if started with -f.
     Please read the CAVEATS section before enabling rwhod forwarding.

CAVEATS

     While rwhod listens on any interface present on the host, it will only
     send (or forward) to the interfaces determined by the -a -b -p -i flags.

     When operating in forwarding mode (with -f ), rwhod forwards all correct
     rwhod packets received on an interface to all the other interfaces. You
     can create a broadcast storm if there is a loop in your network and all
     the routers in the loop run in forwarding mode. To prevent this from
     happenning, rwhod will shut down forwarding (and log the event to the
     syslog) if more than one rwhod packet is forwarded per second on average
     over the last three minutes. If this happens, you must break the loop of
     forwarding routers.

SEE ALSO

     rwho(1), ruptime(1)

BUGS

     Some kind of proxying feature might be useful if your router doesn’t run
     rwhod.

     People often interpret the server dying or network communication failures
     as a machine going down.

     Rwhod doesn’t refresh its interface list, which might be useful when
     using -a -b -p.

HISTORY

     The rwhod command appeared in 4.2BSD.

     Philippe Troin <phil@fifi.org> implemented forwarding and interface
     selection flags.