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32 .\" @(#)rwhod.8 8.2 (Berkeley) 12/11/93
39 .Nd system status server
45 is the server which maintains the database used by the
49 programs. Its operation is predicated on the ability to
53 messages on a network.
56 operates as both a producer and consumer of status information.
57 As a producer of information it periodically
58 queries the state of the system and constructs
59 status messages which are broadcasted or multicasted on a network.
60 As a consumer of information, it listens for other
62 servers' status messages, validating them, then recording
63 them in a collection of files located in the directory
70 to use IP multicast (instead of
71 broadcast) on all interfaces that have
72 the IFF_MULTICAST flag set in their "ifnet" structs
73 (excluding the loopback interface). The multicast
74 reports are sent with a time-to-live of 1, to prevent
75 forwarding beyond the directly-connected subnet(s).
79 argument is supplied with the
83 will send IP multicast datagrams with a
86 via a SINGLE interface rather
90 32 (or MAX_MULTICAST_SCOPE). Note that
96 specifies transmission on one interface only.
102 argument, the program accepts multicast
104 reports from all multicast-capable interfaces. If a
106 argument is given, it accepts multicast reports from only one interface, the
107 one on which reports are sent (which may be controlled via the host's routing
108 table). Regardless of the
110 option, the program accepts broadcast or
111 unicast reports from all interfaces. Thus, this program will hear the
112 reports of old, non-multicasting
114 but, if multicasting is used,
117 won't hear the reports generated by this program.
119 The server transmits and receives messages at the port indicated
120 in the ``who'' service specification; see
122 The messages sent and received, are of the form:
123 .Bd -literal -offset indent
125 char out_line[8]; /* tty name */
126 char out_name[8]; /* user id */
127 long out_time; /* time on */
136 char wd_hostname[32];
140 struct outmp we_utmp;
142 } wd_we[1024 / sizeof (struct whoent)];
146 All fields are converted to network byte order prior to
147 transmission. The load averages are as calculated by the
149 program, and represent load averages over the 5, 10, and 15 minute
150 intervals prior to a server's transmission; they are multiplied by 100
151 for representation in an integer. The host name
152 included is that returned by the
154 system call, with any trailing domain name omitted.
155 The array at the end of the message contains information about
156 the users logged in to the sending machine. This information
157 includes the contents of the
159 entry for each non-idle terminal line and a value indicating the
160 time in seconds since a character was last received on the terminal line.
162 Messages received by the
164 server are discarded unless they originated at an
166 server's port. In addition, if the host's name, as specified
167 in the message, contains any unprintable
170 message is discarded. Valid messages received by
172 are placed in files named
176 These files contain only the most recent message, in the
177 format described above.
179 Status messages are generated approximately once every
186 every 30 minutes to guard against
187 the possibility that this file is not the system
188 image currently operating.
193 Status information should be sent only upon request rather than continuously.
194 People often interpret the server dying
195 or network communication failures
196 as a machine going down.