Copyright 1989 AT&T
Copyright (C) 2001, Sun Microsystems, Inc. All Rights Reserved
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/usr/sbin/in.rwhod [-m [ttl]]
in.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 or multicast messages on a network.
in.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 or multicast on a network. As a consumer of information, it listens for other in.rwhod servers' status messages, validating them, then recording them in a collection of files located in the directory /var/spool/rwho.
The rwho server transmits and receives messages at the port indicated in the rwho service specification, see services(4). The messages sent and received are defined in /usr/include/protocols/rwhod.h and 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 1, 5, and 15 minute intervals prior to a server's transmission. The host name included is that returned by the uname(2) system call. The array at the end of the message contains information about the users who are logged in to the sending machine. This information includes the contents of the utmpx(4) entry for each non-idle terminal line and a value indicating the time since a character was last received on the terminal line.
Messages received by the rwho server are discarded unless they originated at a 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 in.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.
The following options are supported: -m [ ttl ]
Use the rwho IP multicast address (224.0.1.3) when transmitting. Receive announcements both on this multicast address and on the IP broadcast address. If ttl is not specified in.rwhod multicasts on all interfaces but with the IP TimeToLive set to 1 (that is, packets are not forwarded by multicast routers.) If ttl is specified in.rwhod only transmits packets on one interface and setting the IP TimeToLive to the specified ttl.
information about other machines
ruptime(1), rwho(1), w(1), uname(2), services(4), utmpx(4), attributes(5)
This service can cause network performance problems when used by several hosts on the network. It is not run at most sites by default. If used, include the -m multicast option.
This service takes up progressively more network bandwidth as the number of hosts on the local net increases. For large networks, the cost becomes prohibitive.
in.rwhod should relay status information between networks. People often interpret the server dying as a machine going down.