RWHOD(8)

NAME
rwhod - system status server

SYNOPSIS
rwhod [-m [ttl]]

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 or multicast 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 broadcasted or multicasted 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/rwho.

The -m option causes rwhod to use IP multicast (instead of broadcast) on all interfaces that have the IFF_MULTICAST flag set in their "ifnet" structs (excluding the loopback interface). The multicast reports are sent with a time-to-live of 1, to prevent forwarding beyond the directly-connected subnet(s).

If the optional ttl argument is supplied with the -m flag, rwhod will send IP multicast datagrams with a time-to-live of <ttl>, via a SINGLE interface rather than all interfaces. <ttl> must be between 0 and 32 (or MAX_MULTICAST_SCOPE). Note that -m 1 is different than -m, in that -m 1 specifies transmission on one interface only.

When -m is used without a ttl argument, the program accepts multicast rwhod reports from all multicast-capable interfaces. If a ttl argument is given, it accepts multicast reports from only one interface, the one on which reports are sent (which may be controlled via the host's routing table). Regardless of the "-m" option, the program accepts broadcast or unicast reports from all interfaces. Thus, this program will hear the reports of old, non-multicasting rwhods, but, if multicasting is used, those old rwhods won't hear the reports generated by this program.

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(3) 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/rwho. These files contain only the most recent message, in the format described above.

Status messages are generated approximately once every 3 minutes. Rwhod performs an nlist(3) on /kernel every 30 minutes to guard against the possibility that this file is not the system image currently operating.

SEE ALSO
ruptime(1), rwho(1)

BUGS
Status information should be sent only upon request rather than continuously. People often interpret the server dying or network communication failures as a machine going down.

HISTORY
The rwhod command appeared in 4.2BSD.