.TH RWHOD 8C "4 March 1983"
.UC 4
.SH NAME
rwhod \- system status server
.SH SYNOPSIS
.B /etc/rwhod
.SH DESCRIPTION
.I Rwhod
is the server which maintains the database used by the
.IR rwho (1C)
and
.IR ruptime (1C)
programs.  Its operation is predicated on the ability to
.I broadcast
messages on a network.
.PP
.I 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
.I rwhod
servers' status messages, validating them, then recording
them in a collection of files located in the directory
.IR /usr/spool/rwho .
.PP
The
.I rwho
server transmits and receives messages at the port indicated
in the ``rwho'' service specification, see 
.IR services (5).
The messages sent and received, are of the form:
.PP
.nf
.ta 0.5i 1.0i 1.5i
struct	whod {
	int	wd_sendtime;
	int	wd_recvtime;
	char	wd_hostname[32];
	int	wd_loadav[3];
	int	wd_boottime;
	struct	whoent {
		struct	utmp we_utmp;
		int	we_idle;
	} wd_we[1024 / sizeof (struct whoent)];
};
.fi
.PP
All fields are converted to network byte order prior to
transmission.  The load averages are as calculated by the
.IR w (1)
program, and represent load averages over the 5, 10, and 15 minute 
intervals prior to a server's transmission.  The host name
included is a nickname obtained from the file
.I /etc/hosts.local
and is normally a slight abbreviation of the host's name as returned
by the
.IR gethostname (2)
system call.
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 
.IR utmp (5)
entry for each non-idle terminal line and a value indicating the
time since a character was last received on the terminal line.
.PP
Messages received by the
.I rwho
server are discarded unless they originated at a
.I 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
.I rwhod
are placed in files named
.IR whod . hostname
in the directory
.IR /usr/spool/rwho .
These files contain only the most recent message, in the
format described above.
.PP
Status messages are generated approximately once every
60 seconds.  
.I Rwhod
performs an
.IR nlist (3)
on /vmunix every 10 minutes to guard against
the possibility that this file is not the system
image currently operating.
.SH "SEE ALSO"
rwho(1),
ruptime(1)
.SH BUGS
Should handle multiple local networks and relay status
information.  People often interpret the server dieing
as a machine going down.