document distributed with 4.2BSD

[unix-history] / usr / src / usr.sbin / rwhod / rwhod.8

.\" Copyright (c) 1983 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)rwhod.8	6.2 (Berkeley) %G%
.\"
.TH RWHOD 8C ""
.UC 5
.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 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	outmp {
	char	out_line[8];		/* tty name */
	char	out_name[8];		/* user id */
	long	out_time;		/* time on */
};
.sp
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)];
};
.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; they are multiplied by 100
for representation in an integer.  The host name
included is that returned by the
.IR 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 
.IR 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.
.PP
Messages received by the
.I rwho
server are discarded unless they originated at an
.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
3 minutes.
.I Rwhod
performs an
.IR nlist (3)
on /vmunix every 30 minutes to guard against
the possibility that this file is not the system
image currently operating.
.SH "SEE ALSO"
rwho(1C),
ruptime(1C)
.SH BUGS
There should be a way to relay status information between networks. 
Status information should be sent only upon request rather than continuously.
People often interpret the server dying
or network communtication failures
as a machine going down.