=head1	NAME

rshdown - Remote shutdown.

=head1	SYNOPSIS

  rshdown [<configfile>]

=head1	DESCRIPTION

The program listens on an UDP port for shutdown data packets.
If a valid shutdown data packet was received the program shuts down the
computer.

If you have two computers powered by the same UPS you can connect
the signal cable to one of them. If power is off for too long
and the computer with the signal cable goes down it can notify the other
computer to shut down too.

=head1	RETURN VALUE

The program is running as a daemon, it does not return a value.

=head1	EXAMPLE

Create a file containing up to 1500 bytes random data (you can use
the rndbytes program to do so).

Copy this file to /etc/rshdown-secret on both computers. Use a secure
mechanism to transfer the file (i.e. scp) and set permissions to 600.

Choose a free port number on the shutdown master (the computer with the
signal cable) and the shutdown slave (the other computer).
In the example we use port 2 on both systems.

On the shutdown master modify
the startup scripts to create an indicator
file, i.e. ``/var/run/rshdown/rshdown.txt'
on each reboot.

Modify the the shutdown scripts to check for the presence of the indicator
file, if the file exists send the data packet.

  #! /bin/sh
  if [ -f /var/run/rshdown/rshdown.txt ]
  then
    for i in 1 2 3 4 5 6 7 8 9 10
    do
      nc -u -p 2 -w 2 slave 2 < /etc/rshdown-secret
    done
  fi

On the shutdown slave create a shutdown script /etc/powerfail-fast:

  /etc/powerfail-full > /dev/null 2>&1 &

The /etc/powerfail-fast must return immediately, longer processes
(the full shutdown) must go to background.

The /etc/powerfail-full script, i.e.

  /usr/sbin/poweroff

does a shutdown of the system.

Create the configuration file /etc/rshdown.conf

  sender-ip     192.168.1.2
  sender-port   2
  receiver-ip   192.168.1.3
  receiver-port 2
  file          /etc/rshdown-secret
  action        /etc/powerfail.fast

Modify the startup scripts to run

  rshdown /etc/rshdown.conf

when the system is booted.

=head1	AUTHOR

Dirk Krause

=head1	COPYRIGHT AND LICENSE

Copyright (c) 2010, Dirk Krause
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

 * Redistributions of source code must retain the above
   copyright notice, this list of conditions and the
   following disclaimer.

 * Redistributions in binary form must reproduce the above
   copyright notice, this list of conditions and the following
   disclaimer in the documentation and/or other materials
   provided with the distribution.

 * Neither the name of the Dirk Krause nor the names of
   contributors may be used to endorse or promote products
   derived from this software without specific prior written
   permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

=head1	SEE ALSO

rndbytes(1), scp(1), shutdown(1), http://dktools.sourceforge.net/rshdown.html

