OK, Now About UPS's and the Raspberry Pi

I have had a UPS for my NAS for a while now, but this season's storms caused me to seriously think about getting another one for my set of Raspberry Pi's. Every time the wind got over 20 mph, the power would go out, thunderstorms would kill the power, and the occasional dust devil in the right place would cause those short power failures that just mess things up. A couple of the power failures were those messy ones where the power dropped to almost nothing, then came back, went away again, and finally just died for a couple of hours.

I wasn't concerned about spikes; I have a bunch of protectors around for that, but it gets annoying fixing the various software problems power failures make on the Pi. So, I got a second UPS to install where I have my Pi collection. I bought another APC BE550G:


This is big enough to handle the short outages, and has enough guts to run the various things I may hook up. I chose this one because it's the same as the one on my NAS that runs it and several other little computers up in the attic. Why have two different devices?

Yes, it's an expensive solution, but after I buy a power supply board and the circuitry necessary for battery backup on the Pi, I would have spent just as much and still need more for the other little computers. I already know how to make one of these, so it would be just grunt work and not much fun.

The NAS up in the attic has really cool power fail software, so I went looking for something similar to run on the Pi and found a tool called apcusbd. This is a daemon that runs all the time monitoring the USP port on the UPS. When it finds a problem it can send email letting me know as well as messages to anyone logged into the machine. It will also send a power down to the UPS shutting off the power when a timer runs out.

This power down is important. When you halt a Pi, it just halts, there's no power down, and that means you have to unplug, plug to get it to come back online. So, for unattended operation, you have to somehow cycle the power to get the Pi back to working. I have to halt it because, if I don't, it will screw up the file system, or even worse, corrupt the SD card so I have to get it from backup. Been there, done that, too many times.

If I could get this all working correctly, it would go a long ways to solving some of my SD card problems over long periods of time. I dug in and installed, configured, and tested apcusbd. It worked really well on the first try after I configured it. There are literally thousands of sites out there that tell you how to install and configure this software, so I won't repeat it here, but there was one problem: it wouldn't turn the power off on the UPS.

Digging into the configuration did nothing for me; it looked like I got it right, so I started testing pieces of it. Apcupsd allows the use of scripts that I could modify a bit and test the power down functions. When I tried them, they worked and actually turned the power off. This left me confused; if they worked, why didn't the power turn off? I looked through the syslog and found nothing to help in troubleshooting this problem, so I dug into the shutdown procedure of the Pi running under Jessie. Man, what a complex mess that is.

See, systemctl sets run level zero which causes the scripts in /etc/rc0.d to be executed in order and the last one is 'halt'. This seems reasonable, but the shutoff code for the UPS is in the halt script. everything else is already done ... including syslogd which is the thing that logs all the data for the shutdown. No, I couldn't change it to write to a file since the file systems are all remouted read only by that time. There was no way to tell what the heck wasn't happening.

I never managed to solve that problem, so I decided to send the turn off signal to the UPS earlier in the halt steps since the UPS gives me a grace period of over a minute of power after the signal; plenty of time to finish the halt process. To this end, I created a little script to add to the shutdown process that would sense the power failure from apcupsd and send the signal using the scripts that already come with the software. I couldn't get the script to be run by systemctl.

Yes, I spent hours looking on the web for what was preventing it from being used, and found other folk that had the exact same problem. There were exactly zero actual solutions. Lots of talk about run levels, LSB's, running update-rc.d, keeping certain little things out of the script, but nothing definitive that would work. I kept reducing the stuff in the script until I had almost nothing in there and it still wouldn't get run during the shutdown and halt process. What I finally wound up with before I gave up on this idea was:

#! /bin/sh
### BEGIN INIT INFO
# Provides:          davetesting
# Required-Start:
# Required-Stop:
# Default-Start:
# Default-Stop:      0
# Short-Description: Dave Testing
# Description:       Just testing this thing
### END INIT INFO

PATH=/sbin:/bin
echo "Dave Testing in aaa"

echo "Dave inside aaa before the file thing"
echo $1
echo "Dave inside aaa got a $1"

#!/bin/sh

### BEGIN INIT INFO
# Provides:             apcupsd
# Required-Start:       $remote_fs $syslog
# Required-Stop:        $remote_fs $syslog
# Should-Start:         $local_fs
# Should-Stop:          $local_fs
# Default-Start:        2 3 4 5
# Default-Stop:         0 1 6
# Short-Description:    Starts apcupsd daemon
# Description:          apcupsd provides UPS power management for APC products.
### END INIT INFO

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
DAEMON=/sbin/apcupsd
CONFIG=/etc/default/apcupsd
NAME=apcupsd
DESC="UPS power management"

test -x $DAEMON || exit 0
test -e $CONFIG || exit 0

set -e

. $CONFIG

echo "Dave is in ups code messing around"
echo "Dave found $1 "
if [ -f /etc/apcupsd/powerfail ]; then
        echo "Dave Found powerfail"
else
        echo "Dave No powerfail Found"
fi

if [ "x$ISCONFIGURED" != "xyes" ] ;
then
        echo "Please check your configuration ISCONFIGURED in /etc/default/apcupsd"
        exit 0
fi


case "$1" in
        start)
                echo -n "Starting $DESC: "

                rm -f /etc/apcupsd/powerfail

                if [ "`pidof apcupsd`" = "" ]
                then
                        start-stop-daemon --start --quiet --exec $DAEMON
                        echo "$NAME."
                else
                        echo ""
                        echo "A copy of the daemon is still running.  If you just stopped it,"
                        echo "please wait about 5 seconds for it to shut down."
                        exit 0
                fi
                ;;

        stop)
                echo -n "Stopping $DESC: "
                start-stop-daemon --stop --oknodo --pidfile /var/run/apcupsd.pid || echo "Not Running."
                rm -f /var/run/apcupsd.pid
                echo "$NAME."
                if [ -f /etc/apcupsd/powerfail ]; then
                        echo "Dave Doing  powerfail"
                        /etc/init.d/ups-monitor poweroff
                fi
                sync; sync;
                ;;

        restart|force-reload)
                $0 stop
                sleep 10
                $0 start
                ;;

        status)
                #/sbin/apcaccess status
                $APCACCESS status
                ;;

        *)
                N=/etc/init.d/$NAME
                echo "Usage: $N {start|stop|restart|force-reload}">&2
                exit 1
                ;;
esac

exit 0