A while back I needed to get the input voltage from one of our UPSes, so I used bsnmpwalk(1) to get the information needed and ran it in a script with a loop and sleep. Running it in tmux(1), of course.

#!/bin/sh

lastoff="maybe"

while true;
do
  inpvol=$(bsnmpwalk -o quiet -s public@172.20.42.101 1.3.6.1.2.1.33.1.3.3.1.3)

  [ $? != 0 ] && \
    curl -s -X POST \
    https://api.telegram.org/botXXX:YYY/sendMessage \
    -d chat_id=-ZZZ \
    -d text="Something is wrong with the SNMP server"

  [ "${inpvol}" -lt 200 ] && \
    curl -s -X POST \
    https://api.telegram.org/botXXX:YYY/sendMessage \
    -d chat_id=-ZZZ \
    -d text="Power seems to be off. I see Input Voltage as ${inpvol}" && \
    lastoff="true"

  [ "${inpvol}" -ge 200 ] && [ "${lastoff}" == "true" ] && \
    curl -s -X POST \
    https://api.telegram.org/botXXX:YYY/sendMessage \
    -d chat_id=-ZZZ \
    -d text="Power back on. I see Input Voltage as ${inpvol}" && \
    lastoff="false"

  printf "%s  ---  %s\n" "$(date)" "${inpvol}"
  sleep 60
done

This got the job done, but I guess there’s place for improvement (leave a reply).

Anyways, I kept forgetting that I need to run the script in tmux after reboots, so I decided to use daemon(8).

touch /etc/rc.local
chmod +x /etc/rc.local
cat - >> /etc/rc.local
#!/bin/sh

daemon -u nobody -r -R 5 -f -t ups-notifier -o /var/log/ups_notifier.log /usr/local/bin/ups_notifier.sh

Again, there’s a place for improvement, specifically I can use a proper rc.d(8) script, yet again, this gets the job done.

Gotta say, I love the simplicity of FreeBSD.