UPS Monitoring with Raspberry Pi's & PRTG

This super light script will give the ability to do network monitoring on a UPS backup battery that lacks networking (or requires proprietary software), via PRTG.

This script was tested/built for an APC SmartUPS 1500 via USB and also used with Tripp Lite SMART500RT1U, but should work for any UPS that's supported by NUT. You may need to adjust the driver used, my instructions were as-used in my environment.

In Summary

• NUT monitors the battery statistics
• PRTG can monitor the health of the Pi + battery via NUT statistics
• PRTG is given a directive to login to the Pi and run a Python script (via PRTG settings)
• The Python script processes data from Nut and formats it for PRTG's XML and returns the data as sensor + channel values
• Clone the Pi for use in multiple tech closets/floors

My Physical Setup (Yours may differ, depending on battery)

The APC SmartUPS uses the usbhid-ups driver and is accessible by plugging a USB A to B (old printer style) from the UPS, into the Pi. (USB B port is native to the battery.)

Pre-requisite

The Pi will require wifi / network jack and/or a switch accessible, so PRTG can reach it.

Worth Noting

You can have one Pi monitor multiple batteries, but in my environment its one UPS per closet, so I didn't consider such environments in the code. Feel free to adjust to suit your needs.

It is also possible to forgo the Python script and do this entirely via SNMP by extending SNMP with a bash script.

Preliminary Setup

1. Set up a Pi with Raspbian or Noobs
2. Install dependences: sudo apt install nut snmpd snmp snmp-mibs-downloader git
3. Prepare a 'default' setup for cloning, to use on multiple batteries:

Set a Default Static IP

This should be a reserved IP (one you don't plan to use - and is outside of any DHCP scope), as you will have to login to each Pi after it is cloned to set a static IP.

Increment it for each machine using 172.28.4.xx; xx = closet number

sudo pico /etc/dhcpcd.conf

Add the following (make sure the static IP you assign, doesn't already exist -- customize to suit your environment)

# static ip config to the admin network:
interface eth0
static ip_address=172.28.4.xx/24
#static ip6_address=
static routers=172.28.10.1
static domain_name_servers=172.28.5.140 172.28.5.141

---

Setting up NUT

• Declare the UPS in /etc/nut/ups.conf

# tc for tech closet.. name it anything that suits your environment
[tc]
  driver = usbhid-ups
  port = auto
  desc = "TC UPS"

• In /etc/nut/nut.conf, set NUT daemon to run in standalone mode. It's the mode to use on the machine to which the UPS is connected and when this same machine also monitors the UPS

# default config
#MODE=none

# config changed by angela
MODE=standalone

• In /etc/nut/upsd.conf, bind a listening port to the LAN interface if you want to allow other LAN hosts to monitor the UPS through upsd, the UPS network daemon. If not, just keep the first line:

# config added by angela
LISTEN 127.0.0.1

• Set the permissions for upsd in /etc/nut/upsd.users. Only the users (one section = one user) listed in this file will be allowed to read the UPS state:

# config added by angela
[tc]
  password = [yourpassword]
  upsmon master

• Configure the upsmon daemon. Its role is to communicate with upsd to know the UPS status and send specific commands when some events occur. Modify /etc/nut/upsmon.conf as follows:

# config added by angela
MONITOR tc@localhost 1 tc [yourpassword] master

• Make sure to modify the permissions of all NUT configuration files

chown root:nut /etc/nut/*
chmod 640 /etc/nut/*

Auto-start SNMP

systemctl enable snmpd

Start the SNMP daemon (this won't be necessary in subsequent logins, as the 'enable' sets it to auto-start upon boot.

systemctl start snmpd

---

Allow SNMP Remote Probes

This is to monitor the health of the Pi, not the battery (I could not locate the MIBs needed for the APC Smart-UPS 1500)

sudo pico /etc/snmp/snmpd.conf

Under AGENT BEHAVIOR, add (comment out any existing agentAddress entries):

agentAddress udp:161

Under ACCESS CONTROL, add (comment out any existing rocommunity strings) - add the IP of your PRTG installation here:

rocommunity public 172.28.5.1
# any other IP you want to have access to.

Provision your changes with a restart:

service snmpd restart

Testing Commands

To start NUT manually (upsd and upsmon daemons simultaneously):

service nut start

To check both daemons status:

service nut status

To launch the UPS driver (this will be configured to launch on reboot a few lines below here):

upsdrvctl start

To know the UPS status:

upsc ups

To test the server behavior in case of power outage, use the following command:

upsmon -c fsd

---

PRTG Testing Commands

The script is owned by user prtg su - prtg

Execute the script manually (no language prefix necessary, as the script has a shebang on line 1)

/var/prtg/scriptsxml/battery_sensor.py

Create a startup service

rc.local is for the sysadmin/root/sudo user to execute tasks or services after normal system services have started.

This was "deprecated" in distros with systemd but you can restore rc.local-like functionality by simply creating a service, enabling at startup and calling it rc-local.

Create the systemd service

sudo pico /etc/systemd/system/rc-local.service

Add the following to rc-local.service

[Unit]
Description=Create rc.local functionality in systemd
ConditionPathExists=/etc/rc.local

[Service]
Type=forking
ExecStart=/etc/rc.local start
TimeoutSec=0
StandardOutput=tty
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Make the script executable so it may be invoked by the service

chmod +x /etc/rc.local

If you haven't already, pre-pend the shebang to the beginning of /etc/rc.local, otherwise systemd won't run it, and an exit 0

#!/bin/sh

# autostart upsdrvctl for nut
upsdrvctl start

exit 0

Enable it at startup and start it

systemctl enable rc-local && systemctl start rc-local.service

Check for errors (it would crash right away on start, typically)

service rc-local status

---

Create a user so PRTG can login remotely to check on Nut

• Create an SSH key for PRTG to use on Linux-based servers (if you haven't already)
• Go into PRTG dashboard settings and add the key and prtg user for Linux
• Restart the SSH daemon for the changes to take effect:

service ssh restart

On the Pi:

• Make sure PRTG's private key is accessible to ~/.ssh/prtg/ and that you have the SSH pubkey also accessible to any private repo, should you intend to keep a private, customized branch of this script - that way if you make changes, you can push it to all of your installations.

• Make a scripts directory that PRTG knows to look for (it has to be this path, for XML-based output!)

mkdir /var/prtg/scriptsxml

• Clone the remote repo and assign the PRTG scriptsxml directory as the destination:

git clone https://github.com/angela-d/prtg-ups-monitor.git /var/prtg/scriptsxml &&
chmod 750 -R $(find /var/prtg/ -type d) &&
chmod 544 $(find /var/prtg/scriptsxml -type f) &&
chmod 540 -R $(find /var/prtg/scriptsxml -type f)

In summary:

• battery-sensor.py is an executable
• chown to assign permissions to the PRTG user so it can read.
• chmod to change permissions mode.

Useful: Permissions cheatsheet

---

Reduce Writes to the Pi

Since this is a Pi, you don't want the SD card constantly being written to, as such will shorten its lifespan.

Switch to root on the Pi:

sudo su

Create the file:

sudo pico /etc/rsyslog.d/10-prtg.conf

Append to 10-prtg.conf:

# do not log snmp hits from prtg
#
# do not add this until setup testing is done..
if $msg contains 'Connection from UDP: [your-PRTG-ip]' then stop

# include the brackets!
# if $msg contains 'Connection from UDP: [127.0.0.2]' then stop

Restart rsyslog daemon

service rsyslog restart

---

Optional Test code for battery_sensor.py

For working on the script without immediate access to the battery (run upsc tc on your system to generate it).

• Have a textual copy of the xml output
• Replace the subprocess bits with:

# do a loop on a text file of the results we're supposed to iterate from the upsc command
import io
battery_results = subprocess.Popen(["cat", "upsc-output"], stdout=subprocess.PIPE)
for line in io.TextIOWrapper(battery_results.stdout, encoding="utf-8"):

---

Adding the Sensors to PRTG

• Add a new device
• Go to the new device and click the + to Add a sensor
• Click the SSH Script Advanced option

Select a script file from the list. The dropdown menu lists all script files available in the /var/prtg/scriptsxml directory on the target Linux/Unix system. For a script file to appear in this list, store the target file into this directory. Make sure that the script has executable rights.

To show the expected sensor value and status, your files must return the expected XML or JSON format to standard output stdout. Values and message must be embedded in the XML or JSON.

• Customize the channel thresholds by clicking the dual-wheels > Enable alerting based on limits (you won't get alerts or warnings without doing this step!)

Automate Future Installations

Or close enough to it! Clone the Raspberry Pi for easy setup on multiple batteries.

Don't forget to add the Pi's to your updates schedule! They require security patches and bugfixes just like any other Linux system.