Network UPS Tools (NUT)

NUT Server

Pre-requisites: The Wake-on-LAN setup must be completed in order to fully use this guide

You will need a UPS with a USB port for this setup.

Plug your Raspberry Pi into the UPS power socket and connect them via a USB cable.

Install the Network UPS Tools server package on your Raspberry Pi.

sudo apt update
sudo apt install nut nut-server

Inspect the NUT folder. 

sudo ls -l /etc/nut

You should see the following configuration files which we will be customising in this guide.

nut.conf ups.conf  upsd.conf  upsd.users  upsmon.conf  upssched.conf

Identify key information about your UPS.

sudo nut-scanner

Example output:

Scanning USB bus.
No start IP, skipping SNMP
Scanning XML/HTTP bus.
No start IP, skipping NUT bus (old connect method)
Scanning IPMI bus.
[nutdev1]
	driver = "blazer_usb"
	port = "auto"
	vendorid = "0665"
	productid = "5161"
	product = "USB to Serial"
	vendor = "INNO TECH"
	bus = "003"

Back up the exiting ups.conf file as a copy and edit the main file. 

sudo cp /etc/nut/ups.conf /etc/nut/ups.conf.example
sudo nano /etc/nut/ups.conf

Replace the file contents by matching the output from the nut-scanner output above. Use CTRL+T and then CTRL+V to clear all file contents. This defines the user and driver information of your UPS.

Example:

[nutdev1]
    driver = blazer_usb
    port = auto
    desc = "USE PRODUCT OR VENDOR HERE"
    vendorid = 0665
    productid = 5161

CTRL+O, ENTER, CTRL+X to save and exit.

Back up the exiting upsd.conf file as a copy and edit the main file.

sudo cp /etc/nut/upsd.conf /etc/nut/upsd.conf.example
sudo nano /etc/nut/upsd.conf

Replace the file contents with the following. Use CTRL+T and then CTRL+V to clear all file contents. This will enable your other devices (NUT clients) to talk to your NUT server for shutdown/power-on signals.

LISTEN 0.0.0.0 3493

CTRL+O, ENTER, CTRL+X to save and exit.

Back up the exiting nut.conf file as a copy and edit the main file.

sudo cp /etc/nut/nut.conf /etc/nut/nut.conf.example
sudo nano /etc/nut/nut.conf

Replace the file contents with the following. Use CTRL+T and then CTRL+V to clear all file contents. This sets your Raspberry Pi to the NUT server mode.

MODE=netserver

CTRL+O, ENTER, CTRL+X to save and exit.

Back up the exiting upsd.users file as a copy and edit the main file.

sudo cp /etc/nut/upsd.users /etc/nut/upsd.users.example
sudo nano /etc/nut/upsd.users

Replace the file contents with the following. Use CTRL+T and then CTRL+V to clear all file contents. This sets the credentials for the NUT user.

[monuser]
  password = secret
  upsmon master
#"monuser", "secret", and "master" need to match the contents of the upsd.users
# to be set below

CTRL+O, ENTER, CTRL+X to save and exit.

Back up the exiting upsmon.conf file as a copy and edit the main file.

sudo cp /etc/nut/upsmon.conf /etc/nut/upsmon.conf.example
sudo nano /etc/nut/upsmon.conf

Add the following as new lines to the bottom of the existing file content. This defines the actual power monitoring activities and consequent actions upon detecting a power restoration. 

MONITOR nutdev1@localhost 1 monuser secret master
#"monuser", "secret", and "master" need to match the contents of the upsd.users set above
NOTIFYFLAG ONLINE SYSLOG+EXEC+WALL
NOTIFYCMD /etc/nut/online.sh # we will create this shell script later

CTRL+O, ENTER, CTRL+X to save and exit.

Create the online.sh shell script which tells all your devices to power up when it detects that power supply to your UPS has been restored following a power outage.

Note: I am using a simple script to handle the automated power on sequence because I can't get my NUT to work as intended. Let me know if anyone managed to get yours working.

sudo nano /etc/nut/online.sh

Paste the following content. 

#!/bin/bash
# Log the start of the script
logger "NUT: Checking UPS status for ONLINE event"

# Fetch the UPS status
status=$(upsc nutdev1@localhost ups.status)

# Check if the UPS is on battery
if [[ "$status" == "OL" ]]; then
    logger "NUT: UPS on line power detected. Waiting 60 seconds before powering up all devices."
    
    # Wait for 60 seconds
    sleep 60
    
    # Log the power up initiation
    logger "NUT: Initiating power up after 60-second delay."
    /usr/local/bin/wake_devices "UPS online"
else
    logger "NUT: UPS status is not ONLINE (status: $status). No power up triggered."
fi

CTRL+O, ENTER, CTRL+X to save and exit.

This online.sh script makes use of the wake_devices script that we created in the Wake-on-LAN page.

Make this shell script executable but set proper permissions for security.

sudo chmod +x /etc/nut/online.sh
sudo chown root:nut /etc/nut/online.sh
sudo chmod 750 /etc/nut/online.sh

Restart the NUT services.

sudo service nut-server restart
sudo service nut-client restart
sudo systemctl restart nut-monitor
sudo upsdrvctl stop
sudo upsdrvctl start

Inspect the nut-server and nut-monitor for errors.

sudo journalctl -fu nut-server  -o cat | ccze -A
sudo journalctl -fu nut-monitor -o cat | ccze -A

Example output:

#nut-server
Starting Network UPS Tools - power devices information server... 
fopen /run/nut/upsd.pid: No such file or directory 
listening on 0.0.0.0 port 3493 
listening on 0.0.0.0 port 3493 
Connected to UPS [prolink]: blazer_usb-prolink 
Connected to UPS [prolink]: blazer_usb-prolink 
Startup successful 
Started Network UPS Tools - power devices information server. 
User monuser@127.0.0.1 logged into UPS [prolink]

#nut-monitor
Starting Network UPS Tools - power device monitor and shutdown controller... 
fopen /run/nut/upsmon.pid: No such file or directory 
UPS: prolink@localhost (master) (power value 1) 
Using power down flag file /etc/killpower 
Startup successful 
nut-monitor.service: Can't open PID file /run/nut/upsmon.pid (yet?) after start: Operation not permitted 
nut-monitor.service: Supervising process 1206 which is not our child. We'll most likely not notice when it exits. 
Started Network UPS Tools - power device monitor and shutdown controller. 
nut-monitor.service: Supervising process 1206 which is not our child. We'll most likely not notice when it exits. 
nut-monitor.service: Supervising process 1206 which is not our child. We'll most likely not notice when it exits.

CTRL+C to exit logging view.

NUT Clients

The following steps need to be configured on all your other devices (e.g., validator node) to power down gracefully when there is a power outage.

Install the Network UPS Tools client on your device. 

sudo apt update
sudo apt install nut-client

Inspect the NUT folder. 

sudo ls -l /etc/nut

You should see the following configuration files which we will be customising in this guide.

nut.conf  upsmon.conf  upssched.conf

Back up the exiting nut.conf file as a copy and edit the main file.

sudo cp /etc/nut/nut.conf /etc/nut/nut.conf.example
sudo nano /etc/nut/nut.conf

Replace the file contents with the following. Use CTRL+T and then CTRL+V to clear all file contents. This sets your Validator Node to the NUT server mode.

MODE=netclient

CTRL+O, ENTER, CTRL+X to save and exit.

Back up the exiting upsmon.conf file as a copy and edit the main file.

sudo cp /etc/nut/upsmon.conf /etc/nut/upsmon.conf.example
sudo nano /etc/nut/upsmon.conf

Add the following as new lines to the bottom of the existing file content. Replace IP_ADDRESS_OF_NUT_SERVER with the actual internal IP address of your Raspberry Pi. This defines the actual power monitoring activities and consequent actions upon detecting a power restoration. 

MONITOR nutdev1@IP_ADDRESS_OF_NUT_SERVER 1 monuser secret slave
#"upsmon" and "secret" need to match the contents of the upsd.users set in your NUT server
NOTIFYFLAG ONBATT SYSLOG+EXEC+WALL
NOTIFYCMD /etc/nut/onbatt.sh 
# we will create this shell script later

CTRL+O, ENTER, CTRL+X to save and exit.

Create the onbatt.sh shell script which tells your device to shut down gracefully when it detects that power supply to your UPS has been cut off (e.g., due to a power outage).

Note: I am using a simple script to handle the automated shutdown sequence because I can't get my NUT to work as intended. Let me know if anyone managed to get yours working.

sudo nano /etc/nut/onbatt.sh

Paste the following content. 

#!/bin/bash
# Log the start of the script
logger "NUT: Checking UPS status for ONBATT event"

# Fetch the UPS status; Set to the actual IP Address of your NUT server here
status=$(upsc nutdev1@IP_ADDRESS_OF_NUT_SERVER ups.status)

# Check if the UPS is on battery
if [[ "$status" == "OB" ]]; then
    logger "NUT: UPS on battery power detected. Waiting 120 seconds before shutting down."
    
    # Wait for 120 seconds
    sleep 120
    
    # Log the shutdown initiation
    logger "NUT: Initiating shutdown after 120-second delay."
    sudo /sbin/shutdown -h now "UPS on battery power"
else
    logger "NUT: UPS status is not ONBATT (status: $status). No shutdown triggered."
fi

CTRL+O, ENTER, CTRL+X to save and exit.

Make this shell script executable but set proper permissions for security.

sudo chmod +x /etc/nut/onbatt.sh
sudo chown root:nut /etc/nut/onbatt.sh
sudo chmod 750 /etc/nut/onbatt.sh

Allow the nut user to run only the /sbin/shutdown to power down your device without needing the sudo (superuser) password.

sudo visudo

Add the following as a new line in the file.

nut ALL=(ALL) NOPASSWD: /sbin/shutdown

Restart the NUT services.

sudo service nut-client restart
sudo systemctl restart nut-monitor
sudo systemctl status nut-client nut-monitor

Enable auto-power-on in BIOS (Optional)

This is optional as your Raspberry Pi will send a power-on signal to all your devices when power is restored but still good to have as a backup.

  1. Restart your device and press F2 repeatedly during boot to enter BIOS Setup.

  2. Select Advanced, then select the Power menu.

  3. Expand the Secondary Power Settings sub-menu and set After Power Failure to Power On.

  4. Press F10 to save and exit the BIOS Setup.

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