Recently, my home experienced a power outage. My Synology NAS shut down gracefully since it was connected to a UPS, but my Linux server, which wasn’t connected to the UPS, suffered a hard power loss. This can easily lead to data loss or, in severe cases, disk damage! That’s why I finally got around to configuring NUT, which I had been putting off for a while. This article shares how to use NUT to protect multiple devices with a single UPS.

Device Setup

• Synology NAS: Running DSM 7.2

• Linux Server: Running AlmaLinux 8.1

• Schneider APC UPS: Directly connected to the Synology NAS

What is NUT?

To implement this functionality, we need NUT (Network UPS Tools). NUT is an open-source toolkit for monitoring and managing UPS devices, allowing multiple computers to share UPS status information over a network.

Key components include:

How it works:

In this setup, the Synology NAS will act as the primary server, while the Linux server will act as a secondary client.

When mains power is lost, the Linux server can receive power outage information from the upsd service on the Synology NAS, start a countdown to shutdown, and send notifications through scripts (in this case, I’ve configured WeChat Work notifications).

Configuring the Synology NAS UPS Network Server

1. Log into the Synology DSM management interface
2. Open “Control Panel” > “Hardware & Power” > “UPS”

3. Make sure “Enable UPS support” is checked
4. Select “USB” in the “UPS type” option (depending on your UPS connection method)
5. Set custom time or until low battery (if your UPS battery is unreliable, I recommend setting a shorter time)
6. Check Turn off the UPS when the system enters hibernation mode; otherwise, the system will only enter hibernation mode after a power outage and won’t actively shut down
7. Scroll down to the “Enable UPS network server” option and check it
8. Add your Linux server IP address under “Permitted UPS devices”
9. Click “Apply” to save the settings

With this, the Synology configuration is complete.

If you want the system to restart automatically after power is restored, go to “Control Panel” > “Hardware & Power” > “General” and check Restart automatically after a power failure is restored.

Installing and Configuring NUT on the Linux Server

1. First, install the NUT client package:

The current version I installed is 2.8.2 (you can check with upsd -V)

2. Edit the NUT main configuration file:

sudo vi /etc/ups/nut.conf

Set the mode to netclient:

Here are the possible MODE values for reference:

Value	Explanation
standalone	Local UPS connected to this machine, all components (upsdrv, upsd, upsmon) run locally. Used for single machine local UPS management.
netserver	Local UPS connected to this machine, runs upsd, allows other network clients to connect via NUT protocol. Commonly used in Synology setups as a UPS master server.
netclient	No UPS connected to this machine, only connects to a remote UPS host (running upsd). This machine only runs upsmon. This is the most common mode for secondary machines.

3. Edit the monitoring configuration:

sudo vi /etc/ups/upsmon.conf

Add the following line:

The MONITOR configuration format is as follows:

MONITOR (“primary”|“secondary”)

Parameter	Explanation
MONITOR	Fixed keyword indicating this line is a UPS monitoring configuration.
system	UPS name and host address: here it refers to a UPS instance named “ups” running on remote host 192.168.1.7.
powervalue	Indicates the “power redundancy level” of this UPS — it’s one of several UPS systems we rely on. If you have multiple UPS units, set this number for MINSUPPLIES determination (how many power supplies the system needs at minimum to consider itself safe). Usually set to 1.
username	Username for connecting to the remote upsd service. This user must be defined in /etc/nut/upsd.users on the remote host with MONITOR permissions.
password	Password for monuser, corresponding to the password configured in upsd.users.
(“primary”/“secondary”)	Role type: secondary indicates this is a subordinate client that won’t initiate shutdown on its own, but will wait for master notification or monitor events to shut down itself. Common roles are primary (master) and secondary (subordinate).

The default UPS name for Synology is “ups”, 192.168.1.7 is the Synology IP, and the default username and password are monuser and secret. There’s also a way to check the username and password in the troubleshooting section below.

4. Test if the configuration is correct.

   You can start it in DEBUG mode to see if it works properly.

   If everything is normal, you should see output similar to this:

   Network UPS Tools upsmon 2.8.2
      0.000000     fopen /run/nut/upsmon.pid: No such file or directory
      0.000026     Could not find PID file to see if previous upsmon instance is already running!
      0.000080     UPS: [email protected] (secondary) (power value 1)
      0.000139     Using power down flag file /etc/killpower
      0.000267     [D1] debug level is '1'
      0.000615     [D1] Saving PID 1141184 into /run/nut/upsmon.pid
      0.001801     [D1] Succeeded to become_user(nut): now UID=57 GID=57
   Init SSL without certificate database
      0.020004     upsnotify: failed to notify about state 2: no notification tech defined, will not spam more about it
      0.020009     [D1] Trying to connect to UPS [[email protected]]
      0.021112     [D1] Logged into UPS [email protected]
   

   Next, use the upsc command to check the UPS status.

   It will return information about the UPS such as battery level, version, etc.

   Init SSL without certificate database
   battery.charge: 100
   battery.charge.low: 10
   battery.mfr.date: 2001/01/01
   battery.runtime: 868
   battery.runtime.low: 120
   battery.type: PbAc
   battery.voltage: 13.7
   battery.voltage.nominal: 12.0
   device.mfr: American Power Conversion
   device.model: Back-UPS BK650M2-CH
   device.serial: 9Bxxxxxx
   device.type: ups
   driver.name: usbhid-ups
   driver.parameter.pollfreq: 30
   driver.parameter.pollinterval: 5
   driver.parameter.port: auto
   driver.parameter.synchronous: no
   driver.version: DSM7-2-1
   driver.version.data: APC HID 0.96
   driver.version.internal: 0.41
   input.sensitivity: low
   input.transfer.high: 278
   input.transfer.low: 160
   input.voltage: 224.0
   input.voltage.nominal: 220
   ups.beeper.status: enabled
   ups.delay.shutdown: 20
   ups.firmware: 294803G -292804G
   ups.load: 30
   ups.mfr: American Power Conversion
   ups.mfr.date: 2022/10/25
   ups.model: Back-UPS BK650M2-CH
   ups.productid: 0002
   ups.realpower.nominal: 390
   ups.serial: 9B2xxxxxxx
   ups.status: OL
   ups.test.result: Done and passed
   ups.timer.reboot: 0
   ups.timer.shutdown: -1
   ups.vendorid: 051d
   

5. Start and enable the NUT service:

sudo systemctl enable nut-monitor
sudo systemctl start nut-monitor

Notifications to WeChat Work

Finally, I wrote a script on the Linux server to notify WeChat Work of UPS events.

1. Create a notification script on the Linux server:

sudo vi /etc/ups/notify.sh

2. Add the following content (remember to replace YOUR_KEY with your WeChat Work robot key):

#!/bin/bash

WEBHOOK_URL="https://qyapi.weixin.qq.com/cgi-bin/webhook/send?key=YOUR_KEY"

# Get event message
EVENT_MSG="$1"

# Get current time (format: 2025-05-10 18:30:12)
TIMESTAMP=$(date "+%F %T")

# Construct complete push content
MSG="[$TIMESTAMP] $EVENT_MSG"

# Send message to WeChat Work
curl -s -X POST "${WEBHOOK_URL}" \
  -H 'Content-Type: application/json' \
  -d "{
        \"msgtype\": \"text\",
        \"text\": {
            \"content\": \"${MSG}\"
        }
      }" >/dev/null 2>&1

3. Add execution permissions:

sudo chmod +x /etc/ups/notify.sh

4. Test the script:

/etc/ups/notify.sh Test notification

5. Edit the upsmon configuration file:

sudo vi /etc/ups/upsmon.conf

Add the NOTIFYCMD directive pointing to your script:

NOTIFYCMD /etc/ups/notify.sh

Enable the events you want to be notified about in upsmon.conf, for example:

NOTIFYFLAG ONLINE       SYSLOG+EXEC
NOTIFYFLAG ONBATT       SYSLOG+EXEC
NOTIFYFLAG LOWBATT      SYSLOG+EXEC
NOTIFYFLAG FSD          SYSLOG+EXEC
NOTIFYFLAG COMMOK       SYSLOG+EXEC
NOTIFYFLAG COMMBAD      SYSLOG+EXEC
NOTIFYFLAG SHUTDOWN     SYSLOG+EXEC
NOTIFYFLAG REPLBATT     SYSLOG+EXEC
NOTIFYFLAG NOCOMM       SYSLOG+EXEC
NOTIFYFLAG NOPARENT     SYSLOG+EXEC
NOTIFYFLAG CAL          SYSLOG+EXEC
NOTIFYFLAG NOTCAL       SYSLOG+EXEC
NOTIFYFLAG OFF          SYSLOG+EXEC
NOTIFYFLAG NOTOFF       SYSLOG+EXEC
NOTIFYFLAG BYPASS       SYSLOG+EXEC
NOTIFYFLAG NOTBYPASS    SYSLOG+EXEC

6. Restart the nut-monitor service:

sudo systemctl restart nut-monitor

Now, when the UPS status changes, such as when mains power is lost or restored, you will receive notifications on WeChat Work.

Power Outage Test

After everything is configured, you can test by disconnecting the UPS power.

If you have the Synology web interface open, you’ll notice that after the configured time, it will stop services and enter safe mode.

Then, the Linux server will shut down. If you’re connected via SSH at this time, you’ll see:

This indicates that our configuration is working properly.

Troubleshooting

1. How to view log files

If you encounter issues, you can check these log files:

• On Linux: /var/log/messages or journalctl -u nut-monitor
• On Synology: Control Panel > Log Center > System Logs

2. How to view Synology UPS configuration and password

Synology UPS configuration requires SSH access to the Synology backend.

• /etc/ups/ups.conf: View UPS name and configuration, such as:

[ups]   # << name
        driver = usbhid-ups # << driver
        port = auto

• /etc/ups/upsd.users: View users and passwords, such as:

[monuser] # << user
                password = secret # << password
                upsmon master

You can also modify this password, but after modification, you need to restart the upsd service using the following command:

synosystemctl restart ups-usb

4. If your Synology has a firewall enabled, remember to allow port 3493.
5. If you find that your Synology doesn’t shut down properly, but only enters hibernation mode, you can refer to “Synology UPS Automatic Shutdown Settings for Power Outages” to modify the shutdown command.

Conclusion

With this setup, I can now ensure that whenever a power outage occurs, both my Synology NAS and Linux server can safely shut down, avoiding data corruption and filesystem issues~