The issue
Zigbee2MQTT fails to start with SONOFF Dongle-LMG21/-PMG24/-M on Windows. The error log looks like the following:
[2026-02-03 22:08:40] info: z2m: Logging to console, file (filename: log.log)
[2026-02-03 22:08:40] info: z2m: Starting Zigbee2MQTT version 2.8.0 (commit #b0b02c30)
[2026-02-03 22:08:40] info: z2m: Starting zigbee-herdsman (9.0.2)
[2026-02-03 22:08:40] info: zh:ember: Using default stack config.
[2026-02-03 22:08:40] info: zh:ember: ======== Ember Adapter Starting ========
[2026-02-03 22:08:40] info: zh:ember:ezsp: ======== EZSP starting ========
[2026-02-03 22:08:40] info: zh:ember:uart:ash: ======== ASH Adapter reset ========
[2026-02-03 22:08:40] info: zh:ember:uart:ash: Serial port opened
[2026-02-03 22:08:40] info: zh:ember:uart:ash: ======== ASH starting ========
[2026-02-03 22:08:45] info: zh:ember:uart:ash: ======== ASH Adapter reset ========
[2026-02-03 22:08:45] info: zh:ember:uart:ash: ======== ASH starting ========
[2026-02-03 22:08:51] info: zh:ember:uart:ash: ======== ASH Adapter reset ========
[2026-02-03 22:08:51] info: zh:ember:uart:ash: ======== ASH starting ========
[2026-02-03 22:08:56] info: zh:ember:uart:ash: ======== ASH Adapter reset ========
[2026-02-03 22:08:56] info: zh:ember:uart:ash: ======== ASH starting ========
[2026-02-03 22:09:02] info: zh:ember:uart:ash: ======== ASH Adapter reset ========
[2026-02-03 22:09:02] info: zh:ember:uart:ash: ======== ASH starting ========
[2026-02-03 22:09:07] error: z2m: Error while starting zigbee-herdsman
[2026-02-03 22:09:07] error: z2m: Failed to start zigbee-herdsman
[2026-02-03 22:09:07] error: z2m: Check https://www.zigbee2mqtt.io/guide/installation/20_zigbee2mqtt-fails-to-start_crashes-runtime.html for possible solutions
[2026-02-03 22:09:07] error: z2m: Exiting...
[2026-02-03 22:09:07] error: z2m: Error: Failed to start EZSP layer with status=HOST_FATAL_ERROR.
The reason
Zigbee2MQTT relies on SerialPort library to communicate with SONOFF Dongle. The default behavior of SerialPort windows library will pull down the DTR pin which cause SONOFF Dongle into reboot loop.
The option that controls this behavior is hupcl in SerialPort but Zigbee2MQTT (and also ember-zli) doesn’t expose it. A temporary (also ugly) fix would be adding hupcl: false to the serialOpts object of source code file zigbee-herdsman/src/adapter/ember/uart/ash.ts at master · Koenkk/zigbee-herdsman · GitHub at line 457, maybe after xoff: false,.
The solution
Install Zigbee2MQTT
Prerequisite: install Node.js 24, run command corepack enable to enable pnpm.
Pull Zigbee2MQTT source code:
git clone --depth 1 https://github.com/Koenkk/zigbee2mqtt/
Go into zigbee2mqtt root directory, and install dependencies.
pnpm install --frozen-lockfile
Add option hupcl: false to serialOpts
Open file zigbee2mqtt\node_modules\zigbee-herdsman\dist\adapter\ember\uart\ash.js, add option hupcl: false to serialOpts. For example:
const serialOpts = {
path: this.portOptions.path,
baudRate: typeof this.portOptions.baudRate === "number" ? this.portOptions.baudRate : 115200,
rtscts: typeof this.portOptions.rtscts === "boolean" ? this.portOptions.rtscts : false,
autoOpen: false,
parity: "none",
stopBits: 1,
xon: false,
xoff: false,
hupcl: false,
};
Build and start
pnpm run build
pnpm start
Verify but it should work
Once Zigbee2MQTT is started, visit its onboarding page, such as http://localhost:8080.
Choose the right options, such as:
- Coordinator/Adapter Port/Path: COM7
- Coordinator/Adapter Type/Stack/Driver: ember
- Coordinator/Adapter Baudrate: 115200
- Coordinator/Adapter Hardware Flow Control (“rtscts: true”): false
Or, you can create the configuration.yaml file manually if you are familiar with Zigbee2MQTT.