Mosquitto crashing repeatedly with potential memory leak?

[glitter-ball]

I’m running the ‘standard’ HA build (core 2025.12.3 OS 16.3) on a Raspberry Pi with Mosquitto add-on 6.5.2 (core is 2.0.22). At intervals, Mosquitto is quitting and restarting…

[05:52:22] INFO: Service restart after closing
[05:52:25] INFO: Starting mosquitto MQTT broker...
2026-01-06 05:52:25: mosquitto version 2.0.22 starting
2026-01-06 05:52:25: Config loaded from /etc/mosquitto/mosquitto.conf.
2026-01-06 05:52:25: Loading plugin: /usr/share/mosquitto/go-auth.so
[05:52:25] INFO: Successfully send service information to the Supervisor.
2026-01-06 05:52:25: Warning: Mosquitto should not be run as root/administrator.
[05:52:26] INFO: Successfully send discovery information to Home Assistant.
2026-01-06 05:52:25: ├── Username/password checking enabled.
2026-01-06 05:52:25: ├── TLS-PSK checking enabled.
2026-01-06 05:52:25: └── Extended authentication not enabled.
2026-01-06 05:52:25: Opening ipv4 listen socket on port 1883.
2026-01-06 05:52:25: Opening ipv6 listen socket on port 1883.
2026-01-06 05:52:25: Opening websockets listen socket on port 1884.
2026-01-06 05:52:25: Opening ipv4 listen socket on port 8883.
2026-01-06 05:52:25: Opening ipv6 listen socket on port 8883.
2026-01-06 05:52:25: Opening websockets listen socket on port 8884.
2026-01-06 05:52:25: mosquitto version 2.0.22 running
2026-01-06 05:52:29: New connection from 192.168.1.6:59482 on port 1883.
2026-01-06 05:52:29: New connection from ::1:44682 on port 1883.
2026-01-06 05:52:29: New client connected from 192.168.1.6:59482 as ems-esp (p2, c1, k60, u'mqttems').
2026-01-06 05:52:29: Client <unknown> disconnected due to protocol error.
2026-01-06 05:52:33: New connection from 172.30.32.1:41361 on port 1883.
[05:52:35] INFO: Successfully send service information to the Supervisor.
[05:52:40] INFO: Successfully send discovery information to Home Assistant.
2026-01-06 05:52:33: New client connected from 172.30.32.1:41361 as 7e3rsUYvmI39dabKV7ShII (p2, c1, k60, u'homeassistant').
2026-01-06 05:52:40: New connection from 192.168.1.237:56263 on port 1883.
2026-01-06 05:52:40: New client connected from 192.168.1.237:56263 as ESP32_545178 (p2, c1, k120, u'mqttihd').
[05:52:50] INFO: Successfully send service information to the Supervisor.
2026-01-06 05:53:03: New connection from 172.30.32.2:55822 on port 1883.
2026-01-06 05:53:03: Client <unknown> closed its connection.
[05:53:10] INFO: Service restart after closing
[05:53:12] INFO: Starting mosquitto MQTT broker...
2026-01-06 05:53:12: Warning: Mosquitto should not be run as root/administrator.
2026-01-06 05:53:12: mosquitto version 2.0.22 starting
2026-01-06 05:53:12: Config loaded from /etc/mosquitto/mosquitto.conf.
2026-01-06 05:53:12: Loading plugin: /usr/share/mosquitto/go-auth.so
2026-01-06 05:53:12: ├── Username/password checking enabled.
2026-01-06 05:53:12: ├── TLS-PSK checking enabled.
2026-01-06 05:53:12: └── Extended authentication not enabled.
2026-01-06 05:53:12: Opening ipv4 listen socket on port 1883.
2026-01-06 05:53:12: Opening ipv6 listen socket on port 1883.
2026-01-06 05:53:12: Opening websockets listen socket on port 1884.
2026-01-06 05:53:12: Opening ipv4 listen socket on port 8883.
2026-01-06 05:53:12: Opening ipv6 listen socket on port 8883.
2026-01-06 05:53:12: Opening websockets listen socket on port 8884.
2026-01-06 05:53:12: mosquitto version 2.0.22 running
2026-01-06 05:53:17: New connection from ::1:37200 on port 1883.
2026-01-06 05:53:17: Client <unknown> disconnected due to protocol error.
2026-01-06 05:53:17: New connection from 192.168.1.6:59485 on port 1883.
2026-01-06 05:53:17: New client connected from 192.168.1.6:59485 as ems-esp (p2, c1, k60, u'mqttems').
2026-01-06 05:53:20: New connection from 172.30.32.1:53927 on port 1883.
2026-01-06 05:53:20: New client connected from 172.30.32.1:53927 as 7e3rsUYvmI39dabKV7ShII (p2, c1, k60, u'homeassistant').
2026-01-06 05:53:25: New connection from 192.168.1.237:56268 on port 1883.
2026-01-06 05:53:25: New client connected from 192.168.1.237:56268 as ESP32_545178 (p2, c1, k120, u'mqttihd').
[05:53:30] INFO: Successfully send discovery information to Home Assistant.
[05:53:37] INFO: Successfully send service information to the Supervisor.
[05:53:51] INFO: Service restart after closing
[05:53:53] INFO: Starting mosquitto MQTT broker...
2026-01-06 05:53:54: mosquitto version 2.0.22 starting
2026-01-06 05:53:54: Config loaded from /etc/mosquitto/mosquitto.conf.
2026-01-06 05:53:54: Loading plugin: /usr/share/mosquitto/go-auth.so
2026-01-06 05:53:54: ├── Username/password checking enabled.
2026-01-06 05:53:54: ├── TLS-PSK checking enabled.
2026-01-06 05:53:54: └── Extended authentication not enabled.
2026-01-06 05:53:54: Warning: Mosquitto should not be run as root/administrator.
2026-01-06 05:53:54: Opening ipv4 listen socket on port 1883.
2026-01-06 05:53:54: Opening ipv6 listen socket on port 1883.
2026-01-06 05:53:54: Opening websockets listen socket on port 1884.
2026-01-06 05:53:54: Opening ipv4 listen socket on port 8883.
2026-01-06 05:53:54: Opening ipv6 listen socket on port 8883.
2026-01-06 05:53:54: Opening websockets listen socket on port 8884.
2026-01-06 05:53:54: mosquitto version 2.0.22 running
2026-01-06 05:54:00: New connection from ::1:50724 on port 1883.
2026-01-06 05:54:00: Client <unknown> disconnected due to protocol error.
2026-01-06 05:54:00: New connection from 192.168.1.6:59489 on port 1883.
2026-01-06 05:54:00: New client connected from 192.168.1.6:59489 as ems-esp (p2, c1, k60, u'mqttems').
2026-01-06 05:54:04: New connection from 172.30.32.1:55295 on port 1883.
2026-01-06 05:54:04: New client connected from 172.30.32.1:55295 as 7e3rsUYvmI39dabKV7ShII (p2, c1, k60, u'homeassistant').
2026-01-06 05:54:08: New connection from 192.168.1.237:56272 on port 1883.
2026-01-06 05:54:08: New client connected from 192.168.1.237:56272 as ESP32_545178 (p2, c1, k120, u'mqttihd').
[05:54:14] INFO: Successfully send discovery information to Home Assistant.
[05:54:24] INFO: Successfully send service information to the Supervisor.

Concurrent with these Mosquitto logs, the host log appears to be flagging an OOM (out of memory?) event…

2026-01-06 05:53:10.388 homeassistant kernel: oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0,global_oom,task_memcg=/system.slice/docker-eb8afa7a3a23384c6023dbdea7378c2e227a53f049cfe5afc9f5610b7b326900.scope,task=mosquitto,pid=347656,uid=0

2026-01-06 05:53:10.389 homeassistant kernel: Out of memory: Killed process 347656 (mosquitto) total-vm:1433652kB, anon-rss:27008kB, file-rss:672kB, shmem-rss:0kB, UID:0 pgtables:268kB oom_score_adj:200

2026-01-06 05:53:10.389 homeassistant systemd[1]: docker-eb8afa7a3a23384c6023dbdea7378c2e227a53f049cfe5afc9f5610b7b326900.scope: A process of this unit has been killed by the OOM killer.

In parallel, I’m seeing creeping increasing RAM usage with a drop back after each Mosquitto crash:

So… does my Mosquitto instance have a memory leak which is causing the crashes? How do I go about troubleshooting that?

[tom_l]

@glitter-ball

does my Mosquitto instance have a memory leak which is causing the crashes?

Maybe, maybe not. It could be something else leaking causing Mosquitto to crash.

Turn off the broker add-on and see if the leak continues to occur. Yes = not the add-on.

Restart in safe mode and see if the leek continues to occur. No = third party integration.

How much RAM does your pi have?

Do you run the VSCode add-on?

That is a memory hog. So is the Firefox add-on.

[tom_l]

For what it is worth I also run the Mosquitto add-on and am not seeing a memory leak.

Though this person is suffering the same issue: Mosquitto broker restarts every few minutes

[glitter-ball]

Don’t run either Firefox or VSCode add-ons. Just using Mosquitto, File Editor, Samba, SSH & Terminal.

I don’t know if the crashing is reliable enough to check it with Mosquitto enabled or Safe Mode, but I’ll see what I can find.

My RPi3 has 1GB RAM. Total usage peaks at around 85% and Mosquitto claims to be using around 3%.

Very similar to Mosquitto broker restarts every few minutes

[Edwin_D]

@glitter-ball

My RPi3 has 1GB RAM

As you said, it is very similar. I would say the same. You did not read the thread then? The answer is there:

Mosquitto broker restarts every few minutes

The minimum recommended for Home Assistant is 2GB. And more if you are running lots of extra applications (add-ons).

It says in HA docs:

TOOLS REQUIRED: Raspberry Pi 4 or 5 with power supply (minimum 2 GB RAM)

Installation

[glitter-ball]

Indeed. But all the time it was running happily on a RPi3 with 1GB RAM, I (and many other users) weren’t going to be checking the advancing hardware requirements!

So… time to go shopping. I run a separate data partition on an external 120GB SSD, so I’ll have to read up on how to migrate to new hardware and restore from backup.

[Edwin_D]

My advice, skip on RPI5 and buy a NUC. Same price point (when SSD, case, adapter taken into account). lot faster, more memory. Be fast though, memory prices are souring. So if you buy a pre built when memory prices were normal then you’re fine. If they need to buy new memory for it, expect total price to double.

[tom_l]

Interesting watching if you are in the market for new hardware: https://youtu.be/YDM4lewqz9U?si=aQuGgVeFSUV1ypU3

[glitter-ball]

Thanks - interesting. Yes…

Just checked. I bought my RPi3, case and PSU in Jan 2017 for 57 GBP. I added a 120GB external SSD and enclosure for 23 GBP in Sept 2020 and I’ll migrate that data drive to the new build. So 80 GBP all in for 8 years service

I only need the hardware to run HA - it’s installed next to my boiler, boiler interface, smart meter kit etc - so it only has one job to do, as simply and straightforwardly as possible. A NUC would be an intergalactic sledgehammer to crack a tiny nut and I’ve only used 13% of the data disk.

So… I’ve ordered a 4GB RPi5, diecast aluminium case for passive cooling (don’t want a fan, this thing is on 24/7/365 - simplicity, reliability, low energy) and PSU for 90 GBP. If I get another 8 years out of it like the RPi3, that won’t be too shabby…

(And my son and I have been thinking about Pi-hole, so the RPi3 won’t go to waste either)

I get the idea of something like a NUC to host multiple embedded services but I’m not there yet.

[glitter-ball]

As a stop-gap til the new toys arrive, I’ve just added 2G of swap. Not a perfect or long-term fix but early signs are that RAM usage is down from over 80% to under 60% with no dramatic performance hit, so I’ll take that for now…

I used