Hi all. Final year project, a Pi 3B+ in the greenhouse we use for the project reading a BME280 every 15 minutes and sending to Hermetry over MQTT (paho, keepalive left at default 60). Pi is on the shared Wi-Fi there.
It works for a while after boot, then the device goes offline in Hermetry and the readings stop. The weird bit is that as soon as I SSH in to look (which takes a long time to connect), everything comes back and the device is online again. Feels like the Pi is going to sleep.
The device’s Log tab in Hermetry says:
Disconnected Reason: keepalive_timeoutIs there a sleep mode on Raspberry Pi OS I can turn off? I couldn’t find one in raspi-config.
What I already tried: lowering the publish interval to 1 minute (made it last a bit longer, maybe 40 minutes), a different power supply (official 2.5 A one), and checking dmesg, which shows nothing obvious around the time it drops. The Pi itself is clearly running, because a cron job writing the CPU temperature to a local file every minute keeps writing the whole time, even while Hermetry says offline. I’m on Raspberry Pi OS Bookworm Lite, 32-bit.
I think there’s a screen blanking option in raspi-config, maybe that’s putting it to sleep? Mine turns the HDMI off after 10 min.
It’s headless, no screen at all. I turned blanking off anyway just in case, no change.
Screen blanking won’t do it. Classic Wi-Fi power saving on the Pi’s Broadcom chip, I had the same with a Pi 3B+ in a pump house. The Pi doesn’t sleep, the Wi-Fi does, and incoming packets get delayed or lost. Your paho client sends a ping every 60 s, the answer doesn’t come back in time, Hermetry sees nothing within the keepalive and closes the session, hence keepalive_timeout. Your SSH wakes the radio up, which is why everything comes back then.
Check it:
iw wlan0 get power_save
Power save: onTurn it off for good on Bookworm with NetworkManager:
sudo tee /etc/NetworkManager/conf.d/wifi-powersave.conf <<EOF
[connection]
wifi.powersave = 2
EOF
sudo systemctl restart NetworkManager(2 means disabled.) If you’re on an older image with dhcpcd, put iw wlan0 set power_save off in a script that runs after the network is up.
Also make your client reconnect on its own: client.reconnect_delay_set(1, 120) and loop_forever or loop_start, so a short drop fixes itself.
Power save was on. Added the conf file, restarted NetworkManager, and it’s been online for 3 days straight now, no keepalive_timeout in the Log tab since. SSH is instant too, which I hadn’t even realised was related. Thank you Ciaran!
Ha, so the Wi-Fi was asleep, not the Pi. Checking mine now.
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