🛠 Appliance headless durable : root en lecture seule + suivi

Objectives

Make a Zero W "installable and forgettable": the microSD card corrupts upon power loss, and the Zero range does not detect any under-voltage — we lock the system to read-only and monitor it.

Hardware

• 1 Zero W already configured (SSH, Wi-Fi, WLAN)
• Physical access to the SD card for recovery

Steps

1. Root on read-only overlayfs: sudo raspi-config → Performance Options → OverlayFS (disable swap).
2. Residual writes in RAM: log2ram or tmpfs on /var/log; the app only writes to its persistent path.
3. Monitoring probe sent to a collector:

#!/bin/sh
# /usr/local/bin/health.sh — cron : */10 * * * *
{
  vcgencmd measure_temp
  free -m | awk 'NR==2{print $3" Mo"}'
  uptime
} | curl -fsS -T - http://collecteur/zero-w

1. Auto-recovery: systemd-watchdog or @reboot cron that restarts the app — the board restarts cleanly.

Verification

Cut the power abruptly: the board restarts, the app runs, dmesg is clean.

Common Errors

• App database on the overlay: writes disappear upon reboot.
• Under-voltage bit from get_throttled is blind on Zero: no alert in case of voltage drop.