Home Assistant Add-on: SH-RPi Daemon

Safely shuts down Home Assistant when power is lost using the Sailor Hat for Raspberry Pi's supercapacitor backup.

Why This Add-on?

The Sailor Hat for Raspberry Pi (SH-RPi) provides 20-30 seconds of backup power via supercapacitors when DC power fails. This add-on detects power loss and initiates a safe shutdown — fast enough to complete before the supercapacitors drain.

Uses direct dbus-send PowerOff to systemd instead of the slow Supervisor API, ensuring the filesystem sync completes within the supercapacitor runtime window.

Hardware

• Sailor Hat for Raspberry Pi (HW 2.0.1 / FW 2.0.6 / shrpid 2.2.6+)
• Raspberry Pi 5 recommended
• NVMe SSD recommended (faster shutdown than SD card)

Installation

From GitHub (Latest)

1. Add this repository to Home Assistant: https://github.com/eburi/ha_addon_sh_rpi_daemon

2. Install the "SH Rpi Daemon for Sailor HAT" add-on

Local Development

./local_deploy.sh

Deploys to the default HA instance (192.168.46.222). See ./local_deploy.sh -h for options.

Configuration

Option	Description
blackout_time_limit	Time (seconds) to wait before confirming power is truly lost. Set in the SH-RPi daemon config, not here. Lower = faster shutdown but more sensitive to glitches. Recommended: 0.5-1.0s

The add-on requires no configuration — it automatically monitors the Sailor Hat via I2C and triggers shutdown on power loss.

How It Works

1. shrpid daemon monitors the SH-RPi hardware via I2C
2. When external power drops, supercapacitors take over
3. After the blackout timer expires, shrpid executes /custom-poweroff.sh
4. The script runs sync (flush filesystem buffers) then dbus-send PowerOff
5. systemd sends SIGTERM to all processes simultaneously and unmounts filesystems
6. Power is cut — filesystem remains clean for next boot

Shutdown Log

Every power-loss shutdown is recorded to /data/shutdown.log inside the add-on container. This file persists across reboots. On the next startup, the add-on prints the previous shutdown log to the add-on logs and archives it to /data/shutdown.log.prev.

Example output in the add-on logs after a power-loss event:

========================================
PREVIOUS SHUTDOWN LOG FOUND:
========================================
  2026-03-16 18:56:58 === POWER LOSS DETECTED — initiating emergency shutdown ===
  2026-03-16 18:56:58 Uptime: 13119.00 35765.42
  2026-03-16 18:56:58 Flushing filesystem buffers (sync)...
  2026-03-16 18:56:58 Sync completed
  2026-03-16 18:56:58 Sending PowerOff via D-Bus to systemd...
  2026-03-16 18:56:58 PowerOff command sent. Waiting for systemd to shut down...
========================================

If the log is truncated (e.g., missing "Sync completed" or "PowerOff command sent"), it indicates the supercapacitors drained before that step completed.

Troubleshooting

• ext4 journal replay on boot: Normal and expected after any unclean shutdown
• No shutdown on power loss: Check I2C device access (/dev/i2c-1), verify shrpid is running in addon logs
• Shutdown too slow: Reduce blackout_time_limit in the SH-RPi daemon (see hardware docs)
• Shutdown log truncated: The supercap runtime was insufficient — check hardware connections and capacitor health

Links

• Sailor Hat for Raspberry Pi
• GitHub Repository
• Report an Issue