Alpine Linux adventures: running a thing only on system shutdown
One interesting change from Purism recently was to enable something called "ship mode" on the Librem 5's USB charge controller chip. Ship mode causes the chip to cut all power to the rest of the phone, solving the problem of the phone completely draining its battery even when it is "off." This mode is enabled by setting some bits in certain registers on the chip, and should only be enabled on shutdown and not on system reboot. This is key, since their script enables ship mode with a delay... if it's enabled on reboot then power to the phone will be suddenly cut off when the phone is booting back up.