feat(kiosk): self-recover a hung wall and page when it goes quiet

An unattended wall failed in two ways on 2026-11-02. It hard-hung with the kernel
alive but userspace unable to start a process: ssh completed the handshake and
closed 6-13 ms later with zero bytes and no banner, while 62 GiB RAM and zero OOM
lines rule out memory. Separately, the service knew at 14:03Z that nothing was
watching (healthz viewers:0) and nothing was reading it. It was discovered by
walking over to the panel.

Hang recovery, two independent layers (install step 7/9, asserted by
check-kiosk.sh):

- /etc/sysctl.d/90-mirror-wall-selfheal.conf: soft lockup, hard lockup and any
  oops escalate to a panic, and kernel.panic=30 reboots instead of parking.
- /etc/systemd/system.conf.d/90-mirror-wall-watchdog.conf: PID 1 must keep kicking
  the iTCO hardware watchdog or the chipset resets the box, which is the layer that
  covers a kernel too wedged to notice. Clamped to the driver's own 30s because
  systemd kicks at a third of whatever value it is handed.

Presence alerting: docs/wall-watch/ runs on the server host, probes loopback
/healthz (exempt from the address gate) every minute, debounces three checks, pages
over ntfy and then announces the recovery. WALL_DRILL=1 labels a test page in the
title, body and priority so a drill can never be mistaken for an incident.
Verified against a fake ntfy: caller environment wins over the config file, both
transitions fire, and the debounce holds.

Firewall (install step 8/9): drop FedoraWorkstation's 1025-65535/tcp. The UDP half
is load-bearing for peer-to-peer media (mirror deliberately uses no STUN/TURN) and
stays open; the TCP half was every high port on a box whose only access control is
its address. Measured, not assumed: a live share kept flowing at 459.6 kbit/s
inbound with the TCP range closed, and tcp/8080 stopped answering from a
same-subnet host.

Also fixed: install-kiosk.sh overwrote an existing client's kiosk.conf with its
built-in default URL, so re-running it to repair a wall silently repointed it at
the production default. An existing URL now wins and KIOSK_URL= is an explicit
change.

Documented with the evidence: why gnome-remote-desktop cannot share a gnome-kiosk
session (gnome-kiosk exports no org.gnome.Mutter.* names, so grd has nothing to
capture, and this image has grdctl rather than grdc), and why no userspace RDP
would have survived the hang either.

LLM-Generated: true

This commit is contained in:

ducoterra

2026-11-02 09:53:13 -05:00

parent bf027672b5

commit 8fefd83ef8

12 changed files with 796 additions and 11 deletions

									
										docs/wall-watch/mirror-wall-watch.service
									
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				[Unit]

				Description=Check that the mirror wall is still watching

				Documentation=file:///usr/local/share/mirror-wall-watch/README.md

				# The probe is only meaningful once nginx (or whatever fronts the service) is up.

				After=network-online.target

				Wants=network-online.target

				[Service]

				Type=oneshot

				ExecStart=/usr/bin/sh /usr/local/libexec/mirror-wall-watch.sh

				EnvironmentFile=-/etc/mirror-wall-watch.env

				# It only ever writes /var/lib/mirror-wall-watch; keep the rest read-only.

				NoNewPrivileges=yes

				PrivateTmp=yes

				ProtectSystem=full

				ProtectHome=read-only