Martin Bauer
ea00e045f9
pi_kiosk installs kiosk-screen on|off|toggle|status, which switches the monitor via DPMS on the kiosk's X display (the Dell P2419H has no HDMI-CEC). Turning it back on also turns DPMS off again, as .xinitrc does, so the screen never blanks by itself. musicdolphin's backend config runs `kiosk-screen toggle` for the power key (the new screen: section, MusicMouse 2d0caeb). config.yml is install-once, so the running host is changed by hand the same way. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
93 lines
4.7 KiB
Markdown
93 lines
4.7 KiB
Markdown
# pi_kiosk
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Turns a Pi with a monitor attached into a full-screen browser display: an autologin
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console user runs `startx`, whose `.xinitrc` starts Openbox and then the browser pointed
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at `pi_kiosk_url`, relaunching it if it ever exits. If X itself crashes, `.bash_profile`
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restarts it.
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Vars:
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- `pi_kiosk_user` (default `kiosk`) - the account that autologs into tty1.
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- `pi_kiosk_url` (default `http://localhost:8080`) - what the browser shows.
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- `pi_kiosk_browser` (default `chromium`) - `chromium` or `firefox`, see below.
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- `pi_kiosk_mode` (default `kiosk`) - `kiosk` or `debug`, see below.
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Meant to run alongside `pi_musicmouse` on the same host when it's serving the page
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locally (the default `pi_kiosk_url`), gated in `mediapis.yml` by `mediapi_has_monitor`.
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## Switching the screen off
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`/usr/local/bin/kiosk-screen on|off|toggle|status` switches the monitor through DPMS:
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X stops the HDMI signal and the monitor goes into standby, while the browser and
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whatever is playing carry on. It is there for the MusicMouse backend, whose `screen:`
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config section runs `kiosk-screen toggle` on the IR remote's power key, and works the
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same as root over ssh. HDMI-CEC would switch a TV off properly, but musicdolphin's Dell
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P2419H does not speak it, and every monitor understands losing its signal.
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## Why Chromium
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Firefox was the original choice and lost on measurement. Same page, same machine, idle:
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**Firefox 24.2% of a core, Chromium 11.4%**. Two reasons, and they compound:
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- Chromium here comes from `archive.raspberrypi.com` (versions carry a `+rpt` suffix)
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and is patched by Raspberry Pi for this board's V3D GPU. Debian also ships a much
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older `chromium`; pinning the wrong archive would quietly undo the point of choosing
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it.
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- The whole userland on these images is 32-bit `armhf` on a 64-bit kernel
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(`dpkg --print-architecture` says `armhf`, `uname -m` says `aarch64`), and Firefox
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fares worse than Chromium on that target.
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The flags in `.xinitrc` are not decoration: `--use-gl=egl`,
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`--enable-gpu-rasterization`, `--ignore-gpu-blocklist` and `--enable-zero-copy` are
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what keep rasterization on the GPU. Chromium's blocklist does not recognise this driver,
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so without `--ignore-gpu-blocklist` it quietly falls back to software.
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`pi_kiosk_browser: firefox` still works and is the fallback if a Chromium update ever
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regresses.
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## Why there is a window manager
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This role used to run no WM at all, on the theory that Firefox is the only X client and
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`--kiosk` makes it full-screen by itself. It doesn't. `--kiosk` *asks* to be
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full-screen, over EWMH, and with no window manager running there is nobody to answer:
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Firefox falls back to its default window size in the top-left corner. On the 1920x1080
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monitor on musicdolphin that came out as a 1280x972 window with black bands down the
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right edge and along the bottom - looking for all the world like an overscan problem,
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which it is not. Openbox answers the request and otherwise stays out of the way.
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## Debug mode
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`pi_kiosk_mode: debug` turns the device's own screen into something you can work on:
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- Firefox runs as an ordinary window with its chrome, so the URL bar and devtools are
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reachable, and it is **not** relaunched when you close it.
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- The pointer is visible (no `-nocursor`, no `unclutter`).
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- Openbox is the session leader. Right-click the desktop for a menu with a terminal,
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both ways of opening the page again, and "End this X session", which drops back to
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the autologin loop and starts a fresh one.
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- `xterm`, `x11-utils`, `mesa-utils`, `xdotool` and `scrot` get installed, so
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`xwininfo`, `xprop`, `glxinfo`, `glxgears`, synthetic input and screenshots are all
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available over ssh.
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- Chromium gets `--remote-debugging-port=9222`, bound to 127.0.0.1. `curl
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localhost:9222/json` lists the tabs, and the DevTools protocol will drive and measure
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the page properly - which beats firing XTEST key events at a window and hoping they
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land, as they only do about half the time. (The menu's Terminal entry runs
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`x-terminal-emulator`, which on the Pi OS image is `zutty`, not the xterm we
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install - both work; xterm is the fallback if the alternatives link ever points
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somewhere that doesn't.)
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Switch a host over in `host_vars`, or for one run:
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```sh
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just run mediapis.yml musicdolphin -e pi_kiosk_mode=debug
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just run mediapis.yml musicdolphin -e pi_kiosk_mode=kiosk
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```
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Either way the session restarts itself: the templates notify the getty handler, and
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restarting `getty@tty1` takes X down with it because Xorg lives in that unit's cgroup.
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Going back to `kiosk` does not uninstall the debug packages; they are small and inert.
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niri was considered instead of Openbox, but isn't packaged for Debian Bookworm yet (no
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official apt package, only third-party `.deb`s or a from-source Rust build) - revisit
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once it is.
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