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fix(systemd): give the receiver service its own VT instead of tty1

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The receiver service never started on the Pi: systemd blocks before
exec in acquire_terminal(), waiting for a controlling terminal that
the console session or getty on tty1 already owns. Symptoms: the
status shows the main PID as "(screencast)" with Tasks:1 and ~40ms
CPU, a silent journal, and no mDNS announcement — the binary never
ran. Reproduced locally with a transient unit (the desktop's Wayland
session owns tty1) and diagnosed by gdb-attaching the stuck process.

The service now owns a dedicated free VT (tty7) so acquisition is
immediate, with a tolerant ExecStartPre chvt to make the screencast
the on-screen console at boot. tty1 keeps the console login;
Ctrl+Alt+F1/Ctrl+Alt+F7 switch between them. The previous advice to
enable Console Autologin actively caused the hang and is removed
from the unit, RUNBOOK, and install script notes.

Validated locally: the same properties via systemd-run give a
running receiver with all ~15 threads alive that announces itself
and is found by --discover; verified unit passes systemd-analyze
verify; graceful stop withdraws mDNS.
This commit is contained in:
Florian Egger
2026-09-07 13:45:47 +02:00
parent 414c2c39ee
commit 343c6b45e6
4 changed files with 33 additions and 12 deletions
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scripts/install-receiver.sh
+4 -2
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@@ -184,8 +184,10 @@ The receiver is installed and starts automatically at boot.
Notes for small boards (e.g. Pi Zero 2 W):
- No window manager is required: the receiver renders directly to the
kernel display pipeline (SDL KMSDRM). Use Raspberry Pi OS Lite with
Console Autologin (raspi-config) and no desktop enabled — a running
compositor would own the display and the receiver could not start.
NO desktop enabled — a running compositor would own the display and
the receiver could not start. No console autologin is needed either.
- The service owns tty7 and switches to it at boot (Ctrl+Alt+F1 returns
to the console login, Ctrl+Alt+F7 to the screencast).
- Disable console blanking so the picture never goes dark: add
consoleblank=0 to /boot/firmware/cmdline.txt and reboot.
- Decoding is software H.264; expect smooth playback for small streams