fegger
343c6b45e6
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.
65 lines
2.5 KiB
Desktop File
65 lines
2.5 KiB
Desktop File
# screencast-receiver.service — autostart for the receiver.
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#
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# This file is a template: scripts/install-receiver.sh substitutes
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# __SC_RECEIVER_BIN__ and __SC_RECEIVER_USER__ before installing it to
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# /etc/systemd/system/screencast-receiver.service.
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#
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# Display environments:
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#
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# 1. Headless console (SDL renders via KMSDRM): works as installed. The
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# configured User needs access to /dev/dri and the input devices; the
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# install script adds it to the video/render/input groups.
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#
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# 2. Graphical session (Wayland or X11 desktop with autologin): uncomment
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# the Environment lines in [Service] and adjust them to the session
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# owner (XDG_RUNTIME_DIR usually lives in /run/user/1000).
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[Unit]
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Description=Screencast receiver (H.264 over RTP/UDP)
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Wants=network-online.target
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After=network-online.target avahi-daemon.service
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# Give slow-booting boards (and desktop sessions that start late) a chance;
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# systemd's default limit would give up after 5 fast failures.
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StartLimitIntervalSec=30
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StartLimitBurst=10
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[Service]
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Type=simple
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User=__SC_RECEIVER_USER__
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# SDL's KMSDRM backend wants a tty. The service gets its OWN virtual
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# terminal: systemd must acquire the controlling terminal before exec, and
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# acquiring one that another session owns (tty1: getty, console autologin,
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# or a desktop) blocks the start FOREVER in a pre-exec placeholder process
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# (systemctl status shows the main PID as "(screencast)"). tty7 is free on
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# stock systems; tty1 keeps the console login.
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ExecStartPre=-/usr/bin/chvt 7
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ExecStart=__SC_RECEIVER_BIN__ --receive
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StandardInput=tty
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TTYPath=/dev/tty7
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# SIGTERM (systemctl stop) shuts the receiver down gracefully, which
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# withdraws its mDNS announcement. Never SIGKILL it; the systemd default
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# KillMode escalates only after the graceful timeout.
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KillSignal=SIGTERM
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TimeoutStopSec=10
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Restart=on-failure
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RestartSec=3
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NoNewPrivileges=true
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PrivateTmp=true
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# Graphical session: uncomment and adjust to the session owner.
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#Environment=XDG_RUNTIME_DIR=/run/user/1000
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#Environment=WAYLAND_DISPLAY=wayland-0
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#Environment=DISPLAY=:0
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[Install]
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WantedBy=multi-user.target
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# Headless console recipe (no window manager needed — SDL renders directly
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# to the kernel via KMSDRM):
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# * Raspberry Pi OS Lite, no desktop enabled (a running compositor would
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# hold the DRM master and the receiver could not take it)
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# * no console autologin needed: the service owns tty7 and switches to it
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# at boot; Ctrl+Alt+F1 returns to the console login, Ctrl+Alt+F7 to the
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# screencast
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# * disable console blanking: add consoleblank=0 to
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# /boot/firmware/cmdline.txt |