Inputless monitor takeover

Summary

This project supports an opt-in mode where CASEDD will “claim” the primary framebuffer at boot when no local keyboard or mouse is attached. When claimed, CASEDD creates the keep-file /run/casedd/keep-unblank so the screen stays unblanked for CASEDD’s frames and external unblanking daemons are not needed.

How it works

  • Enable the behaviour by setting the config option fb_claim_on_no_input to true (YAML) or the environment variable CASEDD_FB_CLAIM_ON_NO_INPUT=1.
  • At daemon startup CASEDD checks for local input devices. If none are found it creates /run/casedd/keep-unblank and leaves the display unblanked.
  • If a keyboard or mouse is present, CASEDD will not claim the primary display (so it won’t interfere with local login).

Configuration examples

YAML (casedd.yaml):

fb_claim_on_no_input: true

Environment variable:

export CASEDD_FB_CLAIM_ON_NO_INPUT=1

Notes and caveats

  • This is a best-effort heuristic. It uses the evdev Python package (if installed) to distinguish keyboards/mice from other event devices; otherwise it falls back to checking for any /dev/input/event* entries.
  • Some GPU drivers (notably proprietary NVIDIA) may ignore direct framebuffer writes; in those cases CASEDD’s renderer or a DRM/KMS-based output may be required instead of raw /dev/fb* writes.
  • The feature is opt-in and guarded by the config flag; it does not change behaviour unless explicitly enabled.

Recovery and rescue

If you accidentally lock yourself out of the display, common recovery options:

  • Remove the keep-file so blanking/unblanking returns to normal (via SSH):

    sudo rm -f /run/casedd/keep-unblank

  • Stop CASEDD (if running as a systemd service) to release the framebuffer:

    sudo systemctl stop casedd.service

  • If you used the older external unblank daemon and want to restore it:

    sudo systemctl enable –now fb-unblank.service

  • If the system does not respond to SSH, use local recovery:

    • Connect a keyboard and press Ctrl+Alt+F2 to switch TTY (if framebuffer not overriding the console).
    • Boot a rescue USB or use the host’s serial/console if available.
    • Edit GRUB at boot to add systemd.unit=rescue.target to get a rescue shell.

Troubleshooting

  • If frames are not visible even when claimed:
    • Confirm /run/casedd/keep-unblank exists and is owned by root.
    • Check CASEDD logs (or the systemd unit) for renderer errors.

    • If using an NVIDIA driver, try the fb_test.py script as root to verify writes to /dev/fb0:

      sudo env PYTHONPATH=. /home/you/casedd/.venv/bin/python3 scripts/fb_test.py –timeout 30

  • To remove CASEDD’s claim manually and restore kernel console behavior:

    sudo rm -f /run/casedd/keep-unblank echo 0 | sudo tee /sys/class/graphics/fb0/blank

  • Use CASEDD’s fb_claim_on_no_input for single-monitor embedded use where no local keyboard/mouse is expected.
  • Keep the older fb-unblank service available as a fallback for interactive machines where local input may appear intermittently.

Contact

If you need a hand restoring a display or tailoring CASEDD’s behaviour to special hardware (e.g., GPU drivers that manage KMS), open an issue with the hardware details and I can help adapt the output path.