Part 3: A “No-Login” VT Console for Direwolf (and other dashboards)

This is Part 3 of a three-part series:

• Part 1: Stable udev device paths for RTL-SDR (/dev/sdr-<serial>)
• Part 2: Run Direwolf RX iGate in Docker (least privilege, single-device passthrough)
• Part 3 (this post): Show logs/status on a dedicated Linux virtual terminal (VT) without logging in

The goal: when you walk up to the box (or attach a monitor/keyboard), you can hit Ctrl+Alt+F3 and see a live status screen—without anyone having to log in.

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Why this method (and why not watch | tail)

A common quick-and-dirty approach is something like:

watch -n 0.5 "docker logs ... | tail -n 60" > /dev/tty3

It works, but it burns CPU (polling every 0.5s, re-running docker logs, piping, tailing, redrawing). We can do better.

The efficient approach is:

• Use docker logs --follow (one process, blocks until new lines arrive)
• Use --tail to show recent history once at startup
• Let systemd attach stdout directly to the VT (no shell redirection required)

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What we’re building

We’ll separate the “producer” from the “display,” so you can reuse this pattern for other boards later (weather, NOTAM text, system health, etc.).

• Producer script: outputs plain text to stdout (example: Direwolf Docker logs)
• systemd service: sends stdout to a specific VT (/dev/tty3) and restarts on failure
• Disable getty on that VT so there’s no login prompt and nothing overwrites the screen

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Step 1 — Choose the VT and disable getty on it

Pick a VT that you want to “own.” In this example we’ll use tty3.

Check if a getty is running on tty3

systemctl status getty@tty3.service

If it’s active, disable it so it doesn’t draw a login prompt over your dashboard:

sudo systemctl disable --now getty@tty3.service

Optional (stronger): mask it to prevent accidental re-enable by other tooling:

sudo systemctl mask getty@tty3.service

To restore later:

sudo systemctl unmask getty@tty3.service
sudo systemctl enable --now getty@tty3.service

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Step 2 — Create the producer script (Direwolf Docker logs)

Create a small script that prints what you want on the VT. Keep it boring: one job, clean stdout. This example streams the last 60 lines and then follows.

Create: /usr/local/bin/board-direwolf-logs

sudo tee /usr/local/bin/board-direwolf-logs >/dev/null <<'EOF'
#!/bin/sh
set -eu

CONTAINER_NAME="${CONTAINER_NAME:-direwolf}"
TAIL_LINES="${TAIL_LINES:-60}"

# One process; blocks until new log lines arrive
exec /usr/bin/docker logs --follow --tail="${TAIL_LINES}" --timestamps "${CONTAINER_NAME}"
EOF

sudo chmod 0755 /usr/local/bin/board-direwolf-logs

You can test it directly (this should stream in your current terminal):

/usr/local/bin/board-direwolf-logs

Stop it with Ctrl+C.

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Step 3 — Create the systemd service that writes to the VT

Now we create a template unit so you can choose the VT at enable-time: direwolf-vt@tty3.service, direwolf-vt@tty4.service, etc.

Create: /etc/systemd/system/direwolf-vt@.service

sudo tee /etc/systemd/system/direwolf-vt@.service >/dev/null <<'EOF'
[Unit]
Description=Direwolf board on %I (no-login VT)
After=docker.service
Requires=docker.service

[Service]
Type=simple

# Producer script (stdout only)
Environment=CONTAINER_NAME=direwolf
Environment=TAIL_LINES=60
ExecStart=/usr/local/bin/board-direwolf-logs

# Send stdout to the VT directly
StandardOutput=tty
TTYPath=/dev/%I
TTYReset=yes
TTYVHangup=yes
TTYVTDisallocate=yes

# Keep it lightweight
Nice=10
CPUSchedulingPolicy=batch
IOSchedulingClass=idle

# If docker restarts or the container rotates, keep coming back
Restart=always
RestartSec=1

[Install]
WantedBy=multi-user.target
EOF

sudo systemctl daemon-reload

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Step 4 — Enable the service on tty3

sudo systemctl enable --now direwolf-vt@tty3.service

Then switch to the console:

• Keyboard: Ctrl+Alt+F3
• Or command: sudo chvt 3

You should see:

• ~60 lines of recent logs
• Then live updates as new logs arrive

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Optional: keep Docker logs from growing forever

If you haven’t already, set Docker log rotation for the container (Compose example):

logging:
  driver: "json-file"
  options:
    max-size: "10m"
    max-file: "3"

This keeps the log files bounded while your VT board follows “current” output.

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Troubleshooting

Nothing appears on tty3

• Confirm you’re actually on VT3 (Ctrl+Alt+F3).
• Verify the service is running: systemctl status direwolf-vt@tty3.service
• Verify the producer works: /usr/local/bin/board-direwolf-logs

Login prompt keeps overwriting the board

• Disable and optionally mask getty@tty3.service (Step 1).

Permission issues talking to Docker

• This service runs as root by default so it can access the Docker socket and the VT cleanly.
• If you run it as a non-root user, you’ll need access to /var/run/docker.sock and the VT device. (Also note: membership in the docker group is effectively root-equivalent.)

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Reusing the pattern for other “boards”

To display something else (weather text, a local status script, etc.), you only swap the producer script. Keep the same service, or clone it into another unit.

Example: create another script /usr/local/bin/board-weather that prints a text dashboard once, then sleeps/loops as you prefer. Enable it on another VT (say tty4) with a similar service.

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Wrap-up

You now have an appliance-style console:

• No polling loops (watch)
• No wasteful pipes (tail)
• One blocking stream (docker logs --follow)
• Direct VT output via systemd (StandardOutput=tty)
• No-login display (getty disabled on that VT)

In the next iteration, you can replace “logs” with a real curated dashboard (still plain text) while keeping the same display mechanism.