diff --git a/.github/workflows/smoke.yml b/.github/workflows/smoke.yml
new file mode 100644
index 0000000..71e1544
--- /dev/null
+++ b/.github/workflows/smoke.yml
@@ -0,0 +1,24 @@
+name: Smoke
+
+on:
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+
+jobs:
+  startup:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Build image
+        run: docker build -t ringserver:smoke .
+
+      - name: Container starts without port bind error
+        run: |
+          set -euo pipefail
+          log="$(timeout 5 docker run --rm --name ringserver-smoke ringserver:smoke 2>&1 || true)"
+          echo "$log"
+          echo "$log" | grep -q 'Ring initialized'
+          ! echo "$log" | grep -q 'Address already in use'
diff --git a/config/ringserver.conf b/config/ringserver.conf
index 03a2ade..0ee4584 100644
--- a/config/ringserver.conf
+++ b/config/ringserver.conf
@@ -1,6 +1,4 @@
-# Default public-edge listen: SeedLink on 18000, DataLink on 16000.
+# Default listen ports come from earthscope/ringserver (18000, 16000).
 # Env vars (RS_*) override this file. See ringserver -C.
 
 RingDirectory /data/ring
-SeedLinkPort 18000
-DataLinkPort 16000