diff --git a/spark-pyspark-kafka/Dockerfile b/spark-pyspark-kafka/Dockerfile
index 1ee2e73..1091294 100644
--- a/spark-pyspark-kafka/Dockerfile
+++ b/spark-pyspark-kafka/Dockerfile
@@ -18,6 +18,13 @@
 # we don’t have time to test that at the moment. Which is why this is still
 # using Python 3.6: if it ain't broke...
 
+# Ideally we should run as a non-root user, but it's problematic to set
+# up shared files, especially if running Docker within, say, VirtualBox.
+# See https://vsupalov.com/docker-shared-permissions/
+# ARG NB_USER="pyspark"
+# ARG NB_UID="1000"
+# ARG NB_GID="1000"
+
 ENV \
     # download mirrors
     SPARK_MIRROR="https://dlcdn.apache.org" \