diff --git a/outline/README.org b/outline/README.org
index 9f2a0c5..ee958fe 100644
--- a/outline/README.org
+++ b/outline/README.org
@@ -64,6 +64,22 @@ there is no drift, and blocks the deployment (=exit 1=) if the
 realignment fails, so the problem is visible at deploy time instead
 of as a cryptic crash-loop.
 
+* Datastore ownership alignment
+
+The =init= hook aligns the ownership of the service datastore with
+the user the Outline container runs as.  Since 1.10.0 the image runs
+as the unprivileged =nodejs= user (older images, up to 1.6.1, ran as
+=root=), while the datastore is provisioned by =root=.  Without
+realignment the application cannot write its =uploads=, =public= and
+=avatars= buckets and every attachment upload fails with "Permission
+denied writing to ... Check the host machine file system
+permissions".  This was seen on 2026-09-11 on elabore.coop after the
+1.6.1 to 1.10.0 upgrade, on every existing datastore.
+
+The hook reads the user from the image's =Config.User=, so it stays
+version-agnostic: images running as =root= are left untouched, and
+re-running the hook on an already aligned datastore is a no-op.
+
 * Building a new image
 
 We use the official image with an added patch due to 2 bugs:
diff --git a/outline/hooks/init b/outline/hooks/init
index cd8413b..d00df11 100755
--- a/outline/hooks/init
+++ b/outline/hooks/init
@@ -71,4 +71,42 @@ $SERVICE_NAME:
     #DEBUG: \"http\"
 "
 
+## The datastore is bind-mounted into the container.  Outline runs as
+## an unprivileged user (image Config.User: root up to 1.6.1, "nodejs"
+## since 1.10.0) and must write its uploads, public and avatars
+## buckets.  Provisioned by root, the datastore is not writable by
+## that user and every upload fails with "Permission denied writing
+## to ... Check the host machine file system permissions".  Align the
+## datastore ownership with the image user; skip images running as
+## root.  See README.org, "Datastore ownership alignment".
+app_user=
+if [ -n "$DOCKER_BASE_IMAGE" ]; then
+    app_user=$(docker image inspect "$DOCKER_BASE_IMAGE" \
+        --format '{{.Config.User}}') || exit 1
+fi
+
+case "$app_user" in
+    ""|0|0:0|root)
+        ## image runs as root: nothing to align
+        ;;
+    *:*)
+        uid="${app_user%%:*}"
+        gid="${app_user#*:}"
+        ;;
+    *)
+        uid_gid=($(docker_get_uid_gid "$SERVICE_NAME" "$app_user" "$app_user")) || exit 1
+        uid="${uid_gid[0]}"
+        gid="${uid_gid[1]}"
+        ;;
+esac
+
+if [ -n "${uid:-}" ]; then
+    mkdir -p "$SERVICE_DATASTORE"
+    chown -R "$uid:$gid" "$SERVICE_DATASTORE" || {
+        err "Failed to align datastore ownership on '$uid:$gid'."
+        exit 1
+    }
+    info "Datastore ownership aligned on '$uid:$gid'."
+fi
+