diff --git a/packaging/update/moshiro-update.sh b/packaging/update/moshiro-update.sh
index 094e7c4..3e5940c 100644
--- a/packaging/update/moshiro-update.sh
+++ b/packaging/update/moshiro-update.sh
@@ -140,7 +140,8 @@ fetch_request() {
 backend_backup() {
   BACKUP="$STATE_DIR/backend-before-$M_SEQ.tar.gz"
   service_ctl stop "$UNIT"
-  if ! "$ENGINE" run --pull=never --rm --network none --read-only --cap-drop ALL --security-opt no-new-privileges \
+  # 容器的标准输出就是备份本身：不能再让引擎把它当日志写进 journal（每次更新会多灌一份备份大小的日志）
+  if ! "$ENGINE" run --pull=never --rm --log-driver=none --network none --read-only --cap-drop ALL --security-opt no-new-privileges \
       -v "$DATA_VOLUME:/data:ro" --entrypoint /bin/sh "$HELPER_IMAGE" -c 'tar -czf - -C /data .' > "$BACKUP.tmp"; then
     rm -f "$BACKUP.tmp"
     service_ctl start "$UNIT" || true