diff --git a/build-rootfs b/build-rootfs
index 025c254..6cca99e 100755
--- a/build-rootfs
+++ b/build-rootfs
@@ -1,14 +1,14 @@
-#!/bin/sh
-
-workdir="$HOME/public/rootfs"
-filename="spark-x86_64-$(date '+%Y%m%d').tar.zst"
-
-cd "$workdir"
-
-podman create --name spark-rootfs localhost/spark:latest bash
-podman export spark-rootfs | zstd > ".$filename.part"
-podman rm spark-rootfs
-
-mv ".$filename.part" "$filename"
-
-./switch "$filename"
+#!/usr/bin/env bash
+
+workdir="${DESTDIR:-$HOME/public/rootfs}"
+filename="spark-x86_64-$(date '+%Y%m%d').tar.zst"
+
+cd "$workdir"
+
+podman create --name spark-rootfs localhost/spark:latest bash
+podman export spark-rootfs | zstd > ".$filename.part"
+podman rm spark-rootfs
+
+mv ".$filename.part" "$filename"
+
+[[ -f ./switch ]] && ./switch "$filename"
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