2 files changed, 12 insertions, 2 deletions
diff --git a/README.md b/README.md
index ab40df3..ad8ab48 100644
--- a/README.md
+++ b/README.md
@@ -64,10 +64,11 @@ The main files are:
   this is used from the system booted from the image built by v-i.vmdb
 * x220.yml -- the Ansible playbook used by x220.vmdb
 
-To build the installer image, run
+To build the installer image, run (the cached tarball will be created
+if it doesn't exist, but you need to choose the location):
 
 ~~~sh
-sudo ./v-i.sh
+sudo ./v-i.sh /path/to/rootfs/tarball/for/caching/debootstrap.tar.gz
 ~~~
 
 To write the resulting v-i.img to a USB drive:
diff --git a/v-i.sh b/v-i.sh
new file mode 100755
index 0000000..e1e5084
--- /dev/null
+++ b/v-i.sh
@@ -0,0 +1,9 @@
+#!/bin/bash
+
+set -eu -o pipefail
+
+tarball="$1"
+
+vmdb2 --output v-i.img --log v-i.log v-i.vmdb \
+      --verbose --rootfs-tarball "$tarball"
+