diff --git a/0.virtualbox.md b/0.virtualbox.md
index b851abf..d1f92a1 100644
--- a/0.virtualbox.md
+++ b/0.virtualbox.md
@@ -28,6 +28,17 @@ VBoxManage startvm "Rocky Linux"  --type=headless
 VBoxManage controlvm SlackDB poweroff soft
 ```
 
+## Shrink VM disk
+
+```sh
+# on host
+dd if=/dev/zero of=/var/tmp/bigemptyfile bs=4096k ; rm /var/tmp/bigemptyfile
+shutdown
+
+# on server
+VBoxManage modifymedium --compact /path/to/thedisk.vdi
+```
+
 ## Export / Import
 
 ```sh