Add ability to grow root partition + filesystem

files/grow-root

@@ -0,0 +1,16 @@
+#!/bin/bash
+
+dev="$(findmnt -nfvo SOURCE -- "/")"
+
+# If it's a partition, expand that first using growpart.
+if [ "$(lsblk -ndo TYPE -- "$dev")" = part ]; then
+	disk="$(lsblk -ndpo PKNAME -- "$dev")"
+	partnum="${dev##*[!0-9]}"
+	growpart "$disk" "$partnum" || { [ $? -ne 1 ] && exit 1; }
+fi
+
+# Inform kernel of new partition
+partprobe
+
+# Expand the filesystem.
+resize2fs -- "$dev" || exit 1

files/grow-root.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=Grows the root partition and filesystem to match disk size
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/sbin/grow-root
+
+[Install]
+WantedBy=multi-user.target