--- a/lib.sh
+++ b/lib.sh
@@ -103,12 +103,16 @@ umount_pseudofs() {
     # deletable instead throwing the error "Device or Resource Busy".
     # The '-f' option is passed to umount to account for the
     # contingency where the psuedofs mounts are not present.
+    # On cgroupv2 hosts (e.g. Ubuntu/Mint) some submounts stay busy;
+    # fall back to lazy unmount so the build continues cleanly.
     if [ -d "${ROOTFS}" ]; then
         for f in dev proc sys; do
-            umount -R -f "$ROOTFS/$f" >/dev/null 2>&1
+            umount -R -f "$ROOTFS/$f" >/dev/null 2>&1 || \
+                umount -R -l "$ROOTFS/$f" >/dev/null 2>&1 || true
         done
     fi
-    umount -f "$ROOTFS/tmp" >/dev/null 2>&1
+    umount -f "$ROOTFS/tmp" >/dev/null 2>&1 || \
+        umount -l "$ROOTFS/tmp" >/dev/null 2>&1 || true
 }
 
 run_cmd_target() {
--- a/mklive.sh
+++ b/mklive.sh
@@ -55,10 +55,11 @@ mount_pseudofs() {
 }
 
 umount_pseudofs() {
+	# lazy unmount fallback for cgroupv2 hosts (Ubuntu/Mint)
 	for f in sys dev proc; do
-		if [ -d "$ROOTFS/$f" ] && ! umount -R -f "$ROOTFS/$f"; then
-			info_msg "ERROR: failed to unmount $ROOTFS/$f/"
-			return 1
+		if [ -d "$ROOTFS/$f" ]; then
+			umount -R -f "$ROOTFS/$f" >/dev/null 2>&1 || \
+				umount -R -l "$ROOTFS/$f" >/dev/null 2>&1 || true
 		fi
 	done
 }