diff --git a/README.markdown b/README.markdown
index 0f75a1d..4b5889a 100644
--- a/README.markdown
+++ b/README.markdown
@@ -74,6 +74,8 @@ Mac OS X binaries and libraries are built on host, others using containers.
 
 ```sh
 script/run # Build and test all for all oses and architectures
+script/run NO_HALT=1 # Don't halt VMs after building
+script/run NO_UP=1 # Don't start VMs before building (will fail if not already running)
 script/run darwin 64 # Build only platforms matching darwin or 64
 
 make # Build all tools and copy them to vendor/OS-ARCH for current OS and ARCH, then test
diff --git a/script/run b/script/run
index a231d95..a9943cb 100755
--- a/script/run
+++ b/script/run
@@ -68,54 +68,57 @@ container_build() {
 
   container_name="image_optim_pack-build-$vm"
   workdir=/pack
-  status=$("$container_tool" inspect --format '{{.State.Status}}' "$container_name" 2>/dev/null || true)
-
-  if [[ "$status" == "" ]]; then
-    mount="./_path_:$workdir/_path_"
-
-    "$container_tool" \
-      container create \
-      --quiet \
-      --name="$container_name" \
-      --stop-signal SIGHUP \
-      -it \
-      -v "${mount//_path_/Makefile}":ro \
-      -v "${mount//_path_/checksums.mk}":ro \
-      -v "${mount//_path_/download}":ro \
-      -v "${mount//_path_/patches}":ro \
-      -v "${mount//_path_/build/$vm}" \
-      -v "${mount//_path_/vendor/$vm}" \
-      --workdir "$workdir" \
-      "$image"
-
-    "$container_tool" container start "$container_name"
-
-    "$container_tool" exec -it "$container_name" bash -ec "
-      apt update
-      apt -y install make gcc g++ chrpath perl pkg-config autoconf automake libtool nasm cmake cargo patch
-    "
-  fi
-
-  if [[ "$status" = @(created|exited) ]]; then
-    "$container_tool" container start "$container_name"
-  fi
-
-  if [[ "$status" = @(created|exited|running) ]]; then
-    "$container_tool" exec -it "$container_name" bash -ec "
-      apt update
-      apt -y dist-upgrade
-      rustup update
-    "
-  fi
 
-  if ! [[ "$status" = @(|created|exited|running) ]]; then
-    echo "unexpected status $status"
-    exit 1
+  if [[ -z "$NO_UP" ]]; then
+    status=$("$container_tool" inspect --format '{{.State.Status}}' "$container_name" 2>/dev/null || true)
+
+    if [[ "$status" == "" ]]; then
+      mount="./_path_:$workdir/_path_"
+
+      "$container_tool" \
+        container create \
+        --quiet \
+        --name="$container_name" \
+        --stop-signal SIGHUP \
+        -it \
+        -v "${mount//_path_/Makefile}":ro \
+        -v "${mount//_path_/checksums.mk}":ro \
+        -v "${mount//_path_/download}":ro \
+        -v "${mount//_path_/patches}":ro \
+        -v "${mount//_path_/build/$vm}" \
+        -v "${mount//_path_/vendor/$vm}" \
+        --workdir "$workdir" \
+        "$image"
+
+      "$container_tool" container start "$container_name"
+
+      "$container_tool" exec -it "$container_name" bash -ec "
+        apt update
+        apt -y install make gcc g++ chrpath perl pkg-config autoconf automake libtool nasm cmake cargo patch
+      "
+    fi
+
+    if [[ "$status" = @(created|exited) ]]; then
+      "$container_tool" container start "$container_name"
+    fi
+
+    if [[ "$status" = @(created|exited|running) ]]; then
+      "$container_tool" exec -it "$container_name" bash -ec "
+        apt update
+        apt -y dist-upgrade
+        rustup update
+      "
+    fi
+
+    if ! [[ "$status" = @(|created|exited|running) ]]; then
+      echo "unexpected status $status"
+      exit 1
+    fi
   fi
 
   "$container_tool" exec -it "$container_name" make $MAKE_TASK
 
-  "$container_tool" container stop "$container_name"
+  [[ -n "$NO_HALT" ]] || "$container_tool" container stop "$container_name"
 }
 
 container_build linux-x86_64 rust