diff --git a/demos/runtime_boot/README.md b/demos/runtime_boot/README.md
index 47639e53..cd7dc04d 100644
--- a/demos/runtime_boot/README.md
+++ b/demos/runtime_boot/README.md
@@ -11,7 +11,7 @@ The later step will use the image content to generate UnionFS image.
 
 ### Build and start a [`gen_rootfs`](./gen_rootfs) Occlum instance
 
-This `gen_rootfs` mounts a empty UnionFS, copy the BASH Occlum image content to the mount point, unmount the UnionFS. It generates an encrypted UnionFS image containing the BASH image content. The **key** used in this demo is `"c7-32-b3-ed-44-df-ec-7b-25-2d-9a-32-38-8d-58-61"`.
+This `gen_rootfs` mounts a empty **sefs** (uses the lower path as mount target dir), copy the BASH Occlum image content to the mount point, unmount the **sefs**. It generates an encrypted **sefs** image containing the BASH image content. The **key** used in this demo is `"c7-32-b3-ed-44-df-ec-7b-25-2d-9a-32-38-8d-58-61"`.
 
 ### Build customized [`init`](./init)
 
@@ -22,7 +22,7 @@ Occlum [`default init`](../../tools/init) calls syscall (363) `MountRootFS` to m
 The first parameter `key_ptr` is optional.
 The second parameter `rootfs_config` needs to be set as NULL.
 
-But for runtime booting pre-generated UnionFS image, The first parameter `key_ptr` is must to have, the second parameter `rootfs_config` needs have valid members.
+But for runtime booting pre-generated image, The first parameter `key_ptr` is must to have, the second parameter `rootfs_config` needs have valid members.
 ```
 struct user_rootfs_config {
     // length of the struct
diff --git a/demos/runtime_boot/gen_rootfs/src/main.rs b/demos/runtime_boot/gen_rootfs/src/main.rs
index 2fed4956..d6f1fe0c 100644
--- a/demos/runtime_boot/gen_rootfs/src/main.rs
+++ b/demos/runtime_boot/gen_rootfs/src/main.rs
@@ -9,15 +9,14 @@ fn main() {
     println!("{:?}", args);
     fs::create_dir("/mount").unwrap();
 
-    let fs_type = "unionfs";
+    let fs_type = "sefs";
     let mount_path = Path::new("/mount");
-    let source = Path::new("unionfs");
+    let source = Path::new("sefs");
     let flags = MsFlags::empty();
     let key = &args[1];
     let options = format!(
-        "lowerdir={},upperdir={},key={}",
+        "dir={},key={}",
         "./mnt_unionfs/lower",
-        "./mnt_unionfs/upper",
         key
     );
 
diff --git a/src/libos/src/config.rs b/src/libos/src/config.rs
index d1752348..c609f5b2 100644
--- a/src/libos/src/config.rs
+++ b/src/libos/src/config.rs
@@ -578,7 +578,7 @@ impl ConfigApp {
             .find(|m| m.target == Path::new("/") && m.type_ == ConfigMountFsType::TYPE_UNIONFS)
             .ok_or_else(|| errno!(Errno::ENOENT, "the root UnionFS is not valid"))?;
 
-        if upper_layer.is_some() {
+        if lower_layer.is_some() {
             let layer_mount_configs = root_mount_config.options.layers.as_mut().unwrap();
             // image SEFS in layers
             let root_image_sefs_mount_config = layer_mount_configs
@@ -590,12 +590,12 @@ impl ConfigApp {
                 })
                 .ok_or_else(|| errno!(Errno::ENOENT, "the image SEFS in layers is not valid"))?;
 
-            root_image_sefs_mount_config.source = upper_layer;
+            root_image_sefs_mount_config.source = lower_layer;
             root_image_sefs_mount_config.options.mac = None;
             root_image_sefs_mount_config.options.index = 1;
         }
 
-        if lower_layer.is_some() {
+        if upper_layer.is_some() {
             let layer_mount_configs = root_mount_config.options.layers.as_mut().unwrap();
             // container SEFS in layers
             let root_container_sefs_mount_config = layer_mount_configs
@@ -610,7 +610,7 @@ impl ConfigApp {
                     errno!(Errno::ENOENT, "the container SEFS in layers is not valid")
                 })?;
 
-            root_container_sefs_mount_config.source = lower_layer;
+            root_container_sefs_mount_config.source = upper_layer;
         }
 
         if entry_point.is_some() {