overlayfs · shipping · also overlay filesystem

OverlayFS

OverlayFS is a Linux filesystem that combines lower directory trees and an optional upper tree into one merged namespace.

Related Observatory article: OverlayFS on hesela.com

Upper entries take precedence, while directory names can merge. Write access to a lower file can trigger copy-up; a read-write open may cause this even without changing data. With redirect_dir disabled, renaming a lower or merged directory fails with EXDEV. Enabling directory redirects changes that behavior. [1]

Whiteouts suppress matching lower names during lookup without exposing the marker as an ordinary file. They record visibility changes, not removal of the lower object. [2]

Relations

related

Whiteout, Atomic rename, Copy-up (OverlayFS), Metadata-only copy-up

Advantages

• Allows changes in a writable upper tree while retaining lower-layer objects.

Limitations

• Copy-up and directory-rename behavior depend on the operation and configured features.
• A merged pathname view is not evidence of secure erasure or crash durability.

Citations

1. Linux 6.12: Overlay Filesystem, layer lookup, copy-up and directory renames (accessed 2026-11-04)
2. Linux v6.12: OverlayFS ovl_lookup_single, whiteout and opaque-directory lookup (accessed 2026-11-04)

JSON: /data/terms/overlayfs.json