mntoverlay

mntoverlay is a Linux kernel module that provides a way to overlay one filesystem on top of another. It's often used in conjunction with other technologies like overlayfs to create read-write layers on top of read-only images, which is a common pattern in containerization and live operating systems. The primary purpose of mntoverlay is to allow modifications to a filesystem without altering the underlying base filesystem.

This module operates by redirecting filesystem operations. When a write operation is attempted on a file within the overlay, mntoverlay intercepts it and creates a copy of the file in a separate, writable location. Subsequent reads and writes then operate on this copy. This ensures that the original, read-only filesystem remains untouched.

mntoverlay can be a fundamental component in systems that need to maintain a stable base while allowing for dynamic changes. For example, in live USB environments, the core operating system might be mounted read-only, and mntoverlay can be used to enable user installations and configurations without permanently altering the initial image. In container technologies, it can facilitate the creation of layered filesystems where each layer represents a change or an addition, leading to efficient storage and faster image creation. The module's implementation details and specific use cases are often tied to the broader filesystem architecture of the operating system.