ROMFS

ROMFS, short for Read-Only Memory File System, is a simple read-only filesystem implemented in the Linux kernel. It is designed to be compact and easy to implement, making it suitable for embedded systems and for providing static content in ROM or at boot time. As a read-only filesystem, ROMFS does not support file modification after creation; changes require rebuilding the image and reloading.

ROMFS provides a minimal set of filesystem features sufficient to expose files and directories to user space. It is normally used to ship static data such as firmware, boot scripts, or small assets that do not change during operation. The layout is straightforward, optimized for a small footprint rather than performance or advanced features, and it is not intended to replace more capable filesystems.

Historically, ROMFS was used in early Linux distributions and in some embedded contexts, but over time alternatives such as CramFS and SquashFS have become more common due to compression and richer feature sets. ROMFS remains in the kernel primarily for compatibility and for very small embedded use cases where a tiny, no-frills filesystem is desirable.

Limitations include lack of write support, limited metadata capabilities, and no recovery mechanisms. It is read-only by design, and creating or updating a ROMFS image typically requires a dedicated tooling step to generate a binary image from a directory tree.

See also: initramfs, CramFS, SquashFS.