Memory-based root filesystems

Early user space or initial memory images, known as initramfs images, are typically used as early user spaces with the task of mounting complex filesystems, such as for example when an encrypted partition needs to be set up. For that use case, initramfs will prepare the final root filesystem and then perform a switch_root, effectively replacing the old filesystem with the new and running a new init from the new filesystem. initramfs needs to contain all tools needed to mount the final root filesystem.

Other uses for initramfs include rescue and manufacturing systems.

This recipe will show how to configure the Yocto build system to build initramfs images.

Getting ready

When the Linux kernel mounts a file system from physical storage, it keeps a cache for quick access. A memory filesystem is just this kernel cache without a backing store.

An initramfs is a compressed cpio format file that the kernel extracts into a memory filesystem and uses as the root filesystem...