rootfs
also: root filesystem, root fs
The root filesystem (rootfs) is the top-level filesystem mounted at / that contains all essential system directories and files needed to boot and run a Linux system.
The rootfs is the primary filesystem hierarchy starting at the root directory (/). It contains critical system components including /bin, /etc, /lib, /sys, /proc, and other essential directories required for the kernel to function and for the system to boot.
In embedded Linux and container environments, rootfs often refers to the complete filesystem image bundled as a single unit. For example, a container image contains a rootfs with only the application and its dependencies, providing a minimal root filesystem separate from the host system.
The rootfs must be mounted before any other filesystems, and if it becomes corrupted or inaccessible, the system cannot boot. On traditional systems, the bootloader and kernel locate and mount the rootfs from a specified device (like /dev/sda1), while in initramfs scenarios, a temporary rootfs loads first to prepare the real one.