The root filesystem (rootfs)
The root filesystem (rootfs) is the main filesystem for an UNIX-like operative system. It contains the very critical files needed for the whole system to work (for instance, the init process), so if the root filesystem gets corrupted, the system will not work at all!
The root filesystem is the first filesystem the kernel mounts at boot, and it is never unmounted.
A rootfs can be used on several different types of storage devices (disks, flashes, and so on). A filesystem can stay in the RAM or even over the network, and according to the storage device where it's placed on, it can have different formats. This is because it has to take into account some special feature of the underlying storage media. In a typical GNU/Linux system, a rootfs type can be (mostly) EXT3/EXT4 or JFFS2/UBIFS. The first two formats are the standard Linux filesystems used into hard disks, USB storage devices, microSDs, and other block devices, while the JFFS2 and UBIFS are filesystems used...
