This chapter describes the handling of the root file system. In general transactional-update will not modify any other subvolumes or file systems: Information stored on these mounts (such as /var or /home) is usually not supposed to be rolled back. See System setup for a real world setup. There are exceptions for a few dedicated subvolumes such as /boot/grub2/x86_64-efi which also have to be available to be able to update the bootloader; these directories will be bind mounted into the update environment.

transactional-update is based around several concepts of the Btrfs file system, a general purpose Copy-on-Write (Cow) filesystem with snapshot and subvolume support, though support for other file systems is possible (see Porting to other systems for requirements and porting information).