The filesystem

Zainium OS is the reference implementation of the Dualayer Hierarchy Standard (DHS). The root directory holds only /overlayer, user data and the virtual filesystems:

/
├── overlayer/
│   ├── syshub/        the base system (composed view at run time)
│   ├── zexlib/        software you install, package records, flatpak data, shadowed files
│   ├── zaisys/        kernel, initramfs, boot loader (read-only)
│   ├── agents/        instructions and skills for AI coding agents
│   ├── README.zainium  architecture.md  zex.md
│   └── .syshub-pending/   a staged base upgrade (only while one waits)
└── home/  root/  tmp/  run/  dev/  proc/  sys/

There is no /usr, /etc, /var, /bin, /sbin, /lib, /lib64 or /boot at the root.

At run time /overlayer/syshub is read-only, even for root. Its etc and var are writable layers whose changes are kept in /overlayer/zexlib/union/etc and /overlayer/zexlib/union/var, and /overlayer/zaisys is a separate read-only mount.

Zainium names and DHS names

Inside the base

/overlayer/syshub/
├── bin/ sbin/ libexec/         programs
├── lib/                        libraries (and lib/systemd, lib/udev, …)
├── include/                    headers
├── share/                      data files
├── etc/                        system configuration
├── var/                        state of base services
├── x86_64-zainium-linux-musl/  musl: loader, libc, headers, toolchain
├── drivers/
│   ├── modules/<kernel>/       kernel modules
│   └── hardware/firmwares/     firmware
└── engine/services/            syshub.toml (base packages), zex_services.toml (mirrors)

Where FHS paths went

Programs written for FHS systems still find their files: see running FHS software.