Documentation · Engineering
Inside LeivOS.
The end-user product is LeivOS. The kernel is called Uusi. The language most of it is written in is Tape. This page is for developers, evaluators, and the curious — every layer is built in-house.
Kernel
Uusi
x86_64, UEFI
Userland
LeivOS
Compositor, apps, libuusinet
Language
Tape
Scripting + AOT — read more →
The kernel inside
Uusi: small, sharp, ours.
The Uusi kernel boots from UEFI, brings up paging, scheduling, processes, threads, and a window manager — all in a fraction of the code other operating systems need.
- • Preemptive multitasking with per-thread guard pages
- • Userspace network stack and TLS 1.3 written from scratch
- • Per-process address spaces, killable cleanly without taking the GUI down
- • In-tree scripting language for automation: Tape
$ uusi boot --serial
[ok] uefi memory map preserved
[ok] pmm online, 7.8 GiB available
[ok] vmm + slab heap up
[ok] scheduler: 8 logical CPUs
[ok] /dev/wm + compositor
[ok] netd: dhcp BOUND ip=10.0.2.15
[ok] tls 1.3 record layer ready
leivos login:
Kernel & runtime
- Custom x86_64 kernel — bootloader, paging, scheduler, IPC, all in-house
- Written in Assembly (early boot + CPU primitives), C (close-to-metal pieces), and primarily Tape
- Per-process address spaces with hard memory limits and guard pages
- Preemptive scheduling with two-tier fairness
- Slab + free-capable heap, deterministic page allocator
- Cooperative graceful shutdown on faults; the GUI survives
Graphics & desktop
- Window manager with z-order, focus, drag, close, hover
- Damage-rect compositor — only what changed gets redrawn
- Client-owned window buffers, capability-checked surface IDs
- A small widget toolkit, fast launcher, software cursor
Networking
- Userspace network stack: Ethernet, ARP, IPv4, ICMP, UDP, TCP, DHCP, DNS
- TLS 1.3 with X25519, AES-GCM, ChaCha20-Poly1305 — written from scratch
- X.509 chain validation against real RSA-PSS and ECDSA-P256 certificates
- WPA2-PSK Wi-Fi with verified 4-way handshake against captured fixtures
- virtio-net + loopback drivers; a kernel net-poll thread for steady tick
Tape — the in-tree language
- Three runtimes from one source: interpreter, JIT, AOT to native PE
- Full pipeline: scanner → parser → typecheck → bytecode → codegen
- Standard library: io, string, dyn — and a REPL
- Compile-once-run-many .tb bytecode artifacts
- Read the dedicated Tape language documentation for grammar, types, and runtimes
Trust
- No telemetry. No profiling. No background analytics.
- Capability manifest gates privileged ioctls per binary
- Every cryptographic primitive verified against RFC test vectors
- Tape language sources available; OS sources closed for security reasons
Want to read more?