Senior Operating Systems / Hypervisor Engineer

Company: Wasmer (https://wasmer.io)

Type: Full-time

Location: Remote (CET ± 2)

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Build an operating system that runs everywhere

Most engineers spend their careers using operating systems. A few get to build one. This role is for the second group.

At Wasmer, we're building WASIX — an OS emulation layer that brings full POSIX semantics to WebAssembly: threads, processes, fork(), sockets, TTYs, signals, the works. It's the kind of problem where you're reading Linux kernel source in one tab and the WebAssembly spec in another, deciding how mmap should behave on a platform that was never designed to have one.

If that sentence made you lean in rather than close the tab, keep reading.

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What you'll work on

• WASIX itself — designing and implementing syscall semantics, process and threading models, virtual filesystems, and networking stacks on top of WebAssembly. Where Linux behavior and Wasm constraints collide, you'll be the one deciding what "correct" means.
• The Wasmer runtime — the sandboxing, scheduling, and memory-management machinery that makes thousands of Wasm "processes" run safely and fast on a single host. Think hypervisor problems, at a different layer of the stack.
• Making real software just work — porting and running battle-tested Unix software (curl, bash, PostgreSQL-class programs) unmodified on WASIX, and fixing everything that breaks along the way.
• Open source - a good chunk of your work will ship publicly, in one of Wasmers open-source repositories

You're probably a fit if you

• Have 5+ years of systems-level engineering experience, with real-world work on Linux internals, hypervisors (KVM, Xen, Firecracker, etc.), or comparable low-level runtimes — not just as a user, but as someone who has debugged, extended, or built them.
• Have a genuine, self-driven interest in OS and hypervisor design — you have opinions about scheduler behavior, memory models, or syscall interfaces, and can defend them.
• Have proven Rust experience, are fluent C and comfortable diving into large, unfamiliar codebases.
• Know POSIX deeply: processes, signals, sockets, file descriptors, memory management — the stuff most people only meet through man pages.
• Thrive with high ownership: you can take a fuzzy problem ("make signals work correctly under Wasm") and drive it from design to shipped code.
• Live in the CET timezone ± 2.

Bonus points (nice, not required):

• Prior work with WebAssembly, WASI, Emscripten, or other compi