Senior Operating Systems / Hypervisor Engineer - Wasmer

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.

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

• 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.

• Competitive salary and stock options.
• Generous vacation policy.
• Flexible and or remote work policies
• Monthly fitness stipend.
• Monthly stipend for open-source contributions.
• Economic support for skills development, continuous learning, and attending conferences.

Why this role is different

Greenfield OS work is rare. Greenfield OS work with real users is rarer. WASIX already runs real software for real developers - which means your design decisions get stress-tested immediately, not in five years.

You’ll join a small, senior, remote team where the interesting problems aren’t handed down from an architecture committee - you’ll find them, scope them, and solve them. And because we’re open source at our core, the work you do here is yours to point at for the rest of your career.

About Wasmer

Wasmer builds the software powering the next generation of computing platforms - local, cloud, and edge - on WebAssembly. Just as Node.js unlocked server-side JavaScript, we’re unlocking server-side WebAssembly for every language: C/C++, Rust, Go, Python, and beyond.

Our mission is to make software universally available. We’re an open-source-first company, and we believe the best infrastructure is built in public.

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