Why these kernels

The research behind the kernel choice is in docs/RESEARCH.md in the repository; this is the short version.

What ERTS needs from a kernel

Threads with futexes, mmap/munmap (and optionally mremap), epoll or poll, timerfd, eventfd, pipes, Unix socket pairs, fork+execve for the erl_child_setup helper that ERTS starts unconditionally, BSD sockets with sendmsg/recvmsg, getrandom or /dev/urandom, a file system to load .beam files from, signals, and a tty for the shell. It does not need dlopen when NIFs are linked statically.

Asterinas (chosen)

A Linux-ABI compatible kernel written in Rust with a small unsafe core (“framekernel”), 245 syscalls on x86-64 at the pinned commit, virtio-net with a TCP/IP stack, initramfs, ramfs, ext2, SMP. An unmodified static musl beam.smp runs on it as PID 1. The project ships a Docker development container and a build tool (cargo osdk), moves fast, and the two gaps we hit were fixable with a few lines each. MPL-2.0.

Trade-offs: it is a kernel/user split, not a single binary; its memory floor is set by the fixed load address (128 MB) rather than by our image; it is pre-1.0 and some socket options and ioctls are missing.

Hermit (future, M3)

A true unikernel in Rust: the application is linked into libhermit.a and boots as one image. It has threads, futexes, mmap, poll, sockets over smoltcp and virtio-net, but no fork/execve, no pipe/socketpair, no select, no sigaction, and a Newlib-based libc. Running ERTS on it means patching ERTS (the erl_child_setup forker as a thread, pipe emulation, no mremap), porting OTP’s and OpenSSL’s configure to an x86_64-hermit target, and populating its memfs from an embedded archive. The nanovms/erlang patch set for the Nanos unikernel is the closest prior art. Months, not weeks. Everything in this repository (release layout, /init semantics, smoke tests) carries over and becomes the regression baseline.

Considered and rejected

Theseus (no POSIX), Redox (microkernel with relibc, a different porting effort), kerla and maestro (stale or immature), Unikraft, Nanos and OSv (not Rust). A BEAM reimplemented in Rust (BOSS, enigma, AtomVM-style) is a different project: it gives up unmodified OTP, which is the point here.

The Linux reference kernel

make run-m0 boots the same initramfs on a stock Linux 6.1 built by the Firecracker project for its CI (virtio, serial console and initramfs support compiled in, no modules). It is only a debugging aid: anything that works on Linux and fails on Asterinas is a kernel issue, and vice versa. Alpine’s linux-virt was tried first and rejected because it ships virtio_net as a module, which would have forced Linux-only files into the image.