Kerla

Kerla is a monolithic operating system kernel written from scratch in Rust which aims to be compatible with the Linux ABI, that is, it runs Linux binaries without any modifications.

• Implements *NIX process concepts: context switching, signals, fork(2), execve(2), wait4(2), etc.
• Supports commonly used system calls like write(2), stat(2), mmap(2), pipe(2), poll(2), ...
• No disk support for now: initramfs is mounted as the root file system.
• Pseudo file systems: tmpfs and devfs.
• smoltcp-based TCP/IP support.
• Implements tty and pseudo terminal (pty).
• Supports QEMU and Firecracker (with virtio-net device driver).
• Supports x86_64.
• Docker-based initramfs build system.

Check out my blog post for motivation and my thoughts on writing an OS kernel in Rust.

Demo: SSH into Kerla!

You can play with Kerla over ssh. Your login is not visible from others (except me): we automatically launch a dedicated microVM on Firecracker for each TCP connection.

$ ssh root@demo.kerla.dev

If you found bugs or missing features, let me know on GitHub issues :)

Running a Docker Image (experimental)

You can run a Docker image as a root file system (not as a container!) on Kerla Kernel instead of our initramfs built from initramfs directory.

For example, to run nuta/helloworld image (Dockerfile), try the following command:

$ make IMAGE=nuta/helloworld run
...
[   0.029] syscall: execve(439398, 4393b8, 4393c8, 8, 2f2f2f2f2f2f2f2f, 8080808080808080)
[   0.030] syscall: arch_prctl(1002, 4055d8, 0, 20000, 0, ff)
[   0.031] syscall: set_tid_address(4057f0, 4055d8, 0, 20000, 0, ff)
[   0.033] syscall: ioctl(1, 5413, 9ffffeed0, 1, 405040, 9ffffeef7)

 _          _ _                            _     _ _
| |__   ___| | | ___   __      _____  _ __| | __| | |
| '_ \ / _ \ | |/ _ \  \ \ /\ / / _ \| '__| |/ _` | |
| | | |  __/ | | (_) |  \ V  V / (_) | |  | | (_| |_|
|_| |_|\___|_|_|\___/    \_/\_/ \___/|_|  |_|\__,_(_)

This feature is in a very early stage and I guess almost all images out there won't work because:

• They tend to be too large to be embedded into the kernel image.
• They might use unimplemented features (e.g. position-independent executables used in Alpine Linux).

Building and Running the OS

See Quickstart for instructions on building from source, running on emulators, etc.

Current Roadmap

Roadmap - Run a Node.js Web Application on Kerla on Firecracker on AWS

Compatibility

See here for the current status.

Contributing

Send me bug reports, feature requests, and patches on GitHub for example:

• Implementing missing features: majority of existing Linux applications won't work due to the lack of features.
• Writing documentation: I think Kerla could be good material to learn how an operating system kernel works.
• Trying to experiment with Rust-y ideas: for example currently I'm interested in GhostCell.

License

See LICENSE.md.

Related Work

Emulating Linux ABI is not a novel work. Some UNIX-like kernels like FreeBSD and NetBSD already have their own Linux emulation layers. Windows has a well-known feature called Windows Subsystem for Linux (WSL) which enables running Linux binaries seamlessly. WSL 1 implements the feature by ABI emulation. WSL 2 runs the real Linux kernel using the hardware-accelerated virtualization (Hyper-V).

Aside from general-purpose operating systems, there're some attractive projects related to the Linux ABI emualtion. OSv is a unikernel which runs unmodified Linux binaries. rCore is a teaching operating system which implements the Linux ABI in Rust. Noah suggests an intriguing approach to run unmodified Linux binaries on macOS.