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Foreword

Hermes is a capability-based microkernel. As a microkernel, Hermes is responsible for certain core operations of an operating system, including:

  • Physical memory allocation
  • Address space isolation
  • Task scheduling
  • Interprocess communication
  • Interrupt handling and dispatch
  • Capability rights enforcement
  • Userspace I/O port mediation
  • Userspace MMIO mediation

Hermes is a low-level part of a broader operating system design and requires a separate set of drivers and low-level services to provide a higher-level application platform (e.g. POSIX).

Hermes is designed to replace its predecessor, the Helios microkernel.

Important

This documentation is a work in progress. Pages indicated with “🔸” in the sidebar are stubs.

Community

The source code, bug tracker, and mailing lists for Hermes are available on SourceHut.

We meet in #ares on Libera Chat to collaborate and discuss Hermes development.

High-level design

The high-level design of Hermes is to a certain extent inspired by the design of the seL4 kernel, but with many notable differences.

Hermes schedules tasks to execute user code on available CPUs. Each task is provided with a capability space and an address space, either of which may be shared with other tasks in whole or in part, allowing for the implementation of threads, processes, or shared memory IPC.

The capabilities which are available in a task’s capability space define the scope of I/O and IPC operations available to that task, and task isolation is achieved by curating the list of capabilities available to a task. These capabilities may be based on IPC, to communicate with services running in other tasks or processes, or may offer other rights, such as access to IRQs and memory-mapped I/O, to facilitate the implementation of drivers in userspace.

Getting Hermes

The source code for Hermes is available on SourceHut under the GNU GPLv3 license. Information about dependencies and compiling the kernel are provided in the repository.

Booting Hermes

Bootloaders are provided for each supported target in the kernel repository. See System initialization for information about giving the kernel some work to do once booted.

x86_64 EFI

An EFI bootloader is available in ./boot/efi and will be compiled if ENABLE_EFI=1 in your config.mk file. The built EFI bootloader is written to ./boot/efi/bootx64.efi and should be installed at /EFI/boot/bootx64.efi on the EFI System Partition of your boot media.

The EFI bootloader loads the kernel from /hermes of the boot media and loads boot modules from /modules in (ASCII) alphabetical order. The first boot module is used as init by the kernel.

x86_64 multiboot

A multiboot-compatible legacy BIOS bootloader is provided in ./boot/multiboot and will be compiled if ENABLE_LEGACY=1 in your config.mk file. The bootloader is written to ./boot/multiboot/sysboot.mb and should be loaded by a multiboot-compatible bootloader such as syslinux or grub.

Multiboot modules are loaded as boot modules and passed to the kernel in the order defined by the multiboot environment. The first boot module is used as init by the kernel.