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  Hurd Repository

This repository contains software to build a POSIX single system image cluster based on the Hurd operating system.

This software is only useful on a Hurd system, and is not currently production quality, but is in regular use in a development environment, which is Debian GNU/Hurd running in a Linux virtual machine.

Repository Contents

  1. Documentation

    Building an SSI Cluster with GNU/Hurd is a twenty page paper describing the current status of this work.

    There's also LaTeX source for the slide deck that I used for a presentation at Catholic University.

  2. The netmsg server

    netmsg is a Hurd translator that transports Mach messages over TCP/IP; Mach is Hurd's underlying kernel.

    netmsg currently provides no encryption or authentication, and presents a Hurd system's root filesystem to any client connecting on TCP port 2345.

  3. Multi-client libpager

    libpager is the Hurd library responsible for managing access to memory mapped files. The standard libpager only allows access to a single kernel. Since program execution occurs by memory mapping executables and shared libraries, a single-client libpager is not usable in a cluster environment, since programs can not be executed remotely.

    The code is this directory is a drop-in replacement for libpager that supports multiple kernels. Once the Hurd filesystem servers have been linked with this library, remote program execution is possible between machines linked via netmsg.

  4. patches

    This section contains patches to software in the main Hurd repository at git://

    rpctrace is the Hurd equivalent of strace. rpctrace has a serious problem because some Hurd RPCs block the sender while waiting for other RPCs to complete, even if non-blocking behavior has been requested. A major offender here is vm_map, which blocks while waiting for a memory object init/ready exchange. This causes rpctrace to hang when tracing ext2fs, the primary Hurd filesystem translator.

    The rpctrace patches fix this problem, as well as a few others, and also improves rpctrace's documentation. They should be applied, in order, against a current version of either the main Hurd repository, or the Debianized source tree.

Installation Instructions

  1. Follow Debian's installation instructions to install and boot Debian GNU/Hurd in a virtual machine.

  2. Run apt source hurd to download and extract the Hurd source code.

  3. In the Hurd source directory, replace the libpager directory with a symbolic link to the libpager directory from this repository.

  4. In the Hurd source directory, apply patches/libpager.patch to make everything linked with libpager link with stdc++, since the new libpager is written in C++.

  5. In the Hurd source directory, run either dpkg-buildpackage -b to re-build the Hurd packages, or dpkg-buildpackage -T build to build the binaries without making a new Debian package.

  6. Install the new Hurd packages (or just the /hurd/ext2fs.static binary) and reboot the Hurd virtual machine.

  7. In the repository's netmsg directory, run make

  8. You may wish to now run two different virtual machines and connect between them. I usually just connect from one VM to itself for testing purposes.

  9. On one machine, run netmsg -s to start netmsg in server mode.

  10. On the other machine (or in another window), run touch mnt; settrans -a mnt netmsg *HOSTNAME*

  11. You can now work with files on the remotely mounted system.

Future directions

  1. netmsg needs a complete redesign to avoid race conditions when closing ports

  2. Add authentication to netmsg

  3. Use a sequenced datagram protocol for netmsg transport

  4. Rework Hurd authentication along the lines of

  5. 64-bit user space

  6. Patch glibc so that spawn() and fork() can create processes on other nodes

    spawn() should be fairly easy; fork() will be more difficult without vm_attach()

  7. Add a vm_attach() system RPC to attach a memory manager to a previously unmanaged region of memory.

    This would greatly facilitate implementation of fork(). Unmanaged regions of memory that require shared-memory semantics after a fork() could simply be attached to a libpager-based memory manager.

  8. Modify the kernel so that a default memory manager can be associated with a task.

    The task's default memory manager would receive a notification whenever the task allocated unmanaged memory.

    This would allow tasks to span nodes, which would facilitate programs that spawn a lot of threads to achieve parallelism.

    To avoid a race condition if tasks on different nodes allocated the same region of memory near-simultaneously, a handshake between the kernel and the default memory manager would be required whenever a vm_allocate() is attempted.

  9. Persistence

    Checkpointing tasks to allow recovery in the event of node failure

Test Cases

  1. Long, complex compile runs - Hurd, Mach, Linux, glibc, gcc, gdb

    Demonstrates performance improvement even with 32-bit user space

  2. Hoffman - Brent's endgame analysis engine

    Demonstrate support for standard C++ memory management and threading

  3. Meep - MIT's FDTD electromagnetic simulation software

    Demonstrates support for the MPI standard

  4. MySQL

    Demonstrates support for database applications

  5. some kind of Hadoop project

    Demonstrates support for the current cluster computing standard

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