Testing PostgreSQL on Debian/Hurd: A Windows + QEMU Adventure

Curiosity often leads to the most interesting technical adventures. This time, I decided to explore something off the beaten path: running Debian GNU/Hurd inside a virtual machine on my Windows 11 host and compiling PostgreSQL from source.

This post is part 1 of a multi-part series documenting the process, challenges, and discoveries along the way. Future parts will dive deeper into advanced topics, automation, and ongoing compatibility work—so if you're interested in PostgreSQL, alternative operating systems, or open source testing, stay tuned!

What is Debian?
Debian is one of the oldest and most respected Linux distributions, known for its stability, vast software repositories, and commitment to free software principles. While most people associate Debian with the Linux kernel, it’s actually a complete operating system that can run on different kernels.

What is GNU/Hurd?
GNU/Hurd is an alternative kernel developed by the GNU Project. Unlike Linux, GNU/Hurd is built on a microkernel architecture (specifically GNU Mach), aiming for greater modularity and flexibility. While GNU/Hurd is still experimental and not as mature or widely used as Linux, it represents a fascinating approach to operating system design.

Debian GNU/Hurd combines the familiar Debian userland (tools, package management, etc.) with the GNU/Hurd kernel, offering a unique environment for open source enthusiasts and OS tinkerers.

My goal for this experiment was to see how far I could get with a modern database stack—specifically, compiling and running PostgreSQL—on this unusual platform.

Setting Up the VM

Instead of the CD image, I used the pre-built disk image available here. After downloading and extracting the .img file, I launched the VM with QEMU using the following command:

qemu-system-x86_64.exe -machine type=pc,accel=whpx,kernel-irqchip=off -boot d -m 4096 -usb -display default,show-cursor=on -drive file=".\debian-hurd-i386-20250807.img",cache=writeback

Explanation of the command:

• qemu-system-x86_64.exe: Runs QEMU for 64-bit x86 systems (works for 32-bit guests too).
• -machine type=pc,accel=whpx,kernel-irqchip=off: Specifies a PC-type machine, enables Windows Hypervisor Platform acceleration (WHPX), and disables kernel IRQ chip emulation for compatibility.
• -boot d: Boots from the first hard disk.
• -m 4096: Allocates 4GB of RAM to the VM.
• -usb: Enables USB support.
• -display default,show-cursor=on: Uses the default display and ensures the mouse cursor is visible.
• -drive file=".\debian-hurd-i386-20250807.img",cache=writeback: Uses the extracted Hurd disk image as the hard drive and enables writeback caching for better disk performance.

This boots directly into the installed Debian/Hurd system with improved performance and usability on a Windows 11 host.

Preparing to Build PostgreSQL

Debian/hurd is minimal out of the box, so the first step was to install all the build tools and libraries required for compiling PostgreSQL:

sudo apt-get update
sudo apt-get install build-essential git libxml2-dev libxslt-dev autotools-dev automake libreadline-dev zlib1g-dev bison flex libssl-dev libpq-dev ccache

This command installs the compiler, linker, version control tools, XML and SSL libraries, autotools, and all other dependencies PostgreSQL may need for a successful build and test cycle.

Downloading and Compiling PostgreSQL

Instead of downloading a release tarball, I cloned the official PostgreSQL git repository and compiled the master branch:

git clone https://github.com/postgres/postgres.git
cd postgres
./configure --prefix=~/proj/localpg
make
make install

This approach ensures you're building the latest development version of PostgreSQL directly from source, and installs it locally to your user's ~/proj/localpg directory.

Setting Up the Database Cluster

PostgreSQL needs a data directory (cluster) to store its databases. Since the installation was local to my user, I simply initialized the cluster and started the server using the full path to the binaries (since they're not in my PATH):

~/proj/localpg/bin/initdb -D ~/proj/localpg/pgdata
~/proj/localpg/bin/pg_ctl -D ~/proj/localpg/pgdata -l logfile start

Connecting and Creating a Table

With the server running, I connected to the database and created a sample table:

~/proj/localpg/bin/psql -d postgres

Inside psql:

CREATE TABLE test_table (id SERIAL PRIMARY KEY, name TEXT);
INSERT INTO test_table (name) VALUES ('Hello from Debian/Hurd!');
SELECT * FROM test_table;

Example output:

CREATE TABLE
INSERT 0 1
 id |         name         
----+----------------------
  1 | Hello from Debian/Hurd!
(1 row)

Running the Test Suite

To ensure the build was solid, I went back to the source directory and ran:

cd ~/postgres
make check

This runs PostgreSQL's regression tests, verifying that the core features work as expected—even on Hurd. This ran mostly fine (except for a few tests that failed - more to be researched on that failure).

Quick QEMU Tip

When working with QEMU, remember that Ctrl-Alt-G is your friend—it releases the mouse and keyboard from the VM window, making it much easier to switch back to your host system.

Adding a Separate Volume for More Disk Space

The base Debian/Hurd image is quite small and can easily run out of space, especially when compiling large projects or running make check. I frequently hit disk full errors during testing.

Solution:

1. Shutdown the VM.

2. Resize the disk image:

   qemu-img resize debian-hurd-i386-20250807.img +10G
   

   This adds 10GB to the existing disk image.

3. Restart the VM.

4. Create a new partition:

   • Use fdisk /dev/hd0 (or the appropriate device) to create a new partition in the extra space.

5. Format the new partition:

   mkfs.ext4 /dev/hd0s3
   

   (Note: On my setup, the original root partition was /dev/hd0s2, so the new partition created for extra space was /dev/hd0s3. Adjust the device name as needed for your configuration.)

   Although the root volume is of ext2 type (!!!), Debian/Hurd works fine with ext4—so feel free to use ext4 for the new partition.

6. Mount the new volume:

   mkdir -p /mnt/newvol
   mount /dev/hd0s3 /mnt/newvol
   

7. Grant non-root user access:

   • As root, change ownership:

     chown robins:robins /mnt/newvol
     

   • Now your non-root user (e.g., robins) can use /mnt/newvol for compiling PostgreSQL and running make check without running out of disk space.

Why use a non-root user for PostgreSQL? PostgreSQL is designed to run as a non-root user for security reasons. Running the database server or its tests as root can expose your system to unnecessary risks and may even cause certain operations to fail. Always use a dedicated non-root user for installation, testing, and day-to-day database operations.

This approach made it possible to complete the build and test cycle without disk space issues.

Final Thoughts

Running Debian/Hurd in a VM on Windows 11 was surprisingly smooth, though some packages and features are less mature than on Linux. Compiling PostgreSQL from scratch was a great way to explore the system's capabilities and compatibility. If you're looking for a fun, geeky weekend project, give Debian/Hurd a try!

Next Steps & What's Still Pending

This is only part 1 of a multi-part series. In future installments, I'll cover:

• Setting up the PostgreSQL buildfarm for automated testing on Debian/Hurd
• Deeper investigation into SMP/multi-core support (currently not working)
• More QEMU optimization and compatibility testing
• Additional performance tuning and disk management strategies
• Troubleshooting Perl module installation issues (e.g., LWP::Protocol::https, LWP::Simple, Net::SSLeay), which currently fail to install—more research is needed to understand and resolve these problems.
• Investigating why make check did not complete successfully (failed on a few tests)—this requires further research.

Some features, like multi-core support, full buildfarm integration, reliable Perl module installation, and passing all PostgreSQL regression tests, are not yet working or fully tested. These will be explored in detail in future posts. Stay tuned!