#Packer – Michael Waterman

Update 26-12-2025: Uploaded new and improved PowerShell scripts to GitHub. Added Windows 11, Ubuntu Server & Ubuntu Desktop to the repository.

In June 2023, I wrote a blog about the principle of clean source. At its core, clean source is about knowing exactly what you are using as the foundation of your installations, and automating that process so the outcome is predictable and repeatable.

Back then, I relied on what we now have to call legacy tooling. While that approach still works, it was already showing its age. Tools like MDT have been deprecated for quite some time, and although community efforts try to keep them alive, it’s clear that this path is slowly coming to an end.

That realization pushed me to take a step back and ask a simple question: why not approach this from a DevOps mindset instead? As it turns out, that opened the door to some pretty cool possibilities.

While automating my Proxmox environment with Packer, most of the workflow worked flawlessly: Ubuntu autoinstall, cloud-init, SSH provisioning, and qemu-guest-agent all behaved exactly as expected. But every build consistently failed at the very last step, converting the VM into a template, which was very annoying.

Despite the VM installing perfectly, Proxmox refused to stop it cleanly and returned a persistent lock-related error. This led to a surprisingly long troubleshooting process, which eventually revealed a simple root cause: stale lock files left behind from earlier interrupted builds……sigh

In this post, I’ll share the exact error, the steps I went through to diagnose it, and how cleaning up these old lock files immediately restored stable, repeatable builds, it’s been a few very long days…

Tag: #Packer

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Fixing Packer + Proxmox template build failures: “can’t lock file … got timeout”

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