Ramblings on IT and Security

Month: November 2025

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

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…

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