Add serial mode in qemu builder

[ltrager]

Description

Packer is often run in environments that do not have access to a UI. While Packer supports running headless no output is given to the terminal. A template can be constructed today that shows serial output by adding "qemuargs": [[ "-serial", "stdio" ]] and running Packer with PACKER_LOG=1. See the CentOS 8 Packer template as an example.

While this works "2020/09/11 02:04:16 packer-builder-qemu plugin: Qemu stdout" is often mixed in with output which makes things hard to read. Ideally an official option would be added to Packer which adds "-serial stdio" to the qemu arguments and doesn't prepend each line.

Use Case(s)

1. I am working on using gh:canonical/packer-maas to produce the public CentOS images for MAAS. I have been given a Jenkins server to do this but have no access to the Jenkins builders. This makes debugging very hard as I can't VNC in, all I get is the terminal output.
2. Users of gh:canonical/packer-maas run Packer on Ubuntu desktop, remotely on an Ubuntu server over SSH, or in a Jenkins job. As such I have gh:canonical/packer-maas set to run headless. I've been asked to show progress while Packer is running as well as add the ability for users to send me logs.

Potential configuration

"serial": "true/false"

[sylviamoss]

This sounds like a good idea. We’ll take a look when we get a chance.

[MaxPeal]

@sylviamoss @azr any Update on this?

[ghost]

This issue has been automatically migrated to hashicorp/packer-plugin-qemu#5 because it looks like an issue with that plugin. If you believe this is not an issue with the plugin, please reply to hashicorp/packer-plugin-qemu#5.

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.