This issue was originally opened by @ltrager as hashicorp/packer#9927. It was migrated here as a result of the Packer plugin split. The original body of the issue is below.

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"