title: How do I find out the boot command for Packer?
body: <p>If I want to create a virtual machine image using <a href="https://www.packer.io/" rel="noreferrer">Packer</a>, one option is to download an operating system's ISO image and use that as the base for a custom setup. When doing this, one needs to provide the <a href="https://www.packer.io/docs/builders/virtualbox-iso.html#boot_command" rel="noreferrer"><code>boot_command</code></a>, which is an array of strings that tell Packer how to setup the operating system.</p>
  
  <p>Now my question is: How do I find out the correct <code>boot_command</code> steps for a given operating system? Of course I might boot it up manually and write down every single thing I type, but I wonder if there is a more convenient way.</p>
  
  <p>Of course I can also <a href="https://www.google.de/search?q=packer+ubuntu+template" rel="noreferrer">ask Google</a> about it, but is there an "official" way? E.g., are the steps for Ubuntu documented somewhere in the Ubuntu documentation? Or is it actually trial and error, or at least peeking at somebody else's work?</p>