Filesystem changes not fully syncing

[DhashS]

I've noticed that filesystem changes such as large tar files having a different sha256 than the input tar file.

Upstream, I've done something like

sync = [{"type": "shell", "inline": ["sync"]}]
packerfile["provisioners"].extend(paths_mapping)
packerfile["provisioners"].extend(sync)

which is a biiiit tacky for my taste. However, I found a doc section in the packer docs that might be a better way of doing this.

It is important to add a shutdown_command. By default Packer halts the virtual machine and the file system may not be sync'd. Thus, changes made in a provisioner might not be saved.

so maybe try doing this instead?

Thinking about how this should get tested, I'd like to generate a byte pattern, load it in via provisioners, and then immediately halt the machine, boot it back up, and attempt to sha256sum the file and see if it matches.