Error: error downloading ISO: download not supported for scheme 'smb' (Packer)

Error: error downloading ISO: [download not supported for scheme 'smb'] (Packer)

TL;DR

Packer cannot download over SMB. Copy the ISO to a local path or serve it over HTTP(S), then point iso_url there.

The error

==> hyperv-iso: Trying smb://share\up\pub\Conf\2016_64Bits.ISO?checksum=sha256%3A...
==> hyperv-iso: Download failed download not supported for scheme 'smb'
==> hyperv-iso: error downloading ISO: [download not supported for scheme 'smb']
Build 'hyperv-iso' errored: error downloading ISO: [download not supported for scheme 'smb']

Fix it

1. Copy the ISO off the share to the build machine (or a file server you control).

• Success check: the ISO exists at a local or HTTP(S) path.

1. Point iso_url at the new location: a file:// path, an http(s):// URL, or a plain local path.

• Success check: no smb:// anywhere in the config.

1. Keep the iso_checksum so the copy is verified.

• Success check: packer validate passes.

1. Re-run packer build.

• Success check: Retrieving ISO succeeds.

When to use this

You hit this with iso_url pointing at an SMB/UNC share, typically with hyperv-iso on Windows build hosts.

When NOT to use this

Do not use this for HTTP download failures (use the checksum/download troubleshooting) or for checksum mismatches.

Compatibility

Packer 1.x, go-getter download schemes. SMB was never supported.

Variants

• download not supported for scheme '[other]' for any non-supported scheme
• UNC paths (a UNC server/share path) auto-converted to smb:// and failing the same way

Root cause

Packer downloads via go-getter, which supports http/https, file, and a few others, but not SMB. UNC paths get rewritten to smb:// and rejected.

Edge cases

• Mounting the share to a drive letter and using the mounted path works, since Packer then sees a local file.
• Large ISOs over HTTP are fine; the checksum still guards integrity.