Error: no checksum found in file: URL (Packer iso_checksum)

Error: no checksum found in: ... in "file:..." (Packer iso_checksum)

TL;DR

The checksum file is not in a format Packer's parser understands (PGP-signed, commented, or header lines). Download the file, extract the raw [sha] [filename] line, and use sha256:[hash] directly instead of file:.

The error

Error: 1 error(s) occurred:

* no checksum found in: http://channels.nixos.org/nixos-21.11/latest-nixos-minimal-x86_64-linux.iso.sha256 in "file:http://channels.nixos.org/nixos-21.11/latest-nixos-minimal-x86_64-linux.iso.sha256"

Fix it

1. Download the checksum file and inspect it: look for -----BEGIN PGP SIGNED MESSAGE-----, # comments, or SHA256 (...) BSD-style lines.

• Success check: you see why the parser choked.

1. Extract the GNU-style line ([hash] [filename]) for your ISO. If the file is PGP-signed, strip the signature armor first.

• Success check: you have a bare hex hash.

1. Set iso_checksum = "sha256:[hash]" (or sha1:, sha512:, md5: to match) instead of file:.

• Success check: packer validate passes.

1. Re-run packer build.

• Success check: the ISO verifies and the build proceeds.

When to use this

You hit this at packer validate with iso_checksum = "file:[url]" where the remote file is PGP-signed or otherwise non-GNU.

When NOT to use this

Do not use this for Error downloading checksum file (network failure fetching the file) or for hash mismatches (wrong hash, right format).

Compatibility

Packer 1.x, go-getter checksum parsing. Affects Red Hat-family mirrors especially.

Variants

• no checksum found in: naming Fedora/CentOS/RHEL CHECKSUM files
• BSD-style SHA256 (file) = hash lines (four words; sometimes parsed, sometimes not)

Root cause

Go-getter's checksum parser only handles lines with exactly two (GNU), four (BSD), or zero words. PGP armor, comments, and Hash: headers produce lines it cannot parse, so it reports no checksum found.

Edge cases

• Some mirrors serve different formats per release. Re-check the file format when you bump versions.
• none disables verification entirely; acceptable for trusted local ISOs, not for downloads.