RescueUSB
Check an ISO will boot your machine before you spend 20 minutes writing it.
Free right now — no account, no card
Preview
1 interface design, then a screenshot of it running. Drag, scroll or use the arrows.
Free while we’re in preview
Get RescueUSB
Check an ISO will boot your machine before you spend 20 minutes writing it.
The Mac button is for Apple Silicon. On an older Intel Mac, get this one instead.
One file, both ways. Double-click it for the window. Run the same file from a command prompt with arguments and it behaves as the command-line tool, because the engine is inside it. Nothing else to download and nothing to keep beside it.
Early preview. The window has been built and run, but not yet on a real Windows PC or Mac, so expect rough edges. The engine underneath it is fully tested.
- One file — no installer
- Runs on your machine, offline
- Source code published below
Free while in preview. It isn’t signed yet, so Windows or macOS will ask you to confirm the first time you open it. At launch, RescueUSB is included in every plan along with the rest of the range.
Three questions, asked beforehand
Did the download arrive intact? Is this image bootable, and on which firmware? Will it fit the stick? verify, boot and preflight answer those by reading the image’s raw bytes.
verify streams the file once for SHA-256, and MD5 when asked, then compares against what the publisher announced. It understands the SHA256SUMS format Linux distributions publish and the BSD tagged form. SHA-1 and SHA-512 lines are reported as skipped rather than quietly ignored.
boot is the heart of it: the El Torito boot record at sector 17, the catalog it points at, the validation entry whose 16-bit checksum is genuinely recomputed instead of printed, the default entry, and every section that follows. The EFI entry under a platform 0xEF section header decides whether a UEFI machine will boot the image, and it’s the part most inspection tools stop short of.
It never writes anything
Not to a USB stick, not to any device, not to the image itself. Raw-device writing needs privileged access and getting it wrong destroys the wrong disk, so it’s deliberately absent. Use your platform’s own writer for that step.
It doesn’t check GPG signatures either. Matching a hash from a checksum file an attacker also replaced proves nothing.
Reading on the job itself
- How to check an ISO before you write it to a USB stick Check the hash against the one the publisher printed, then look inside the image for the boot structures — ...
Advanced & technical details Command-line builds, source code, checksums and a recorded session — for developers and IT teams
A working prototype of the pre-flight bootability verifier: it checks a downloaded image against its published checksum, then parses the El Torito boot catalog — the structure that actually makes an ISO bootable — validating the catalog's own 16-bit checksum and reporting whether the image boots on legacy BIOS, UEFI, both, or not at all. Verified against real genisoimage output: it caught a one-byte corruption in the boot catalog that isoinfo reports as perfectly healthy. Read-only; writing to USB devices needs privileged raw-device access and is on the roadmap.
Naming status
Working name only — brand verdict **CAUTION** (Medium). Collision: Rescue USB. Prefer more distinctive branding.
What it draws on
Existing paid software whose best ideas shaped this program: PowerISO, DAEMON Tools Ultra, BurnAware Professional, WinToUSB Professional.
Command line
There is nothing extra to install. The program you download is the command-line tool as well: give it arguments instead of double-clicking it and it runs as one, with its output on your terminal. The standalone builds below are the same engine on its own, for machines where you would rather not ship a window at all.
rescueusb - pre-flight bootability verifier for ISO disc images
Answers three questions before you write an image to a USB stick: did the
download arrive intact, is the image actually bootable, and on which firmware.
rescueusb only ever reads: it never writes to a device and never modifies an
image.
USAGE
rescueusb <command> [options]
COMMANDS
verify <file.iso> [--sha256 H] [--md5 H] [--checksum-file F] [--json]
Hash the image and compare against published checksums.
boot <file.iso> [--json]
Decode the El Torito boot record and boot catalog, verify the
catalog's 16-bit validation checksum, and report BIOS/UEFI
bootability.
preflight <file.iso> [--target-size N] [--json]
Combined readiness report: size, sector alignment, ISO 9660
volume, boot catalog, firmware support, and whether the image
fits the destination device.
help Show this help.
OPTIONS
--sha256 HASH Expected SHA-256 hash (64 hex characters)
--md5 HASH Expected MD5 hash (32 hex characters)
--checksum-file FILE Published checksum file: "<hash> <filename>" lines,
or the BSD "SHA256 (file) = hash" form
--target-size N Capacity of the destination device, in bytes; a
suffix such as 8G, 16GB or 512MiB is also accepted
--json Emit machine-readable JSON
-h, --help Show this help
EXIT STATUS
0 the answer is yes: checksums match, the image boots, all checks pass
1 the command could not be carried out (missing file, unreadable image)
2 the report is complete but the answer is no: a checksum mismatched, the
image will not boot, or a pre-flight check failed
NOTES
...Recorded from the shipped binary, not written by hand.
Source
Every file the program is built from:
console.go · console_test.go · guided.go · main.go
SHA-256 checksums · build instructions & scope notes · full build plan