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Rufus is a small Windows utility that turns an ISO image into bootable USB installation media. It does not merely copy the ISO. It rewrites the selected USB’s partitions and files so the computer firmware can start from it.
Download Rufus from its official site
Open rufus.ie and use a current stable Windows build. The page lists Standard and Portable executables. Either can perform this task. The portable filename is clearly labeled; the important safety point is that the file came from the official site. This lesson does not hardcode a Rufus version because stable releases change.
Run Rufus. Windows may ask for administrator permission because writing a bootable device requires low-level access. Confirm only after checking that the application is Rufus from the source you selected.
Identify the exact target USB
Insert the USB flash drive. In Rufus, read the Device field. Compare:
- Manufacturer or model name when shown.
- Total capacity. Windows and Rufus may show a slightly smaller usable number than the number printed on the package.
- Whether unplugging that USB makes the entry disappear, if you remain uncertain.
Do not select a device merely because it has a familiar drive letter. Do not proceed if Rufus lists an external backup disk and you cannot tell the devices apart.
Select the Ubuntu ISO
Beside Boot selection, choose SELECT. If the control currently says DOWNLOAD, open its small menu and change it to SELECT first. SELECT means you already have the official ISO and are choosing it from the computer.
Open the Downloads folder and choose the completed ubuntu-26.04-desktop-amd64.iso file from Lesson 1.2. Rufus reads it and updates several fields.
Check the screen from top to bottom:
- Device: the exact USB that may be erased.
- Boot selection: the Ubuntu Desktop ISO.
- Partition scheme and Target system: keep the values Rufus selected for the image on the first attempt.
- Volume label: a human-readable USB label; the image may supply it.
- File system and Cluster size: keep the selected defaults.
Canonical’s current guide says most Rufus options are safe to leave at their defaults. It documents GPT with UEFI (non CSM) as a fallback when a modern computer already failed to boot the default result. It is not a setting every beginner must force before trying the normal result.
Start the write and read every prompt
Select START. Rufus may show several dialogs in this order.
ISOHybrid image detected
An ISOHybrid image can be used as an optical-disc image and as the source for USB media. Keep Write in ISO Image mode selected, as Canonical’s current USB guide directs, and continue.
Additional files are required
Rufus may need to download a small boot component that matches the image. If this prompt appears while using the official Rufus application and official Ubuntu ISO, select Yes. A failure here usually means the network request failed; do not substitute a file from an unknown site.
Data-destruction warning
This is the last useful pause before Rufus erases the selected USB.
Final USB check before OK
- The Device field matches the USB’s brand or model.
- The displayed capacity matches that USB, allowing for normal size rounding.
- The USB contains no file that exists nowhere else.
- The Boot selection is the official Ubuntu Desktop ISO.
- No external backup disk is being mistaken for the target.
Select OK only when every check is true. Rufus may remove more than one existing partition from that USB. That is expected for the selected target and disastrous for the wrong target.
Wait for READY and eject safely
Do not remove the USB while the progress bar is moving. When writing finishes, the status area reads READY. Select CLOSE, then use Windows Eject for the USB before removing it.
Windows may think the USB looks unusual
After writing, Windows might show only one small partition, report less visible capacity, or ask to format a partition it does not understand. Do not format it. Ubuntu installation media can contain a layout Windows does not present like an ordinary storage drive.
Cancel any format prompt. Safely eject the device. After the installation, the USB can be returned to ordinary storage using a deliberate repartition or format operation—but only after you no longer need it as installation media.
Common mistakes and recovery
The wrong Device was selected but START was not confirmed. Stop, close the dialog, and correct Device. No write has occurred yet.
The wrong USB was erased. Stop using it immediately. Do not copy new files onto it. Recovery may require specialist tools and is not guaranteed; restore from the backup if one exists.
The ISO was copied onto the USB before Rufus. That does not matter once the correct Rufus write is completed because Rufus replaces the USB layout.
Rufus fails before READY. Save the exact error, verify the ISO, try a direct USB port, and recreate the media. Lesson 2.3 provides a symptom-led checklist.
Windows asks to format the new USB. Cancel. That request does not prove the write failed.
Practice
Knowledge check
Before selecting START, point to Device and Boot selection and explain the difference: Device is the physical USB that will be erased; Boot selection is the ISO file read from the computer.
What to learn next
Continue to Boot Ubuntu from the USB Drive when Rufus reached READY. If the USB is absent from the boot menu or starts Windows instead, use the safe USB boot checks first.