How to Fix an Ubuntu Live USB That Won’t Boot

An Ubuntu live USB that will not boot usually fails at one of two points: the computer does not detect the drive, or Ubuntu starts and then shows a black screen or freezes. If the USB is missing from the boot menu, verify and rewrite the ISO. If Ubuntu reaches its menu but the display fails, try a safe-graphics entry if offered or boot once with nomodeset.

Use the one-time boot menu first. Rewriting erases the USB, so back up its files; the other steps below do not change your installed system.

Check and recreate the Ubuntu USB

A bootable USB must be written from the ISO; copying the ISO file is not enough. Download it from Ubuntu’s official download page. If the download might be incomplete, compare its SHA-256 checksum with Ubuntu’s published value using its verification instructions.

Use a USB drive with at least 8 GB and an imaging tool for your computer: Disks or Startup Disk Creator on Ubuntu, Rufus on Windows, or balenaEtcher on macOS. Select the ISO as the source and USB as the destination. Check the drive label and capacity carefully because writing erases that device. Wait for completion and eject it safely.

If Rufus made a USB that will not boot on a modern Windows PC, Ubuntu recommends GPT with “UEFI (non CSM)” as the target system. Keep the other defaults. Try a direct USB port without a hub or a different stick if it remains undetected. See the official guide for platform-specific steps.

Select the USB from the computer’s boot menu

Restart with the USB connected and tap the one-time boot-menu key. F12 is common on PCs; Esc, F2, or F10 are other possibilities. Check the startup prompt or manual because the key varies by model.

Select the USB entry. On a UEFI system, choose its UEFI entry when available. Use the one-time picker instead of changing the persistent boot order. If the computer returns to your usual OS, retry the menu or recreate the drive. When the Ubuntu installer starts, choose Try Ubuntu to preview the live desktop rather than installing. The official guide shows the current boot process.

Use safe graphics or add nomodeset

If Ubuntu’s menu appears but the screen goes black or startup freezes, try an entry labeled Ubuntu (safe graphics) if present. Its name and availability vary by release and hardware.

If there is no safe-graphics entry, or it does not help, test nomodeset for one boot. At GRUB, highlight the try/install entry and press E. Find the line beginning with linux; add nomodeset before ---, or at the line’s end if the marker is absent. Keep the other parameters. Press Ctrl+X to boot; some GRUB menus indicate F10 instead.

nomodeset stops kernel display-mode changes for this startup. It is a testing fallback and can leave a basic resolution without graphics acceleration. The edit lasts only for this boot; restart normally if it does not help. See the Linux kernel parameter documentation.

If Ubuntu still will not start

After choosing Ubuntu, give a slower flash drive a few minutes to load. If startup repeatedly stops at the same point, note the last message on screen before testing another port, drive, or graphics option.

• No USB entry appears: Reseat the drive, try another port or flash drive, and rewrite the ISO with a supported imaging tool.
• The usual operating system loads: Reopen the boot menu and choose the USB entry. With Rufus, check the GPT and UEFI (non CSM) settings described above.
• Ubuntu’s menu appears, then hangs: Try safe graphics if offered, then test nomodeset. Disconnect other external devices while troubleshooting.
• An error appears: Record its exact text, Ubuntu release, computer model, and graphics hardware.

If none of these checks works, verify the ISO again and test the stick on another computer if possible. If it boots there, investigate the original computer’s firmware or graphics compatibility; if not, check the ISO and USB drive.