If your PC now boots straight into Windows, first check whether your firmware is simply choosing Windows Boot Manager before Ubuntu. Select the Ubuntu boot entry from the computer’s one-time boot menu; if Ubuntu or GRUB starts, change the firmware boot order rather than reinstalling GRUB. If no working Ubuntu entry exists, use Ubuntu live media and repair the bootloader only after confirming whether the installation uses UEFI or legacy BIOS.
First check whether GRUB is missing or just being skipped
A PC that starts Windows without showing GRUB does not necessarily mean Windows erased GRUB. The firmware may still have a working Ubuntu entry but start Windows Boot Manager first. Ubuntu’s recovery guidance describes the scenario of another operating system being installed and Ubuntu no longer appearing at startup; the firmware’s boot choice is an important first distinction.
- Restart the computer and open its one-time boot menu. The key varies by manufacturer; common examples include F12, F11, Esc, or a key shown briefly during startup.
- Look for an entry named Ubuntu, or another entry that corresponds to the Linux installation, and select it.
- If Ubuntu or GRUB loads, open the firmware setup screen and place the working Ubuntu entry ahead of Windows Boot Manager in the boot order. Firmware labels and menus differ by computer.
If the Ubuntu entry is absent or selecting it does not start Ubuntu, continue with recovery media. Do not use a legacy-BIOS repair procedure on a UEFI installation, or the reverse: Ubuntu documents separate UEFI GRUB and legacy grub-pc boot paths in its UEFI documentation.
Choose the recovery path that matches the symptom
| What you see | Likely next step |
|---|---|
| Ubuntu starts from the firmware boot menu, but the PC normally starts Windows | Change firmware boot priority; do not reinstall GRUB. |
| The Ubuntu entry is missing or fails, and GRUB never appears | Boot Ubuntu live media in the same mode—UEFI or legacy—as the installed system, then inspect and repair the boot setup. |
| GRUB appears, but Windows is not listed | Investigate GRUB menu discovery and configuration; this is different from the firmware bypassing GRUB. |
Use Ubuntu live media to diagnose and repair GRUB
If the installed Ubuntu system will not start, boot from Ubuntu installation media or a LiveUSB and choose the live-session option. The live environment gives you a way to inspect the installation without first booting the installed system. Boot it in the same firmware mode used by the installed operating systems, because UEFI and legacy bootloader repairs are not interchangeable.
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Ubuntu’s Boot-Repair guide documents running Boot-Repair from an Ubuntu live session, including cases where GRUB stops appearing after another operating system is installed. The tool can produce a Boot-Info diagnostic summary. Review that summary before attempting an automatic repair; if the diagnosis is unclear, seek experienced help rather than changing advanced options at random. The guide warns that altering advanced settings can make the problem worse.
- Create Ubuntu live media from an Ubuntu image using a USB drive or other supported installation media. The drive is only a way to boot the recovery environment; it does not fix GRUB by itself.
- Use the computer’s one-time boot menu to start the media in the same mode as the installed operating systems. If the firmware offers separate entries for the USB in UEFI and legacy modes, select the matching one.
- Start the live session and follow the Boot-Repair guide to produce and review its diagnostic summary.
- If the diagnosis matches the problem and you understand the proposed action, use the guide’s Recommended Repair option. If it does not match, or you are unsure, stop and get advice before applying repairs.
- Restart and remove the live media when prompted, then check whether the firmware starts Ubuntu/GRUB and whether both operating systems are available.
If GRUB opens but Windows is missing from its menu
When GRUB itself appears, firmware boot priority is no longer the immediate issue. The problem is that the menu does not include Windows. Ubuntu’s GRUB installation guidance explains updating the GRUB menu after installation, but Windows detection behavior and relevant settings can vary by Ubuntu release. Check instructions for the release installed on your PC before running a command or changing a detection setting; do not assume one command is universal.
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Pause before making changes if you cannot identify the UEFI or legacy layout, the diagnostic summary does not clearly match the failure, or repeated repair attempts have not restored startup. Unclear partition layouts or damaged EFI files can make a generic repair risky. Avoid formatting or reinstalling either operating system as a first response if your goal is to preserve the existing installations.
Microsoft’s BCDBoot documentation covers adding a Windows installation to a Windows boot menu; it is not a guide to restoring Ubuntu’s GRUB menu.
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