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I have reinstalled Ubuntu on an USB SDD. I have Windows 10 on SDD with my motherboard. The Ubuntu GRUB menu won't show Windows 10.

I have used os-prober. It says "ls: cannot open directory '/boot/efi': Permission denied". I have updated GRUB. I have used Grub Customizer. I also went into BIOS and made sure that Ubuntu is the first SDD.

In the BIOS, I have one EFI Ubuntu SDD. I have regular Ubuntu SDD. The regular Ubuntu SDD won't boot up. it will go straight into Windows 10.

I have used Boot-Repair, It says that "LegacyWindows detected. Please enable BIOS-compatibility/CSM/Legacy mode in your UEFI firmware, and use this software from a live-CD (or live-USB)."

I do not what to do with this issue.

I may use F12 to boot between Ubuntu 20.04 and Windows 10... but GRUB menu is easier.

Any help with this ?

Christian Bearsly Clark
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  • Post link to Summary Report from Boot-Repair. Are all systems installed in UEFI boot mode or all in BIOS boot mode? If not then you can only boot from UEFI boot menu. And then is Windows fast start up off. https://askubuntu.com/questions/1148120/ubuntu-18-0x-not-detecting-windows-ssd-during-installation & https://askubuntu.com/questions/963087/install-dual-boot-ubuntu-with-windows-10-and-raid-on#963100 IF UEFI hardware, better to have Windows in UEFI boot mode, but that is a total reinstall as Windows only boots in UEFI mode from gpt drives and MBR to gpt will erase drive. – oldfred Mar 24 '21 at 14:21
  • Here is the upload from boot-repair. – Christian Bearsly Clark Mar 25 '21 at 03:56
  • Here is the Summary Report from Boot-Repair. A language that I don't understand. In the past installments, Wibndows 10 will appear on GRUB menu but mot this time.

    'https://paste.ubuntu.com/p/j4QZb3NdJB/

     – Christian Bearsly Clark Mar 25 '21 at 04:02
  • You have new UEFI system & Ubuntu installed in UEFI boot mode to sda. But Windows is in BIOS boot mode on NVMe drive. UEFI & BIOS are not compatible. Or grub can only boot other installs in same boot mode. You can continue the way you are, but best is to reinstall Windows in UEFI boot mode. That will erase NVMe drive as Windows will change from 40 year old MBR(msdos) to gpt partitioning. Microsoft has required vendors to install in UEFI/gpt mode since 2012. Or create 1MB unformatted partition on sda and only use Boot-Repairs advanced mode to install grub to sda. You want Windows boot on NVMe. – oldfred Mar 25 '21 at 12:00
  • Oh ! Yeah! Thank You so much. I am All Good with F8 or F12. My Windows 10 drive is my main drive, on my motherboard.

    It’s so weird because I have elementary OS on another SDD USB and the grub menu see Windows 10. I also have Ubuntu DDE on another SDD USB and the grub menu see Windows 10.

    I have installed the same way too..... So Weird.

    Again, Thank You.

     – Christian Bearsly Clark Mar 26 '21 at 00:21

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