I've recently got an HP laptop and had what I now consider "usual" woes in getting it set up with Linux. I wanted to dual boot to be able to test some "real" Windows software, though I'm beginning to wonder about the sanity of that. In any event, I got Linux Mint 20.2 well established and the machine was running nicely, but I did a quick Windows boot to see if there were security updates (I'm using Defender, despite McAfee's insistence I ante up money). There were, and some others that decided to take a while. Then when one of the many Windows reboots while installing updates went on I got something like "Error 3F0: no OS. Please install an operating system". After some blue air, I got out my install USB and ran boot repair. This got me back my Grub bootup. However, next Windoze boot and ... same thing. Pretty soon I decided to put the bootrepair.iso on a Ventoy disk, which is not a bad idea as a general safety measure. Scott told me about rEFInd from Rod Smith. That is interesting too, and I was able to put its iso file on a 128 MB very old USB. It lets me reboot too, but really I'd like not to have to plug in USBs all the time. The rEFInd pages gave some good info about "boot coup" incidents like this. See https://www.rodsbooks.com/refind/bootcoup.html#refind-mkdefault I looked into the Windows ones. The suggested fix is launch windows e.g., with rEFInd usb, then open CMD.exe as Administrator and type bcdedit /set "{bootmgr}" path \EFI\refind\refind_x64.efi However, I don't really want to boot with rEFInd all the time, mostly because I am more familiar with odl-fashioned grub menu. So in Linux I mounted my EFI partition by sudo fdisk -l to identify the dev name (in my case nvme0n1p1) and then sudo mkdir /mnt/efi sudo mount /dev/nvme0n1p1 /mnt/efi and then I looked in the ubuntu directory and found three efi files: grubx64.efi shimx64.efi mmx64.efi I'm guessing mmx64 is maybe a memory test. Some net postings say shimx64.efi is used if Secure Boot enabled (not on my machine) and grubx64.efi should be the grub one. So I entered bcdedit /set "{bootmgr}" path \EFI\ubuntu\grubx64.efi Several win and lin boots seem to be OK. No more "please install an OS". As an "as and when only" practitioner of fixes like this, I appreciated Smith's rEFInd pages. Not a light read, but he knows his stuff. John Nash To unsubscribe send a blank message to linux+unsubscribe [ at ] linux-ottawa [ dot ] org To get help send a blank message to linux+help [ at ] linux-ottawa [ dot ] org To visit the archives: https://lists.linux-ottawa.org