I have a new single boot PC. I did a fresh install of Ubuntu 20.04.3 LTS from a USB (this is not a dual boot machine). I encountered issues and so have reinstalled several times and still cannot get to boot into Ubuntu.

My BIOS lists the following boot options and this is what happens when I try them each separately:

  • "ubuntu" - takes me to a screen with a grub> prompt

  • "UEFI OS" - takes me to a screen with a grub> prompt

  • "ubuntu (P4: Samsung SSD 870 EVO 1TB)" - takes me to a screen which says "Invalid signature detected. Check Secure Boot Policy in Setup"

  • "UEFI OS (P4: Samsung SSD 870 EVO 1TB)" - takes me to a screen with a grub> prompt

  • "UEFI: Samsung SSD 870 EVO 1TB" - takes me to a screen with a grub> prompt

  • "ubuntu (P4: Samsung SSD 870 EVO 1TB)" - identical to the third option above but this one takes me to a grub> prompt

Disk layout

enter image description here

I have clearly royally shafted my hard-disk and yes you guessed it I really do not know what I am doing. I don't care about anything on the disk, it is empty anyway so happy with any "nuclear" suggestions. Just want to get Ubuntu up and running.

  • Have you updated UEFI firmware & SSD firmware? (May not be related to specific issue.) Did you install in UEFI boot mode every time? Its as if your are booting one grub (like BIOS) but install is now UEFI or vice-versa. And invalid signature often related to UEFI Secure Boot, it that off? Please copy & paste the pastebin link to the Bootinfo summary report ( do not post report), do not run the auto fix till reviewed.Lets see details, use ppa version with your USB installer (2nd option) or any working install, not Boot-Repair ISO help.ubuntu.com/community/Boot-Repair
    – oldfred
    Commented Jan 8, 2022 at 3:48
  • @oldfred thanks so much for offering to help. I may well have tried to update the firmware, if by that you mean the option that the Ubuntu install offers to install 3rd Party Software. It asked me for a password that I would need to use later. However I never used it later on reboot, I think I must have missed the point in the reboot that offered me the opportunity to complete that operations - was it where I got a DOS style menu screen asking me for a MOK? Here is my pastebin link paste.ubuntu.com/p/GYmZxP8PNB Commented Jan 8, 2022 at 9:07
  • @oldfred also don't know if it helps, but here is a screenshot of my disks taken whilst in the Live Ubuntu session booted from my USB. !Drives. Commented Jan 8, 2022 at 9:26
  • Welcome, in the installation process do you select "Erase disk and install Ubuntu"? There are apparently 2 EFI partitions, there should be just 1. What version of Ubuntu are you using? Commented Jan 8, 2022 at 10:46
  • @schrodigerscatcuriosity yeah I was sure I chose erase disk. Ubuntu version is 20.04.3 LTS. Commented Jan 8, 2022 at 11:59

2 Answers 2


I used gparted to create a new parition table, reinstalled Ubuntu and all seems well now. Thank @oldfred, @hermann and @schrodigerscatcuriosity.


As you are seeing a grub prompt and not grub rescue, I assume GRUB itself is fine, but cannot access the configuration. You should be able to use the grub shell to gain some information.

Typing ls and hitting tab, grub should give you a list of storage devices (hd0) (hd1). If no storage devices are shown, then the UEFI firmware does something weird and is incompatible with grub.

You can also load modules providing additional features into grub, e.g. by entering insmod part_gpt. Now tab completion on ls should also provide information about GPT partitions (hd0,gpt1) (hd0,gpt2) and their file-systems.

After loading insmod ext2, you should be able to access your root partition. /boot/grub/grub.cfg should exist on one of the file-systems. Tab completion will help you look for it. You can load it via configfile (hdx,gpty)/boot/grub/grub.cfg. Then grub should switch to menu mode and give you access to the Ubuntu installation.

  • typing ls and hitting tab just gives me a list of commands. Typing ls and hitting enter gives me (porc) (hd0) (hd0,msdos5) (hd0,msdos2) (hd0,msdos1). After installing part_gpt and ext2 ls (hd0,msdos5)/ gives lost+found/ boot/ swapfile etc/ media/ var/ bin dev/ home/ lib lib32 lib64 limx32 mnt/ opt/ proc/ root/ run/ sbin snap/ srv/ sys/ tmp/ usr/ cdrom/. Commented Jan 8, 2022 at 11:45
  • configfile (hd0,msdos5)/boot/grub/grub.cfg briefly gave me an error about a missing font file and then rebooted into a graphical login screen. So wow and thank you. But restarting takes me back to the grub> prompt. Is there a way to fix this permanently @Herman? Commented Jan 8, 2022 at 11:52
  • Since the partitions are listed as msdos I assume your drive is partitioned with MBR (for legacy BIOS / CSM boot), not with GPT (needed for UEFI boot). Yet your UEFI seems to load GRUB just fine. I am surprised this even works. Do you have more than one drive in your system?
    – Hermann
    Commented Jan 8, 2022 at 12:04
  • No just one drive. I have to say that as part of trying to get this system to work (prior to coming to this forum and therefore really just flailing around in the dark) in between reinstall I messed around with "BIOS" UEFI settings so could have triggered all sorts of weird behaviour in the Ubuntu installer. Is there anyway I can just go back to a blank slate and start again? Commented Jan 8, 2022 at 12:23
  • @fponknevets you can use efibootmgr from a live usb to handle the UEFI entries in the BIOS. Commented Jan 8, 2022 at 12:28

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