My Ubuntu 18.04 Computer always boots to the grub> prompt

[CatKiller]

On the "cat /boot/…" command in the terminal, I tried typing the first two letters (i.e. ca) and then I pressed the [Tab] key. I got no results. I then pressed the [Tab] key again. At that point I guess I got my various options. I then typed one of those options (i.e. canberra-gtk-play) and the [Tab] key. Again I got no results.

cat is cat. You want that command. It's the path that you need to establish. I have no idea what canberra is, or why you'd choose to use it now.

To use tab completion, you'd do (as root in this case) cat /bo<Tab>e<Tab>E<Tab>u<Tab>g<Tab>.cfg. That would complete the path, if the file is actually in that place. If any of those Tab-completions don't complete, pressing Tab twice will show you what's available at that point.

To use cd and ls to identify the correct path, you would do

cd /boot
ls

Then, if the output shows "efi" you'd do

cd efi
ls

and so on until you'd identified the grub.cfg that's in your EFI. cd changes directory. ls lists the contents of the directory you're in. cat puts the contents of a file on the screen.

In particular, you keep randomly capitalising Ubuntu in the path in your posts here. Case is important. We need to know if you're putting a typo into the path you're using, or if the file exists but is in a different place, or if the file doesn't exist at all. If the file exists and has the incorrect information in, that's one fix. If the file doesn't exist at all, that's a different one.

Use code tags when you're posting terminal output here. It makes it much easier to read.

However I am not sure how to use the ls command to get my computer to boot to Ubuntu's 18.04 Desktop screen as opposed to the grub prompt (i.e. grub>).

You already know how to make it boot: it can't find the next stage until you tell it where to look. As soon as you do that, it boots fine. This part is telling it the right place to look from the start.

[DZDB]

I got really busy. Now I am coming back to my issue. After oldfred's post, I performed the following actions:

1) I started my computer and it booted to the grub > prompt.

2)

I performed the following commands at the grub prompt>

grub> set root=(hd0,4)
grub> linux /boot/vmlinuz-4.2.0-16-generic root=dev/sda4
grub> initrd /boot/initrd.img-4.2.0-16-generic
grub> boot

This got me to the Ubuntu 18.04 desktop screen.


3) I went into the terminal and I typed the following:

sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair


The above commands enabled me to successfully install the Boot Repair application.


4) I then launched Boot-Repair by typing (without the quotes) "boot-repair" in the terminal.

5) I then clicked on "Recommended repair (repairs most frequent problems)".

6) This performed a scanning action. I then received the following error message:

"Please use this software in a live-session (live-CD or live-USB). This will enable this feature. Operation Aborted."


Obvioulsy I am a beginner. I do not know what it means by "using this software in a live-session (I would use live-USB)".


Can someone please help me?

[oldfred]

Some functions can only be done on unmounted systems, so you can use the Ubuntu live installer, your flash drive or DVD in live mode and add Boot-Repair to it.
You can run the report from your installed system.

you can from your system try just the re-install of grub.
sudo grub-install /dev/sda
sudo update-grub

If UEFI entries need to be updated, there are mulitple other grub install commands.

[DZDB]

SOLVED

I solved my problem by doing a reinstall.

During the installation process, when I got to the "Installation type" screen, I chose the following option:

Erase disk and Install Ubuntu 18.04
Warning: This will delete all your programs, documents, photos, music and other files in all operating systems.

Before I was choosing an option that read as follows (this may not be verbatim):
Erase Ubuntu 18.04 and reinstall Ubuntu 18.04


Please note that I am a newby. So I could never understand the suggestions to adjust the commands in the root directory. For a newby like me, it was best to just wipe out the hard disk and start clean. This was actually my mom's computer. The only thing she really needs is a browser so that she can surf the internet, watch YouTube videos and read her emails. Therefore erasing the disk and reinstalling Ubuntu 18.04 was not a very time consuming process.

I want to give many thanks to everyone who tried to assist me.