Okay, this might have been the worst computer mistake I've ever made, but I hope all my data is not lost!!/ I left this G-Drive plugged in as I rebooted my laptop. I'm new to Linux, I have Ubuntu 16.04 since July. By the next moment I looked at my laptop, "it was doing something strange" instead of booting my system normally, and I desperately tried to stop that. I unplugged the external HDD quickly. But ever since this happened, I couldn't get my system boot. Is it lost???
After I try to boot now...It does want me to log in and it does say Ubuntu 16.04 there, and I type in my log-in and password, but all that comes in is-- it stays a black screen with a command line -terminal.. What should I type in there that would bring my system back to work?
I am able to get to GRUB but I don't know what and how should I choose, to get everything back.
I'm terrified that I lost all my stuff over this stupidest mistake...
In the worst case, if it can't be brought back with a special boot setting, is there a way to rescue the data from my laptop's hard drive? I can't imagine it would get erased just by a "wrong boot".

What is a "G-Drive"?
What do you mean by "something strange"? You'll need to be more specific.
From your post, it appears Ubuntu 16.04 is the only OS installed, correct?
Do you see the Grub menu you previously saw when booting?

Having another drive attached on reboot in itself is not expected to produce the results you are reporting as it should still boot whatever the default was in the BIOS unless some change was made.

G-Drive is a 320 GB external hard drive which I used to create backups.
But for some reason, my Ubuntu couldn't access it, when I plugged it in again (after a couple of months not using it), while a Windows computer did with no problems. So I left this HDD plugged in, while rebooting my Ubuntu, and that's what screwed everything up...
When I turn it on: a purple GNU GRUB screen shows up (GNU GRUB version 2.02~beta2-36ubuntu3.14), with 4 choices:
Ubuntu,
Advanced options for Ubuntu,
Memory test (memtest86+)
Memory test (memtest86+, serial console 115200)

If I hit Ubuntu, something starts loading (black screen) with " /dev/sda1 ........
Then among the lines there are a few yellow and red lines showing failed elements (?!), then 2 minutes later this will load:
Ubuntu 16.04.3 LTS amn tty1
amn login:

---
Then I log in, and then the following lines appear and my system is still nowhere...;
/usr/lib/update-notifier/update-motd-fsck-at-reboot: 33: /usr/lib/update-notifier/update-motd-fsck-at-reboot: cannot create /var/lib/update-notifier/fsck-at-reboot: Read-only file system
Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.10.0-40-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage

0 packages can be updated.
0 updates are security updates.

The programs included with the Ubuntu system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. "

........And a few more lines about this, then the last line is like a command line:
amn@amn:~$

I'm typing this on my phone (exact details) so I left off a few more lines about this no warranty stuff.

So I think I did set the external hard drive to be only readable, when I was trying to get my Ubuntu be able to access it (slight change in its mounting settings... According to YouTube tutorials)
But I did not mean to boot my laptop from this HDD... I think that was the mistake that causes the issue now...
I only suspect this and I'm mostly in the dark.. Really appreciate your help!!

This external drive is used for backups of what? Your Ubuntu? You mention this drive is accessible in windows, is this some other machine with windows on it? What filesystem type is on the drive? Do you have windows on the same drive as Ubuntu and if so, which version?

I doubt that. Plugging in an external drive with no OS on it to boot with just backup data with out changing the boot priority in the BIOS won't do that. Illogical.

Do you have any Ubuntu Live DVD/flash drive that you can use to get boot repair? Answering the above questions would be a good first step but boot repair output would be more helpful.

1 members found this post helpful.

so where did you actually install ubuntu to internal hd or external?
how many internal "drives" do you have? how many external?
has it been working earlier, i.e. did you get to a normal ubuntu desktop?
do you think that another version of ubuntu is installed on the external hd (unlikely)?
is the bios maybe set to boot from an external usb hard drive first?

many questions.

when you stopped hyperventilating, pleasetry to give us some detailed & cool-headed answers.
also please keep in mind that many of us do not use windows.

Yancek: thanks a lot for your time and helpful attention again.

The external drive had a backup of all my personal stuff in a folder. (The usual documents, pictures, etc) But for some reason it stopped being accessible on my Ubuntu -- I only have Ubuntu as my OS, nothing else, and it was working fine before this happened. Sorry that I forgot to mention it.

So another computer, with Windows 10 on it, could see what was in this external drive, and mine couldn't. I don't know the filesystem it had... I think I created it just before installing Ubuntu and getting rid of Windows 10, that I had before.
Ah, so that's why it wouldn't work... I forgot the fact that I made the backup when I still had Windows, in July.

"Do you have any Ubuntu Live DVD/flash drive that you can use to get boot repair?"
I did the installation from a flash drive.
Now I took the laptop in the meantime to a repair place and it's there, so from this point I just hope the issue is truly not threatening my data stored in the internal hard drive and just a boot issue and I pray that it's all solved already...

Ondoho:
Ubuntu installed as my only operating system, on internal hd. I had Windows 10 before, couldn't stand it, wiped it out and put on an Ubuntu. No dual boot or any other complications.
There was no other version of Ubuntu installed on the external drive, just backup data.

"is the bios maybe set to boot from an external usb hard drive first?"
I dont't know. It may be.

I do not use Windows either anymore, I'm just a newbie to Linux but love it. It worked great since July except a few bugs.

Check your BIOS and verify that the internal is set to first boot priority.

With the external drive plugged in, boot the Ubuntu flash drive you used to install it and when you get to the Desktop, open a terminal and run the following command and post the output:

That's a lower case Letter L in the command. If another computer with windows on it was able to read the disk it likely had a windows filesystem.

Just noticed the above statement. I hope it's not the standard computer repair shop which sees the solution as re-installing windows. Did you explain in detal that you had a Linux system and you wanted to keep it?

1 members found this post helpful.

We were directed to this one ("clickaway") because best buy doesn't deal with Linux, and they do... I'm less worried about reinstalling it than rescuing my data... Now the person who has my laptop just told us that he couldn't just copy and rescue the Main folders from the internal hard drive, but only sub-folder by sub-folder so it would take like 3 hours for him, therefore it will cost like $500.
And that he'd reinstall a different version of Linux. What could be the reason for only being able to transfer my data per sub-folders, not like, let's say, the whole Pictures - folder? You guys think it is possible?
He did seem to understand Linux and said he has it himself, with a virtualbox.

ouch.
if i was you, i'd first attempt this myself, i.e. you boot the machine with some live medium (a usb stick linux live distro nothing special, can be the standard ubuntu .iso etc.).
with this you can look at both internal and external hard drives "from the outside" and copy over (to some additional storage) everything you deem important.

BUT, i'd still try to fix this for a while. the bios thing, maybe.

i just remembered that lenovo yoga has been tricky for some people, with regards to linux. some research might be in order.

1 members found this post helpful.

If you have your external drive back, I would suggest that you plug in the Ubuntu flash drive and attach the external drive and boot Ubuntu from the flash drive.
Once booted to the Desktop in Ubuntu, run the command: sudo parted -l and post the output.

Copying large amounts of data can take a lot of time but it's not like someone has to sit there and watch the process. I don't know why your IT person believes he can only copy in the manner he indicated, doesn't make sense to me. Need more details if you want help.

In your post above (post #3) you indicate there is a message indicating 'read-only filesystem' which probably means a filesystem check is needed.

1 members found this post helpful.

Alright, I got my laptop back from the wicked repair, hopefully nothing got more damaged.
I'm starting to understand... So I need to use the flash drive with the Ubuntu on it, that I used for installing it in the past, and I will be able to get into a portable mode, and save my data onto an external drive?
I'm not sure if I will be able to do this from the same flash drive without changing anything on it? (a bootable Ubuntu 16.04)

And do I need to change the filesystem on the external drive (*I will use another, newer one), in order to use it for this data rescue?

From #8:
"Check your BIOS and verify that the internal is set to first boot priority."
How do I check that?

Which drive are you referring to? The one with your data on it that you are having problems with? If so, no don't change the filesystem unless there is nothing on it you want to keep. Not really sure what you are trying to do now, do you want to copy data from the unbootable internal to another drive?

I believe you can access the BIOS on your Lenovo by tapping the F2 key on boot. You should see a message immediately after booting telling you which key to use to enter setup/BI0S.

Is there a particular reason why you refuse to post the output of the parted -l command as this would give some useful information on your system?

No, I didn't mean the problematic drive- my internal drive with the data I want to save, I meant a "healthy" external drive for transferring my data on it, from ther laptop.

Yes, the reason is that I don't know where to type that command.