How To Use These Powerful Tools?

[abrogard]

I have read testdisk.pdf and haven't found my answer there unfortunately.

I am a bit lost.

My linux mint 2T machine won't boot.

It boots into 'GRUB' and I ctrl-D and get a normal looking login screen. I login. I get a message 'unable to launch... back to default'. I click 'okay'.

I get a black screen. And that's it. Blank, black, end of the world.

I don't know how to use this Gparted Rescue disk thing that I've got on a USB and have booted from and tried to fix things with. It seems to be great/powerful. But I am not sure what things to do first for the best.

What to do?

I will clearly state it as I see it: I need to shrink a main partition on a bootable but unusable linux mint disk and create another so's I can install a fresh instance.

FYI I have messed around a lot.

The 2T has only about 500G of data on it. It is all on one big partition filling the disk.
And there's something wrong somewhere in that data partition. I found. Later.

Reached a stage where I decided best bet was to shrink that partition and then create a new one on the blank space and install a new instance of Mint and hopefully access the old data from there.

I got Gparted on USB and booted from it and run it but Gparted couldn't shrink the partition.
It told me to run e2fsck and I did but it didn't help.

Now I have this system rescue 'disk' (bootable USB) and I've been trying to fix things from it.

I waited 6 hours or something for it to diskcheck and it finished up showing me a list of 20 'partitions' ( not the same as the 'partitions' I usually see of which there's only four on the disk: one big data one ) and I see some data ones there that seem to have my files on them. But messing around trying to actually go into the directories and find individual files and see if they were readable I miskeyed somehow and found myself right back at the beginning and couldn't get back to that partioning page.

I don't want to sit through another 6 hours waiting.

And I've realised maybe I should be employing other options first ?
So I came here.
And read the .pdf
and still am very unsure.

Sorry to be a nuisance but I'd appreciate some direction if I can get some.

[recuperation]

I got Gparted on USB and booted from it and run it but Gparted couldn't shrink the partition.
It told me to run e2fsck and I did but it didn't help.

I will clearly state it as I see it: I need to shrink a main partition on a bootable but unusable linux mint disk and create another so's I can install a fresh instance.

When you have problems with a certain disc the first rule to follow is not to write on it. Trying to shrink a possible defective partition will certainly aggravate your situation even more. Installing a secondary linux on a possibly broken device is a very bad idea.

To rescue data you should either use a pendrive linux or another working linux machine where you install smartmoontools, ddrescue and TestDisk.
The Gparted Rescue CD and the System Rescue CD come with all free tools already included - at least when I checked this in September 2023.
I like the Linuxmint distribution but the disadvantage of using it from a pendrive is that you have to have an internet connection to temporarily install all three tools mentioned above. Using it in persistent mode or from a fixed disc will heal this problem.

FYI I have messed around a lot.

Basically you did not describe specifically what the problems are. "messing around a lot" is not a problem description. A good description would describe how your setup was in terms, what you did to mess up your computer and how the situation is now.

For boot problems I can only give you the generic advice to use the repair functions of your linux distribution. If e2fsck fails you might have more than a boot problem.

[abrogard]

Yes. Thank you for that. Including the criticisms. Especially the criticisms. Very justified. I just didn't think. A bit at my wits end.
Sorted out a bit now. I've got the bad disk mounted on a new mint install I've put up and I've copied all my data off it. Surprised to find less than 100G that I wanted. But there you are.
So I am about ready to wipe the whole thing with a reformat and see if that makes it good.
Just want to be sure I have copied everything I want and then I'll go for it.
And I won't mess with disks before getting my data in future.
New HDD, new Linux, add in the bad disk, get the data. That's what I will do.

Thanks for your help. I appreciate it.

[recuperation]

I forget to mention that you find additional information beyond the manual following these links:

https://www.cgsecurity.org/wiki/TestDisk
https://www.cgsecurity.org/wiki/TestDisk_Step_By_Step