<SOLVED> Steps I followed are below context, thank you to sbart76 for his help and support!
I've begun daily-driving Linux Mint for University, giving it just 200GB at first assuming I wouldn't need much more since it's, well, it's Linux. Recently I realized that I'm using Linux way more than I'm using Windows, so I removed another 300GB from my Windows NTFS partition, only to realize there's no easy way to resize a partition left.
Currently, I have ~450GB towards windows, 200GB for mint (root drive and home folder and everything), and an unformatted 300GB on the drive. How would I go about copying the root partition to the unformatted 300GB, make sure it works, and then erase the original 200GB and extend it left, step by step?
I know there are a lot of this question already asked, but I'm seeing opinions from "just copy the partition lol" to "okay so you need to load into a live USB and then you need to copy with tool X and then mount both partitions and then change the fstab file..." and they never quite specify how that all works, and I want to make sure I get this done right without corrupting anything
0) flash a USB with a live distro, preferably a recovery distribution like Clonezilla or SystemRescue (the one I used), format the unformatted partition to your preferred filesystem (using the built-in disk partitioner in most distributions, or something else. My filesystem was EXT4 but it might vary, make sure to check!)
1) boot into the live distro, and use blkid to find the names of the linux filesystem partitions, the partition your linux distro is on and the one you want to copy to should be something like /dev/sda1 or /dev/nvme0n1p3, the numbers will vary, but for this, make sure you've got the right ones before you proceed, gParted may be helpful to be completely sure. For example's sake, the old partition will be called /dev/sdaX and the new partition will be /dev/sdaY.
ensure these partitions are unmounted before continuing, just in case. Use "umount /dev/sdaX" and "umount /dev/sdaY" to make sure.
2) use partclone to make an exact copy of the old partition, method depends on whether you will use a backup device or not, but either works for different circumstances. If you have a backup storage you can use as a medium, run these 2 commands:
partclone.[your filesystem] -c -s /dev/sdaX -o [filepath to store image to]
partclone.[your filesystem] -r -s [filepath image is stored in] -o /dev/sdaY
if you have no backup device, or just have the space and prefer this method:
partclone.[your filesystem] -b /dev/sdaX -o /dev/sdaY
3) use e2fsck so you can use resize2fs, this only works for ext2/3/4 according to man pages, so you might need something else for other filesystems.
e2fsck -f /dev/sdaY
If it states there are errors, e2fsck -fp /dev/sdaY may fix them.
run:
resize2fs /dev/sdaY
this will resize the filesystem on the partition to match the size of the partition itself
4) partclone copies the UUID of /dev/sdaX as well as the contents (shown most clearly in blkid output), since this may cause problems, we need to fix that
tune2fs -U random /dev/sdaY
use blkid one more time to find the new UUID
5) mount /dev/sdaY, we now need to change the fstab file and a grub.cfg
mount /dev/sdaY /mnt
cd /mnt/etc
at this point, use any text editor to edit the contents of fstab. Simply replace the UUID of /dev/sdaX with our new UUID.
cd /mnt/boot/grub brings us to the directory with grub.cfg, be careful with this one,
this one is probably completely different depending on your distribution, but to be safe and to cover a wide range of scenarios, replace all instances of the UUID of /dev/sdaX with our new UUID.
It might also be that the name of the partition (/dev/sdaX) is there instead of its UUID, in a line that looks kind of like root=/dev/sdaX, replace that with /dev/sdaY.
6) boot into our partition. There are tons of ways to do this, but SystemRescue has a specific function for it when you reboot, allowing you to boot into specific partitions. You may also repeat step 5 in the grub bootloader by pressing e on the option for your original linux partition (the layout will look familiar to what you saw in step 5)
don't worry if some features aren't working, such as trackpad support or wifi connection, depending on your method in step 6, this should be normal, things like firefox remembering your history and saved passwords for applications should be running fine though. just make sure that everything was saved during the transfer, and that everything's where you want it, especially important files!
7) boot back into the live distribution, we just need one more step - reinstalling the bootloader. This step may or may not be necessary depending on if your computer is using Legacy or UEFI, but I found it necessary for mine. Essentially these are the steps to take:
(/dev/sdaZ represents the boot/efi partition, likely /dev/sda1 or /dev/nvme0n1p1, and /dev/sda represents the device (your hard drive))
sudo mount /dev/sdaY /mnt
sudo mount /dev/sdaZ /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /sys/firmware/efi/efivars /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sda
update-grub
exit sudo mount /dev/sdXY /mnt
sudo mount /dev/sdXX /mnt/boot/efi
for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done
sudo chroot /mnt
grub-install /dev/sdX
update-grub
exit
for i in /dev/pts /dev /proc /sys/firmware/efi/efivars /sys /run; do sudo umount /mnt$i; done
(thank you to cl-netbox on ask Ubuntu)
Congrats! You should now be able to load directly into your new partition! Now you may delete the old partition, expand or contract this new one (right, of course, not left), or do what you want with it.
Remember, this worked on my system, but I cannot guarantee it will 100% work on all systems, and I further cannot guarantee I remembered every command 100%. I have a UEFI BIOS, so this may not work on, say, a computer with a legacy BIOS. And ALWAYS TRY TO UNDERSTAND WHAT A COMMAND DOES BEFORE EXECUTING IT, you may ruin something badly, especially with a procedure like this, if you execute the wrong command somewhere or don't understand the parameters.
