New Linux user here, thus please hold your laugh.
Due to users suggestions I removed the previous post and re-wrote a new one correctly
Ubuntu version: Ubuntu 18.04.4 LTS
I installed windows and two Linux distributions on my PC. I use Windows for specific apps, one Linux Ubuntu for other apps and other Ubuntu for internet. The "not booting or working properly linux" Linux few days ago prompted an error: "0 MB disk space left". This day it even no longer booted properly, saying there is no space for that at all so I am writing this post from the "still booting and working properly linux" Ubuntu.
*After more thorough analysis it turned out, that even thou every single OS is installed on a separate partition with enough disk space somehow - as I browsed the partitions - it turns out that one of the Linuxes has been installed inside the folder created for other Linux.
This is the directory that I have found while browsing the system partition of my working system:
/media/$user/(broken-linux partition-uuid)/home/(broken-linux $user)
The /home folder of the "not booting or working properly linux" is available within the disk space of "working linux".
I have no idea how did this happen, but I suspect that this is the "culprit". Do I have to remove both linux distributions, delete partitions and re-install them again properly or there is some way to fix it without so much work? I was suggested running live USB of linux installation and run gparted from there as I could resize any partition from there, but the one that has no space - sda7 - doesn't enable me to increase the size:
The reason you have not been able to resize sda7 is that it is tightly sandwiched between sda4 and sda5. What I would do to increase sda7 is the following:
Good luck.