Ubuntu fails to start as /home partition is full after docker installation

[mahesh]

Hello community,

I recently cannot start my Ubuntu system anymore as my separate /home partition is completely filled up.

What happened?
I tried to install the software ncbi/pgap with a docker container, I used the software docker for the first time. During the installation process, the installation stopped with the message that there was no more disk space available. After I restarted the system I could not boot linux anymore. Initially, I vaguely remember, there was an error message about no disk space. But now, 4 weeks later, the message shown is "[Failed] Failed to start Manage, Install and Generate Color Profile", or "[Failed] Failed to start Modem Manager" or "...Hostname service" or "...Login service", interchangeably, eventually ending up on a black screen with a flashing dash.

What have I tried to solve the problem?
- I started the "Advanced options for Ubuntu" to do an automated clean up. However, this process initially always cancelled due to not enough disk space available. In the meantime (4 weeks later), the program starts, but does not remove any files.
- I booted linux from a live USB stick. This automatically also mounted the linux partitions on my hard disk. There I could see the following partitioning:
o Partition A: 30 GB completely full (that is likely my /home partition)
o Partition B: 119 GB (my swab)
o Partition C: 11 TB, ~7TB available (that should be my root)
o 3,5 TB unallocated
- I tried gparted in order to allocate more disk space from the root to the /home partition. However, I was not able to do that as (as far as I understood) the partition was at the beginning of the disk and the unallocated disk space at the end.
- I searched the /home partition for "docker" files. I found some, but nothing extraordinary large. I also could not delete them as I did not have the permission.
- I did not know which other files I could delete without damaging the system in the /home partition to make more space. The /home folder within this partition, however, seemed to be completely empty.

How can you help me?
- Firstly, I would need to get my linux system back running. Do you have any tips for me?
- Are there any specific locations where docker might have stored the large data that filled up the partition, so that I can remove these?
- In order to avoid this problem in the future; is there any way to tell docker to use the root partition for installation instead of using the /home partition?

I will be very grateful for tips!
Best wishes, Janko