Warning
Use a sudo-capable account, keep shell history for audit, and back up critical paths before changing boot, SSH, or package state.
What you will achieve
Find what ate your disk — and free space without deleting the wrong database.
1) Identify full filesystem and inode exhaustion
df -h
df -i2) Find biggest directories quickly
sudo du -xhd1 / | sort -h3) Reclaim safe space
sudo journalctl --vacuum-time=7d
sudo apt clean
sudo docker system prune -af