If I type:
df -h
It shows me 12G used.
But If I use this command:
du -h -x / | sort -hr >> /home/log_size.txt
This will give me:
If I sum /usr + /var + /root, this won't give me about 12G used... So where can I find the other files that are used in the 12G?
I found the solution myself.
Firstly type this command:
lsof -n | grep deleted
Are you getting any output? If you are, then find what program uses those open files and restart the related services.
In fact find processes that have used "deleted files", then restart all processes, in my case it was nginx.