Find a unit
df -H
Find a folder
du -s -h * | sort -nr
Verify if now it's ok:
df -H
If not free space now you need find a process a take PID number
lsof + L1
Kill a process by PID
kill - 9 PID <- this is a PID number
Article for clean old data from server
https://www.getpagespeed.com/server-setup/clear-disk-space-centos