When the root directory is used up, we have to find out which file take up most of the space first, and then we have to confirm if these files are nessesary for the system running, if not, we can delete them mannually to release the space.
Here i have a command to check the size of the files one by one under each directory as the picture below. (for each directory, use the command: du -h --max-depth=1)
Check the directory one by one, then find out which file and directory is very large, which you can delete when you are sure that they are useless, if you are not sure, please get help from R&D.
Here, we also have a common experience to check if the file we find is useless:
With "history" command, we can check if customer ever installed any other software, comparing the name of the files and logs with the installed software, when they are the same, i think we can delete it by ourselves.