I want to copy everything in root / to my external hard disk before I upgrade my OS so I'll have everything just in case something goes wrong. Is the following the most appropriate command for it?
username@machine:/$ sudo cp -r . /media/username/TOSHIBA EXT/root_copy/
To add to what P.P has said, you don't really want to copy every directory. I use tar to backup everything that I need, and "exclude" the directories I don't need. The command basically goes tar (options) BACKUP-FILENAME TARGET. If you run the following command it should do the trick.
sudo tar -cvpzf /media/username/TOSHIBA EXT/root_copy/root-copy.tar.gz --exclude='/mnt' --exclude='/run' --exclude='/proc' --exclude='/sys' --exclude='/media' --exclude='/dev' --exclude='/lost+found' --exclude='/tmp' --exclude='/boot' --exclude=".*lost+found" / 2> /root/tar-errors.txt
I know it looks like a lot, but tar is going to create a backup at /media/username/TOSHIBA /EXT/root_copy/. The file name is root-copy.tar.gz. It will exclude each of the directories that I have mentioned with --exclude, and lastly it will dump any errors that occur in a file named /root/tar-errors.txt.
Another benefit to using tar this way, is that the backup file will be a "zipped tarball". It's essentially a compressed archive so you will save space on your external drive.
I am sure there are more simple ways of doing this but I have always used this method to backup my systems.
