The backup tool in the live disk is not complete. It's tricky to install all the necessary components to get the backup working properly. You could simpler backup your /home folder with the cp command.
You can do this by, first mount your destination backup device (which may already be mounted since it's your /dev/sdb device.
Create a backup area for your destination and perform one of these two commands:
$ sudo cp -pvau ~/ /mnt/backupdir/
In the preceding command the /mnt/backupdir is the backup destination directory where you will be backing up your space. It will create a folder by the your username in the /mnt/backupdir folder.
This space could have been created on a partition off your /dev/sdb drive.
Alternatively you could backup your whole '/home` folder with this command:
$ sudo cp -pvau /home /mnt/backupdir/
This command would result in a folder called /mnt/backupdir/home with your personal home folder under there.
The copy arguments are:
p - preserve ownership and time stamps
v - give a verbose output during the process
a - archive (perform a recursive copy of all files and folders)
u - update files that have changed if they already exist in the destination.
You said you were concerned about during something "radical" which could loose your personal data.
Installing or reinstalling Ubuntu will not touch your /home folder or any other folders that you created on your installed partition unless you specifically elect the format option during the installation process. As long as you don't put a check mark in format your personal data will be preserved.
It's important to always have backups of your important data. But the install process will advise you that your data will be erased and not recoverable if you select to format. Also if you don't checkmark the format option, it'll still advise you which directorys (the system folders) that will be erased and recreated.
If you open timeshift Then click settings and go to the filters tab, you can exclude the music and video folders. The include hidden option backs up your hidden direct (the folders that begin with .) and unless you keep your videos and music in hidden files, you should be fine. If you turn on the include root option, it backs up the /root directory, so if you wanted to back those up, then sure, knock yourself out.
Restoring to existing system just overwrites your current system with the backup. Restoring to an empty partition does exactly what it says.
Best Answer
Many many folders are affected when installing software. For a complete picture see How to understand the Ubuntu file system layout? Directories you will need are /bin/, /sbin/, /usr/, /etc/, /var/ , /lib/, /home/, /opt/ (3rd party software goes to /opt/; might be empty). /boot/ might be needed too depending on what you install.
I would reconsider if I was you. Your approach is pretty Windows oriented. The directories you need are almost all of them. And there are better methods.
There is a method you might like:
/var/cache/apt/archives/holds all the installer files you need if you want to restore your system. If you back that up and re-install Ubuntu you can copy them back to/var/cache/apt/archiveand can use thedpkgcommand to restore them. That would require you to backup that directory and your /home/ (all settings are there). This might be a good option to restore a system with a re-install and after installing a manual update of those packages and a restore of your /home/.If you want to do this a full system backup is the best option. It would stop you from picking directories and the directories you do not nee is marginal at best. You can even automatic this with an rsync backup where the system only copies what got changed. Saves a lot of disk space. Have a look at ...
A full system backup is a good method in case your hardware is going to act up. Think bad sectors, crashes due to hardware failure. Upgrading to a new release that might fail. Or to copy your system over to a new harddisk, or new system. We are talking about some of the bigger problems computers can have or software can cause.
It also guarantees you backup everything. So if there is some obscure directory we know nothing about that you would have liked to see a backup of this makes sure it will be there on the backup.
In case of you wanting to save yourself from yourself a full system backup is overkill. If the main concern is editing files that might go wrong and you effectively kill your system yourself the best approach is to create a backup of the file you want to edit. Let's assume you want to manually edit a file called "test". A simple...
will create a file with the date with seconds include.
This will be more than enough to keep your system from breaking down by your own hands. Normally you can still boot and restore your file but if needed you can also use a live dvd to just copy the file back over the original file with...
are restore your system to a working one.
If you keep forgetting to make backups: Gedit is capable of making automated backups (it adds "~" at the end of the file before you save the changed one).