Which directories should I backup in Ubuntu 10.04, so that I can keep safe my configurations, apps and Ubuntu necessary files?
Your "/home" and "/etc/apt" folders. Backing up these two should be enough. Your home folder hosts the config. files of all your apps and the apt folder contains all the repository and 'gpg key' information. Backing up and restoring these will ensure that you won't have to add all the additional repos/PPAs or configure apps everytime you make a fresh install. As for backing up your apps, I'd suggest you use the 'mint backup manager' to make a backup list of your installed apps. Or as Richard mentioned above, you'll have to backup the bin,var,usr folders as well, which I personally don't advice.
Sorry if my advice is too Retro for you, firevas. I am a BSD Unix guy myself, not much for new-school Linux...
First up, you didn't understand me the way I'd want you to! :D You may have been offended by the last sentence of my post, so let me make things clear first. I 'personally don't advice' the backing up of those folders, 'TO THE OP'. Whatever you've posted is absolutely correct, I don't deny that. But restoring the bin, var, and usr folders "might" give rise to unexpected consequences for the OP, not you & me, for example. Once go through the first sentence of your post. It was in the same context. Hope you got me now. No offence meant. :)
And sorry I didn't know expressing my 'personal' opinion might offend some one, even if I didn't mean it.
No offense was take, No worries. I tend to forget how complex Unix can be.
So does backing up "/home" & "/etc/apt", plus using Mint for the list of installed apps also cover us for any packages we install using Synaptic package manager, or should e include some other folder (maybe one Richard mentioned) to avoid having to go through these dependencies again?
I had an experience where I spent a lot of time getting my IDE all decked out, but I pushed it too far & filled my SSD (only 4GB) & messed up my system. Want to keep snapshots on my external 16GB usb-drive to avoid a re-occurrence of this.
Yup. It should. What the Mint backup tool basically does is, it makes a list of all your installed apps with the dependencies. So when you want to restore the installation, you can simply click the "restore software selection" option. This will download all the files afresh from the internet and install them. If you don't delete your apt cache, you can backup the var/cache directory as well to avoid downloading again (if there is a new version of an app released at that time, it will be downloaded, nevertheless), as mentioned by Richard. But basically, we should look to keep the backup as minimal as possible.
I would probably just backup the Home folder. But to answer your question, The bin,var,usr and home folders. Word of advice, There are commands that will wipe the file system and all mounted drives. It would be wise to backup the folders to a external that will not stay connected to the computer.