Do I need to back up my files from Windows before installing Ubuntu dual boot?

Question

I would of course assume the answer is no, however I wanted to confirm this is so, in case there could be a chance that I might lose some files on accident.

Answer 1

Although installing Ubuntu alongside Windows in a dual-boot configuration shouldn't, and typically doesn't, cause any data loss, it is nonetheless a very good idea for you to have a backup, at least of your documents and any other important files, that is, files you would be upset if you lost.

I'd say the three chief reasons for this are that:

1. There's a small risk of data loss when resizing and moving partitions and editing partition tables. This was bigger decades ago, but it's not zero today. In particular, it's likely to occur if the computer suddenly turns off during the operation, which could happen in a power failure.
2. There's a small risk you may make a mistake while installing Ubuntu. The installer tries to warn about operations that could cause data loss, but it gives a lot of information, and in practice people sometimes do accidentally tell it to overwrite their existing systems. (Furthermore, this risk does not drop to zero even among very experienced users.)

The popular question How do I recover my accidentally lost Windows partitions after installing Ubuntu? is probably an example of one of those (though I'm not certain which).

Far less serious than those first two situations but also more likely:

3. Sometimes installing Ubuntu temporarily prevents other operating systems, including Windows, from booting. This shouldn't happen and usually doesn't, but it sometimes does. This is temporary in the sense that you can fix it, and also in the sense that it's still possible to access the data, whether or not you fix it. But it's frustrating, and not being sure if you've lost data when it first happens is quite unpleasant.

Those are the reasons to have a backup--at least of your documents and other important files--when you're installing Ubuntu in a dual-boot configuration. You should, as Marcus Müller says, always have backups of your important stuff anyway, regardless of what operating system you're using. Data loss can occur at any times. Hard disks (even SSDs) don't last forever and can lose data even before they fail, and various causes ranging from malware to user error can cause files to be accidentally deleted or modified. If you already have a backup, then (a) good, and (b) I recommend making sure it's up to date before installing Ubuntu.

Once Ubuntu is installed, you should continue maintaining backups of your documents and important files, no matter where you store them. For information on some backup strategies and how to apply them in Ubuntu, see What's a good back-up strategy for 1 desktop PC?