Before you start, make sure to back up every file that is now on your system. If this is the first time a non-native operating system is going to be installed on your computer, it is quite likely you will need to re-partition your disk to make room for Debian GNU/Linux. Anytime you partition your disk, you run a risk of losing everything on the disk, no matter what program you use to do it. The programs used in the installation of Debian GNU/Linux are quite reliable and most have seen years of use; but they are also quite powerful and a false move can cost you. Even after backing up, be careful and think about your answers and actions. Two minutes of thinking can save hours of unnecessary work.
Jestliže budete instalovat Linux na počítač, kde již máte jiný operační systém, přesvědčete se, že máte po ruce média pro jeho instalaci. Obvykle to není potřeba, ale zvlášť v případě, kdy byste se chystali přerozdělit systémový disk, by se vám mohlo stát, že bude nutné znovu nainstalovat zavaděč původního systému, nebo dokonce celý systém.