No, what I mean is to boot a LiveCd or the installation USB-drive, this installer is itself a linux-system. So you will be able to explore your new installed system from "the outside". In order to mount a partition, you'll need an empty directoy, for example /mnt, I'd recommend to create two directories (when the Live-CD/USB) is running
mkdir /mnt/bootpartition /mnt/rootpartition
mount /dev/sda? /mnt/bootpartition
mount /dev/sda? /mnt/rootpartition
where you please substitute the "?" with the partitionnumbers of the boot- and the rootpartition. Afterwards you can use
in order to check if you have access to the devices.