Is it possible to partially format a HDD ? I'd like to

run a magnet over part of the hdd instead of the whole disk

>>55447220
This.

>>55447201
Wipe free space you mean?

Download Eraser. Chose to erase empty space. Chose gutman 35 pass erasing method. Wait until the end of times. Done.

>>55447363
this

thanks, i'll try it after a defragmentation.

You can do this using dd which is native to flavors of Debian.

You can write zeros or random data starting at a specific sector, cylinder, or byte all the way to a specified endpoint. You can pinpoint the data in between partitions as long as you know where they start.