Shredding files from under linux or Windows - all HDD than and how?

Question

Data recovery

I sell two hard drives of 320GB each, on which there is a lot of information, both textual and graphic. It is necessary to delete all data in such a way that no one can restore them in any way, since hard beats are not for home use.
Actually, how can you quickly and reliably overwrite information with zeros a couple of times?
So far I have found Paragon Hard Disk Manager with the function of erasing data - but I don’t know if it’s worth trusting.
What can you advise from software or methods?

Answer 1

Thanks to plin2s and 3vi1_0n3 for the tip
I did this from the terminal:sudo dd if=/dev/urandom of=/dev/sda bs=2M

Answer 2

linux: shred, set on the whole device

Answer 3

dd or the same badblocks in write mode.

Answer 4

shred -zn10 /dev/hdb

Answer 5

You can do this for example (bash):

for i in {1..10}
do
  dd if=/dev/urandom of=/dev/ваш-диск bs=1M
done