[Nottingham] Very slow dd if=/dev/random

Paul Sladen nottingham at mailman.lug.org.uk
Tue Jul 29 10:24:01 2003

On Tue, 29 Jul 2003, Martin wrote:

Hello Martin,

> Meanwhile, I tried:
> dd if=/dev/random of=/dev/hdg bs=1M

`/dev/random' produces very good quality random numbers--and consequently
there aren't many of these.  What will normally happen is that a stream of
random numbers will be stored up over many hours and these will be emptied
very quickly if you try and copy a whole megabyte of them.  It's designed
for fetching the odd 4-bytes or so;  not several GB's worth.

`/dev/urandom' produces ``good enough'' random numbers, in quantity--this
is probably the source that you want for overwriting a disk with.

Out-of-interest, what's wrong with using `/dev/zero', which produces a very
high quality stream of bits, generally uncontaminated by "ones"?

War is inconsistent with Truth.  Nottingham, GB