CrunchBang Linux

el_koraco

#!/loony/bun

From: inside Ed

Registered: 2011-07-25

Posts: 4,646

So how long do I let /dev/urandom do its thang on the disk?

I'm giving my old laptop away. I'm too lazy to bother downloading DBAN or something, so I'm running

dd if=/dev/urandom of=/dev/sda

on the hard drive from an Ubuntu Live USB which I'll be installing from later on. Presumably dd will finish at some point, but I'm not so sure the measly laptop will be able to handle 100% CPU for long. Should I wait until the thing is done, or can I Ctrl+C at some point, and if so, when?

Last edited by el_koraco (2012-04-29 15:28:21)

xaos52

The Good Doctor

From: Planet of the @s

Registered: 2011-06-24

Posts: 4,324

Re: So how long do I let /dev/urandom do its thang on the disk?

generate a file with, say 250MB of random data, then make a little script that copies that file all over your disk.
EDIT: if you break the running process, you will have to start all over again, unless the dd exits saying how much data it already wrote.
I read somewhere that hitting keys randomly or moving the cursor helps it collect randomness. I did this once, long time ago and had to resort to generating a smaller file and copying that all over.

Last edited by xaos52 (2012-04-29 16:37:43)

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lain

#! Junkie

Registered: 2011-11-03

Posts: 313

Re: So how long do I let /dev/urandom do its thang on the disk?

You don't have to use /dev/urandom. /dev/true should be enough... unless you wan't to give the laptop to the CIA.

Let's do some math's on that. The chance of recovering an overridden bit on a hd was something around 7/8 I think. Which means that you could recover a byte only by a chance of ~34%. THAT means that you could recover the ASCII encoded word 'Hello' by a chance of ~0.47%... and so forth.

Just use /dev/true and stop worrying.

Should I wait until the thing is done, or can I Ctrl+C at some point, and if so, when?

That would mean that you end up with a half overwritten drive where the not-overwritten things could be recovered.

Edit: If you're interested in that topic, I suggest you read this: Overwriting Hard Drive Data

Last edited by lain (2012-04-29 16:44:53)

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el_koraco

#!/loony/bun

From: inside Ed

Registered: 2011-07-25

Posts: 4,646

Re: So how long do I let /dev/urandom do its thang on the disk?

Good info on /dev/true. /dev/urandom copied 28 GB of data in 40 minutes. So it would have taken up to six hours for a complete wipe. Not my thang

p120d16y

#! Die Hard

From: Midwest

Registered: 2011-08-08

Posts: 800

Re: So how long do I let /dev/urandom do its thang on the disk?

I always use DBAN; you could just partition the disk and randomly write it like others have said. Or just delete all your stuff after a backup, then partition. You're still good unless you're giving it to the CIA.

Last edited by p120d16y (2012-05-01 18:08:26)

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All tyranny needs to gain a foothold is for people of good conscience to remain silent.
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