On Fri, 18 Jan 2002 10:10:46 PST, Richard Chadderton said: > > On Fri, 18 Jan 2002 Valdis.Kletnieksat_private wrote: > > > > dd if=/dev/urandom of=/dev/hdb > > > > GAAAK!!!! No! No! No! > > > > This will *NOT* do what you want it to do. > > Well, at the risk of descending into a flame war over a trivial point, yes > it _does_ do what I want. I think you misunderstood the objective. The > point was _not_ to create ideal random data for the disk, but simply to > overwrite it with something. Anything. Your MP3 collection. Grandma's Right. *THAT* I agree with. The point I took objection to was the implication that /dev/urandom was a good source for large pseudorandom streams. Sure, if it's a box you're about to surplus ANYHOW, the fact that it degrades to a pseudorandom stream and hoses every user of /dev/random probably doesn't matter. What *does* matter is all the cargo-cult programmers out there who will then *literally* use /dev/urandom in something without understanding the implications of it in a production system. "Hmm... I saw somebody use it to zero out a 40G disk drive, it must be basically for free..". (For bonus points - if you're using trinux or some other cd/zip based linuxoid to wipe a system before discarding it, what rate will it converge on if you accidentally use /dev/random in the above 'dd' command? Hint - you're probably almost never doing a long seek on the hard drive ;) Personally, the systems we've been surplusing lately, I've been recommending at least 4 passes - all zeros x'00000', all ones x'ffffffff', alterneting bits x'5555', and a pseudorandom pass. Throw a pass of x'aaaa' in after the 5555 if you're bored. And remember - if you need more than a few bytes, use /dev/urandom to seed a good user-space pseudorandom bitstream generator. /Valdis ----------------------------------------------------------------- This list is provided by the SecurityFocus ARIS analyzer service. For more information on this free incident handling, management and tracking system please see: http://aris.securityfocus.com
This archive was generated by hypermail 2b30 : Sun Jan 20 2002 - 08:31:08 PST