Re: How to use /dev/random

[HIToC <hitoc_mail@yahoo.it>]

On Friday 23 September 2005 17:44, Glynn Clements wrote:
> HIToC wrote:
> > > You can also read a number of random bytes from /dev/(u)random with dd:
> > >
> > >         dd if=/dev/urandom of=/tmp/randnums bs=1 count=500
> > >
> > > This reads a sequence of 500 bytes from /dev/urandom and writes them
> > > to /tmp/randnums.
> >
> > I have read that the problem of /dev/random is mainly on boot, when there
> > are few iteration from the user. For this reason is useful first save on
> > a temporary_random file a 512 bytes block on shutdown of the system. Then
> > on the new booting, to put the 512 bytes saved on the
> > temporary_random file in the /dev/random device.
> > With this procedure we have the random device ready
> > afterwards boot.
> >
> > I have two questions:
> > 1) the size of /dev/random is 512 bytes, or the number of bytes
> > 	increase over the new iteration of the user (like mouse clicks,
> > 	key strokes, ecc..)?
>
> The size of the entropy pool is fixed at 512 bytes.
>
> > 2) Where can I put the scripts to read the random number on shutdown
> > 	or to write the previously saved bytes, on boot?
>
> Typically such scripts live in /etc/init.d. The format of the script
> needs to be compatible with your OS distribution. Look at existing
> scripts for clues. Most distributions already contain a suitable
> script (e.g. on Gentoo, it's /etc/init.d/urandom).
>
> There are a number of comments regarding saving and restoring entropy
> in drivers/char/random.c in the Linux kernel source code.

Thanks all for your useful help!!
-- 
With regards,


					HIToC
					hitoc_mail@yahoo.it