Date: Tue, 8 Mar 2016 02:10:37 +0100 From: Polytropon <freebsd@edvax.de> To: Rick Miller <vmiller@hostileadmin.com> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: When is /dev/random created? Message-ID: <20160308021037.84bd0d21.freebsd@edvax.de> In-Reply-To: <CAHzLAVFJ%2BYAUjEDCvPzhuSYNM9FyhoZ5=M_kLOXwDrEU6bHS0Q@mail.gmail.com> References: <CAHzLAVFJ%2BYAUjEDCvPzhuSYNM9FyhoZ5=M_kLOXwDrEU6bHS0Q@mail.gmail.com>
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On Mon, 7 Mar 2016 19:04:57 -0500, Rick Miller wrote:
> Hi all,
>
> I was intrigued when I noticed an mfsBSD disk image did not have
> /dev/random and decided to check the distribution from which the image was
> installed. dev/ existed only in base.txz and as an empty directory.
That's correct. /dev is a mountpoint for a virtual file system
for the device files. Example output from the "mount -v" command:
devfs on /dev (devfs, local, multilabel)
So when devfs is started, /dev gets populated.
> Does this mean /dev/random is created on boot?
Yes. The whole /dev content is under management of devfs (and devd).
> /etc/rc.d/random exists as
> a typical start script, but doesn't appear to test the existent, much less
> create, /dev/random.
It contains the following sequence in the feed_dev_random() function:
cat "${1}" | dd of=/dev/random bs=8k 2>/dev/null
So this one creates /dev/random if it doesn't already exist.
However, I think the devfs initialization already makes sure
the device file exists. The magic should be located somewhere
in the kernel virtual file system sources...
> Section 5.12, Random Number Generator of the D&I of FreeBSD, while it
> touched on /dev/random, didn't describe when or how it is created.
>
> So, at what point does /dev/random get created when it doesn't exist?
When /etc/rc.d/random is executed. The function random_start()
tests for write access to /dev/random:
if [ -w /dev/random ]; then
and then feeds it:
feed_dev_random "${seedfile}"
where the called function would perform
cat "${1}" | dd of=/dev/random bs=8k 2>/dev/null
As mentioned, that would create /dev/random, but the test of -w
already implies that it exists (-w = exists and can be written to).
--
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...
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