kernel: Entropy device is blocking

sam samwun at
Fri Jan 28 09:02:28 PST 2005

Joerg Sonnenberger wrote:

On Fri, Jan 28, 2005 at 09:57:49PM +0800, sam wrote:

Every now and then when I freshly install FreeBSD, I sometimes get an 
error message saying "kernel: Entropy device blocking" when I turn on 
sshd in rc.conf file. I have search around in google but coudln't find a 
right fix for it.

The problem is that during boot, only a small amount of entropy
is generated. Since sshd depends on full random bits, it can't
and doesn't the normal /dev/urandom. /dev/random can block, if
not enough random bits are available.
I'm not sure what triggers the omission of a normal entropy
level for you. It could happen in a low-irq environment like
pure ramdisks or so, it might be enough to just create some process
doing nothing. Very difficult to say. One idea to find out the 
amount of entropy needed is changing the rc.d script to run
sshd under ktrace and check for the read calls to /dev/random.

It may be the problem with the hardware. I install the system in a old 
and dirty PIII machine. I m going to install it in the IBM notebook and 
see if this makes any difference.


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