/dev/random empty?

Darren McGrandle darren at mcgrandle.com
Mon Jul 18 22:35:53 PDT 2005


Robert,

Thank you, that explains what I am seeing!  And indeed I am 
out of entropy.  I'll try out your suggestions, thank you.

-Darren

> /dev/random is a blocking device. That means if its empty you, or your
> program, will have to wait until it refills. urandom and frandom are
> non-blocking, that means they never run out and you only have to wait
> for the speed of the device, which may be 0.5MB per second or so
> (frandom is faster than urandom). 

> Try:
> cat /proc/sys/kernel/random/entropy_avail
> 
> this will tell you how much entropy you have in core memory, and how 
> much /dev/random has available.
> 
> Most entropy comes from your mouse, if you have one. The keyboard and network 
> traffic is also used. The kernel is coded to decide how to use entropy 
> sources, like the keyboard and mouse. You can use audio-entropyd, or 
> hw_random, if you have those devices, to refill your random device 
> constantly.
> 
> Also see:
> http://www.linuxfromscratch.org/hints/downloads/files/entropy.txt
> 
> In other words, what you are saying is normal, especially if you 
> cat /dev/random. Think of /dev/random as a swimming pool, or sink full of 
> water. It's easy to drain, and you have to wait a bit to let it refill 
> depending on how much input sources you have.
> 
> robert






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