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warren
Asked: 2011-08-23 13:59:30 +0800 CST

How to fix the entropy pool issue with RHEL 5.x

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RHEL 5.x has an entropy-generation problem (held-over from kernel 2.4). Following directions from here has produced little-to-no results:

How to increase entropy pool on a 2.6 kernel RHEL/Fedora system without keyboard/mouse.

A good source of entropy is needed for random number generation. This affects services that go via SSL amongst other things. In 2.6 kernels the entropy sources of a system are keyboard, mouse and some IRQ interrupts. There are two random number sources on linux - /dev/random and /dev/urandom. /dev/random will block if there is nothing left in the entropy bit bucket. If your system does not have keyboard and mouse, you can use 'rngd' daemon to perform the task. You can see the entropy valu using following command. 

    #cat /proc/sys/kernel/random/entropy_avail

Now, start the 'rngd' daemon using following command and monitor the entropy on the system.

    #rngd -r /dev/urandom -o /dev/random -f -t 1
    #watch -n 1 cat /proc/sys/kernel/random/entropy_avail

What other fixes are available for this issue?

background

There is a known issue (on HP's side) with one component in the current version of Server Automation that takes a long time to startup due to a small entropy pool on RHEL 5. I'm trying to find a workaround until/unless it's fixed on the vendor's part.

rhel5 entropy-pool hp-server-automation

4 Answers

  1. As has been pointed out, colocated servers, lacking that random human being to create entropy, generally don't have much of it to spare. If you have a physical server with a spare USB port, and a demonstrable need for high-grade entropy, you could do worse than get yourself an Entropy Key. I don't normally recommend specific products on SF, but I rather like this one, and it does the job nicely.

    Here's the depth of my pool before fitting the key: pool depth before key

    and here's the pool after: pool depth after key

    Declaration of interest: I have no connection with the makers except that I bought one of their products, at full price, and like it.

    Edit (July 2015): the Entropy Key website has for some time said that they're out of stock, and they don't know when they'll have more made. However, OneRNG, a project to make a completely-open, verifiable, USB-connected entropy generator, was fully funded on kickstarter, and at the time of writing intends to start selling them via a webstore once their kickstarter obligations are fulfilled.

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  2. I don't know how much entropy you need, but you could use the HTTP API on random.org to feed entropy into your system (try rand_add). Or you could use something like the Entropy Gathering Daemon.

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  3. Change the t parameter to .1 or .001

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  4. Best Answer

    Also found this article, "Cut your WebLogic startup time in half on Linux", via a coworker this week.

    The problem is worse in VMs than on physical machines because there is a lack of "driver noise".

    update 31 Mar 2016

    You can also run haveged. Or try twuewand.

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