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https://issues.apache.org/jira/browse/SOLR-16644?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17769400#comment-17769400
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Shawn Heisey commented on SOLR-16644:
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I've been reading up on the RNG changes once I saw this issue. They've finally
gotten to the point where there is no difference between {{/dev/random}} and
{{{}/dev/urandom{}}}. The info I read said that there is one more thing to
clean up for that, but for most setups they have reached that goal.
This command, copying 4MiB of random data, completes instantly every time for
me on a fully updated Ubuntu 22 system running a 6.1 kernel:
{code:java}
dd if=/dev/random of=/dev/null bs=1024 count=4096 iflag=fullblock{code}
If I run that same command on a fresh non-updated Ubuntu 20 install with kernel
5.4, it consistently takes over 10 seconds.
I wonder if there is a foolproof way of detecting when a Linux system has the
new RNG, that doesn't require special utilities?
> Entropy warning thresholds need to be revisited
> -----------------------------------------------
>
> Key: SOLR-16644
> URL: https://issues.apache.org/jira/browse/SOLR-16644
> Project: Solr
> Issue Type: Bug
> Reporter: Ishan Chattopadhyaya
> Priority: Major
> Labels: newdev
> Time Spent: 50m
> Remaining Estimate: 0h
>
> As per the following, newer kernels (5.15+) have recalibrated the entropy
> levels from 0-4096 to 0-256. Hence, everything is throwing a warning:
> {code}
> Warning: Available entropy is low. As a result, use of the UUIDField, SSL, or
> any other features that require
> RNG might not work properly. To check for the amount of available entropy,
> use 'cat /proc/sys/kernel/random/entropy_avail'.
> {code}
> Here's where I found out about this change:
> https://askubuntu.com/questions/1427470/entropy-is-stuck-at-256-after-upgrading-to-kernel-5-15-0-47
> We might need to intelligently report the low entropy (based on kernel
> version).
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