Linux 4.18 Lands Random Patch To Fix Slow Boot Times For Some Systemd-Based Boxes

Written by Michael Larabel in Linux Kernel on 29 July 2018 at 08:03 AM EDT. 21 Comments
Last week I wrote about a change for the Linux kernel would better protect entropy sent in from user-space as a change driven as a result of some Linux distributions (such as Fedora) using a CPU jitter random number generator to resolve the lack of entropy at boot time and that on systemd-enabled Linux systems sometimes leading to slow boot times. That change has now ended up being queued into Linux 4.18 rather than having to wait for 4.19.

That protection is by mixing entropy sent in from user-space with RdRand. While not everyone trusts Intel's RdRand hardware, the CPU jitter RNG isn't necessarily the safest either but this is basically mixing the two together to create a bit more randomness than relying upon a single source. See the aforelinked article for more background information on the situation and how the lack of entropy was leading to stalled boot processes for some Linux systems -- particularly VMs -- over the lack of entropy following a recent CVE change.

As of this weekend in Linux 4.18 Git, the change has landed after originally being queued for the "-next" cycle (Linux 4.19) but then Ted Ts'o deciding to get this change into 4.18.
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Michael Larabel is the principal author of and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via

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