[tor-bugs] #24500 [Core Tor/Tor]: Confusing log message "Can't get entropy from getrandom()"

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#24500: Confusing log message "Can't get entropy from getrandom()"
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 Reporter:  arma          |          Owner:  (none)
     Type:  defect        |         Status:  new
 Priority:  Medium        |      Milestone:
Component:  Core Tor/Tor  |        Version:
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:
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Comment (by yawning):

 > The middle line is confusing -- why can't we get the entropy from it?

 It's a system call.  The usual case for this failing is that the kernel is
 too old (`ENOSYS`), but the distribution they are supposedly using has a
 kernel that is 3.17 or newer.

 This should probably log errno, though I am uncertain as to how useful
 that will be since the code is smart enough to retry on `EINTR` and
 `EAGAIN`.

 >Does that mean Tor has failed at something important? What should the
 relay operator do?

 Using `getrandom()` is preferable to reading from `/dev/urandom`, but
 there is a fallback path, so it's not fatal, just odd.  The relay operator
 should figure out why `getrandom()` is failing.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24500#comment:2>
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