Is there a way to monitor /dev/random?

Question

We're investigating some JDBC issues, and one of the possible problems is /dev/random being exhausted. The workaround is to switch the JVM to using /dev/urandom, but I wan't to try and determine whether or not the /dev/random is being exhausted.

Is there a way to check if the entropy pool is being exhausted? I've gone hunting for nagios plugins and general bash commands, but I've turned up nothing.

score 17 · Accepted Answer · answered Aug 09 '13 at 02:16

17

Sure! Ask /proc/sys/kernel/random/entropy_avail.

answered Aug 09 '13 at 02:16

Shane Madden

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But... every time I run that I lose entropy! – Andrew Aug 09 '13 at 02:19
@Andrew: There's no reason why you should. – David Schwartz Aug 09 '13 at 02:36
@David. Entropy does reduce as you run cat /proc/sys/kernel/random/entropy_avail, but only to a point, it will then level out and hover at around the same level – GeoSword Aug 09 '13 at 08:53
Perfect, exactly what I was looking for, cheers. – Josh Smeaton Aug 09 '13 at 14:25
I don't know whether this answer ever was correct, but it [does not seem to be for today's kernels](https://security.stackexchange.com/a/127498/165862). `entropy_avail` only measures the size of the input pool, *not* how many bits can be read from `/dev/random`. – leopold.talirz Oct 02 '20 at 21:04

score 2 · Answer 2 · edited Jun 14 '15 at 20:18

2

as read someplace else... each new process get entropy from /dev/random

a simple way to avoid stealing the pool is a program, such as:

#!/usr/bin/env python

import time

while True:
    with open('/proc/sys/kernel/random/entropy_avail', 'r') as f:
        print(f.read().rstrip())
    time.sleep(1.0)

edited Jun 14 '15 at 20:18

kasperd

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answered Jun 14 '15 at 20:14

Guillaume

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more easy: watch cat /proc/sys/kernel/random/entropy_avail – David Muñoz Jun 16 '18 at 22:51

Is there a way to monitor /dev/random?

2 Answers2