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diff --git a/health/guides/entropy/lowest_entropy.md b/health/guides/entropy/lowest_entropy.md new file mode 100644 index 00000000..b53aed2c --- /dev/null +++ b/health/guides/entropy/lowest_entropy.md @@ -0,0 +1,30 @@ +### Understand the alert + +This alert presents the minimum amount of entropy in the kernel entropy pool in the last 5 minutes. Low entropy can lead to a reduction in the quality of random numbers produced by `/dev/random` and `/dev/urandom`. + +The Netdata Agent checks for the minimum entropy value in the last 5 minutes. The alert gets raised into warning if the value < 100, and cleared if the value > 200. + +For further information on how our alerts are calculated, please have a look at our [Documentation](https://learn.netdata.cloud/docs/agent/health/reference#expressions). + +### What is entropy and why do we need it? + +Entropy is similar to "randomness". A Linux system gathers "real" random numbers by keeping an eye on different events: network activity, hard drive rotation speeds, hardware random number generator (if available), key-clicks, and so on. It feeds those to the kernel entropy pool, which is used by `/dev/random`. + +Encryption and cryptography applications require random numbers to operate. A function or an algorithm that produces numbers -*that seem to be random*- is very predictable, if you know what function is used. + +In real life, we use our surroundings and our thoughts to produce truly random numbers. A computer can't really do this by itself, so it gathers numbers from a lot of sources. For example, it can get the CO2 levels in a room from a sensor on the system and use that as a random number. + +This way all the values are random and there is no pattern to be found among them. + +### Troubleshoot the alert + +The best tool to troubleshoot the lowest entropy alert is with `rng-tools`. + +If `rng-tools` are not available for your platform, or you run into trouble, you can use the tool `haveged` as an alternative. + +### Useful resources + +1. [Entropy](https://unixhealthcheck.com/blog?id=472) +2. [rng-tools](https://github.com/nhorman/rng-tools) +3. [How to add more entropy to improve cryptographic randomness on Linux](https://www.techrepublic.com/article/how-to-add-more-entropy-to-improve-cryptographic-randomness-on-linux/) +4. [Haveged Installation - Archlinux Wiki](https://wiki.archlinux.org/title/Haveged#Installation) |