| 1 | ### Understand the alert |
| 2 | |
| 3 | 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`. |
| 4 | |
| 5 | 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. |
| 6 | |
| 7 | For further information on how our alerts are calculated, please have a look at our [Documentation](/src/health/REFERENCE.md#expressions). |
| 8 | |
| 9 | ### What is entropy and why do we need it? |
| 10 | |
| 11 | 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`. |
| 12 | |
| 13 | 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. |
| 14 | |
| 15 | 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. |
| 16 | |
| 17 | This way all the values are random and there is no pattern to be found among them. |
| 18 | |
| 19 | ### Troubleshoot the alert |
| 20 | |
| 21 | The best tool to troubleshoot the lowest entropy alert is with `rng-tools`. |
| 22 | |
| 23 | If `rng-tools` are not available for your platform, or you run into trouble, you can use the tool `haveged` as an alternative. |
| 24 | |
| 25 | ### Useful resources |
| 26 | |
| 27 | 1. [Entropy](https://unixhealthcheck.com/blog?id=472) |
| 28 | 2. [rng-tools](https://github.com/nhorman/rng-tools) |
| 29 | 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/) |
| 30 | 4. [Haveged Installation - Archlinux Wiki](https://wiki.archlinux.org/title/Haveged#Installation) |