OS: Linux

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/randomand /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.

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.1

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.

For further information, please have a look at the References and Sources section.

References and Sources
  1. Entropy
  2. rng-tools
  3. How to add more entropy to improve cryptographic randomness on Linux
  4. Haveged Installation - Archlinux Wiki

Troubleshooting Section

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.

Install and setup rng-tools

rng-tools is a random number generator daemon.
It monitors a set of entropy sources, and supplies entropy from them to the system kernel’s /dev/random machinery.2


Debian-based platforms

root@netdata~ # sudo apt-get update
root@netdata~ # sudo apt-get install rng-tools

RHEL/Fedora/CentOS machines

  1. Change to the root account;
root@netdata~ # su
  1. And then install;
root@netdata~ # yum install rng-tools

After the Installation

You can run the service using the following command;

root@netdata~ # service rngd start

And also you can check the daemon status using the following command;

root@netdata~ # service rngd status
Install Haveged

Ideally, a system with high entropy demands should have a hardware device to generate random
numbers. For example, a TPM is such a device. However, there are also several software-only options you may install, like haveged (read more).


Debian-based platforms

  1. To install haveged, run:

    root@netdata~ # sudo apt-get install haveged
  2. Set haveged up to start at boot with the command sudo update-rc.d haveged defaults.3

RHEL/Fedora/CentOS machines

  1. Change to the root account:

    root@netdata~ # su
  2. Install haveged:

    root@netdata~ # yum install haveged
  3. Set haveged to start at boot with the command chkconfig haveged on.3