Entropy Statistics Test

Entropy is similar to "randomness". A Linux system gathers real random numbers by keeping an eye on different events such as network activity, hard drive rotation speed, hardware random number generator (if available), key-clicks, and so on. The entropy pool is a store of randomness which gets built up by the keystrokes, interrupts, etc. and drained by the generation of random numbers. These random numbers are fed to the kernel entropy pool, which is used by /dev/random. Applications that use crypto functions, use /dev/random as their entropy source, or in other words, the randomness source.

If /dev/random runs out of available entropy, it will be unable to serve out more randomness and the application waiting for the randomness may stall until more random bits are available. Hence, it is important to track the usage of the entropy pool, especially in environments where the SSL-enabled applications are supported for randomness. The Entropy Statistics test helps administrators in this regard!

This test monitors the kernel entropy pool and reports the total size of the entropy pool. This test also reports the amount of random bits available for use in the entropy pool. Using this test, administrators can figure out if the entropy pool is running out of random bits / bytes.

Target of the test : A Linux system only

Agent deploying the test : An internal agent

Outputs of the test : One set of results for every server being monitored

Configurable parameters for the test

Parameter	Description
Test period	How often should the test be executed .
Host	The host for which the test is to be configured.
Timeout	Specify the duration (in seconds) for which this test should wait for a response from the target server. If there is no response from the target server beyond the configured duration, the test will timeout. By default, this is set to 30 seconds.

Measurements made by the test

Measurement	Description	Measurement Unit	Interpretation
Entropy size	Indicates the total size of the entropy pool.	Bytes
Entropy available	Indicates the amount of random bits / bytes that is currently available for use in the entropy pool.	Bytes	A value close to Entropy size measure indicates that the entropy pool is running out of random bits / bytes.
Entropy availability	Indicates the percentage of random bits / bytes that is available for use in the entropy pool.	Percent	A value close to 100 indicates that the entropy pool is running out of random bits / bytes.