# System Entropy¶

- randomgen.entropy.random_entropy(
*size=None*,*source='system'*)¶ Read entropy from the system cryptographic provider

- Parameters:
**size**int or tuple of ints, optionalOutput shape. If the given shape is, e.g.,

`(m, n, k)`

, then`m * n * k`

samples are drawn. Default is None, in which case a single value is returned.**source**str {‘system’, ‘fallback’, ‘auto’}Source of entropy. ‘system’ uses system cryptographic pool. ‘fallback’ uses a hash of the time and process id. ‘auto’ attempts ‘system’ before automatically falling back to ‘fallback’

- Returns:
**entropy**scalar or arrayEntropy bits in 32-bit unsigned integers. A scalar is returned if size is None.

Notes

On Unix-like machines, reads from

`/dev/urandom`

. On Windows machines reads from the RSA algorithm provided by the cryptographic service provider.This function reads from the system entropy pool and so samples are not reproducible. In particular, it does

*NOT*make use of a bit generator, and so`seed`

and setting`state`

have no effect.Raises RuntimeError if the command fails.