That's what this demo code project is about:

https://git.zx2c4.com/seedrng/tree/seedrng.c

https://git.zx2c4.com/seedrng/about/

https://twitter.com/EdgeSecurity/status/1509002499507818500

It's trying to do the seed file thing the "right way", and be portable enough that init systems can just copy and paste this where it fits.