[agwa]

Cryptographically-secure PRNGs are also deterministic, but as long as you have at least 256 bits of unpredictable seed, the output remains unpredictable to an attacker for practically forever.

Linux used/uses user input and network jitter as the seed to a deterministic CSPRNG. It continuously mixes in more unpredictable bits so that the CSPRNG can recover if somehow the kernel's memory gets exposed to an attacker, but this is not required if the kernel's memory remains secure.

To reiterate, running out of entropy is not a thing.