https://en.wikipedia.org/wiki//dev/random#Linux has :
> In October 2016, with the release of Linux kernel version 4.8, the kernel's /dev/urandom was switched over to a ChaCha20-based cryptographic pseudorandom number generator (CPRNG) implementation [16] by Theodore Ts'o, based on Bernstein's well-regarded stream cipher ChaCha20.
> In 2020, the Linux kernel version 5.6 /dev/random only blocks when the CPRNG hasn't initialized. Once initialized, /dev/random and /dev/urandom behave the same. [17]