Random

There are two random-number devices in the kernel. Historically:

• /dev/random blocked until it had sufficient entropy to return a random value
• /dev/urandom never blocked but resorted to a pseudorandom number generator (PRNG) in the case of insufficient entropy

However, in 2020 the behavior of /dev/random was changed to make it behave more like the getrandom syscall, in that it blocks only on initialization and provides cryptographic-strength random numbers thereafter without blocking. This has resulted in a blurring of the lines between the two random devices and an effort to remove /dev/urandom for good.