Esta é uma questão complicada. Eu responderei citando algumas fontes.
% bl0ck_qu0te%No kernel padrão do Ubuntu 12.04 é 3.11 .
Em wiki
% bl0ck_qu0te%Do Linux página de manual
% bl0ck_qu0te% Cite de random
sources, do kernel 3.11.10.10
* Theory of operation
* ===================
*
* Computers are very predictable devices. Hence it is extremely hard
* to produce truly random numbers on a computer --- as opposed to
* pseudo-random numbers, which can easily generated by using a
* algorithm. Unfortunately, it is very easy for attackers to guess
* the sequence of pseudo-random number generators, and for some
* applications this is not acceptable. So instead, we must try to
* gather "environmental noise" from the computer's environment, which
* must be hard for outside attackers to observe, and use that to
* generate random numbers. In a Unix environment, this is best done
* from inside the kernel.
*
* Sources of randomness from the environment include inter-keyboard
* timings, inter-interrupt timings from some interrupts, and other
* events which are both (a) non-deterministic and (b) hard for an
* outside observer to measure. Randomness from these sources are
* added to an "entropy pool", which is mixed using a CRC-like function.
* This is not cryptographically strong, but it is adequate assuming
* the randomness is not chosen maliciously, and it is fast enough that
* the overhead of doing it on every interrupt is very reasonable.
* As random bytes are mixed into the entropy pool, the routines keep
* an *estimate* of how many bits of randomness have been stored into
* the random number generator's internal state.
Sim, é inteligente o suficiente para usar fontes baseadas no usuário , mas você pode configurar mais se quiser.
Existem núcleos com geradores aleatórios que têm mais fontes de entropia, incluindo ruído em entradas de áudio e outros, como vídeo, censores de coolers, etc. aqui se for interessante em entropia de áudio. Espero que você encontre outros kernels sozinho.
Mas /dev/random
deve ser suficiente para a maioria das tarefas por padrão.
Leia também esta questão em stackoverflow