...
Note. These pseudo random number generators use mathematical algorithms to produce a sequence of numbers with good statistical properties, but the numbers produced are not genuinely random. For true additional randomness, Linux users can use the character devices /dev/random or /dev/urandom, but it is advisable to retrieve only a small number of characters from these devices. (The device /dev/random may block for a long time if there are not enough events going on to generate sufficient randomness; /dev/urandom does not block.)
...