On Unix systems, random numbers are generated in a number of ways and random data can serve many purposes. From simple commands to fairly complex processes, the question “How random is random?” is worth asking.
EZ random numbers
If all you need is a casual list of random numbers, the RANDOM variable is an easy choice. Type “echo $RANDOM” and you’ll get a number between 0 and 32,767 (the largest number that two bytes can hold).
$ echo $RANDOM 29366
Of course, this process is actually providing a “pseudo-random” number. As anyone who thinks about random numbers very often might tell you, numbers generated by a program have a limitation. Programs follow carefully crafted steps, and those steps aren’t even close to being truly random. You can increase the randomness of RANDOM’s value by seeding it (i.e., setting the variable to some initial value). Some just use the current process ID (via $$) for that. Note that for any particular starting point, the subsequent values that $RANDOM provides are quite predictable.
Source: NW Security 1