Idiom #69 Seed random generator
Use seed s to initialize a random generator.
If s is constant, the generator output will be the same each time the program runs. If s is based on the current value of the system clock, the generator output will be different each time.
r = Random.new(s)
Don't use system time to seed; not specifying s is far superior. (Docs: If number is omitted, seeds the generator using a source of entropy provided by the operating system, if available (/dev/urandom on Unix systems or the RSA cryptographic provider on Windows), which is then combined with the time, the process id, and a sequence number.)