RANDOM in bash
is a built-in variable that outputs a random number between 0 and 32767. You can reseed it simply by setting it to any new integer value. the current epoch second value is a good choice.
RANDOM=$( date +%s )
Edit: I should also mention that it's really only pseudo-random. It will always output the same sequence of values if seeded with the same number. See the bash
man page for a complete description.
is not a command, but a C library function, and isn't usable inside the shell itself. Other than that I don't know much about it.