You can use the command-line switch -var, as in the
example below, and type a seed, like 4827938, on
the command line, instead of using echo RANDOM,
which presumably has the shell generate a seed.
LAMMPS assumes most people want to specify
the seed, so they can reproduce the run later,
by using the same seed. Rather than use a seed
hidden from the user, which can never be re-generated.