localhost$ RANDOM=1; echo
    $(echo $RANDOM $RANDOM $RANDOM) $(echo $RANDOM $RANDOM $RANDOM)
32422 12519 25748 12519 25748 6973

The first child starts with 32422. This is the result of RANDOM=1.
The second child starts with 12519. Executing the child and
change_random() calls the rand() to advance the seed. Thus 12519
advances from 32442, which is also in the second random number
of the first child.

"Ensure next child gets a (slightly) different $RANDOM sequence."
As the comment explains, the next child receives a different $RANDOM
seed than before, which advances one seed only one step forward.

Thank you for your review, I learned about OpenBSD's implementation
due to your help.

2026년 5월 22일 (금) 오후 10:21, Theo de Raadt <deraadt@openbsd.org>님이 작성:
>
> Biarder <mss091204.1@gmail.com> wrote:
>
> > Currently, ksh(1) uses rand(3) and modular arithmetic to calculate
> > $RANDOM.  However, OpenBSD recommend using arc4random_uniform(3)
> > to calculate a uniform random integer because rand function is
> > predictable and also has modular bias when modulo operation is
> > performed.
>
> Your change is incorrect.  There are situations when ksh randomness
> must follow the rand() method.
>
> This is handled by not using arcrandom(), but by using the rand()
> which _is_ arc4random() behind the scenes unless srand_deterministic()
> is called.  And srand_deterministic() is called, in those circumstances,
> to satisfy that requirement.
>
> It is in the manual page.
>
>      RANDOM     A random number generator.  Every time RANDOM is referenced,
>                 it is assigned the next random number in the range 0-32767.
>                 By default, arc4random(3) is used to produce values.  If the
>                 variable RANDOM is assigned a value, the value is used as the
>                 seed to srand_deterministic(3) and subsequent references of
>                 RANDOM produce a predictable sequence.
>
> This work was done in 2004.  When making changes, please look at the history
> of the code you are touching.  In this case 'grep arc4random' would have found
> you this reference, the commit message, and this text above.  If you had
> done 'man rand', you would have learned the rest of it.
>
>