"bin/elasticsearch-certutil ca" not working

[varom]

I am getting following error :

same for:
bin/elasticsearch-certutil cert --ca elastic-stack-ca.p12

I'm just beginner in ES and i want to setup TSL communication in cluster based on:
https://www.elastic.co/guide/en/elasticsearch/reference/6.5/configuring-tls.html#node-certificates
, however can't generate certificate using above commands.

I'm executing it from: /opt/apps/elasticsearch/6.5.1/elasticsearch-6.5.1/bin$
and the script is there:
ES is version 6.5.1

Of course i was googling the issue, but could not find any solution.
Thx for any help.

[Yang_Wang]

You need execute the command in the parent folder of bin, i.e. in your case, it should be /opt/apps/elasticsearch/6.5.1/elasticsearch-6.5.1.