fyi
I get warnings when Elasticsearch.service starts. Don't know if this is important but it's considering reporting to the maintainers, which is done herewith. Elasticsearch aarch64 (RPi4).
openjdk version "11.0.12" 2021-07-20
OpenJDK Runtime Environment (build 11.0.12+7-post-Debian-2deb10u1)
OpenJDK 64-Bit Server VM (build 11.0.12+7-post-Debian-2deb10u1, mixed mode
Oct 17 13:02:49 ****** systemd[1]: Starting Elasticsearch...
Oct 17 13:03:04 ****** systemd-entrypoint[688]: WARNING: A terminally deprecated method in java.lang.System has been called
Oct 17 13:03:04 ****** systemd-entrypoint[688]: WARNING: System::setSecurityManager has been called by org.elasticsearch.bootstrap.Elasticsearch (file:/usr/share/elasticsearch/lib/elasticsearch-7.15.1.jar)
Oct 17 13:03:04 ****** systemd-entrypoint[688]: WARNING: Please consider reporting this to the maintainers of org.elasticsearch.bootstrap.Elasticsearch
Oct 17 13:03:04 ****** systemd-entrypoint[688]: WARNING: System::setSecurityManager will be removed in a future release
Oct 17 13:03:27 ****** systemd-entrypoint[688]: WARNING: A terminally deprecated method in java.lang.System has been called
Oct 17 13:03:27 ****** systemd-entrypoint[688]: WARNING: System::setSecurityManager has been called by org.elasticsearch.bootstrap.Security (file:/usr/share/elasticsearch/lib/elasticsearch-7.15.1.jar)
Oct 17 13:03:27 ****** systemd-entrypoint[688]: WARNING: Please consider reporting this to the maintainers of org.elasticsearch.bootstrap.Security
Oct 17 13:03:27 ****** systemd-entrypoint[688]: WARNING: System::setSecurityManager will be removed in a future release
Oct 17 13:04:18 ****** systemd[1]: Started Elasticsearch.
