[horizontal] `ES_USER`:: The user to run as, defaults to `elasticsearch`. `ES_GROUP`:: The group to run as, defaults to `elasticsearch`. `JAVA_HOME`:: Set a custom Java path to be used. `MAX_OPEN_FILES`:: Maximum number of open files, defaults to `65536`. `MAX_LOCKED_MEMORY`:: Maximum locked memory size. Set to `unlimited if you use the `bootstrap.memory_lock` option in elasticsearch.yml. `MAX_MAP_COUNT`:: Maximum number of memory map areas a process may have. If you use `mmapfs` as index store type, make sure this is set to a high value. For more information, check the https://github.com/torvalds/linux/blob/master/Documentation/sysctl/vm.txt[linux kernel documentation] about `max_map_count`. This is set via `sysctl` before starting elasticsearch. Defaults to `262144`. `LOG_DIR`:: Log directory, defaults to `/var/log/elasticsearch`. `DATA_DIR`:: Data directory, defaults to `/var/lib/elasticsearch`. `CONF_DIR`:: Configuration file directory (which needs to include `elasticsearch.yml` and `logging.yml` files), defaults to `/etc/elasticsearch`. `ES_JAVA_OPTS`:: Any additional JVM system properties you may want to apply. `RESTART_ON_UPGRADE`:: Configure restart on package upgrade, defaults to `false`. This means you will have to restart your elasticsearch instance after installing a package manually. The reason for this is to ensure, that upgrades in a cluster do not result in a continuous shard reallocation resulting in high network traffic and reducing the response times of your cluster.