booting elasticsearch on machine with 2GB RAM

elasticsearch heap-memory elasticsearch-5

You should set Xms and Xmx in the jvm.options file. (/etc/elasticsearch/jvm.options)

You can also use environment variables (ES_JAVA_OPTS="-Xms1g -Xmx1g"), but you need to comment out the settings in jvm.options for that to work.

PS: Assuming 5.x since you didn't specify the version.

CodeHunter