On Linux systems, ulimit can be used to change resource limits on a temporary basis. Limits usually need to be set as root before switching to the user that will run Elasticsearch. For example, to set the number of open file handles (ulimit -n) to 65,536, you can do the following:

sudo su  
ulimit -n 65536 
su elasticsearch 

The new limit is only applied during the current session.

You can consult all currently applied limits with ulimit -a.

On Linux systems, persistent limits can be set for a particular user by editing the /etc/security/limits.conf file. To set the maximum number of open files for the elasticsearch user to 65,536, add the following line to the limits.conf file:

elasticsearch  -  nofile  65536

This change will only take effect the next time the elasticsearch user opens a new session.

# session    required   pam_limits.so

When using the RPM or Debian packages, system settings and environment variables can be specified in the system configuration file, which is located in:

However, for systems which uses systemd, system limits need to be specified via systemd.

When using the RPM or Debian packages on systems that use systemd, system limits must be specified via systemd.

The systemd service file (/usr/lib/systemd/system/elasticsearch.service) contains the limits that are applied by default.

To override them, add a file called /etc/systemd/system/elasticsearch.service.d/override.conf (alternatively, you may run sudo systemctl edit elasticsearch which opens the file automatically inside your default editor). Set any changes in this file, such as:

[Service]
LimitMEMLOCK=infinity

Once finished, run the following command to reload units:

sudo systemctl daemon-reload

The preferred method of setting Java Virtual Machine options (including system properties and JVM flags) is via the jvm.options configuration file. The default location of this file is config/jvm.options (when installing from the tar or zip distributions) and /etc/elasticsearch/jvm.options (when installing from the Debian or RPM packages). This file contains a line-delimited list of JVM arguments, which must begin with -. You can add custom JVM flags to this file and check this configuration into your version control system.

An alternative mechanism for setting Java Virtual Machine options is via the ES_JAVA_OPTS environment variable. For instance:

export ES_JAVA_OPTS="$ES_JAVA_OPTS -Djava.io.tmpdir=/path/to/temp/dir"
./bin/elasticsearch

When using the RPM or Debian packages, ES_JAVA_OPTS can be specified in the system configuration file.

The JVM has a built-in mechanism for observing the JAVA_TOOL_OPTIONS environment variable. We intentionally ignore this environment variable in our packaging scripts. The primary reason for this is that on some OS (e.g., Ubuntu) there are agents installed by default via this environment variable that we do not want interfering with Elasticsearch.

Additionally, some other Java programs support the JAVA_OPTS environment variable. This is not a mechanism built into the JVM but instead a convention in the ecosystem. However, we do not support this environment variable, instead supporting setting JVM options via the jvm.options file or the environment variable ES_JAVA_OPTS as above.