[[setting-system-settings]]
=== Configuring system settings

Where to configure systems settings depends on which package you have used to
install Elasticsearch, and which operating system you are using.

When using the `.zip` or `.tar.gz` packages, system settings can be configured:

* temporarily with <<ulimit,`ulimit`>>, or
* permanently in <<limits.conf,`/etc/security/limits.conf`>>.

When using the RPM or Debian packages, most system settings are set in the
<<sysconfig,system configuration file>>. However, systems which use systemd
require that system limits are specified in a
<<systemd,systemd configuration file>>.

[[ulimit]]
==== `ulimit`

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:

[source,sh]
--------------------------------
sudo su  <1>
ulimit -n 65536 <2>
su elasticsearch <3>
--------------------------------
<1> Become `root`.
<2> Change the max number of open files.
<3> Become the `elasticsearch` user in order to start Elasticsearch.

The new limit is only applied during the current session.

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


[[limits.conf]]
==== `/etc/security/limits.conf`

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:

[source,sh]
--------------------------------
elasticsearch  -  nofile  65536
--------------------------------

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

[NOTE]
.Ubuntu and `limits.conf`
===============================
Ubuntu ignores the `limits.conf` file for processes started by `init.d`.  To
enable the `limits.conf` file, edit `/etc/pam.d/su` and uncomment the
following line:

[source,sh]
--------------------------------
# session    required   pam_limits.so
--------------------------------
===============================


[[sysconfig]]
==== Sysconfig file

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

[horizontal]
RPM::     `/etc/sysconfig/elasticsearch`
Debian::  `/etc/default/elasticsearch`

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


[[systemd]]
==== Systemd configuration

When using the RPM or Debian packages on systems that use
https://en.wikipedia.org/wiki/Systemd[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:

[source,sh]
---------------------------------
[Service]
LimitMEMLOCK=infinity
---------------------------------

Once finished, run the following command to reload units:

[source,sh]
---------------------------------
sudo systemctl daemon-reload
---------------------------------

[[jvm-options]]
==== Setting JVM options

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:

[source,sh]
---------------------------------
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
<<sysconfig,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.