OpenSearch/docs/reference/setup/sysconfig/configuring.asciidoc

[[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
---------------------------------