Elasticsearch OpenSearch Bootstrap.Memory_Lock is Set to False

By Opster Team

Updated: Oct 19, 2023

| 2 min read


OpenSearch performance can be heavily penalised if the node is allowed to swap memory to disk. OpenSearch can be configured to automatically prevent memory swapping on its host machine by adding the bootstrap memory_lock true setting to opensearch.yml. If bootstrap checks are enabled, Elasticsearch will not start if memory swapping is not disabled. You can learn more about bootstrap checks here: Bootstraps Check in OpenSearch – A Detailed Guide With Examples.

Note: It may be perfectly valid to have 

bootstrap.memory_lock: false

In your configuration if you have taken alternative steps to stop memory swapping. See Other ways of Preventing Memory Swapping below.

How to resolve it

Edit opensearch.yml to include the following setting:

bootstrap.memory_lock: true

You can check whether the setting has worked by running:

GET _nodes?filter_path=**.mlockall

You should see true in the output.

  "nodes" : {
"ifU4SFrKTcCaR5Om0uFFbw" : {
  "process" : {
    "mlockall" : true

If on the other hand you see false, then further configuration is necessary.

RPM and Debian SystemD installations

sudo systemctl edit opensearch 

Add the following:

sudo systemctl daemon-reload

.zip and .tar.gz installations

Add the following line to  /etc/security/limits.conf

opensearch  -  nofile  65535

Other ways of preventing memory swapping

There are other ways of preventing memory swapping other than using 

bootstrap.memory_lock: false

Turn off all swapping on Linux option 1

sudo swapoff -a

This doesn’t require a restart of OpenSearch.

To disable permanently (upon restart) edit /etc/fstab file

Comment out any lines containing “swap” below is just an example

#/dev/mapper/ubuntu--vg-swap_1 none        swap sw          0  

Turn off all swapping on Linux using sysctl option 2

Edit /etc/sysctl.conf


Checking memory swapping is effective


GET _nodes/stats/os

You should see the following in the response for each of the nodes:

"swap" : {
      "total_in_bytes" : 0,
      "free_in_bytes" : 0,
      "used_in_bytes" : 0