[[executable-jna-tmpdir]]
=== Ensure JNA temporary directory permits executables

[NOTE]
This is only relevant for Linux.

{es} uses the Java Native Access (JNA) library, and another library called
`libffi`, for executing some platform-dependent native code. On Linux, the
native code backing these libraries is extracted at runtime into a temporary
directory and then mapped into executable pages in {es}'s address space. This
requires the underlying files not to be on a filesystem mounted with the
`noexec` option.

By default, {es} will create its temporary directory within `/tmp`. However,
some hardened Linux installations mount `/tmp` with the `noexec` option by
default. This prevents JNA and `libffi` from working correctly. For instance,
at startup JNA may fail to load with an `java.lang.UnsatisfiedLinkerError`
exception or with a message that says something similar to
`failed to map segment from shared object`, or `libffi` may report a message
such as `failed to allocate closure`. Note that the exception messages can
differ between JVM versions. Additionally, the components of {es} that rely on
execution of native code via JNA may fail with messages indicating that it is
`because JNA is not available`.

To resolve these problems, either remove the `noexec` option from your `/tmp`
filesystem, or configure {es} to use a different location for its temporary
directory by setting the <<es-tmpdir,`$ES_TMPDIR`>> environment variable. For
instance:

* If you are running {es} directly from a shell, set `$ES_TMPDIR` as follows:
+
["source","sh",subs="attributes"]
--------------------------------------------
export ES_TMPDIR=/usr/share/elasticsearch/tmp
--------------------------------------------

* For installs done through RPM or DEB packages, the environment variable needs
to be set through the <<sysconfig,system configuration file>>.

* If you are using `systemd` to run {es} as a service, add the following
line to the `[Service]` section in a <<systemd,service override file>>:
+
[source,text]
--------------------------------------------
Environment=ES_TMPDIR=/usr/share/elasticsearch/tmp
--------------------------------------------

If you need finer control over the location of these temporary files, you can
also configure the path that JNA uses with the <<set-jvm-options,JVM flag>>
`-Djna.tmpdir=<path>` and you can configure the path that `libffi` uses for its
temporary files by setting the `LIBFFI_TMPDIR` environment variable. Future
versions of {es} may need additional configuration, so you should prefer to set
`ES_TMPDIR` wherever possible.

NOTE: {es} does not clear out the `/tmp` directory, as this could be an
unwelcome behavior in the event of a power outage or an Out of Memory error.
Instead, it's expected that temporary directories are cleaned out automatically
by the system on events such as a reboot. This is the behavior with the Linux
link:https://www.kernel.org/doc/html/latest/filesystems/tmpfs.html[tmpfs]
file system, for example.
