[[gc-logging]]
=== GC logging

By default, {es} enables GC logs. These are configured in
<<jvm-options,`jvm.options`>> and output to the same default location as
the {es} logs. The default configuration rotates the logs every 64 MB and
can consume up to 2 GB of disk space.

You can reconfigure JVM logging using the command line options described in
https://openjdk.java.net/jeps/158[JEP 158: Unified JVM Logging]. Unless you
change the default `jvm.options` file directly, the {es} default
configuration is applied in addition to your own settings. To disable the
default configuration, first disable logging by supplying the
`-Xlog:disable` option, then supply your own command line options. This
disables __all__ JVM logging, so be sure to review the available options
and enable everything that you require.

To see further options not contained in the original JEP, see
https://docs.oracle.com/en/java/javase/13/docs/specs/man/java.html#enable-logging-with-the-jvm-unified-logging-framework[Enable
Logging with the JVM Unified Logging Framework].

==== Examples

* Change the default GC log output location to `/opt/my-app/gc.log` by
  creating `$ES_HOME/config/jvm.options.d/gc.options` with some sample
  options:
+
[source,shell]
--------------------------------------------
# Turn off all previous logging configuratons
-Xlog:disable

# Default settings from JEP 158, but with `utctime` instead of `uptime` to match the next line
-Xlog:all=warning:stderr:utctime,level,tags

# Enable GC logging to a custom location with a variety of options
-Xlog:gc*,gc+age=trace,safepoint:file=/opt/my-app/gc.log:utctime,pid,tags:filecount=32,filesize=64m
--------------------------------------------

* Configure an {es} <<docker,Docker container>> to send GC debug logs to
  standard error (`stderr`). This lets the container orchestrator
  handle the output. If using the `ES_JAVA_OPTS` environment variable,
  specify:
+
[source,sh]
--------------------------------------------
MY_OPTS="-Xlog:disable -Xlog:all=warning:stderr:utctime,level,tags -Xlog:gc=debug:stderr:utctime"
docker run -e ES_JAVA_OPTS="$MY_OPTS" # etc
--------------------------------------------