/WEB-INF/classes/META-INF/portal-log4j-ext.xml
<?xml version="1.0"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<category name="com.liferay.portal.kernel.servlet.filters.invoker">
<priority value="DEBUG" />
</category>
</log4j:configuration>
add log4j.dtd
to <liferay webapp root>/WEB-INF/classes/META-INF/
folder.
Log for log4j.dtd
can be found from <liferay webapp root>/WEB-INF/lib/portal-impl.jar
.