Solr 1.0 to 1.3

Solr uses JDK standard logging, (ie; the java.util.logging.* package), an overview of how that can be configured at the JVM level can be found here...

http://java.sun.com/j2se/1.5.0/docs/guide/logging/overview.html

...but many servlet containers provide alternate log configuration options in their configuration files. You should consult your servlet containers documentation to see what options are available.

The Solr Admin console has a screen for toggling the logging level globally. This is a transient setting good for doing diagnostic work, but does not persist after reboot.

If you don't know much about JDK containers or servlet containers and want a quick recipe for modifying the logging settings for default Solr example/ setup, see LoggingInDefaultJettySetup.

Solr 1.4 and Above

Starting with Solr 1.4, the Solr Code base compiles against the "SLF4J" API and provides a runtime jar (slf4j-jdk14-X.Y.Z.jar) that implements SLF4J using JDK standard logging -- so all of the information above regarding Solr 1.3 still applies by default.

Users who want an alternate logging implementation (log4j, logback etc) will need to repackage the .war file and replace slf4j-jdk14-X.Y.Z.jar with an alternate implementation.

More Info: http://www.slf4j.org/