In the left panel of the WebSphere web console, expand Troubleshooting and select Logs and trace. Select one of your WebSphere application servers (aka JVM). Select Diagnostic Trace. Options to configure the trace.log are displayed.

Tracing is used when you are attempting to debug a specific feature of WebSphere. For example, let's say some issue is occurring when attempt to stop or start an application server. The -trace option can be used along with the stopServer.sh and startServer.sh commands to add tracing events to trace.log and SystemOut.log.

${was_install_root}/profiles/your_profile/bin/stopServer.sh server01 -trace
${was_install_root}/profiles/your_profile/bin/startServer.sh server01 -trace