How to make debug statements visible in the Canton Sandbox logs

Three years ago, to make debug statements visible in the sandbox logs, @cocreature suggested the following:

…write a custom logback configuration file
You can find the default logback config used by daml sandbox at
$HOME/.daml/sdk/$YOUR_SDK_VERSION/daml-sdk/sandbox-logback.xml .

Today’s Canton-based Daml SDK does not have a sandbox-logback.xml file.

Two questions:

  1. Where can I find the equivalent in the Daml SDK 2.6? Is this logback.xml the one I’m looking for?

  2. What do I need to add to the logback file to include the output of debug statements in the log file?

The daml sandbox command is a very thin wrapper around the canton application. If you need to debug, I’d recommend to run canton directly:

https://docs.daml.com/canton/tutorials/getting_started.html

For debugging, you might find these two guides helpful:

https://docs.daml.com/canton/usermanual/monitoring.html#logging

https://docs.daml.com/canton/usermanual/troubleshooting_guide.html

For large models and in-depth debugging, I’m sure you are right, @Ratko_Veprek – run canton directly.

I was still curious, for the use case of simple tutorials and demos, how to get visibility to debug output when using daml start and Navigator. I learned more about Logback than I wanted. Here is what I found works:

  1. Copy the Canton logback.xml file into your project root.
    jar xf ~/.daml/sdk/<SDK VERSION>/canton/canton.jar logback.xml

  2. Add the following to the logback.xml before the closing </configuration>:

     <if condition='isDefined("LOG_DAML_TRACELOG")'>
       <appender name="TRACELOG_FILE" class="ch.qos.logback.core.FileAppender">
         <file>log/trace.log</file>
         <encoder>
           <pattern>%date [%thread] %-5level %logger{10} &entityCorrelationIdTrailingSpaceReplace;</pattern>
         </encoder>
       </appender>
       <logger name="daml.tracelog" level="DEBUG">
         <appender-ref ref="TRACELOG_FILE" />
       </logger>
     </if>
    
  3. export _JAVA_OPTIONS="-Dlogback.configurationFile=./logback.xml"

  4. TRACELOG_FILE=1 daml start

I now see the output of my debug statements in a log/trace.log file.

If this looks good to others, we could add it to the default logback.xml file.

Actually, I get duplicate entries in my log/trace.log file. As best I can tell, that is not related to my logback.xml edits. So I’ll leave that for another question.

To further extend on this topic, is it possible to define a new logback file in ledger run time? Or any way to change log level while ledger is still running?