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7. Standardize log output

· One min read




  • ADR 2 is not completely relevant now, we have migrated recently the logs in the client to stderr. Only the result of the command execution is in stdout. This makes it possible to exploit the result, see our blog post.
  • Mithril aggregator logs are always redirected to stdout but it mixes 2 types of CLI commands, some of which would benefit from the logs output to stderr.
  • Mithril aggregator and Mithril client CLI have not a consistent log strategy, that's why we need to standardize them.


  • For commands that provide a result or execute an action, logs are sent to stderr. Only the result of the command is sent to stdout.
  • For commands that launch a program without an expected result (server), logs are sent to stdout.


  • End users who use stdout logs would have a breaking change. They will have to retrieve the logs that come from stderr in addition.
  • Commands genesis, era and tools from Mithril aggregator now send their logs to stderr.