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Reviewed on: 2020-08-27

log_listener is a command line tool for retrieving log messages from fuchsia.logger.Log and either writing them to disk or printing them.


This tool is included in the core build product.


log_listener is typically invoked via the fx log command:

$ fx log --help

It can also be run directly on a Fuchsia shell:

$ fx shell log_listener --help


Unit tests for log_listener are available in the log_listener_tests package.

$ fx test log_listener_tests

Source layout

The implementation is located in src/ Unit tests are co-located with the code.

Persisting logs to disk

An instance of log_listener is always started to persist logs to disk, but by default is set to use 0 bytes of disk space. To change how much disk space log_listener is allowed to use to persist logs, append this argument to your fx set invocation:

--args 'max_log_disk_usage="64000"'

This will cause logs to be placed in /data/logs.all_logs. Once this file reaches half of the allowed maximum, it is renamed to /data/logs.all_logs.old and future data is written to a newly-created /data/logs.all_logs.