`ros2log` new 1st class command group support

[fujitatomoya]

Description

Provide a dedicated ros2log command group in ros2cli repository to inspect and manipulate ROS 2 runtime logging configuration on nodes. This would unify and improve the user experience for logging-related actions (such as setting/getting log level) compared to the existing scattered approaches (e.g., ad-hoc subcommands or raw service calls).

Motivation

Logging configuration from the command line is limited or inconsistent (e.g., only default log-level flags in some commands), and there is no central dedicated CLI for logging operations. As ROS 2 logging is crucial for debugging and production diagnostics, users need a clear and ergonomic CLI to interact with it.

• Consistent CLI UX for logging across ROS 2.
• Avoids error-prone workflows (e.g., manual service calls).
• Makes logging control discoverable via ros2 log --help.
• Facilitates production debugging and runtime introspection.

Design / Implementation Considerations

Proposed Functionality: Introduce a new ros2 log CLI with subcommands

Subcommand	Description
ros2 log list	List nodes that support runtime log configuration
ros2 log levels	Show all valid log level values (e.g., DEBUG, INFO, WARN, ERROR, FATAL)
ros2 log get <node>	Retrieve the current log level of a node (Could optionally show all loggers under that node)
ros2 log set <node> <level>	Set the log level of a node
ros2 log watch <node> <level>	Tail/monitor logs from a node via rosout (it tries to enable content filtering from rmw implementation)
ros2 log describe <node>	Display metadata (available loggers, effective levels).

Note that above are just ideas, we might need more options and arguments for basic design.

We probably need to add some facility or API for client interface to get available logger names in the node from the logger hash map maintained in rcutils.
It would be nice to manage the endpoints with --all/-a options to set(reset) the logger levels globally.

Additional Information

Related Information:

• Add verb for setting a node's log level #1060
• List loggers of a node. ros2#1762
• External logging level configuration ros2#1355
• Command to monitor and pretty print the rosout logs #849 #850
• Command to monitor and pretty print the rosout logs #849
• https://docs.ros.org/en/rolling/Tutorials/Demos/Logging-and-logger-configuration.html#logger-level-configuration-externally

[fujitatomoya]

@mjcarroll i just added this to Lyrical Luth project board.

this item has been discussed in ROS Japan Developer Meeting, and we are happy to make contribution for this new feature.

[fujitatomoya]

@Decwest CCed

[mjcarroll]

I'm absolutely in favor of this improvement. The proposed UX would be substantially better than the current status quo.

[fujitatomoya]

@mjcarroll thanks for the comment. we will come up with more detailed design later.

[fujitatomoya]

Including some people who showed interests on this topic from related PRs and issues.

@nnarain @christophebedard @ahcorde @rodericktaylor @guillaumeautran

[fujitatomoya]

@nnarain @christophebedard @ahcorde @rodericktaylor @guillaumeautran

I created the REP openrobotics/reps#20, please have a look at it and share your feedback.

[guillaumeautran]

You have probably seen this already but we do have the equivalent of ros2 log watch command in our ros2cli extensions here: https://github.com/clearpathrobotics/clearpath_ros2cli/tree/rolling/ros2rosout

I'll be happy to lend a hand with the implementation of this proposal.