How to View Apollo Logs?
==========================

How can I view Apollo log files? And how can I print logs to the terminal?

-  Maintainer: \ daohu527@gmail.com
-  Version: 1.0.0
-  Date: 05/09/2024
-  Description:

Answer
------

Apollo provides five log levels: DEBUG, INFO, WARN, ERROR, and FATAL. By default, the system only saves logs of level INFO and above, and only outputs logs of level WARN and above to the terminal.

Log File Storage
~~~~~~~~~~~~~~~~

Apollo's log files are saved by module and are located in the ``data/log`` folder. A new log file is created based on the current timestamp each time the system starts, and it is linked to the corresponding ``ModuleName.INFO.log`` file for quick access. Historical log files are saved according to their timestamps.

For example, when the perception module is started, the system will create a new log file based on the current timestamp and link it to ``perception.INFO.log``.

If you want the logs to output to a separate file, you can use the following method, and the logs will be saved in the ``ModuleName.INFO.log`` file.

.. code:: cpp

   ALOG_MODULE("ModuleName", INFO) << "Hello world!";

Terminal Log Printing
~~~~~~~~~~~~~~~~~~~~~

By default, DEBUG-level logs are not displayed, but you can enable DEBUG log display by modifying the value of ``GLOG_v`` in the ``cyber/setup.bash`` file to ``4``.

.. code:: bash

   # Enable DEBUG logs
   # for DEBUG log
   export GLOG_v=4

If you want the log information to be output both to the terminal and to the log file, you need to set the value of ``GLOG_alsologtostderr`` to ``1``. By default, this value is 0 (i.e., not output to the terminal).

.. code:: bash

   # export GLOG_alsologtostderr=0

   # Allow logs to be output to the terminal as well
   export GLOG_alsologtostderr=1

Make sure to execute the command ``source cyber/setup.bash`` in the terminal to apply these modifications.