Log Files

You may notice with colcon-common-extensions installed there’s not much output to the console when you run colcon build or colcon test. The log output isn’t lost; it was written to the log directory.

Note

The --event-handlers argument can be used to output build logs to the console. For example, colcon build --event-handlers console_direct+ or colcon test --event-handlers console_direct+ will output everything in real time.

Let’s look at the log directory from What is a Workspace?.

log
├── build_2022-05-20_11-50-03
│ ├── events.log
│ ├── foo
│ │ ├── command.log
│ │ ├── stderr.log
│ │ ├── stdout.log
│ │ ├── stdout_stderr.log
│ │ └── streams.log
│ └── logger_all.log
├── COLCON_IGNORE
├── latest -> latest_build
├── latest_build -> build_2022-05-20_11-50-03
├── latest_test -> test_2022-05-20_11-50-05
└── test_2022-05-20_11-50-05
    ├── events.log
    ├── foo
    │ ├── command.log
    │ ├── stderr.log
    │ ├── stdout.log
    │ ├── stdout_stderr.log
    │ └── streams.log
    └── logger_all.log

The directory build_<date and time> contains all logs from the invocation of colcon build. test_<date and time> contains all the logs from the invocation of colcon test. On platforms that support symbolic links, latest_build points to the most recent build, and latest_test does the same for tests.

More generally, any verb that generates logs (e.g. build, test, test-result) will put them into a subdirectory named <verb>_<date and time>. latest_<verb> will point to the logs of the most recent invocation of that verb. The symbolic link latest will point to the most recent logs for any colcon verb.

Each <verb>_<date and time> directory has these files:

  • events.log contains all internal events dispatched. This file is mostly for debugging purposes.

  • logger_all.log contains all logging messages regardless of the log level. The first line of this file contains the exact command line invocation including all the arguments passed.

Notice each <verb>_<date and time> directory has a foo directory. More generally, a directory for every package is created. Package log directories have these files:

  • command.log contains the commands invoked for the package, e.g. calls to python setup.py.

  • stdout.log contains all the output printed to stdout.

  • stderr.log contains all the output printed to stderr.

  • stdout_stderr.log contains all the output printed to either stdout or stderr in the order they appeared.

  • streams.log combines the output of all log files in the order they appeared.

Note

colcon does its best to read concurrently from stdout and stderr to preserve the order, but it can’t guarantee correct order of log messages in all cases.