MariaDB Fails to log in error log
You can execute this to see where the error log file is supposed to be written:
show global variables like 'log_error';

This can (sometimes) show a relative path, relative to the datadir.
From the documentation:

The error log is active by default. The log-error=filename option determines where the output will be written. If no file name is specified, the log will be written to host-name.err. If no absolute path is specified, the file will be written to the data directory (determined by the value of the datadir system variable).
On Unix systems, if the --log-error option is not used, the errors are written to stderr (usually, the command line).
On Windows, if the --console option is specified, and --log-error is not used, the errors are written to the console. If --log-error is present, --console is ignored.

Additionally, for warning messages, the log_warnings variable need to be &gt; 0. There are different warning levels, and the higher the value of log_warnings, the more kinds of warning messages are logged. For details, see the documentation for the log_warnings variable.
To see you current setting, run:
show global variables like 'log_warnings';