rebar3/test/upgrade_project/rel/files/sys.config

[
 %% SASL config
 {sasl, [
         {sasl_error_logger, {file, "log/sasl-error.log"}},
         {errlog_type, error},
         {error_logger_mf_dir, "log/sasl"},      % Log directory
         {error_logger_mf_maxbytes, 10485760},   % 10 MB max file size
         {error_logger_mf_maxfiles, 5}           % 5 files max
        ]}
].