http://hadoop.apache.org/common/docs/current/mapred-default.html

If job tracker is static the history files are stored in this single well known place. If No value is set here, by default, it is in the local file system at ${hadoop.log.dir}/history. User can specify a location to store the history files of a particular job. If nothing is specified, the logs are stored in output directory. The files are stored in "_logs/history/" in the directory. User can stop

[shokai]

hadoopのコマンドラインオプション

[mogwaing]

default values in mapred-site.xml