HADOOP-2838, a new feature was introduced to set environment variables via the Hadoop config 'mapred.child.env' for child tasks. There are some further fixes and improvements around this feature, e.g. HADOOP-5981 were a bug fix; MAPREDUCE-478 broke the config into 'mapred.map.child.env' and 'mapred.reduce.child.env'. However the current implementation is still not complete. It does not match its documentation or original intend as I believe. Also, by using ‘:’ (colon) and ‘;’ (semicolon) in the configuration syntax, we will have problems using them on Windows because ‘:’ appears very often in Windows path as in “C:\”, and environment variables are used very often to hold path names. The Jira is created to fix the problem and provide support on Windows.