There is rare happenings during map or reduce phase, but mostly in map phase, the Exception messages:
java.lang.Throwable: Child Error
Caused by: java.io.IOException: Task process exit with nonzero status of 126.
and error logs are cleaned, so It's very hard to debug.
but I compared DefaultTaskController.java with 0.22, they use "bash command" to start the job scritp, but 1.0.4 use "bash, "-c", command".
I removed "-c", everything is ok, 126 error code never happen again.
I read man document of bash, it indicates when fork a new thread with write command, another thread with "bash -c" also has a writable fd. so I think it could return 126 status occasionally.
So, there is only one line fix for this issue.