Hadoop namenode和mapred未启动

我已经在ubuntu 13.10上安装了hadoop，但是当我使用start-all.sh启动所有守护进程时。只有辅助名称节点正在启动。这将显示在屏幕上

starting namenode, logging to /home/shubham/Downloads/hadoop-1.2.1/libexec/../logs/hadoop-shubham-namenode-shubham-pc.out
localhost: starting datanode, logging to /home/shubham/Downloads/hadoop-1.2.1/libexec/../logs/hadoop-shubham-datanode-shubham-pc.out
localhost: secondarynamenode running as process 9580. Stop it first.
starting jobtracker, logging to /home/shubham/Downloads/hadoop-1.2.1/libexec/../logs/hadoop-shubham-jobtracker-shubham-pc.out
Error: Could not find or load main class export
localhost: starting tasktracker, logging to /home/shubham/Downloads/hadoop-1.2.1/libexec/../logs/hadoop-shubham-tasktracker-shubham-pc.out

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日志文件中有什么？检查namenode、datanode日志。