[jira] [Created] (HADOOP-14855) Hadoop scripts may errantly believe a daemon is still running, preventing it from starting

["Aaron T. Myers (JIRA)" <ji...@apache.org>]

Aaron T. Myers created HADOOP-14855:
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             Summary: Hadoop scripts may errantly believe a daemon is still running, preventing it from starting
                 Key: HADOOP-14855
                 URL: https://issues.apache.org/jira/browse/HADOOP-14855
             Project: Hadoop Common
          Issue Type: Bug
          Components: scripts
    Affects Versions: 3.0.0-alpha4
            Reporter: Aaron T. Myers


I encountered a case recently where the NN wouldn't start, with the error message "namenode is running as process 16769.  Stop it first." In fact the NN was not running at all, but rather another long-running process was running with this pid.

It looks to me like our scripts just check to see if _any_ process is running with the pid that the NN (or any Hadoop daemon) most recently ran with. This is clearly not a fool-proof way of checking to see if a particular type of daemon is now running, as some other process could start running with the same pid since the daemon in question was previously shut down.



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