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https://issues.apache.org/jira/browse/HADOOP-14855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16159246#comment-16159246
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Aaron T. Myers commented on HADOOP-14855:
-----------------------------------------
Gotcha, all makes sense. I figured I wasn't the first person to encounter this,
but couldn't find the JIRA. I'll go ahead and close this one as a dupe of
HADOOP-9085.
> 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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