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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14855) Hadoop scripts may errantly believe a daemon is still running, preventing it from starting
Date Thu, 21 Sep 2017 19:00:08 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16175291#comment-16175291
] 

Allen Wittenauer commented on HADOOP-14855:
-------------------------------------------

FYI JDK 9 includes JEP 102, Process API Updates, will provide a much more sane way for the
JDK to find it's pid.

> 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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