[jira] [Commented] (HADOOP-14818) Can not show help message of namenode/datanode/nodemanager when process started.

["Jack Bearden (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-14818?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16260426#comment-16260426 ] 

Jack Bearden commented on HADOOP-14818:
---------------------------------------

Hello! :)  
[~GergelyNovak], I applied your patch and it does now indeed produce help output for hdfs daemon commands while they are running. Nice!

While this appears to fix the issue, what would be the impact on our users? I can see a few potential side-effects from this:
# The changing of the exit code from 1 to 0 may break existing user's health checks
# Automation relying on a text output of this call (e.g. checking process ID of the namenode) will no longer work
# Help output may be misleading if the daemon commands for the namenode are expected to be executed when the daemon is not running


> Can not show help message of namenode/datanode/nodemanager when process started.
> --------------------------------------------------------------------------------
>
>                 Key: HADOOP-14818
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14818
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: bin
>    Affects Versions: 3.0.0-beta1
>            Reporter: Wenxin He
>            Assignee: Gergely Novák
>            Priority: Minor
>         Attachments: HADOOP-14818.001.patch
>
>
> We should always get the help message whenever the process is started or not.
> But now,
> when datanode starts, we get an error message:
> {noformat}
> hadoop# bin/hdfs datanode -h
> datanode is running as process 1701.  Stop it first.
> {noformat}
> when datanode stops, we get what we want:
> {noformat}
> hadoop# bin/hdfs --daemon stop datanode
> hadoop# bin/hdfs datanode -h
> Usage: hdfs datanode [-regular | -rollback | -rollingupgrade rollback ]
>     -regular                 : Normal DataNode startup (default).
> ...
> {noformat}



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