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https://issues.apache.org/jira/browse/HDFS-3618?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13435937#comment-13435937
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Vinay commented on HDFS-3618:
-----------------------------
* Regarding StreamPumper thread getting hanged:
I tried to reproduce issue by creating a small pause using debug point before
starting the thread for reading streams inside
{{SshFenceByTcpPort.execCommand(Session, String)}}, before executing
{{errPumper.start();}}.
By the time I release the debug point, {{exec}} was closed. And {{errPumper}}
got hanged.
*# We can start the threads for reading streams only if {{exec}} is not closed.
*# We can wait till {{exec}} is closed before getting exitStatus.
* Regarding nc command not found case I think we can handle as following
*# If the command present and process running with specified port, then nc exit
code will be 0
*# Command present and no process is running with that port, then nc exit code
will be 1.
*# If command itself will not present then exit code will be 127.
*# If command dont have permissions then exit code will be 126 ( as Uma
mentioned)
Here we need to treat only return code 1 as success, others should be treated
as failed.
One configuration we can introduce to specify the alternative {{nc}} command
(netcat) in case its not present in the machine.
> SSH fencing option may incorrectly succeed if nc (netcat) command not present
> -----------------------------------------------------------------------------
>
> Key: HDFS-3618
> URL: https://issues.apache.org/jira/browse/HDFS-3618
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: auto-failover
> Affects Versions: 2.1.0-alpha
> Reporter: Brahma Reddy Battula
> Attachments: zkfc_threaddump.out, zkfc.txt
>
>
> Started NN's and zkfc's in Suse11.
> Suse11 will have netcat installation and netcat -z will work(but nc -z wn't
> work)..
> While executing following command, got command not found hence rc will be
> other than zero and assuming that server was down..Here we are ending up
> without checking whether service is down or not..
> {code}
> LOG.info(
> "Indeterminate response from trying to kill service. " +
> "Verifying whether it is running using nc...");
> rc = execCommand(session, "nc -z " + serviceAddr.getHostName() +
> " " + serviceAddr.getPort());
> if (rc == 0) {
> // the service is still listening - we are unable to fence
> LOG.warn("Unable to fence - it is running but we cannot kill it");
> return false;
> } else {
> LOG.info("Verified that the service is down.");
> return true;
> }
> {code}
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