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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3618) SSH fencing option may incorrectly succeed if nc (netcat) command not present
Date Tue, 10 Jan 2017 21:31:58 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3618?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15816250#comment-15816250
] 

Kihwal Lee commented on HDFS-3618:
----------------------------------

The "-z" option is supported by the plain old BSD implementation of netcat. It looks like
newer distros are moving to NMAP's netcat replacement, which does not support "-z".

Someone suggested an equivalent of "-z" for nmap-ncat.
http://unix.stackexchange.com/questions/296023/whats-the-gnu-netcats-z-equivalent-option-in-nmap-ncat

A lazy way out is simply making the entire command configurable.  One could also make it detect
which variant is available.  {{nc -z 127.0.0.1 1234}} will return 2 if the host has nmap-ncat
and 0 or 1 if bsd nc. 

> 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: 2.0.0-alpha
>            Reporter: Brahma Reddy Battula
>            Assignee: Vinayakumar B
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-3618-04.patch, HDFS-3618.patch, HDFS-3618.patch, HDFS-3618.patch,
zkfc.txt, zkfc_threaddump.out
>
>
> 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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