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From "Yongjun Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5767) Nfs implementation assumes userName userId mapping to be unique, which is not true sometimes
Date Tue, 21 Jan 2014 00:39:19 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877036#comment-13877036
] 

Yongjun Zhang commented on HDFS-5767:
-------------------------------------

Hi [~brandonli]. 

This new example you provided seems to be a mistake that the administrator made, so I think
the redundant entry in the same database definitely need to be removed. 

My last question was about the case I'm not sure, that is, when nsswitch.conf specifies 
   passwd files ldap

And there may be two entries for the same user (the user "hadoop" example in your post of
17/Jan/14 14:30), one in /etc/passwd, the other in ldap. 

In this case, are you also suggesting removing one entry from either /etc/passwd or ldap,
so there are no overlap between the entries in different databases specified in nsswitch.conf
need to be mutual exclusive)? or "getent passwd" should return only the first entry found?
 
Just want to clarify, thanks.


> Nfs implementation assumes userName userId mapping to be unique, which is not true sometimes
> --------------------------------------------------------------------------------------------
>
>                 Key: HDFS-5767
>                 URL: https://issues.apache.org/jira/browse/HDFS-5767
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: nfs
>    Affects Versions: 2.3.0
>         Environment: With LDAP enabled
>            Reporter: Yongjun Zhang
>            Assignee: Brandon Li
>
> I'm seeing that the nfs implementation assumes unique <userName, userId> pair to
be returned by command  "getent paswd". That is, for a given userName, there should be a single
userId, and for a given userId, there should be a single userName.  The reason is explained
in the following message:
>  private static final String DUPLICATE_NAME_ID_DEBUG_INFO = "NFS gateway can't start
with duplicate name or id on the host system.\n"
>       + "This is because HDFS (non-kerberos cluster) uses name as the only way to identify
a user or group.\n"
>       + "The host system with duplicated user/group name or id might work fine most of
the time by itself.\n"
>       + "However when NFS gateway talks to HDFS, HDFS accepts only user and group name.\n"
>       + "Therefore, same name means the same user or same group. To find the duplicated
names/ids, one can do:\n"
>       + "<getent passwd | cut -d: -f1,3> and <getent group | cut -d: -f1,3>
on Linux systms,\n"
>       + "<dscl . -list /Users UniqueID> and <dscl . -list /Groups PrimaryGroupID>
on MacOS.";
> This requirement can not be met sometimes (e.g. because of the use of LDAP) Let's do
some examination:
> What exist in /etc/passwd:
> $ more /etc/passwd | grep ^bin
> bin:x:2:2:bin:/bin:/bin/sh
> $ more /etc/passwd | grep ^daemon
> daemon:x:1:1:daemon:/usr/sbin:/bin/sh
> The above result says userName  "bin" has userId "2", and "daemon" has userId "1".
>  
> What we can see with "getent passwd" command due to LDAP:
> $ getent passwd | grep ^bin
> bin:x:2:2:bin:/bin:/bin/sh
> bin:x:1:1:bin:/bin:/sbin/nologin
> $ getent passwd | grep ^daemon
> daemon:x:1:1:daemon:/usr/sbin:/bin/sh
> daemon:x:2:2:daemon:/sbin:/sbin/nologin
> We can see that there are multiple entries for the same userName with different userIds,
and the same userId could be associated with different userNames.
> So the assumption stated in the above DEBUG_INFO message can not be met here. The DEBUG_INFO
also stated that HDFS uses name as the only way to identify user/group. I'm filing this JIRA
for a solution.
> Hi [~brandonli], since you implemented most of the nfs feature, would you please comment?

> Thanks.



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