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https://issues.apache.org/jira/browse/HDFS-5767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13877004#comment-13877004
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Brandon Li commented on HDFS-5767:
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There are many ways things can go wrong. NSS configuration is correct doesn't
mean the user name id mapping is correct.
For example, in /etc/passwd, suppose we have
"test1:x:502:502::/home/test1:/bin/bash". By mistake, we added
"test1:x:503:503::/home/test1:/bin/bash" again to the end of the file. When we
do "getent passwd test1", most likely it returns the first found entry
"test1:x:502:502::/home/test1:/bin/bash". However, "getent passwd" will return
both test1 entries with different ids.
That's why we added the comments in the code, to remind administrator to remove
the duplicated entries as the above example.
> 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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