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https://issues.apache.org/jira/browse/HDFS-5767?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13883234#comment-13883234
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Yongjun Zhang commented on HDFS-5767:
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Hi [~brandonli],
What I suggested in my last update is a simplified solution for unique
<userName, userId> mapping. I don't have solution that supports multi-mapping
yet (I also put this aside a bit due to other stuff), but let me take a further
look on that.
BTW, for your info, http://linux.die.net/man/5/nsswitch.conf defines the
search order as:
"One or more service specifications e.g., "files", "db", or "nis". The order of
the services on the line determines the order in which those services will be
queried, in turn, until a result is found. "
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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