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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3608) fuse_dfs: detect changes in UID ticket cache
Date Thu, 19 Jul 2012 17:36:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13418483#comment-13418483
] 

Aaron T. Myers commented on HDFS-3608:
--------------------------------------

bq. I only made it possible to change the timer period so I could do some testing on the command
line. If we later decide it should be configurable by end-users, let's address that in a follow-up
JIRA.

I'd agree with you that there's not much point in wanting to change the recheck interval if
it weren't for the fact that given the way it's currently implemented the cache expiry period
is determined only based on the recheck interval. It certainly seems reasonable to me that
an administrator might want to turn up or down the cache expiry period.
                
> fuse_dfs: detect changes in UID ticket cache
> --------------------------------------------
>
>                 Key: HDFS-3608
>                 URL: https://issues.apache.org/jira/browse/HDFS-3608
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 2.1.0-alpha
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>            Priority: Minor
>         Attachments: HDFS-3608.004.patch, HDFS-3608.006.patch, HDFS-3608.007.patch, HDFS-3608.008.patch
>
>
> Currently in fuse_dfs, if one kinits as some principal "foo" and then does some operation
on fuse_dfs, then kdestroy and kinit as some principal "bar", subsequent operations done via
fuse_dfs will still use cached credentials for "foo". The reason for this is that fuse_dfs
caches Filesystem instances using the UID of the user running the command as the key into
the cache.  This is a very uncommon scenario, since it's pretty uncommon for a single user
to want to use credentials for several different principals on the same box.
> However, we can use inotify to detect changes in the Kerberos ticket cache file and force
the next operation to create a new FileSystem instance in that case.  This will also require
a reference counting mechanism in fuse_dfs so that we can free the FileSystem classes when
they refer to previous Kerberos ticket caches.
> Another mechanism is to run a stat periodically on the ticket cache file.  This is a
good fallback mechanism if inotify does not work on the file (for example, because it's on
an NFS mount.)

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