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From s29752-hadoopu...@yahoo.com
Subject Re: Hadoop Permissions Question -> [Fwd: Hbase on hadoop]
Date Fri, 09 May 2008 18:34:03 GMT
Hi Stack,

> One question this raises is if the "hbase:hbase" user and group are being derived from
the Linux file system user and group, or if they are the hdfs user and group?
HDFS currently does not manage user and group information.  User and group in HDFS are being
derived from the underlying OS (Linux in your case) user and group.

> Otherwise, how can we indicate that "hbase" user is in the hdfs group "supergroup"? 
In Hadoop conf, the property dfs.permissions.supergroup specifies the super-user group and
the default value is "supergroup".  Administrator should set this property to a dedicated
group in the underlying OS for HDFS superuser.  For example, you could create a group "hdfs-superuser"
in Linux, set dfs.permissions.supergroup to "hdfs-superuser" and add "hdfs-superuser" to hbase's
group list.  Then, "hbase" becomes a HDFS superuser.

I don't know why superuser privilege is required to run HMaster.  I might be able to tell
if a complete stack track is given.


----- Original Message ----
From: stack <stack@duboce.net>
To: hadoop-user@lucene.apache.org
Sent: Thursday, May 8, 2008 8:44:42 PM
Subject: Hadoop Permissions Question -> [Fwd: Hbase on hadoop]

Can someone familiar with permissions offer an opinion on the below?

We have an issue with hbase on hadoop and file system permissions we  
hope someone already knows the answer to.  Our apologies if we missed  
that this issue has already been addressed on this list.

We are running hbase-0.1.2 on top of hadoop-0.16.3, starting the hbase  
daemon from an "hbase" user account and the hadoop daemon and have  
observed this "feature".   We are running hbase in a separate "hadoop"  
user account and hadoop in it's own "hadoop" user account on a single  

When we try to start up hbase, we see this error message in the log:

2008-05-06 12:09:02,845 ERROR org.apache.hadoop.hbase.HMaster: Can not  
start master
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native  
    at java.lang.reflect.Constructor.newInstance(Constructor.java:494)
    at org.apache.hadoop.hbase.HMaster.doMain(HMaster.java:3329)
    at org.apache.hadoop.hbase.HMaster.main(HMaster.java:3363)
Caused by: org.apache.hadoop.ipc.RemoteException:  
org.apache.hadoop.fs.permission.AccessControlException: Superuser  
privilege is required
         ... (etc)

If we run hbase in the hadoop user account we don't have any problems.

We think we've narrowed the issue down a bit from the debug logs.

The method "FSNameSystem.checkPermission()" method is throwing the  
exception because the "PermissionChecker()" constructor is returning  
that the hbase user is not a superuser or in the same supergroup as  

   private void checkSuperuserPrivilege() throws  
AccessControlException {
     if (isPermissionEnabled) {
       PermissionChecker pc = new PermissionChecker(
           fsOwner.getUserName(), supergroup);
       if (!pc.isSuper) {
         throw new AccessControlException("Superuser privilege is  

If we look at at the "PermissionChecker()" constructor we see that it  
is comparing the hdfs owner name (which should be "hadoop") and the  
hdfs file system owner's group ("supergroup") to the current user and  
groups, which the log seems to indicate the user is "hbase" and the  
groups for user "hbase" only include "hbase" :
   PermissionChecker(String fsOwner, String supergroup
       ) throws AccessControlException{
     UserGroupInformation ugi = UserGroupInformation.getCurrentUGI();
     if (LOG.isDebugEnabled()) {
       LOG.debug("ugi=" + ugi);

     if (ugi != null) {
       user = ugi.getUserName();
       isSuper = user.equals(fsOwner) || groups.contains(supergroup);
     else {
       throw new AccessControlException("ugi = null");

The current user and group is derived from the thread information:
   private static final ThreadLocal<UserGroupInformation> currentUGI
     = new ThreadLocal<UserGroupInformation>();

   /** @return the {@link UserGroupInformation} for the current thread  
   public static UserGroupInformation getCurrentUGI() {
     return currentUGI.get();

which we're hoping might be enough to illuminate the problem.

One question this raises is if the "hbase:hbase" user and group are  
being derived from the Linux file system user and group, or if they  
are the hdfs user and group?
Otherwise, how can we indicate that "hbase" user is in the hdfs group  
"supergroup"? Is there a parameter in a hadoop configuration file?  
Apparently setting the groups of the web server to include  
"supergroup" didn't have any effect, although perhaps that could be  
for some other reason?

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