[Samba] Samba 4 two DCs no matching UID/GID

Tim rintimtim at gmx.net
Wed Dec 10 14:53:48 MST 2014

Am 10. Dezember 2014 22:26:52 MEZ, schrieb Rowland Penny <rowlandpenny at googlemail.com>:
>On 10/12/14 21:05, Tim wrote:
>> Thanks for your answer and time you offer for me. That makes it a bit
>> clearer.
>> I searched the web and found that rsat needs to have the nis tools 
>> installed. 
>Good luck with trying to install 'Service for NIS', it installs on a 
>windows AD DC, you haven't got a windows AD DC, you have a Samba AD DC 
>and  guess what, it already has the core of 'Service for NIS'

I meant the nis tools feature for getting the Unix attributes tab in rsat/ADUC. Sorry that I was misunderstood.

>> Does it create Unix uid/gid automatically then? 
>> Without rfc2307 information it makes no sense to me to have a *nix 
>> machine for file services and another one for backup purposes, when 
>> uid and gid are not same (due to preserve acls).
>> And for now the xid is set on the FS.
>Hard luck, that is just the way it is, **WHY* *do you think that it is 
>recommended to not use the DC as a fileserver ???
>> I haven't created a user or group with rsat nis tools enabled yet.
>> I strongly hope that nis information will be generated automatically 
>> in the AD then. I'll try it tomorrow.
>If you use the UNIX_Attributes tab in ADUC to give your users 
>'uidNumbers' etc, then it is likely that you will start at '10000'.

That's what I will do.

>you give your first user a 'uidNumber' then the next ID number will be 
>stored in AD.

Just to be sure: So once a user got the first uid in Unix tab in ADUC all new created users or groups with ADUC will get assigned a uid/gid automatically in Unix attributes tab?

For now, no user or group created with ADUC (without NIS tools installed) got an id in Unix tab. It's just empty.

>> Manual setting these attributes will not be comfortable and could be 
>> forgotten when creating a new user or group. In the end filesystem 
>> permissions on different filers will be corrupt - especially when one
>> DC will crash.
>That is why I am advising you to use ADUC, it is either that or writing
>your own bash script around samba-tool or the ldb-tools.
>> Am 10. Dezember 2014 20:58:06 MEZ, schrieb Rowland Penny 
>> <rowlandpenny at googlemail.com>:
>>     On 10/12/14 18:58, Tim wrote:
>>>     At the moment numbers start at 3000000 and counting. In my eyes
>>>     it would make sense, that these number be stored in the AD when
>>>     provisioned with rfc2307. Or it should be replicated by drs.
>>     The numbers you are seeing are coming from idmap.ldb, now as you
>>     are using Sernet packages on Centos7, this will be in
>>     /var/lib/samba/private/idmap.ldb. The number 3000000 is an
>>     xidNumber and is the result of samba4 mapping SID-RID to
>>     that Unix will understand.
>>     If you just used the Samba4 AD DC for authentication and didn't
>>     store *anything* on the DC, you wouldn't need 'xidNumbers',
>>     'uidNumbers' or 'gidNumbers', but then there is 'Sysvol'. You
>>     this for GPO's etc, but again, access is only allowed by windows
>>     users, so the xidNumbers are sufficient. I hope you can see, if
>>     you only have windows users, you only need rfc2307 attributes
>>     you store users files on the DC.
>>     As for storing Unix ID numbers in AD when provisioning with
>>     rfc2307, this does not and will not happen, Windows does not give
>>     users the rfc2307 attributes when 'Service for NIS' is added to
>>     and for a very good reason, all users might not require them.
>>>     says the following:
>>>     No need for manual ID counting when using the default Microsoft
>>>     tools. E. g. the next free UID and GID is stored directly in
>>>     Active Directory and will be incremented when creating a new
>>>     or group.
>>>     But what is needed for this? Manual setting of NIS domain in
>>>     attributes?
>>     If you create your users with samba-tool on the DC, one of the
>>     options is '--uid-number=', but you have to enter the number
>>     yourself, samba-tool has nowhere to store the next uidNumber.
>>>     The problem chapter describes my situation - but both DC have
>>>     idmap_ldb:use rfc2307 = yes
>>     The setting just tells the DC to use rfc2307, it does not set
>>     as I said, this is done by idmap.ldb, only problem is that the
>>     xidNumbers for a user are not forced to be the same on **both**
>>     Rowland
>>>     I forgot to say that my server is CentOS 7 with most recent
>>>     SerNet Samba 4.1.13
>>>     Am 10. Dezember 2014 19:25:50 MEZ, schrieb Rowland Penny
>>>     <rowlandpenny at googlemail.com>:
>>>         On 10/12/14 17:30, Tim wrote:
>>>>         I will try this tomorrow. Possibly this is my fix.
>>>>         When a domain is provisioned with rfc2307 it would make
>>>>         sense that Unix attributes especially uid/gid would
>>>>         automatically be set.
>>>         This is a common misconception, it does not happen, one
>>>         reason being, what number do you start at ??
>>>>         A member also needs this to be set for unique fs acls
>>>         This is where winbind works if there are RFC2307 attributes
>>>         in AD, it can be set up to pull all the required attributes
>>>         from AD, this is one of the reasons that it is recommended
>>>         use member servers with a DC.
>>>         Rowland
>>>>         Am 10. Dezember 2014 18:07:02 MEZ, schrieb Rowland Penny
>>>>         <rowlandpenny at googlemail.com>:
>>>>             On 10/12/14 16:33, Tim wrote:
>>>>>             I think I will only need uid and gid due to fs stuff.
>>>>>             There are only Windows clients in that domain.
>>>>>             So when the IDs are the same on both DCs, all will be
>>>>>             fine I think.
>>>>>             In RSAT there are no Unix attributes set. As an
>>>>>             example: user1 has uid 3000021 on DC1 (first
>>>>>             provisioned one). DRS seems fine. On DC2 user1 gets
>>>>>             3000017.
>>>>>             If I set ID in RSAT Unix attributes after choosing
>>>>>             domain, the IDs mentioned above will be overwritten?
>>>>>             Standard in Unix attributes is that ID is not set.
>>>>>             I set ID 2000021 in RSAT this ID will be set for user1
>>>>>             on both DCs because of use rfc2307 = yes?
>>>>>             Regards
>>>>>             Tim
>>>>>             Am 10. Dezember 2014 16:10:58 MEZ, schrieb Rowland
>>>>>             Penny <rowlandpenny at googlemail.com>:
>>>>>                 On 10/12/14 14:39, Tim wrote:
>>>>>                     I found this. But I didn't find it related to
>>>>>                     DC idmapping replication. I have two pieces of
>>>>>                     hardware. My goal is realize an active
>>>>>                     directory for the windows clients and a file
>>>>>                     server. The AD should have redundancy (this is
>>>>>                     why I provisioned two DCs). The file should
>>>>>                     integrate snapshots like a NetApp system
>>>>>                     (snapshots are done by rsnapshot). The
>>>>>                     functionality works so far by mounting cifs
>>>>>                     shares read only of the backup hardware. But I
>>>>>                     will try this via NFS due to permissions.
>>>>>                     Mounting cifs shares leads to irritating
>>>>>                     permissions of ~snapshot folders ("Everyone"
>>>>>                     has full permissions). So how would sssd help
>>>>>                     to replicate the ids regarding idmapping to
>>>>>                     secondary DC? It seems that this is my only
>>>>>                     problem. Another option is to have only one DC
>>>>>                     with NFS regarding snapshots and a file server
>>>>>                     who is integrating the snapshots as mentioned
>>>>>                     above. But then I have to backup the idmapping
>>>>>                     file of the file server or does it get the ids
>>>>>                     from the AD DC so that I don't have to backup?
>>>>>                     The FS stores the ACL by using the IDs. I am
>>>>>                     using XFS. Thanks in advance Tim Am 10.
>>>>>                     Dezember 2014 13:48:40 MEZ, schrieb Rowland
>>>>>                     Penny <rowlandpenny at googlemail.com>: On
>>>>>                     10/12/14 12:21, rintimtim at gmx.net wrote:
>>>>>                     for the advice of copying the idmap.ldb. That
>>>>>                     works. After adding zum users the uid and gid
>>>>>                     begin to differ again. I read that it is not
>>>>>                     recommended to run a DC as a fileserver but in
>>>>>                     my case it's not really an option. It's a
>>>>>                     network of twelve clients, so four servers are
>>>>>                     incommensurate to this amount of clients. I
>>>>>                     searched regarding sssd, because my
>>>>>                     nsswitch.conf also has it. But how do I have
>>>>>                     configure it all? My actual nsswitch.conf
>>>>>                     provides the following: passwd: files sss
>>>>>                     shadow: files sss group: files sss services:
>>>>>                     files sss netgroup: files sss Another
>>>>>                     alternative seems to be regarding the
>>>>>                     with my unidirectional rsync replication of
>>>>>                     sysvol-folder. *Gesendet:* Mittwoch, 10.
>>>>>                     Dezember 2014 um 11:01 Uhr *Von:* "Rowland
>>>>>                     Penny" <rowlandpenny at googlemail.com> *An:* Tim
>>>>>                     <rintimtim at gmx.net>, samba at lists.samba.org
>>>>>                     *Betreff:* Re: [Samba] Samba 4 two DCs no
>>>>>                     matching UID/GID On 09/12/14 22:49, Tim wrote:
>>>>>                     But will this idmap.ldb change work for
>>>>>                     upcoming new users or groups so that uid/gid
>>>>>                     will not be different? The wiki tells us about
>>>>>                     built-in groups. Those have the right ids. Am
>>>>>                     9. Dezember 2014 23:03:44 MEZ, schrieb Rowland
>>>>>                     Penny <rowlandpenny at googlemail.com>: On
>>>>>                     09/12/14 21:07, Tim wrote: Hello all, I have a
>>>>>                     fresh install of two CentOS 7 machines. On DC1
>>>>>                     I made a domain provision with --use-rfc2307.
>>>>>                     In DC2 I made a join as DC - both exactly as
>>>>>                     the wiki advised. In fact of its missing I
>>>>>                     added the idmap use rfc2307 yes parameter to
>>>>>                     smb.conf. I will have an extra share on both
>>>>>                     DCs. Today I realized, that wbinfo shows
>>>>>                     different UID/GID for the same users or groups
>>>>>                     on the DC's. I created the users/groups via
>>>>>                     RSAT. I don't have a Unix attributes tab in
>>>>>                     RSAT. Is that my problem for different
>>>>>                     Thanks in advance Tim Hi, I think your problem
>>>>>                     is that idmap.ldb does not replicate to the
>>>>>                     DC, this means that users get different UID's
>>>>>                     on the two DC's. If you run: ldbedit -e nano
>>>>>                     /var/lib/samba/private/idmap.ldb on each DC,
>>>>>                     you will be able to see the differences. The
>>>>>                     cure ? copy idmap.ldb from the first DC to any
>>>>>                     secondary DC's after the join. It is
>>>>>                     here:
>>>>>                     , near the bottom of the page. Rowland I take
>>>>>                     it that you didn't read this page on the wiki:
>>>>>                     You are running into one of the problems why
>>>>>                     is not recommended to use the DC as a
>>>>>                     fileserver, you have two choices here, either
>>>>>                     set up a separate member server to use as a
>>>>>                     fileserver, or use sssd or nlscd to pull the
>>>>>                     RFC2307 attributes that you will need to add
>>>>>                     the users/groups. Whatever you do, you will
>>>>>                     need to copy idmap.ldb to any secondary DC's.
>>>>>                     Rowland Did you search on the samba wiki ????
>>>>>                     Rowland
>>>>>                 OK, another
>>>>>                 The only way to ensure that your users have
>consistent uidNumbers &
>>>>>                 gidNumbers on **any**  Unix machine, is to use the
>RFC2307 attributes.
>>>>>                 The attributes are all available out of the box
>with Samba4, you just
>>>>>                 have to give your users and groups the required
>>>>>                 Once you have given your users & groups these
>attributes, you then have
>>>>>                 to use something to pull these attributes. Winbind
>is available from
>>>>>                 Samba, but winbind on the DC is different from the
>winbind that is used
>>>>>                 on a member server or client. The winbind that is
>available on the DC
>>>>>                 will not pull any RFC2307 attributes other than
>'uidNumber' &
>>>>>                 'gidNumber'. What this means is, if you want to
>use different
>>>>>                 unixHomeDirectories & loginShell's, you need to
>use sssd or nlscd.
>>>>>                 Rowland
>>>>             By default, no users have a uidNumber and no groups
>>>>             a gidNumber. If you use the UNIX_Attributes tab in
>>>>             the default start number is 10000, though you can
>>>>             this, I wouldn't bother. Just update any users via
>>>>             AD will then store the next uidNumber (or gidNumber)
>>>>             you. If you then go to the DC and run 'getent passwd
>>>>             <the user you just updated on ADUC>', you will find
>>>>             the users ID number will have changed to whatever you
>>>>             used in ADUC. This same command should give the same
>>>>             result on the second DC, though there may be a problem
>>>>             on both DC's if the cache hasn't cleared, if so, wait a
>>>>             short while, or run 'net cache flush'.
>>>>             If you update users with ADUC, do not add users with
>>>>             samba-tool and try to add the users uidNumber at the
>>>>             same time, you could use a number that is already in
>>>>             for another user. You can use the same number for a
>>>>             group as a user, they are different objects.
>>>>             If you do use ADUC to add the users uidNumber and the
>>>>             user already has any info stored on the DC, you will
>>>>             need to change the ownership of this info to the user
>>>>             (the info will show as belonging to the users old
>>>>             uidNumber).
>>>>             Rowland

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