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

Rowland Penny rowlandpenny at googlemail.com
Wed Dec 10 08:10:58 MST 2014

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 snapshot 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 the 
> 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:
>         Thanks 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 to 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 idmap.ldb with my unidirectional rsync
>         replication of the 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 uid/gid? Thanks in advance Tim Hi, I
>         think your problem is that idmap.ldb does not replicate to the
>         new DC, this means that users get different UID's on the two
>         DC's. If you run: ldbedit -e nano -H
>         /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
>         documented here:
>         https://wiki.samba.org/index.php/Join_a_domain_as_a_DC , near
>         the bottom of the page. Rowland I take it that you didn't read
>         this page on the wiki:
>         https://wiki.samba.org/index.php/Samba_AD_DC_HOWTO You are
>         running into one of the problems why it 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 to 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 ???? :
>     https://wiki.samba.org/index.php/Local_user_management_and_authentication/sssd
>     Rowland

OK, another wikipage: https://wiki.samba.org/index.php/RFC2307_backend

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 attributes.

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.


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