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

rintimtim at gmx.net rintimtim at gmx.net
Thu Dec 11 04:44:12 MST 2014

Thanks for your advice regarding modifying the ldb. Before I do that I have to tell that uids and gids are automatically assigned in ADUC Unix tab.

All have to do is to choose the NIS domain. After changing this field all other Unix attributes are automatially filled in. So this works.

I tried something different for testing: 

I added a user with samba-tool using a script and assigned a random (based on date) number for uid:
Script add-ad-user:
samba-tool user create $1 --uid-number=$(date +%H%M%S)

Calling the script add-ad-user test1

Something interesting happens: The random uid is assigned to that user in rfc2307. Both DC's have this same uid when I do "wbinfo -i test1". The unix tab of ADUC remains empty.
I added "add user script = /path/to/script/add-ad-user %u" to smb.conf in global section but unfortunatly it doesn't work. I guess due to the servers role of AD Controller.

If a domain is provisioned with rfc2307 it seems to me just a small step of setting uid in rfc2307 when a user or group is created by ADUC. Something for Samba Devs?


Gesendet: Donnerstag, 11. Dezember 2014 um 10:56 Uhr
Von: "Rowland Penny" <rowlandpenny at googlemail.com>
An: Tim <rintimtim at gmx.net>
Cc: samba at lists.samba.org
Betreff: Re: [Samba] Samba 4 two DCs no matching UID/GID
On 10/12/14 21:53, Tim wrote:
> 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'
>> installed,
> 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?
>> NO NO
>>> 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.
>> But
>>> 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.
>> Once
>> 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.
>> Rowland
>>> 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
>> something
>>> 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
>> need
>>> 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
>> when
>>> 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
>> AD
>>> and for a very good reason, all users might not require them.
>> https://wiki.samba.org/index.php/Using_RFC2307_on_a_Samba_DC#Configuring_RFC2307_and_NIS_Extensions_in_a_Samba_AD
>>>> 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
>> user
>>>> or group.
>>>> But what is needed for this? Manual setting of NIS domain in
>> Unix
>>>> 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
>> set
>>>> idmap_ldb:use rfc2307 = yes
>>> The setting just tells the DC to use rfc2307, it does not set
>> any,
>>> 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**
>> DC's
>>> 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
>> right?
>>>> 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
>> to
>>>> 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
>> uid
>>>>>> 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.
>> E.g.
>>>>>> 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
>> 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[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[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[https://wiki.samba.org/index.php/Local_user_management_and_authentication/sssd]
>>>>>> Rowland
>>>>>> OK, another
>> wikipage:https://wiki.samba.org/index.php/RFC2307_backend[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.
>>>>>> Rowland
>>>>> By default, no users have a uidNumber and no groups
>> have
>>>>> a gidNumber. If you use the UNIX_Attributes tab in
>> ADUC,
>>>>> the default start number is 10000, though you can
>> change
>>>>> this, I wouldn't bother. Just update any users via
>> ADUC,
>>>>> AD will then store the next uidNumber (or gidNumber)
>> for
>>>>> you. If you then go to the DC and run 'getent passwd
>>>>> <the user you just updated on ADUC>', you will find
>> that
>>>>> 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
>> use
>>>>> 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

OK, lets sort your problem of having an empty unix tab:

Install ldb-tools if not already installed.
Create an ldif file, call it something like update.ldif

changetype: modify
replace: msSFU30MaxUidNumber
msSFU30MaxUidNumber: <start number>
changetype: modify
replace: msSFU30MaxGidNumber
msSFU30MaxGidNumber: <start number>

replace <lowercase-domain-name> with your domain/workgroup name.
replace DC=example,DC=com with your rootdse.
replace <start number> with the number that you want your ID numbers to
start at.

Now add the ldif:

ldbmodify --url=/var/lib/samba/private/sam.ldb /path/to/your/ldif

replace /path/to/your/ldif with the path to your ldif i.e. if your ldif
is in roots dir and you named it as suggested '/root/update.ldif'
You may also have to change the path to sam.ldb.

If you now go to ADUC and open a UNIX_Attribute tab, it should now
contain an ID number.


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