[Samba] Samba + sssd deployment: success and failure

Goetz, Patrick G pgoetz at math.utexas.edu
Wed Jun 12 19:40:03 UTC 2019

I agree with putting the sssd discussion to bed, but am still interested 
in clearing up some confusion, as I'm concerned I might be missing 

On 6/12/19 12:44 PM, Rowland penny via samba wrote:
> On 12/06/2019 17:43, Goetz, Patrick G via samba wrote:
>> On 6/12/19 11:10 AM, Rowland penny via samba wrote:
>>> Why are you using sssd on a standalone server ?
>>> your users will be in /etc/passwd and the Samba database, I don't think
>>> sssd can talk to the Samba database.
>> I'm pretty sure what happens when you set [server role = standalone] is
>> that Samba then defers to /etc/nsswitch.conf for how authorization
>> should happen, and since sss is listed there and is set up to query the
>> AD domain, that's how users get authenticated.
> Yes, but this will be different from the local Samba database.

Yes, but that's part of the point.  I don't *want* a local Samba 
database.  I want all authentication to occur through one of the AD 
domain controllers, assisted by ephemeral cache files.

>> In particular, it's not actually a standalone server but rather an AD
>> domain member
> No, it is schizophrenic server, it is in two minds ;-)

How so?  I have exactly one daemon in charge of authentication, I don't 
want or need nmbd, and I want smbd to just use NSS for authentication. 
This seems like a streamlined deployment, and of course the 
authorization agent could be sssd or winbind.

>> so that Security Group-authorized domain users can use
>> their AD domain credentials for authentication on the machine.  There is
>> an entire lab of linux workstations set up this way.  Users log in to a
>> workstation using their AD credentials and their home directory (and
>> various data/software directories) are automounted from the same
>> fileserver we're trying to set Samba up on.  sssd also provides a
>> caching service to assist with timely authorization.  As I mentioned
>> previously, sssd bundles together the functionality of pam_ldap, nscd,
>> and probably some other tools.  This was all working fine until we
>> acquired the need to mount filesystems to a few Windows machines as well
>> (due to some compute-intensive analysis software that runs only on 
>> Windows).
>> After doing some more reading about winbind (the 2007 Carter "Using
>> Samba" book --
> Don't read that, it is 2019 (just in case you missed it) and that book 
> is well out of date.
>> aside: why don't we have any updated Samba
>> documentation?!  Will post separately about the state of the smb.conf
>> man page), I have no a priori objections to using winbind instead of
>> sssd.  In particular, I wasn't aware that winbind had a PAM hook
>> allowing it to provide authentication for other services.  I do care
>> about clean, modular system design, though:
> So why are you using two programs when just one will do ?
>>       Other Services           | Autonomous     |
>>         Requiring     ------>  | Authentication | <-----  Samba smbd
>>       Authentication           | Service        |
>>                                     |
>>                                     |
>>                                     v
>>                        Can interface with LDAP/AD
>> It looks like the thing in the middle could be sssd or winbind; however
>> most of our linux boxes which are AD domain members don't provide SMB
>> file sharing services.
> So what ? just because they are Unix domain members, this doesn't mean 
> you have to use everything AD provides.
>> I only want to have to debug one
>> AD-authentication service (that's headache enough, believe me), so would
>> it make sense to run winbind on machines that are only using Samba for
>> administrative local use (i.e. no need to install full-blown Samba)?
> Unless you are talking standalone Unix machines (in which case they will 
> not be domain members), then yes. I cannot understand your problem here, 
> you are quite prepared to install Samba & sssd on the same computer and 
> configure both, but don't want to just configure Samba alone to do the 
> same thing.
>> I looked at the winbind rid service, and am worried this will map SIDs.
>> The other features I'm looking for:
>>    - We don't have and can't get the POSIX subsystem in our AD 
>> deployment,
>>      so I want the UID = SID;
> I think you mean 'RID' instead of 'SID'

Yes, you're right.  The Windows people seem to use the terms synonymously.

>>   i.e not mapped in any way in order to
>>      facilitate subsequent aggregation (say of storage) of what are
>>      now independent labs.
>>    - Must support AD Security Groups because this is how we limit access
>> to particular machines.
> Definitely doable with winbind, you just need to set the permissions 
> from Windows.

Actually, this is handled using an AD GPO, which sssd is able to read 
and use.  Doing this via GPO means we can simplify the configuration of 
hundreds of machines.

>>    - It would be nice to be able to use AD groups for authorization; then
>> I wouldn't have to manage local groups in /etc/group (although ansible
>> makes this less of a chore than it used to be).  Right now this doesn't
>> seem to work with sssd; i.e. you can't chgrp files/folders to the AD
>> groups listed using, say `id pgoetz` on the domain-bound linux machine.
> A 'local' group is unknown to AD (whether you use winbind or sssd), so 
> connecting an AD user to a local group isn't going to work.

Let me clarify.  It would be nice to assign AD Security Groups as 
file/folder groups even if they can't own files on linux.

> Rowland

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