[Samba] winbind causing huge timeouts/delays since 4.8

Rowland Penny rpenny at samba.org
Sun Feb 24 19:22:51 UTC 2019

On Sun, 24 Feb 2019 19:56:27 +0100
Viktor Trojanovic via samba <samba at lists.samba.org> wrote:

> On 24.02.2019 19:25, Ralph Böhme via samba wrote:
> > Am 24.02.2019 um 18:48 schrieb Rowland Penny via samba
> > <samba at lists.samba.org>:
> >> On Sun, 24 Feb 2019 18:28:43 +0100 Ralph Böhme <slow at samba.org>
> >> wrote:
> >>> Am 24.02.2019 um 16:42 schrieb Rowland Penny via samba
> >>> <samba at lists.samba.org>:
> >>>> On Sun, 24 Feb 2019 15:58:39 +0100 Ralph Böhme <slow at samba.org>
> >>>> wrote:
> >>>>> Another thing that a customer has just been bitten by, was a
> >>>>> subtle bug in winbindd's idmap cache that resulted in all
> >>>>> xid2sid requests going through the idmap backend, iow winbindd
> >>>>> issued LDAP requests. With a few thousand users, things came to
> >>>>> a grinding halt.
> >>>>>
> >>>>> https://bugzilla.samba.org/show_bug.cgi?id=13802
> >>>>>
> >>>>> Patch just landed upstream.
> >>>> That is the bug I was referring to and probably (amongst all the
> >>>> other cruft) what was causing the OP's problem.
> >>> Unlikely.
> >> It is was I thought, but as the OP's setup is so convoluted, it is
> >> hard to say.
> > I don't think it's convoluted, it's certainly beyond the simple
> > standard setup we all wish everybody was using, but I don't think
> > it is broken as is. I just think an appropriate analysis requires
> > more resources then is available on the list.
> >
> >>>> However, this has nothing to
> >>>> do with using the 'ad' backend with Active Directory. We keep
> >>>> dancing around this problem, saying things like 'we need to fix
> >>>> this', we have been saying this since Samba 4 was released.
> >>> Which problem? Fix what? Been saying what?
> >> There have been numerous discussions about the 'ad' backend over
> >> the years and they have all gone nowhere. The 'ad' backend still
> >> works in the same way as it did when Samba 4 was released and you
> >> still have to store the next uidNumber & gidNumber outside AD if
> >> you use the Samba tools.
> > Looks like you're mixing AD DC use case with member server use
> > case. Can we please keep that seperate? Afaict, the one has nothing
> > to do with the other.
> I'm confused.. how is the choice of the idmap backend related to an
> AD DC use case?

Only in the case of wanting the same ID everywhere.

> >>>> Windows Uses the SID-RID to identify the user and the domain it
> >>>> comes from, surely we can find a way to do this for Samba, we are
> >>>> half way there with the 'rid' backend.
> >>> I'm not really what "there" implies for you, but it seems
> >>> idmap_autorid is eventually the backend that takes you "there". :)
> >> No it doesn't, at the moment, the only way to get the same ID on
> >> all Unix machines (this includes DC's) is to use the 'ad' backend.
> > Sure. But only certain use cases require the same id on all
> > machines, many don't. I'm just saying that you should better not
> > use idmap_ad, but instead use eg idmap_autorid unless you're setup
> > requires idmap_ad.
> Would you, or someone else mind sharing some of these use cases when 
> idmap_ad would be necessary and when idmap_autorid would suffice? 

My understanding is, like the 'rid' backend, if you use the same
smb.conf on all Unix domain members, you will get the same ID.

> Specifically, in which situations do I absolutely need the ID to be
> the same on each member, and in which cases could I actually go
> without this? For example, if my AD is managed by Samba only but I
> only have Windows users who will never have to log in to a unix box,
> are there still advantages of the ad backend over the (auto)rid one?

If your users never log into a Unix domain member or store files on
one, then do not even need to consider a winbind backend.

> I assume that most readers of the wiki will, like me, find that
> "central administration of ID's inside the AD" and "ID's not stored
> in a local database that can corrupt with lost file ownership" seem
> like really important arguments (btw, the last point is not stated as
> a disadvantage for the rid/autorid backend in the wiki). Reading
> this, it just seems that the ad backend is always the right one
> except that it's a headache to manage.

It isn't really a headache to manage, once you get your head around
it ;-)

> To put it differently, if Samba was improved in such a way that we
> could use the ad backend without having to manually manage the
> rfc2307 attributes, wouldn't this be the best if not only solution we
> needed?

I think you are mistaking using a subset of the RFC2307 attributes with
using most of them. If you use any backend other than 'ad' (and I
include a DC here) all you get is a uidNumber for a user, or a
gidNumber for a group. Using the 'ad' backend gets an ID number that
you set, plus individual login shells, Unix home dirs etc


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