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Re: [Samba] winbind causing huge timeouts/delays since 4.8

On 24.02.2019 20:22, Rowland Penny via samba wrote:
On Sun, 24 Feb 2019 19:56:27 +0100
Viktor Trojanovic via samba <samba@xxxxxxxxxxxxxxx> wrote:

On 24.02.2019 19:25, Ralph Böhme via samba wrote:
Am 24.02.2019 um 18:48 schrieb Rowland Penny via samba
On Sun, 24 Feb 2019 18:28:43 +0100 Ralph Böhme <slow@xxxxxxxxx>
Am 24.02.2019 um 16:42 schrieb Rowland Penny via samba
On Sun, 24 Feb 2019 15:58:39 +0100 Ralph Böhme <slow@xxxxxxxxx>
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.


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.
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.
In my understanding, the idmap backend only needs to be specified in the smb.conf for member servers. That's why I still don't see how it is related to a AD DC use case. I take it I'm missing something crucial here.

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.

In a Windows clients only environment, I thought that having AD member servers implied that files were stored on them.

But I take it from what you write that as soon as some kind of access is needed, we are actually speaking about a "login", even if it's just on the share level and the user never sees a shell.

In which case, yet again, the question comes up which back end to use. I'll get to that further below.

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 ;-)

For very large environments, I guess you would just script it either with samba-tool or powershell. But having to do it manually and remember that for every user, computer, and group 1-2 attributes need to be set, and kept track of, does seem like a nuisance.

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
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

I guess I was. Are you saying, then, that if I have no need for individual login shells and *nix home dirs (which in a pure Windows client environment I clearly have not), the ad back end isn't really offering any advantage for me?

What still confuses me here is how the wiki states that in case of rid/autorid information about file ownership is lost if the local tdb fails and cannot be restored. I assume this does not mean that the actual ownership information is stored in tdb (or in the AD, for that matter) but that the user ID used in the ACL needs to be retrieved from somewhere, and in case of the ad back end this ID is being retrieved from the AD directly, in case of the rid back end it's retrieved from the local store only. And yet you said that on member servers with identical smb.conf files (I assume you were talking about the global section only), IDs would always be the same. Naturally, two questions come up:

1) If one member server fails, wouldn't it be possible and sufficient to just regenerate the tdb using the same smb.conf? If this yields the same results every time, then why would I even worry about a corrupted tdb?

2) If IDs were the same on all member servers, wouldn't that also mean that I should be able to restore the corrupted tdb on one member server using a valid tdb from another member server? And how would I go about that in practice?

I hope this makes sense.


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