internal-use-only SIDs being mapped to GIDs on users

Hi,
it seems there were similar issues discussed in bug 1307778
They got resolved groupds with no GID in AD, but still ended up having the issue around S-1-18-1 that you reported.

Looking back how the other issue was fixed I really think you should try to recreate the issue on the latest version in Ubunutu (e.g. 4.7.6+dfsg~ubuntu-0ubuntu2 in Ubuntu Cosmic or even newer but not yet released 4.8.2 from https://launchpad.net/~ahasenack/+archive/ubuntu/samba-merge-4.8-1778125).

This most unlikely is a bug in Ubuntu, but in the upstream code.
Therefore if reproducible there report it upstream in https://bugzilla.samba.org/enter_bug.cgi and report back here the bug id so we can track and include the fix.

Also check your group mapping, using "net groupmap list"

net groupmap list only shows Administrators and Users.

the problem does not exist on 18.04.

I realize it's not a bug "in ubuntu", but in the version of samba that ubuntu 16.04 is using. from experience I can tell you that reporting it to samba is just going to result in them saying "compile your own newer samba version", which does nothing to get ubunut's LTS samba package to not give this message.

> the problem does not exist on 18.04.

OK, so I'll mark this bug as Triaged as I think it's clear what behaviour needs to change. I'm setting this as Importance: Low though, since I think this affects only unusual end-user configurations of Ubuntu. I don't expect the Ubuntu server team to work on this any time soon, but if you can provide a patch and help drive the QA required to get a fix into 16.04, we'd be happy to take it.

> ...which does nothing to get ubunut's LTS samba package to not give this message.

In Ubuntu we can cherry-pick an upstream fix (or come up with our own fix) and apply it to 16.04. How practical this is depends on the exact fix.

If this bug previously existed upstream and has since been fixed in a newer upstream release, it would be helpful to find the upstream bug reference (if it exists) and the upstream VCS commit(s) that fix the problem.

If you can volunteer your help, please see https://wiki.ubuntu.com/StableReleaseUpdates#Procedure for details. The first step though is to figure out a patch that works for the samba package in Ubuntu 16.04, which can be done independent of Ubuntu processes.