Help with standalone samba SID-uid mapping

[Chris Roehrig <croehrig@house.org>]

I'm trying to set up samba (standalone) following these instructions:
	https://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-mapping-samba

but I'm having no luck getting my samba user/groups to appear correctly using the <cygwin unix="601"/> comment field as described in the document.

I'm using samba 4.13.14 on Ubuntu 20.04 with security = user (smbpasswd).   winbindd is not installed and I'm not using any LDAP or AD anywhere.

E.g. here is what is on the server (croehrig:croehrig = 601:601; cristina:cristina = 603:603)
housesrv[3]% ls -l /House/Users
total 17
drwxr-xr-x  9 cristina cristina 22 Jan 12 16:06 cristina
drwxr-xr-x 30 croehrig croehrig 53 Jan 13 09:47 croehrig


Here are the ACLs and SIDs when looking on the windows client:
tyto[5]% icacls \\\\housesrv\\Users\\\*
\\housesrv\Users\cristina S-1-5-21-751087815-2087572193-42305691-1001:(F)
                          S-1-22-2-603:(RX)
                          Everyone:(RX)

\\housesrv\Users\croehrig S-1-5-21-751087815-2087572193-42305691-1000:(F)
                          S-1-22-2-601:(RX)
                          Everyone:(RX)

As you can see, the gid is mapping to the S-1-22-2-<gid> as described in the document above, but
the uid is using a domain-specific SID with different RIDs. 


On the windows client I have the same users and groups set up locally (SAM) with appropriate SID mappings to the same uid/gids (601/603) in the Cygwin /etc/passwd and /etc/group.     This has all been working well to ensure e.g. rsync preserves permissions and ownership between cygwin and Linux.  (The windows groups are called 'grp-croehrig' and 'grp-cristina' since windows users and groups share a namespace, but they are mapped to 'croehrig' and 'cristina' in /etc/group).


Here is how the SMB share looks under Cygwin:
tyto[6]% ls -l //housesrv/Users/
total 0
drwxr-xr-x 1 Unknown+User Unix_Group+603 0 Jan 12 16:06 cristina
drwxr-xr-x 1 Unknown+User Unix_Group+601 0 Jan 13 09:47 croehrig
tyto[7]% ls -ln //housesrv/Users/
total 0
drwxr-xr-x 1 4294967295 4278190683 0 Jan 12 16:06 cristina
drwxr-xr-x 1 4294967295 4278190681 0 Jan 13 09:47 croehrig

I have added the SAM desc/comment field as described in the document above:  i.e.
	net localgroup grp-croehrig /comment:'<cygwin unix="601"/>'
	net user croehrig /comment:'<cygwin unix="601" group="grp-croehrig" />'
and restarted all Cygwin processes, but it doesn't seem to have any effect ('net user croehrig' shows the comment is indeed present).     I guess I don't understand how that comment field works.


Anyone have any advice? 

Thanks,
-- Chris