[Samba] Winbind UID/GID unification across multiple machine solution

malk at sidehack.sat.gweep.net malk at sidehack.sat.gweep.net
Sat Jan 10 18:10:54 GMT 2004

I developed a solution to the problem where you might have systems
setup w/ winbind mapping GIDs and UIDs, NSS, and PAM setup so windows users
can login, but winbind maps possible different UIDs/GIDs from system
to system preventing unified UIDs/GIDs in your environment.

I tried having one box setup with NSS winbind / PAM etc. plus I made that
system an NIS master w/ a script to periodically pull the windows UIDs
and GIDs into passwd and group maps.  The NIS clients did NIS in nsswitch.conf
with PAM windbind auth and winbind doesn't map UID/GIDs but rather rely
on NIS.  This almost worked except NIS didn't deal with blanks in the group
names -- an NIS API call for group info would get hosed (the IDs were ok, but
the names would be inconsistent).

So I wrote a client / server daemon pair where the one host doing UID/GID
mapping w/ winbind would periodically build passwd and group style compressed
files of the mapped users and groups (using simple getent calls).  The clients
would periodically connect and download the passwd/group files if anything
changed since the last time the connected.  The server would also only
obviously generate new passwd/group data when something changes.
The clients would then install the mapped passwd / group entries in
/etc/passwd and /etc/group.  The proper pwent locking is done during
/etc file update by the client to prevent other applications from getting
inconsistent pwent calls during an update.  The clients can do winbind PAM,
but simply use files in nsswitch.conf -- it works great.

It may not scale as well as pure NIS or LDAP backends etc., but it's pretty
easy to setup and it's been a great solution for my office environment.
It puts very minimal load on my network -- the PDC or BDC on the local
network gets some bursty traffic once in a while from the server, but
otherwise it's left alone.  If each box was doing winbind mapping along
with authentication, I would imagine it would be more traffic than the
setup I'm doing.

I'm sending this mail to see if anyone is interested using my setup.  If
so, I'll put up a section on my website w/ source code and simple instructions
to implement this.

If there's a better way to do it, let me know -- I couldn't find anything
so I rolled my own and I'd like to offer back the solution to anyone else
who needs it.  I'm aware that perhaps in the future Samba will
use an algorithm based UID to GID mapping making this setup unnecessary.

I've seen reports of slowness when NSS calls are being made when there's
lots of large groups in the windows domain -- I've seen that on my 
machine that does the mappings.  On the client machines, the problem
is solved because is uses local /etc files that are populated by the
client side daemon -- it's great since only one machine (the master
server) has the potential slowness and in my situation that machine
doesn't need to be fast -- it's job is mainly to do the mappings.

Eric Malkowski

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