When using a straight LDAP backend in Samba4 (passdb backend = ldapsam:ldap://<server>) running on RHEL6 the ldapsam.so isn't found and I get the following error in the smbd.log:


 ../source3/passdb/pdb_interface.c:168(make_pdb_method_name)
  No builtin nor plugin backend for ldapsam found

The workaround is a simple

cp -v /usr/lib64/samba/pdb/ldap.so /usr/lib64/samba/pdb/ldapsam.so

I've had to do this on a couple of servers before and believe this should be fixed upstream in core samba.

Here is the exact package version:

rpm -qi samba4

Name        : samba4                       Relocations: (not relocatable)
Version     : 4.0.0                             Vendor: Red Hat, Inc.
Release     : 63.el6_5.rc4                  Build Date: Fri 01 Aug 2014 21:00:25 BST
Install Date: Tue 02 Dec 2014 16:51:29 GMT      Build Host: x86-029.build.eng.bos.redhat.com
Group       : System Environment/Daemons    Source RPM: samba4-4.0.0-63.el6_5.rc4.src.rpm
Size        : 1125820                          License: GPLv3+ and LGPLv3+
Signature   : RSA/8, Tue 05 Aug 2014 06:27:40 BST, Key ID 199e2f91fd431d51
Packager    : Red Hat, Inc. <http://bugzilla.redhat.com/bugzilla>
...


Thanks

Hari Sekhon
http://www.linkedin.com/in/harisekhon