I have installed CentOS on one of our servers. I have also setup and configured OpenLDAP on that server and have proceeded to configure the server to authenticate via LDAP. I am only putting my user accounts in LDAP leaving all the system accounts in /etc/passwd and /etc/shadow. I also created an account that I can use to login to the server if LDAP has failed this is a user account that is in /etc/passwd and /etc/shadow that is not in LDAP.
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To fix the problem you need to edit /etc/ldap.conf and add all the local users to the
nss_initgroups_ignoreusers
http://www.centos.org/modules/newbb/viewtopic.php?topic_id=9832