Open Directory is a key component of Mac OS X Server. It consists of OpenLDAP, MIT Kerberos, Password Server and a tool chain that enables GUI administration. Sadly, adding new ldap schemas to the directory server is not documented in the advanced administration guides and you have to tinker with the command line tools. I could not find any good documentation how you to add a custom LDAP schema, so I’ll show my solution here.
Mac OS X Server 10.5 ships with OpenLDAP 2.3. This release supports run-time configuration, which means that the LDAP schemas are stored within the directory server and you cannot simply put your new schema file in /etc/openldap/schema/; you have to convert it to an LDIF file and load this into the directory itself. This can be done during run-time but it breaks replication if you do so. So, instead you have to create a proper old-style config and run a manual conversion to the new run-time config.
To do so, you need to place the new schema file in /etc/openldap/schema/some-new.schema. This directory is copied to new replicas when you join them, so you won’t break the Apple tool chain. Then, you need to include the new schema file from /etc/openldap/slapd.conf; this has no direct effect but slaptest(1) uses this to re-create the run-time config. Finally, convert the old-style config to a new run-time config using slaptest(1) like “slaptest -f slapd.conf -F slapd.d” and restart slapd:
cd /etc/openldap cp some-new.schema schema/ cat >> slapd.conf <<HERE include /etc/openldap/schema/some-new.schema HERE mv slapd.d slapd.d_bak slaptest -f slapd.conf -F slapd.d launchctl unload /System/Library/LaunchDaemons/org.openldap.slapd.plist launchctl load /System/Library/LaunchDaemons/org.openldap.slapd.plist
Beware: we are deleting the old run-time config here and create a new one from the static config. If you have changed the config without adopting the old-style config, you might loose modifications. So, check twice if all required schemas are included from slapd.conf. AFAIK, Kerio Mailserver is troublesome here as it is not adding the include lines to slapd.conf. Though, thise procedure is exactly what the Apple tool chain does on replication and I suggest you do it exactly this way. Good luck!