This is a short tutorial that wants to describe how to install and configure a LDAP Server in order to share users’ accounts whitin a local network. In particular, we will see how to install and configure a client/server OpenLDAP service on Scientific Linux hosts.
To install OpenLDAP service on server, as root user on a SL5 host, we have to install openldap-servers package:
$ yum install openldap-servers
Instead, as root user on a SL6 host we have to install both openldap and openldap-servers packages:
$ yum install openldap openldap-servers
OpenLDAP installs several files in /etc and other places. The slapd daemon’s configuration file is slapd.conf and can be found in /etc/openldap. First of all make sure service is not running:
(SL5) $ service ldap stop (SL6) $ service slapd stop
Then, edit /etc/openldap/slapd.conf. We have to edit 5 entries: database, suffix, rootdn, rootpw and directory. It should look something like:
database bdb suffix "dc=example,dc=com" rootdn "cn=Manager,dc=example,dc=com" # Cleartext passwords, especially for the rootdn, should be avoided. # See slappasswd(8) and slapd.conf(5) for details. # Use of strong authentication encouraged. # rootpw secret directory /var/lib/ldap
For example, define ourselves as a company called storm.cnaf.infn.it. We can leave default value for database entry, bdb, that stands for Berkeley Database. The suffix entry is our main domain or organization. So, we can changed it to:
The dc stands for domainComponent. Next, the rootdn. This means root Distinguished Name. Every entry in an LDAP database has a distinguished name. The default is Manager. In our example we will use root instead of Manager, so according to the suffix we have to change it to:
Next the password. If we desire an encrypted password, we can launch slappasswd command, insert our password and replace secret with the outputted string. So it will look something like:
We can leave default value for directory entry: /var/lib/ldap. Now we have to clean up previous LDAP content and configuration with the following command:
(SL5) $ rm -rf /var/lib/ldap/* (SL6) $ rm -rf /etc/openldap/slapd.d/*
Then we have to create the DB_CONFIG file into /var/lib/ldap/ directory (or copy it from OpenLDAP example file /etc/openldap/DB_CONFIG.example).
# $OpenLDAP: pkg/ldap/servers/slapd/DB_CONFIG,v 22.214.171.124 2007/12/18 11:53:27 ghenry Exp $ # Example DB_CONFIG file for use with slapd(8) BDB/HDB databases. # # See the Oracle Berkeley DB documentation # <http://www.oracle.com/technology/documentation/berkeley-db/db/ref/env/db_config.html> # for detail description of DB_CONFIG syntax and semantics. # # Hints can also be found in the OpenLDAP Software FAQ # <http://www.openldap.org/faq/index.cgi?file=2> # in particular: # <http://www.openldap.org/faq/index.cgi?file=1075> # Note: most DB_CONFIG settings will take effect only upon rebuilding # the DB environment. # one 0.25 GB cache set_cachesize 0 268435456 1 # Data Directory #set_data_dir db # Transaction Log settings set_lg_regionmax 262144 set_lg_bsize 2097152 #set_lg_dir logs # Note: special DB_CONFIG flags are no longer needed for "quick" # slapadd(8) or slapindex(8) access (see their -q option).
To initialize the LDAP database we have to create a pair of files, one for the organization and one for the root DN. For example, create storm.cnaf.infn.it.ldif as follow:
dn: dc=storm,dc=cnaf,dc=infn.it objectClass: dcObject objectClass: organization dc: storm o: StoRM
It contains the organization entry. Then create root.storm.cnaf.infn.it.ldif as follow:
dn: cn=root,dc=storm,dc=cnaf,dc=infn.it objectClass: organizationalRole cn: root
and this contains the root DN. Now we have to initialize DB files for content in /var/lib/ldap directory:
$ echo "" | slapadd -f /etc/openldap/slapd.conf
This is required, otherwise you will get this error:
bdb_db_open: database "dc=example,dc=com": db_open(/var/lib/ldap/id2entry.bdb) failed: No such file or directory (2).
Now, only if host is SL6, convert configuration file into dynamic configuration under /etc/openldap/slapd.d directory:
$ slaptest -f /etc/openldap/slapd.conf -F /etc/openldap/slapd.d
For both SL5 and SL6, set permissions:
chown -R ldap:ldap /var/lib/ldap
and, only on SL6, add:
chown -R ldap:ldap /etc/openldap/slapd.d
Now we can initialize LDAP DB with already defined initial content, by launching the following commands:
slapadd -l storm.cnaf.infn.it.ldif slapadd -l root.storm.cnaf.infn.it.ldif
So we are ready to add to our LDAP database the necessary users and groups. In particular we need storm and gridhttps users and also relative groups. But, how can we organize our directory tree? In a UNIX file system, the top level is the root. Underneath the root you have numerous files and directories. As mentioned above, LDAP directories are set up in much the same manner. Into the directory’s base are conventionally created containers that logically separate data. For historical reasons, most LDAP directories set these logical separations up as OU entries. OU stands for “Organizational Unit”, which in X.500 was used to indicate the functional organization within a company. Current LDAP implementations have kept the ou= naming convention. In our case, we can define a pair of Organizationa Unit: People and Group as follow:
dn: ou=People,dc=storm,dc=cnaf,dc=infn.it objectClass: organizationalUnit objectClass: top ou: People
dn: ou=Group,dc=storm,dc=cnaf,dc=infn.it objectClass: organizationalUnit objectClass: top ou: Group
Then, we can define storm and gridhttps users and groups, as follow:
dn: uid=storm,ou=People,dc=storm,dc=cnaf,dc=infn.it objectClass: account objectClass: posixAccount objectClass: top objectClass: shadowAccount cn: storm gidNumber: 494 homeDirectory: /home/storm uid: storm uidNumber: 495
dn: cn=storm,ou=Group,dc=storm,dc=cnaf,dc=infn.it objectClass: posixGroup objectClass: top cn: storm gidNumber: 494
dn: uid=gridhttps,ou=People,dc=storm,dc=cnaf,dc=infn.it objectClass: account objectClass: posixAccount objectClass: top objectClass: shadowAccount cn: gridhttps gidNumber: 504 homeDirectory: /home/gridhttps uid: gridhttps uidNumber: 503
dn: cn=gridhttps,ou=Group,dc=storm,dc=cnaf,dc=infn.it objectClass: posixGroup objectClass: top cn: gridhttps gidNumber: 504
Set the various GIDs and UIDs values as you want. Then we can add the users and groups defined to the LDAP server database, with the following commands:
slapadd -l storm.Group.storm.cnaf.infn.it.ldif slapadd -l gridhttps.Group.storm.cnaf.infn.it.ldif slapadd -l storm.People.storm.cnaf.infn.it.ldif slapadd -l gridhttps.People.storm.cnaf.infn.it.ldif
Using a free program like Apache Directory Studio we can easily connect to the LDAP server and add other entries, export ldif configurations, etc. Important: as you can see from the files above, a user must contain account, posixAccount and shadowAccount objectClasses, a group instead must define only a posixGroup objectClass.
To start server:
(SL5) $ service ldap start (SL6) $ service slapd start
To install OpenLDAP service on a client, as root user on a SL5 host, we have to install openldap-clients and nss_ldap packages:
$ yum install openldap-clients nss_ldap
Instead, as root user on a SL6 host we have to install both openldap-clients and nss-pam-ldapd packages:
$ yum install openldap-clients nss-pam-ldapd
Be sure that service nscd is stopped:
$ service nscd status
Modify /etc/nsswitch.conf by adding “ldap” to the following lines:
passwd: files ldap shadow: files ldap group: files ldap
If SL5, modify both /etc/ldap.conf and /etc/openldap/ldap.conf by adding:
uri ldap://<ldap-server-hostname> base dc=storm,dc=cnaf,dc=infn.it
If SL6 modify both /etc/openldap/ldap.conf and /etc/nslcd.conf by adding:
uri ldap://<ldap-server-hostname> base dc=storm,dc=cnaf,dc=infn.it
From a configured client we need to know UIDs and/or GIDs of server’s LDAP users. That users has not to be defined as UNIX-users on clients. To query the LDAP server from one of the clients type, for example, you can list all the contents in db:
$ ldapsearch -x -b 'dc=storm,dc=cnaf,dc=infn.it'
you can search a particular uid or group:
$ ldapsearch -x "uid=storm" $ ldapsearch -x "group=storm"
or you can get the UID or GID of a username:
$ id -u storm $ id -g storm
Verify that the obtained values are equals to the previous defined.