5.3. Configuring a Linux System as an IdM Client
There are two elements to prepare before beginning the client setup process for the Red Hat Enterprise Linux client:
- There must be a way to connect the client machine to the Kerberos domain, either by having an available Kerberos identity (such as the admin user) or by manually adding the client machine to the KDC on the server with a one-time password before beginning the enrollment process for the client machine.
- If there is an Active Directory server on the same network that serves DNS records, the Active Directory DNS records could prevent the client from automatically detecting the IdM server address. The
ipa-client-installscript retrieves the Active Directory DNS records instead of any records that were added for IdM.In this case, it is necessary to pass the IdM server address directly to theipa-client-installscript.
5.3.1. Installing the Client (Full Example)
- Install the client packages. These packages provide a simple way to configure the system as a client; they also install and configure SSSD.For a regular user system, this requires only the
ipa-clientpackage:[root@client ~]# yum install ipa-client
An administrator machine requires theipa-admintoolspackage, as well:[root@client ~]# yum install ipa-client ipa-admintools
- If the IdM server is configured as the DNS server and is in the same domain as the client, add the server's IP address as the first entry in the list of name servers in the client's
/etc/resolv.conffile.Note
If every machine in the domain will be an IdM client, then add the IdM server address to the DHCP configuration. - Run the client setup command.
[root@client ~]# ipa-client-install --enable-dns-updates
The--enable-dns-updatesoption updates DNS with the client machine's IP address. This option should only be used if the IdM server was installed with integrated DNS or if the DNS server on the network accepts DNS entry updates with the GSS-TSIG protocol.Options foripa-client-installare listed in theipa-client-installmanpage. - If prompted, enter the domain name for the IdM DNS domain.
DNS discovery failed to determine your DNS domain Please provide the domain name of your IPA server (ex: example.com): example.com
- If prompted, enter the fully-qualified domain name of the IdM server. Alternatively, use the
--serveroption with the client installation script to supply the fully-qualified domain name of the IdM server.DNS discovery failed to find the IPA Server Please provide your IPA server name (ex: ipa.example.com): server.example.com
Important
This must be a valid DNS name, which means only numbers, alphabetic characters, and hyphens (-) are allowed. Other characters, like underscores, in the hostname will cause DNS failures. - The client script then prompts for a Kerberos identity to use to contact and then join the Kerberos realm. When these credentials are supplied, then the client is able to join the IdM Kerberos domain and then complete the configuration:
Continue to configure the system with these values? [no]: y User authorized to enroll computers: admin Synchronizing time with KDC... Password for admin@EXAMPLE.COM: Successfully retrieved CA cert Subject: CN=Certificate Authority,O=EXAMPLE.COM Issuer: CN=Certificate Authority,O=EXAMPLE.COM Valid From: Tue Aug 13 09:29:07 2013 UTC Valid Until: Sat Aug 13 09:29:07 2033 UTC Enrolled in IPA realm EXAMPLE.COM Created /etc/ipa/default.conf New SSSD config will be created Configured /etc/sssd/sssd.conf Configured /etc/krb5.conf for IPA realm EXAMPLE.COM Failed to update DNS records. Adding SSH public key from /etc/ssh/ssh_host_rsa_key.pub Adding SSH public key from /etc/ssh/ssh_host_dsa_key.pub Could not update DNS SSHFP records. SSSD enabled Configured /etc/openldap/ldap.conf NTP enabled Configured /etc/ssh/ssh_config Configured /etc/ssh/sshd_config Client configuration complete.
- Test that the client can connect successfully to the IdM domain and can perform basic tasks. For example, check that the IdM tools can be used to get user and group information:
[jsmith@client ~]$ id [jsmith@client ~]$ getent passwd admin [jsmith@client ~]$ getent group admins
- If an NFS server is already configured, then set NFS on the client system to work with Kerberos.An NFS server must already be configured within the domain. This is covered in Section 18.2, “Configuring Automount”.
Note
To help troubleshoot potential NFS setup errors, enable debug information in the/etc/sysconfig/nfsfile.RPCGSSDARGS="-vvv" RPCSVCGSSDARGS="-vvv"
- On an IdM server, add an NFS service principal for the NFS client.
[root@client ~]# kinit admin [root@client ~]# ipa service-add nfs/ipaclient.example.com@EXAMPLE
Note
This must be run from a machine with the ipa-admintools package installed so that theipacommand is available. - On the IdM server, obtain a keytab for the NFS service principal.
[root@client ~]# ipa-getkeytab -s server.example.com -p nfs/ipaclient.example.com@EXAMPLE -k /tmp/krb5.keytab
- Copy the keytab from the IdM server to the IdM client. For example:
[root@client ~]# scp /tmp/krb5.keytab root@client.example.com:/etc/krb5.keytab
- Configure the
/etc/exportsfile on the NFS server./ipashare gss/krb5p(rw,no_root_squash,subtree_check,fsid=0)
- Create the mount point.
[root@client ~]# mkdir /mnt/ipashare
- On the client, mount the NFS share. Use the same
-o secsetting as is used in the/etc/exportsfile for the NFS server.[root@client ~]# mount -v -t nfs4 -o sec=krb5p nfs.example.com:/ /mnt/ipashare
5.3.2. Examples of Other Client Installation Options
There are a number of different configuration options with the
ipa-client-install command which can be used to configure the client system in different ways, depending on the infrastructure requirements.
Example 5.1. Enabling DNS Updates
Depending on the DHCP configuration, the IP addresses of clients can change with some regularity. If the IP address changes, this can cause discrepancies between the DNS records in the IdM server and the actual IP addresses in use, which could affect policies set within IdM and communications between clients and services.
The
--enable-dns-updates option sets the System Security Services Daemon to update the DNS entries whenever the IP address for a client changes.
[root@client ~]# ipa-client-install --enable-dns-updates
Example 5.2. Specifying Domain Information
When just running the client installation command, the script prompts for required IdM domain information, including the name of an IdM server to register with, the DNS domain name, and the Kerberos realm and principal.
All of the basic information can be passed with the installation command (which is useful for automated installations).
--domainfor the DNS domain name (which is only used if the IdM server is configured to host DNS services)--serverfor the IdM server to register with (which can be any server or replica in the topology)This must be a valid DNS name, which means only numbers, alphabetic characters, and hyphens (-) are allowed. Other characters, like underscores, in the hostname will cause DNS failures.--realmfor the Kerbero realm name and, optionally,-pfor a Kerberos principal name
[root@client ~]# ipa-client-install --domain EXAMPLE.COM --server server.example.com --realm EXAMPLE -p host/server.example.com
Example 5.3. Setting a Specific IdM Server
There can be multiple servers and replicas within the IdM server topology. When a client needs to connect to a server for updates or to retrieve user information, it (by default) uses a service scan to discover available servers and replicas in the domain. This means that the actual server to which the client connects is random, depending on the results of the discovery scan.
It is possible to set a specific server within the IdM domain which is used for client updates; if for some reason, connecting to that server fails, then the client can discover another server within the domain for failover.
The preferred server is set in the
--fixed-primary option.
[root@client ~]# ipa-client-install --fixed-primary server.example.com
Example 5.4. Disabling System Authentication Tools
Red Hat Enterprise Linux uses the
authconfig tool to set and update authentication clients and settings for a local system. Identity Management uses the System Security Services Daemon (SSSD) to store IdM server configuration and to retrieve policy information, users, passwords, and groups configured within the IdM domain.
It is strongly recommended that you use authconfig and SSSD to manage your user, group, and other IdM client configuration.
There may be some situations where an administrator wants to disable dynamic changes to system authentication configuration. In that case, it is possible to disable IdM from making updates to
authconfig or SSSD.
The
--noac option prevents any changes through authconfig. The --no-sssd option prevents IdM from using SSSD.
[root@client ~]# ipa-client-install --noac --no-sssd
A related option is
--preserve-sssd. While this allows the client to change the SSSD configuration file to configure the IdM domain, it saves the old SSSD configuration.
Example 5.5. Disabling Password Caching
One of the primary functions of SSSD is password caching. Normally, when a system uses an external password store, authentication fails if that password store is ever inaccessible. However, SSSD can cache passwords after a successful authentication attempt and store those passwords locally. This allows users to log in and access domain services (which they have previously accessed) even if the IdM server is inaccessible.
In highly-secure environments, it may be necessary to prevent password caching to prevent potentially unauthorized access. In that case, the
--no-krb5-offline-passwords option can be used to prevent passwords from being cached in SSSD.
[root@client ~]# ipa-client-install --no-krb5-offline-passwords
