Fox's latest work, Red Hat Enterprise Linux 5 Administration Unleashed, arrived this month intended as a tome of knowledge for intermediate to advanced Linux system administrators. Before it was published, Fox sat down with SearchEnterpriseLinux.com to provide some insight on the latest version of the Linux community's leading commercial distribution, Red Hat Enterprise Linux 5 (RHEL 5).
What general best practices or tips can you share to make an upgrade to RHEL 5 a smooth one?
Tammy Fox: Performing an upgrade with the installation program basically updates any existing RPM packages on your system. If the new version of the package includes changes that make your existing configuration invalid, some packages will try to migrate your existing data, but it is not required.
The best practice is to have your data on a dedicated storage system that does not get reformatted during a fresh installation. Depending on the size of your organization, this can be a SAN, a data cluster, or just a set of dedicated hard drives in the system. Back up any existing data and configuration files, and perform a fresh installation. Restore your configuration files one by one, testing each program. Be sure to pay close attention to whether or not the software version has changed from your previous version of RHEL to RHEL 5. Finally, reconnect your data storage solution and perform any additional tests necessary.
Of course, all of these steps should be performed on a test system before the plan is implemented on a production system.
What are some key differences between what administrators see in RHEL 4 deployments, and RHEL 5 ones?
Fox: The most immediate change they will notice is the introduction of installation codes. During installation, an installation code must be entered. These codes are generated by Red Hat. Depending on what services you purchased, they unlock different RHEL 5 components such as virtualization and high availability. RHEL 5 also uses new RPM GPG keys. If upgrading, you will need to install the new keys before updating packages.
The next big noticeable change is the move to YUM for software management and maintenance. In previous versions of RHEL, the up2date command could be used to download and install software updates from Red Hat Network. It has been replaced with the YUM command, and all the up2date graphical program has been replaced with a graphical program that use YUM as well. If you schedule package updates and installation with the RHN Web site, you will not notice a difference.
Administrators must also consider whether to use the virtualization feature in RHEL5. (Editor's Note: Due to trademark issues, Red Hat currently refers to Xen-based hypervisor technology as virtualization.) If your hardware is supported and you have systems with enough resources to share between the host system and the virtual machines, virtualization can help reduce the number of physical machines that need to be maintained. If you are a hosting service or allow your customers shell access to their Web site, virtualization can be beneficial.
Administrators should read the release notes for a complete list of caveats and known issues with RHEL 5. For example, dual-booting with Windows Vista requires additional steps for GRUB to boot Windows Vista.
Has SELinux become any easier to use with RHEL 5?
Fox: As with any developing open source technology, SELinux is improving with each release and version of Red Hat Enterprise Linux and Fedora. Of course there will be IT managers who continue not to use SELinux, but the version in RHEL 5 has improved significantly.
With the introduction of the SELinux Management Tool and the SELinux Troubleshooter, it is much easier to determine which services and programs are protected by SELinux. It is also much easier to customize the policy without having to write your own policy. SELinux booleans are used for this and can be enabled and disabled with the SELinux Management Tool.
The SELinux Troubleshooter alerts administrators of when a service has failed to start due to SELinux. It also provides suggestions on how to work around the issue without just disabling SELinux protection for the service.
How has the typical Red Hat Linux administrator's job changed with the introduction of Xen to RHEL 5?
Fox: With the introduction of virtualization in RHEL 5, administrators must now consider whether to continue using individual physical servers for each operating system instance or whether the performance of a virtual machine (VM) will suffice. Certainly, Web hosting companies who offer dedicated Web servers will benefit from virtualization since each client can have their own IP address and guest OS. The VMs on a host system can't access the data on the other VMs or the host, so client data is separated, yet one physical server can serve multiple clients.
IT managers should know that there are hardware requirements for virtualization. Currently, virtualization on RHEL 5 is only supported on x86 and x86_64 systems. It is offered for the Itanium2 but only as a technology preview. In addition to the obvious need for enough processors, memory and disk space to dedicate to each VM, the processor must have Physical Address Extension support. To use full virtualization -- the guest OS does not have to be aware of the VM layer -- the processor must be 64-bit and must have a hardware virtual machine layer.
An eWEEK review of RHEL5 said the Xen support is "half-baked" -- what are your thoughts on this?
Fox: As with SELinux, you will see the virtualization support improve over time. The basic functionality is there. You can create a virtual machine, install a guest OS on the VM, and connect to the guest OS as if it is a OS running on a separate set of hardware. The VM has its own IP address, doesn't have access to the data on its host system, and so on.
There are still parts that can be greatly improved, as with any software when it is first introduced. Because it is open source, it is important to provide these types of new technologies so that they can be used by the masses and so other developers and companies will get behind it. A few of the known issues such as the virtual Machine Manager not being able to start the VM are listed in the RHEL 5 release notes. However, this particular issue has a workaround by starting the VM from the command line first. This issue is also discussed in my book.