Mastering Linux System Administration. Richard Blum

      You may perform the CentOS installation on a physical system, or you may install it as a virtual machine on a host system. Thus, in the next few sections, we'll look at the hardware requirements needed for installing the CentOS distribution directly on a physical server and for installing it within a virtualized environment.

      Hardware Requirements

      If you plan on installing the CentOS 8 distribution directly on a headless server, your computer must support a 64‐bit processor architecture. Here is a list of a few that will work well:

       AMD amd64

       ARM64 (not supported by RHEL)

       Intel amd64

       POWER9 (not supported by RHEL)

Besides having the proper processor on your system, you need to have enough resources available to avoid a sluggish system. Table 4.1 shows the recommended resources to support a well‐running CentOS distro.

TABLE 4.1: Recommended Server Resources for CentOS Distribution

RESOURCE	MINIMUM	RECOMMENDED
CPU	1.8 GHz	2 or more GHz
Memory	2 GB	2 GB per logical CPU
Disk space	10 GB	20 or more GB

      Notice the “per logical CPU” tag in the recommended memory. This is because CentOS can support some rather powerful CPUs, and it treats every core (or thread) in a multicore (or thread) processor as a logical CPU. So if you have a dual‐core processor, it is recommended that you have 4 GB of RAM on your system, while a quad‐core processor needs 8 GB of memory.

      Also, keep in mind that these recommendations are only for the operating system. Increase these resources to meet the needs of the application(s) you will run on the server.

      If you don't have access to a physical server, you can set up a virtual environment on a laptop or an old desktop. Using a virtualized system on your laptop provides a great deal of flexibility. Wherever you go with your laptop, you can learn about Linux.

      Virtual Server Requirements

      If you plan on running the CentOS distribution as a virtual machine (VM), you need to ensure that the host machine's operating system is supported by the hypervisor.

      For this book, we're focusing on the Oracle VirtualBox hypervisor software. Here are a few of the operating systems on which it can run:

       Windows 8.1

       Windows 10

       macOS High Sierra

       Ubuntu 18.04LTS

      This list is always evolving. Thus, it's a good idea to visit the Oracle VirtualBox manual website, virtualbox.org/manual, and view the currently supported host operating systems.

Running a virtualized environment will increase the needed resources on your system. You'll need to make sure that the host machine can handle not only the hypervisor, but the CentOS VM as well. Table 4.2 lists the recommended host machine resources for a virtualized CentOS server.

TABLE 4.2: Recommended Host Machine Resources for a CentOS VM

RESOURCE	MINIMUM	RECOMMENDED
CPU	2 GHz dual core	2 or more GHz dual core
Memory	4 GB	16 or more GB
Free disk space	25 GB	30 or more GB

      These resource recommendations are guidelines, not rules. Thus, you may need slightly more resources or get by with a fewer. Also, these recommendations assume you are running only one VM at a time. You'll need more resources on your system if you plan on running multiple VMs at the same time or running a VM along with several other apps.

      After you have the right level of resources on your host system, you're ready to start downloading the needed software. We'll cover this in the next section.

Finding the Software

      After you determine that you have the appropriate resources, but before you start the installation process, you need to have the proper software. You'll want to make sure that you get the correct version and type. For the larger software files, it's also critical to verify that no corruption has occurred when the software was downloaded. If you have a corrupt software file, you'll end up needlessly wasting your time or, worse, delaying the completion of an important installation project.

      Oracle VirtualBox

      We recommend that you use Oracle VirtualBox as the hypervisor on your system. If you did not download this software when you read Chapter 2, you can now download the latest version of this software from virtualbox.org.

      It is important that you get the correct platform package of VirtualBox. You'll see a list of potential host systems on the VirtualBox website, such as the following:

       Windows

       macOS

       Linux

      Make sure to select the VirtualBox package for the system on which the CentOS virtual machine will be running. Often, people make an incorrect choice because they confuse the host system with the virtual machine. Here's an example that may help: if you have a laptop running Windows where you plan on installing CentOS as a VM, then Windows is the host, and you'll want to download the VirtualBox package for Windows. Our examples in this chapter are based on a Windows 10 host system.

      CentOS

      To install CentOS as a VM, besides the hypervisor software (and the correct amount of resources on the host machine), you need a CentOS ISO image file.

       Real World Scenario

      Understanding an ISO Image File

      An ISO image file (also called an ISO image) is a specially formatted package file that contains all of the files needed to boot a system. The ISO image file is used to boot and then install the distribution.

To find the needed CentOS ISO image file, first go to the website: centos.org/download/. The type of processor you have will determine your next step. Click the