To complete this recipe, it is assumed that you are using a typical Windows-based (Windows 7, Windows Vista, or similar) or OS X computer with full administration rights. You will need an Internet connection to download the required installation files and also need access to a standard DVD/CD disk burner with the appropriate software, in order to create the relevant installation disks from the image files. For the purpose of this recipe, it is assumed that all the downloads will be stored on Windows in your personal C:\Users\<username>\Downloads folder, or if using an OS X system, in the /Users/<username>/Downloads folder.

Regardless of the type of installation files you download, the following techniques can be applied to all the image files supplied by the CentOS project:

So what have we learned from this experience?

The act of downloading a CentOS installation image is just the first step towards building the perfect server. Although this process is very simple, many do forget the need to confirm the checksum. In this book, we will work with the minimal installation image, but you should be aware that there are other installation options available to you, such as NetInstall, DVD, Everything, and various LiveCDs.

Before we begin, it is assumed that you have followed the previous recipe in which you were shown how to download a minimal CentOS image and confirm the checksum of the relevant image files. It is also assumed that all the downloads (including the downloaded ISO file) are stored on Windows in your C:\Users\<username>\Downloads folder or if using a OS X system, in the /Users/<username>/Downloads folder. Next, you will need a free USB device which can be discovered by your operating system, with enough total space, and which is empty or with data on it that can be discarded. The total space of the USB device needed for preparing as an installation media for CentOS 7 for the minimal version must be roughly 700 megabyte. If you are working on a Windows computer, you will need a working Internet connection to download additional software. On OS X, you need an administrator user account.

To begin this recipe, start up your Windows or OS X operating system, then connect a free USB device with enough capacity, and wait until it gets discovered by File Manager under Windows or Finder under OS X.

So what have we learned from this experience?

The purpose of this recipe was to introduce you to the concept of creating an exact copy of a CentOS installation ISO file on a USB device, using the dd command-line program. The dd program is a Unix based tool which can be used to copy bits from a source to a destination file. This means that the source gets read bit by bit and written to a destination without considering the content or file allocation; it just involves reading and writing pure raw data. It expects two file name based arguments: input file (if) and output file (of). We will use the CentOS image file as our input filename to clone it exactly 1:1 to the USB device, which is accessible through its device file as our output file parameter. The bs parameter defines the block size, which is the amount of data to be copied at once. Be careful, it is an absolute expert tool and overwrites any existing data on your target while copying data on it without further confirmation or any safety checks. So at least double-check the device drive letters of your target USB device and never confuse them! For example, if you have a second hard disk installed at D: and your USB device at E: (on OS X, at /dev/disk2 and /dev/disk3 respectively) and you confuse the drive letter E: with D: (or /dev/disk3 with /dev/disk2), your second hard disk would be erased with little to no chances of recovering any lost data. So handle with care! If you're in doubt of the correct output file device, never start the dd program!

In conclusion, it is fair to say that there are other far more convenient solutions available for creating a USB installation media for CentOS 7 than the dd command, such as the Fedora Live USB Creator. But the purpose of this recipe was not only to create a ready-to-use CentOS USB installer but also to get you used to the dd command. It's a common Linux command that every CentOS system administrator should know how to use. It can be used for a broad variety of daily tasks. For example, for securely erasing hard disks, benchmarking network speed, or creating random binary files.

Before we begin, it is assumed that you have followed the previous recipe in which you were shown how to download a CentOS image, confirm the checksum of the relevant image files, and create the relevant installation optical disks or USB media. Your system must be a 64 bit (x64_86) architecture, must have at least 406 MB RAM to load the graphical installer 1 GB or more is recommended if installing a graphical window manager such as Gnome), and have at least 10 GB free hard disk space.

To begin this recipe, insert your installation media (CD/DVD or USB device), restart the computer, and press the correct key for selecting the boot device during startup. Then choose the inserted device from the list (for many computers, this can be reached using F11 or F12 but can be different on your system. Please refer to your motherboard's manual).

In this recipe, you have discovered how to install the CentOS 7 operating system. Having covered the typical approach to the graphical installation process, you are now in a position to develop the server with additional configuration changes and packages that will suit the role you intend the server to fulfill. This graphical installer has been built with the aim to be very intuitive and flexible, and makes installation very easy as it will guide the user through some mandatory tasks that he has to fulfill before the installation of the main system can be started.

Before we begin, it is assumed that you already know how to download and checksum a CentOS 7 installation image and how to create the relevant installation media from it. For this recipe here, we will need to download and create installation media for the netinstall image (download the latest CentOS-7-x86_64-NetInstall-XXXX.iso file) instead of the minimal ISO shown in another recipe in this chapter. Also, it is assumed that you have at least gone through the graphical installation procedure once to exactly know how to boot from your installation media and work with the installer program.

To begin this recipe, insert your prepared netinstall media, boot your computer from it, and wait for the welcome screen to appear:

The purpose of this recipe was to introduce you to the concept of the CentOS network installation process, in order to show you just how simple this approach can be. By completing this recipe you have not only saved time by limiting your initial download to those files that are required by the installation process, but you have also been able to take advantage of the full graphical installation method without the need for a complete DVD suite.

To successfully complete this recipe, you will need access to an already installed CentOS 7 system to retrieve the kickstart configuration file we want to work with and use for automated installation. On this pre-installed CentOS server, you also need a working Internet connection to download additional software.

Next, we will need to download and create installation media for the DVD or the Everything image (download the latest CentOS-7-x86_64-DVD-XXXX.iso or CentOS-7-x86_64-Everything-XXXX.iso file), instead of the minimal iso file shown in another recipe in this chapter. Then you need another USB device which must be read and writable on Linux systems (formatted as FAT16, FAT32, EXT2, EXT3, EXT4, or XFS filesystem).

For this recipe to work, we first need physical access to an existing kickstart file from another finished CentOS 7 installation, which we will use as a template for a new CentOS 7 installation.

In this recipe, you have seen that every server running a CentOS 7 installation keeps the kickstart file in its root directory, which contains detailed information on how the system had been set up during the installation. The kickstart files can be used to automate the installations of multiple systems with the same configuration. This can save a lot of time doing repetitive work as no user interaction during installation is needed. Also, we can use this method if the target machines don't meet the minimum requirement in RAM for graphical based installations but when needed other features the text mode installer does not provide such as custom partitioning of the system. Kickstart configuration files are simple plain text files which can be created manually from scratch. Because there are quite a number of different commands available to construct your system using the kickstart syntax, we used an existing file as a template and customized it to fit our needs, instead of starting out completely new. We did not use the minimal installation image to drive our kickstart installation because we installed some extra packages not included on the minimal ISO file, such as the Apache webserver.

To complete this recipe, you will require access to an already installed CentOS 7 operating system (minimal or any other CentOS 7 installation type will work) with root privileges. Also, you need to have some basic experiences with a text based editor, such as nano, for changing the configuration files.

We begin this recipe by opening the main GRUB2 configuration file with our text editor of choice and modifying it.

Having completed this recipe, we now know how to customize the GRUB2 boot loader. In this very easy recipe, we only showed you very basic modifications to the boot loader but it can do much more! It supports a broad variety of filesystems and can boot almost any compatible operating system. This is also particularly useful if you plan to run multiple operating systems on the same machine. To learn more about GRUB2's configuration file syntax type the info grub2 | less command and go to the section 6.1 Simple configuration handling (read the recipe Navigating text files with less in Chapter 2, Configuring the System to learn how to browse this document).

To complete this recipe, you will require a standard installation media (CD/DVD or USB device) of the CentOS 7 operating system. For recovering the data from the system, you will need to connect some sort of external storage device to the system, such as an external hard disk or a working network connection to another computer to copy all your precious data to a different location.

To begin this recipe, you should boot your server from the CentOS installation CD/DVD or the USB device and wait until the first welcome splash screen appears with the cursor waiting at the Test this media & install CentOS 7 menu option.

There are a broad variety of problems which can be resolved by the tools provided through the rescue mode environment. Often these problems refer to booting problems but can also be from different types, such as forgetting the root password. Rescue mode can be a life-saver and an understanding of it is a very important skill to learn. It was felt that such a recipe should thus remain close at hand.

To complete this recipe, you will require a minimal installation of the CentOS 7 operating system with root privileges and a connection to the Internet in order to facilitate the download of additional packages.

We will begin this recipe by updating the system.

The purpose of this recipe is to enhance the minimal installation of the CentOS 7 operating system and by doing this you have not only introduced yourself to the Yellowdog Updater Modified (YUM) package manager (something to which we will return to later on in this book), but you now have a system that is capable of running a vast amount of applications right out-of-the-box.

So what have we learned from this experience?

We started the recipe by updating the system in order to ensure that it is up to date. At this stage, it is often a good idea to reboot the system. It is not expected that we will do this very often but it is expected when updating for the first time after the installation of the operating system, as it is most likely that there are major changes available. The reason behind this is typically based on the desire to take advantage of a new kernel or revised security updates. In the next phase, the recipe showed you how to add a series of package groups that may prove to be more than useful in the future. To save time, we wrapped the instruction to install the three main package groups: Base, Development Libraries, and Development Tools. The preceding action alone installs over 200 individual packages, thereby giving your server the ability to compile the code and run a vast array of applications out-of -the-box, that you may need over the life time of your server. To see a list of all the packages within a group, for example, from Base, run the yum groupinfo Base command. Another package we installed was policycoreutils-python which provides tools and programs to manage the security enhanced access control to Linux, which we will use quite often throughout the chapters of this book.