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CentOS 7 Linux Server Cookbook, Second Edition

Chapter 1. Installing CentOS

In this chapter, we will cover:

Downloading CentOS and confirming the checksum on Windows or OS X
Creating USB installation media on Windows or OS X
Performing an installation of CentOS using the graphical installer
Running a netinstall over HTTP
Installing CentOS using a kickstart file
Re-installing the boot loader
Troubleshooting the system in rescue mode
Getting started and customizing the boot loader
Updating the installation and enhancing the minimal install with additional administration and development tools

Downloading CentOS and confirming the checksum on Windows or OS X

In this recipe, we will learn how to download and confirm the checksum of one or more CentOS 7 disk images using a typical Windows or OS X desktop computer. CentOS is made available in various formats by HTTP, FTP, or the rsync protocol from a series of mirror sites located across the world or via the BitTorrent network. For downloading very important files from the Internet, such as operating system images, it is considered best practices to validate those files' checksum, in order to ensure that any resulting media would function and perform as expected when installing. This also makes certain that the files are genuine and come from the original source.

Getting ready

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.

How to do it...

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:

Let's begin by visiting http://www.centos.org in a web browser and navigate to the button link Get CentOS Now. Then click the link list of the current mirrors in the text.
The mirror sites are categorized, so from the resulting list of links, choose a mirror that is geographically near your current location. For example, if you are in London (UK), you can choose a mirror from EU and United Kingdom. Now choose a mirror site by selecting either the HTTP or the FTP link.
Having made your selection, you will now see a list of directories of all the available CentOS versions. To proceed, simply click the appropriate folder that reads 7. Next, you will see an additional list of directories, such as atomic, centosplus, cloud, and so on. We proceed by choosing the isos directory.
CentOS 7 currently only supports the 64-bit architecture, so browse to the only directory available labeled x86_64, which is a container for the 64-bit version.
You will now be presented with a series of files available for download. Begin by downloading a copy of the valid checksum result identified as md5sum.txt.
If you are new to CentOS or are intending to follow the recipes found throughout this book, then the minimal installation is ideal. This contains the least amount of packages to have a functional system, so choose the following (XXXX is the month stamp of this release):
```
CentOS-7-x86_64-Minimal-XXXX.iso
```
On a Windows-based system only (on Mac, this tool is already available in the system), visit http://mirror.centos.org/centos/dostools/ in your browser and download the program md5sum.exe.
Now on Windows, open the command prompt (typically found at Start | All Programs | Accessories | Command Prompt) and type the following commands into the window that will open (press the Enter key at the end of all the lines):
```
cd downloads
dir
```
On OS X, open the program Finder | Applications | Utilities | Terminal, then type the following commands (press the Enter key at the end of all the lines):
```
cd ~/Downloads
ls
```
You should now see all the files in your download folder (including all the downloaded CentOS installation image files, the md5sum.txt file and on Windows, the md5sum.exe program).
Based on the file names shown, modify the following command in order to check the checksum of your downloaded ISO image file. On Windows, type the following command (change the XXXX month stamp accordingly):
```
md5sum.exe CentOS-7-x86_64-Minimal-XXXX.iso
```
On OS X, use instead:
```
md5 CentOS-7-x86_64-Minimal-XXXX.iso
```
Press the Return key to proceed and then wait for the command prompt to respond. The response is known as the MD5 sum and the result could look like the following:
```
d07ab3e615c66a8b2e9a50f4852e6a77  CentOS-7-x86_64-Minimal-1503-01.iso
```
Now look at the the sum and compare against the relevant listing for your particular image file in md5sum.txt (open in a text editor). If both the numbers match, then you can be confident that you have indeed downloaded a valid CentOS image file. If not, your downloaded file is probably corrupted, so please restart this procedure by downloading the image file again.
When you have finished, simply burn your image file(s) to a blank CD-ROM or DVD-ROM using your preferred desktop software, or create a USB installation media from it, as we will show you in the next recipe in this chapter.

How it works…

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.

Creating USB installation media on Windows or OS X

In this recipe, we will learn how to create a USB installation media on Windows or OS X. Nowadays, more and more server systems, desktop PCs, and laptops get shipped without any optical drive. Installing a new operating system, such as CentOS Linux using USB devices gets essential for them as no other installation option is available, as there is no other way to boot the installation media. Also, installing CentOS using USB media can be considerably faster than using the CD/DVD approach.

Getting ready

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.

How to do it...

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.

On a Windows based system, we need to download an additional software called dd. Visit http://www.chrysocome.net/dd in your favorite browser. Now download the latest dd-XX.zip file you can find there, with XX being the latest stable version number. For example, dd-0.5.zip.
On Windows, navigate to your Downloads folder using File Manager. Here you will find the dd-05.zip file. Right-click on it and click on Extract All, and extract the dd.exe file without creating any subdirectory.
On Windows, open the command prompt (typically found at Start | All Programs | Accessories | Command Prompt) and type the following commands:
```
cd downloads
dd.exe --list
```
On OS X, open the program Finder | Applications | Utilities | Terminal, and then type the following commands:
```
cd ~/Downloads
diskutil list
```
On Windows, to spot the name of the right USB device you want to use as installation media, look into the output of the command under the removable media section. Below that, you should find a line starting with Mounting on and then a drive letter, for example, \.\e:. This cryptic written drive letter is the most important part we need in the next step, so please write it down.
On OS X, the device path can be found in the output of the former command and has the format of /dev/disk<number>, where number is a unique identifier of the disk. The disks are numbered, starting with zero (0). Disk 0 is likely to be the OS X recovery disk, and disk 1 is likely to be your main OS X installation. To identify your USB device, try to compare the NAME, TYPE, and SIZE columns to the specifications of your USB stick. If you have identified the device name, write it down, for example, /dev/disk3.
On Windows, type the following command, assuming your USB device selected as a installation media has the Windows device name \\.\e: (change this as required and be careful what you type – this can create tremendous data loss). Also, substitute XXXX with the correct iso file version number in the next command:
```
dd.exe if=CentOS-7-x86_64-Minimal-XXXX.iso of=\\.\e: bs=1M
```
On OS X, you need two commands which will ask for the administrator password (replace XXXX and disk3 with the correct version number and the correct USB device path):
```
sudo diskutil unmountDisk /dev/disk3
sudo dd if=./CentOS-7-x86_64-Minimal-XXXX.iso of=/dev/disk3 bs=1m
```
After the dd program finishes, there will be some output statistics on how long it took and how much data has been transferred during the copy process. On OS X, ignore any warning messages about the disk not being readable.
Congratulations! You now have created your first CentOS 7 USB installation media. You now can safely remove the USB drive in Windows or OS X, and physically unplug the device and use it as a boot device for installing CentOS 7 on your target machine.

How it works...

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.

Performing an installation of CentOS using the graphical installer

In this recipe, we will learn how to perform a typical installation of CentOS using a new graphical installer interface introduced in CentOS 7. In many respects, this is considered to be the recommended approach to installing your system, as it not only provides you with the ability to create the desired hard disk partitions but also to customize your installation in lots of ways (for example, keyboard layout, package selection, installation type, and so on). Your installation will then form the basis of a server on which you can build, develop, and run any type of service you may want to provide in the future.

Getting ready

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.

How to do it...

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).

On the welcome splash screen, the option Test this media & install CentOS 7 is preselected and we will use this option. When you are ready, press the Return key to proceed.
After loading some initial files, the installer then starts to test the installation media. A single test should take between 30 seconds to five minutes and will report if there are any errors on your installation media. When this process is complete, the system will finally load the graphical installer.
The CentOS installer will now present the graphical installation welcome screen. From this point onwards, you can use your keyboard and mouse (the latter is highly recommended), but remember to enable the number lock on your keyboard if you intend to use the keypad.
On the left side you see the main language category and on the right side, the sub-languages for the installer. You can also search for a language using the textbox on the left bottom. All changes to your language settings will take effect immediately, so when you are ready, choose the Continue button to proceed.
Now we reach the main installation menu, which is called Installation summary.
Most options shown here already have some predefined values and can be used without changing, others which do not have any default value and which need your attention are labeled with a red exclamation mark like the Installation Destination under System category. So let's click on it using the mouse.
After clicking the Installation Destination button, you will see a graphical list of all the hard disk devices currently connected to your computer, which you can use for installing the operating system on. You can select your target hard disk by clicking on the correct hard disk symbol. It will then put a check mark on it. If you are unsure about the right hard disk, try to identify it by comparing its brand and total size shown in the menu. Before the installation can proceed, you must select a hard disk. Be careful and choose your target hard disk wisely as it will erase any existing data on it during the installation. When you are ready, click the Done button.
If your selected hard disk already contained data, then when clicking on Done, you may see what could be described as a warning/error message. The message may read: You don't have enough space available to install CentOS. Don't worry! This is to be expected and the message is simply asking you to re-initialize your hard disk because CentOS can only be installed on an empty disk. In most cases, especially if you have more than one partition on the hard disk, simply click on Reclaim space which will show a new window with a detailed list of all the partitions on this drive. Here just click on Delete All and then again on Reclaim space to discard any data on this disk, which will complete the task of disk initialization and enable you to proceed to the next step. When finished, click the Done button.
Back at the Installation Summary screen, the exclamation mark on the Installation Destination item should be gone now.
Optionally, we can click on Network & Hostname under System category. On the following page, on the left side, you can choose the primary network adapter you would like to connect to the Internet and select it by clicking on it. For the selected device, click on the switch on the right side to enable and connect it automatically using the On position of the switch. Finally, before closing this submenu, change the hostname in its text field to something appropriate. Click Done.
Now back at the Installation Summary screen, all the important settings have been made or have got predefined values, and all the exclamation marks are gone. If you are happy with these settings, click on the Start installation button or change the settings appropriately.
On the next screen, you will be required to create and confirm a root password for the root user while the new system gets installed in the background. Choose a secure password with not less than six characters.
Here on this screen you can also create a standard user account which is highly recommended. If you create a new user do not check Make this user administrator. When you are ready, click Done (if you entered a weak password, you have to confirm this by clicking twice)
CentOS will now partitionate and format your hard disk in the background and resolve any dependencies, and the installer will begin writing to the hard disk. This may take some time, but a progress bar will indicate the status of your installation. When finished, the installer will inform you that the entire process is complete and that the installation was successful. So when you are ready, click on the Reboot button. Now release your installation media from the drive.
Congratulations! You have now installed CentOS 7 on your computer.

How it works…

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.

Key benefits

A practical guide to install, configure, administer and maintain CentOS 7 servers

An in-depth guide to the CentOS 7 operating system, exploring its various new features and changes in server administration

Presents tricks and solutions to tackle common server issues with the help of practical examples and real-life scenarios

Description

This book will provide you with a comprehensive series of starting points that will give you direct access to the inner workings of the latest CentOS version 7 and help you trim the learning curve to master your server. You will begin with the installation and basic configuration of CentOS 7, followed by learning how to manage your system, services and software packages. You will then gain an understanding of how to administer the file system, secure access to your server and configure various resource sharing services such as file, printer and DHCP servers across your network. Further on, we cover advanced topics such as FTP services, building your own DNS server, running database servers, and providing mail and web services. Finally, you will get a deep understanding of SELinux and you will learn how to work with Docker operating-system virtualization and how to monitor your IT infrastructure with Nagios. By the end of this book, you will have a fair understanding of all the aspects of configuring, implementing and administering CentOS 7 Linux server and how to put it in control.

What you will learn

Install and configure CentOS 7 Linux server system from scratch using normal and advanced methods

Maintain a performance-based and secure server solution by deploying expert configuration advice and managing software packages

Monitor, manage and develop your server s file system to maintain a stable performance

Gain best practice methods on sharing files and resources through a network

Install and configure common standard services such as web, mail, FTP, database and domain name server technologies

Introduce you to the world of operating-system-level virtualization using the Docker platform.

Understand the fundamentals of the Security-Enhanced Linux access control architecture

Monitor your IT infrastructure using Nagios

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Paperback book shipped to your preferred address

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Mike Feb 18, 2017

Was very helpful, I had never used this version of Linux before.

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edgar p. Oct 29, 2017

Great book.

J. Osborne Feb 19, 2016

This is the book I have been looking for. It walks you through step by step from installation to having a complete server up and running. Other books tend to show you the technical use of the commands but don't apply the use to specifically setting up a server. Well written and easy to understand. This book will get new CentOS users up and running with a basic linux server while providing useful information for those that already have a better understanding of Linux servers. Great book!

Paul McDowell Dec 01, 2020

CentOS 7 is kind of a slap in the head to those of us used to the more conventional server platform OS setups. This book helps get you past a lot of that.

Amazon Customer Jan 11, 2018

Excellent! Taught me how to do many things that was second nature with CentOS 6 exactly how to do it in CentOS 7.

CentOS 7 Linux Server Cookbook, Second Edition: Get your CentOS server up and running with this collection of more than 80 recipes created for CentOS 7 - essential for Linux fans! , Second Edition

What do you get with Print?

CentOS 7 Linux Server Cookbook, Second Edition

Chapter 1. Installing CentOS

Introduction

Downloading CentOS and confirming the checksum on Windows or OS X

Getting ready

How to do it...

How it works…

Creating USB installation media on Windows or OS X

Getting ready

How to do it...

How it works...

Performing an installation of CentOS using the graphical installer

Getting ready

How to do it...

How it works…

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