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

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.

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.

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.

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 the tests finish, the graphical installer will load and present the typical graphical installation summary screen.

Before we can install CentOS over the network, we have to make sure that we have a working network connection. Therefore, you should first click on the Network & Host name menu entry and activate one of your network adapters to the connected state. Refer to the normal installation recipe for more details.

Next, click on Installation source to enter the settings. As we will be installing over HTTP (also referred to as the URL method), you should leave the default On the network selected in the Which installation source would you like to use? section.

Now type in the following URL in the standard http:// textfield, which we will use to download all the required installation packages at http://mirror.centos.org/centos/7/os/x86_64/.

Alternatively, you can also use a personal repository which you would have to create in advance (see Chapter 4, Managing Packages with YUM)

When you are ready, click on Done to start the initialization process.

On success, the installer will begin to retrieve the appropriate install.img file. This may take several minutes to complete, but once resolved, a progress bar will indicate all the download activity. When this process finishes successfully, the exclamation mark at the installation source will go away but another one will pop up which will tell the user that it is missing the software selection. Click on it and choose whatever fits your need. As for the purpose of this recipe, just select Minimal install under Base environment and then click on Done.

If the Which installation source would you like to use stays greyed out and cannot be changed, then there are connection problems with your network adapter. If this is the case, go back to configure Network & Hostname and change the network settings until the connected state can be reached.

CentOS 7 will now install the operating system the usual way and will congratulate you when this process finishes. It may be slower than installing from a physical installation media since all the packages have to be retrieved from the Internet.

Log in as root on the existing CentOS 7 system and make sure the kickstart configuration file exists by typing the following command and pressing the Return key to execute (this will show you the details of the file):

ls -l /root/anaconda-ks.cfg

Next, physically plug in a USB device and then type the following command, which will give you a list of all the hard disk devices currently connected to the computer:

fdisk -l

Try to identify the device name by comparing its size, partitions, and identified filesystems with the specifications of your USB device. The device name will be of kind /dev/sdX, where X is an alphabetical character, such as b, c, d, e, … and so on. If you cannot find the right device name for your USB media using the fdisk command, try the following trick: run fdisk -l twice - first with plugged-out and then with plugged-in USB device and compare how the second output changed - it has one device name more than the first output: your device name of interest !

If you have found the right device name in the list, create a directory to mount it to the current filesystem:

mkdir /mnt/kickstart-usb

Next, actually mount the stick to this folder, assuming that your USB partition of choice is at /dev/sdc1 (change this as required):

mount /dev/sdc1 /mnt/kickstart-usb

Now we will create our working copy of the kickstart file on the USB device for customizing:

cp /root/anaconda-ks.cfg /mnt/kickstart-usb

Next, open the copied kickstart file on the USB device with your favorite text editor (here we will use the editor nano, if you have not installed it yet type yum install nano):

nano /mnt/kickstart-usb/anaconda-ks.cfg

We will now modify the file for installing CentOS on a new target system. In nano, use the up and down arrow keys to go to the line which starts with (<your_hostname> will be the name of the hostname you gave during installation e.g. minimal.home):

network  --hostname=<your_hostname>

Now edit the <your_hostname> string to give it a new unique hostname. For example, add a -2 to the end of any existing name, as shown next:

network  --hostname=minimal-2.home

Next, move the cursor down using the up and down arrow keys until it stops at the line which says %packages. Append the following lines right below it (you can further customize this and provide additional packages that you want to install automatically):

mariadb-server
httpd
rsync
net-tools

Now save and close the file, to do this in the nano editor use the key combination Ctrl+o (which means, hold down the Ctrl key on the keyboard and then the o key without releasing the Ctrl key) to write the changes. Then press Return to confirm the filename and Ctrl+x to exit the editor.

Next, install the following CentOS package:

yum install system-config-kickstart

Now we validate the syntax of our kickstart file using the ksvalidator program, which is included in the package we just installed:

ksvalidator /mnt/kickstart-usb/anaconda-ks.cfg

If the config file is error-free, unmount the USB stick now by using the following commands:

cd
umount /mnt/kickstart-usb

When you get a new command prompt again, unplug the USB device with the kickstart file for using on the target machine physically from the system.

Now you need physical access to the target machine you want to install CentOS on, using the kickstart file just created. Disconnect any other external file storage(s) that you do not need during the installation.

Power on the computer and put in your prepared CentOS installation media (must be a CentOS DVD or Everything installation disk image prepared on a CD/DVD disc or a USB device installer). Also connect to the computer the USB stick containing the kickstart file you just created in the earlier steps (if you using a USB drive for installing CentOS then you will need two free USB ports in total to complete this recipe).

Next, start the server and press the correct key during the initial bootup screen, associated with booting the CentOS installation media you just connected.

After the CentOS installer starts loading, the common standard CentOS 7 installation welcome screen will show up and the option Test this media & install CentOS 7 will be pre-selected by the cursor.

Next, press the Esc key on your keyboard once to switch to the boot: prompt.

Now we are ready to start the kickstart installation. To do this, you need to know the exact partition name on the USB device where the kickstart file is located. Type the following command, assuming that your partition is at /dev/sdc1 (change this as required), and press the Return key to start the kickstart installation process:

linux ks=hd:sdc1:/anaconda-ks.cfg

The new system now gets installed automatically using the instructions from the provided kickstart file. You can watch the installation output messages as it is showing the user detailed installation progress.

If the system has finished installing, reboot the system and log in to your new machine to verify that the new system has been setup the way we described using the kickstart file.

First log in as root into your system and create a copy of the GRUB2 configuration file for backup and rollback, if needed. Press the Return key to finish:

cp /etc/default/grub /etc/default/grub.BAK

Open the main GRUB2 configuration file that we want to edit with the following command and press the Return key (here we will use the editor nano, if you have not installed it yet type yum install nano):

nano /etc/default/grub

Press the Return key in the first line where the cursor is at to insert a new line at the top, and then insert the following line:

GRUB_HIDDEN_TIMEOUT=0

Add a # sign to the beginning of the following line, as shown:

GRUB_TIMEOUT=0

Now save the file in the nano using Ctrl+o (and Return to confirm the filename to save). Use Ctrl+x to exit the editor and then run the following command:

dmesg | grep -Fq "EFI v"

If the preceding command does not produce any output, run the following command:

grub2-mkconfig -o /boot/grub2/grub.cfg

Otherwise, if there is an output, run:

grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg

If grub2-mkconfig is successful, it will print Done. Now reboot your system using the following command:

reboot

During the rebooting process, you will notice that the GRUB2 boot menu will not appear any more and the system will boot up faster.

To update the system, log in as root and type:

yum -y update

CentOS will now search for the relevant updates and, if available, they will be installed. On completion and depending on what was updated (that is, kernel and new security features to name but a few), you can decide to reboot your computer. To do this, type:

reboot

Your server will now reboot and return to the login screen. We will now complete this recipe and enhance our current installation with a series of package groups that will prove to be very useful in the future. To do this, log in as root and type:

yum -y groupinstall "Base" "Development Libraries" "Development Tools"
yum -y install policycoreutils-python