Süsteemihaldus 2019/20 kevad

Lab2 Bootstrapping CentOS 7

In this lab we will cover the installation process relying mainly on the bootstrapping way, which illustrates some of the essential steps of the installation. By using the installer application, eventually it will hide all the important steps and making user friendly. However, we are aiming the expert level understanding of the GNU/Linux OS, therefore we will try to avoid wizards and helpers.

Creating the VM

First let's create VM suitable to run CentOS. This newly created VM becomes our temporary environment for installing CentOS 7.

Once the ISO downloaded and is valid, we may create VM and install Debian

• For VirtualBox :
  • Open the VirtualBox application, and click New Button
    • Give a new VM a name
    • Choose a type Linux
    • Choose version Redhat (64-bit)
    • Click Next
    • Specify amount of memory 1024MB, as this will be enough for testing purposes
    • Click Next
      • Select Create a virtual hard disk now
    • Click Next
      • Select VDI (VirtualBox Disk Image)
    • Click Next
      • Select Dynamically allocated
    • Click Next
      • Set 10 GB as size
    • Click Create
  • The newly created VM should be visible in the VM list (in the left in VirtualBox main window you should see it listed
  • Right-click on it and select Settings
    • Go to System -> Processor tab -> select 2 CPU cores and Enable PAE/NX -> Acceleration tab -> Verify that Enable VT-x/AMD-V is marked -> Click OK.
    • Go to Storage -> Click Controller: SATA -> Click second icon with green "plus sign" called Add hard disk -> Create new disk -> Select VDI (VirtualBox Disk Image) -> Select Dynamically allocated -> 10GB -> Click Create -> Click OK.
  • We will also need to attach the CentOS 8 bootable ISO to the VM
  • Under Storage -> select Controller: IDE -> Click first icon with green "plus sign" called Add optical drive -> Locate the downloaded CentOS ISO and add it to the Virtual machine

After you have started the virtual machine the CentOS boot menu should appear:

• Please select First option Install CentOS Linux 7 and hit Enter
• The standard boot process will take place and bring to an installation prompt
• Select a language according to your preferences

Now we are ready to begin preparations and start installing CentOS!

Preparing the disks

The first thing we need to do is to switch to root shell in order to have access to utils like:

• fdisk, mkfs, mkswap, tune2fs, mount, vi, mdadm, lvm-tools, cryptsetup/dm-crypt (etc.)
• ... which we will use to setup the disks up.

Changing to root shell

You need to switch to another TTY inside the CentOS installation. To do that we need to send the keys Ctrl-Alt-F2 to the VM

• On windows this should work normally
• If your VirtualBox host machine is running linux, your host may capture the keys instead.
• In that case you will need to select Input under your running VM and open the Soft Keyboard

You should see a root shell starting with [anaconda root@localhost /]#

Now we can start partitioning and formatting our HDD.

Partitioning virtual HDD (DOS or GPT)
First of all make sure we have HDD in our system at all:

• # fdisk -l or
• # lsblk
• ... should give us an information about attached hard drives and partitions
  • We should see /dev/sda (the first hard drive) and /dev/sdb (the second hard drive) both empty with 10 GiB of free space each.

The correct output for p command in fdisk

• In case you did something wrong or want to redo you can use # fdisk /dev/sda and then hit d to delete partitions.

The correct output for lsblk command

RAID 1 for better data reliability
RAID (Redundant Array of Independent Disks, originally Redundant Array of Inexpensive Disks) is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both.

Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance. The different schemes, or data distribution layouts, are named by the word "RAID" followed by a number, for example RAID 0 or RAID 1. Each schema, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives. https://en.wikipedia.org/wiki/RAID

• Now lsblk output should look like this

• You can check status of RAID arrays with cat /proc/mdstat command

For added security lets encrypt the data parts of our disks
dm-crypt is a transparent disk encryption subsystem in Linux kernel versions 2.6 and later and in DragonFly BSD. It is part of the device mapper infrastructure, and uses cryptographic routines from the kernel's Crypto API. The dm-crypt device mapper target resides entirely in kernel space, and is only concerned with encryption of the block device – it does not interpret any data itself. It relies on user space front-ends to create and activate encrypted volumes, and manage authentication. At least two frontends are currently available: cryptsetup and cryptmount. The cryptsetup command-line interface, by default, does not write any headers to the encrypted volume, and hence only provides the bare essentials: encryption settings have to be provided every time the disk is mounted (although usually employed with automated scripts), and only one key can be used per volume; the symmetric encryption key is directly derived from the supplied passphrase. https://en.wikipedia.org/wiki/Dm-crypt

• You can chek if the newly opened disk is available in lsblk list

LVM

In Linux, Logical Volume Manager (LVM) is a device mapper target that provides logical volume management for the Linux kernel. Most modern Linux distributions are LVM-aware to the point of being able to have their root file systems on a logical volume.

LVM is used for the following purposes:

• Creating single logical volumes of multiple physical volumes or entire hard disks (somewhat similar to RAID 0, but more similar to JBOD), allowing for dynamic volume resizing.
• Managing large hard disk farms by allowing disks to be added and replaced without downtime or service disruption, in combination with hot swapping.
• On small systems (like a desktop), instead of having to estimate at installation time how big a partition might need to be, LVM allows filesystems to be easily resized as needed.
• Performing consistent backups by taking snapshots of the logical volumes.

LVM can be considered as a thin software layer on top of the hard disks and partitions, which creates an abstraction of continuity and ease-of-use for managing hard drive replacement, repartitioning and backup.

If done correctly lsblk should look like something like this

• To verify previous command you can use blkid command

Configuring the installation disks

First we need to reboot the instance to let CentOS know we've changed the device configuration. The easiest way to do this is to enter the command reboot into the terminal session.

Once again choose Install CentOS 7 and let it boot into the graphical interface.

Now we will choose the option INSTALLATION DESTINATION, after which we should see the 2 disks we configured partitioning on. Select both of them (make sure both of the tickboxes are checked) and from the bottom select I will configure partitioning. After clicking Done in the upper left corner, we can now configure CentOS to use our partitioing scheme.

Firstly in the sidebar we click Unknown, while CentOS is capable of recoqnizing the encrypted partitions, it is a more rarely used feature. Select the Encrypted (LUKS) option and insert your passphrase to unlock the crypt-lvm.

Next we will need to configure each of the partitions.

Configuring your Installation

Without any configuration, CentOS 7 will be installed in what's called a Minimal or headless configuration. This means that no graphical user interfaces will be installed. The reason for this is that CentOS is mainly used as a server operating system and any unneccesary overhead would be wasteful

For configuring our installation, first lets add a Graphical interface which will be installed during the setup.

Next we'll configure our locale settings - these are mainly a personal preference but it's still good to atleast familiarize yourself with the options.

Lastly, we'll configure the network and hostname settings.

Once the configuration is done, check Begin Installation

Adding an user Currently our setup only has the root user enabled. Once the installation start we can add an additional user that does not have all the system privileges.

  If you cannot finish the task in class, and you did the task on class computers, then you can access your machine by going to:

     ssh <username>@adalberg.ut.ee

   There you have the same home directory as in the classrooms. Then you can copy the VM image files to your computer with tools like scp, rsync or filezilla. (Can do this from anywhere)

CONGRATULATIONS you have completed the lab 2.

Lab 001 Live Videos