Distributions And Bootup

Question 1

What are the main three families of Linux distributions?

Answer 1

• Red Hat Famility Systems (like CentOS or Fedora)
• SUSE Family Systems (like openSUSE)
• Debian Family Systems (like Ubuntu or Linux mint)

Question 2

Name a few facts about the Red Hat Enterprise Linux family

Answer 2

• Fedora serves as a upstream testing platform for RHEL
• supports multiple hardware platforms
• uses dnf, the rpm-based package manaer to install, update and remove packages in the system
• widely used by enterprises which host their own systems
• Kernel version 5.14 is used in RHEL/CentOS 9 Stream, 4.18 heavily patched in RHEL CentOS 8 Stream

Question 3

Name a few facts about the SUSE distribution family

Answer 3

• Kernel version 5.14 used in openSUSE Leap 15.4
• uses rpm-based zypper package manager to install, update and remove packages in the system
• includes YaST (Yet Another Setup Tool) application for system administration purposes
• widely used in retail and many other sectors

Question 4

Name a few facts about the Debian distribution family

Answer 4

• is upstream for several other distributions
• commonly used both on servers and desktop computers
• pure open source community project
• aims at good compromise between long term stability and ease of use
• Kernel Version 5.19 in Ubuntu 22.04 LTS (long Term support)
• widely used for cloud deployments
• uses dpkg-based APT package manager

Question 5

What does this term mean?
Kernel

Answer 5

• brain of the linux Operating System
• controls the hardware and makes it interact with the applications
• glue between hardware and applications
• example: Linux kernel

Question 6

What does this term mean in Linux?
command line

Answer 6

• interface for typing commands on top of the operating system

Question 6

What does this term mean?
distribution

Answer 6

• collection of programs combined with the linux kernel
• making up a Linux-based OS

Question 6

What does this term mean?
boot loader

Answer 6

• program that boots the operating system
• i.e: GRUB / ISOLINUX

Question 7

What does this term mean in Linux?
service

Answer 7

• program that runs as a background process
• i.e.: httpd, nfsd, ntpd, ftpd, named

Question 7

What does this term mean in Linux?
desktop environment

Answer 7

• graphical user interface on top of OS

Question 7

What does this term mean in Linux?
X Window system

Answer 7

• graphical subsystem on nearly all Linux systems

Question 7

What does this term mean in Linux?
filesystem

Answer 7

• method for storing and organizing files
• i.e. ext3, ext4, FAT, XFS, NTFS; Btrfs

Question 8

What does this term mean in Linux?
shell

Answer 8

• command line interpreter that interprets the command line input and instructs the OS to perform any necessary tasks and commands
• i.e. bash, tcsh, zsh

Question 9

What are the steps of the Linux boot process?

Answer 9

1. Power ON
2. BIOS
3. Master Boot Record (MRB) or EFI Partition
4. Boot Loader (i.e. GRUB)
5. Kernel
6. Initial RAM disk -initramfs
7. /sbin/init (parent process)
8. Command Shell using getty
9. Graphical User Interface (X Window or Wayland)

Question 10

What is part of the first steps?

Answer 10

• Basic Input/Output System (BIOS) initializes the hardware
• hardware includes: keyboard, screen, and tests the memory
• also called POST (Power on Self Test)
• after this remainder of the boot process is controlled by OS

Question 11

Where is BIOS stored?

Answer 11

• on read-only memory (ROM) chip on the motherboard

Question 12

What comes after POST in the boot process?

Answer 12

• system control passes from BIOS to boot loader
• machine does not access any mass storage media
• information on date, time and most important peripherals are loaded from CMOS values

Question 13

Where is the boot loader stored?

Answer 13

• usually stored on one of the systems storage devices (hard disk or ssd)
• there either in the boot sector (for traditional BIOS/MBR (Master Boot Record) systems) or EFI partition (for more recent Extensible Firmware Interface systems EFI/UEFI)

Question 14

What is the boot loader responsible of when loading Linux?

Answer 14

• loading the kernel image and initial RAM disk or filesystem (which contains some critical files and device drivers needed to start the system) into memory

Question 15

What happens in the first stage of the boot loader? (BIOS/MR)

Answer 15

Systems using BIOS/MBR:
- boot loader resides in first sector of hard disk, known als Master Boot Record (MBR)
- size of MBR is just 512 bytes
- boot loader examines partition table and find bootable partition
- once found, it then searches for the second stage boot loader, example GRUB, and loads it into RAM

Question 16

What happens in the first stage of the boot loader? (EFI/UEFI)

Answer 16

• UEFI firmware reads its Boot manager data to determine which UEFI application is to be launched and from where (disk and partition)
• firmware then launches the UEFI application (i.e. GRUB) as defined in boot entry in the firmware’s boot manager
• more complicated but more versatile than the older MBR methods

Question 17

What happens in the second stage of the boot loader?

Answer 17

• second stage boot loader resides under /boot
• splash screen is displayed, which allows us to choose which OS and/or kernel to boot
• after OS and kernel are selected, boot loader loads the kernel of the OS into RAM and passes control to it
• kernels are almost always compressed, so first job is to uncompress themself
• after this it will check and analyze the system hardware and initialize any hardware devices built into the kernel

Question 18

What does the initramfs filesystem image contain?

Answer 18

• programs and binary files that peform all actions needed to mount the propert root filesystem
• including providing the kernel functionality required for the specific filesystem that will be used
• locating and loading the** device drivers **for mass storage controllers by using udev system
• udev (user device) is responsible for figuring out which devices are present, locating the device drivers they need to operate properly and loading them
• after the **filesystem **has been found, it is checked for errors and mounted

Question 19

What does the mount program do?

Answer 19

• instructs the OS that a filesystem is ready for use and associates it with a particular point in the overall hierarchy of the filesystem (the mount point)
• if this is successful, initramfs is cleared from RAM and init program on the root filesystem (/sbin/init) is executed

Question 20

What does init do? Initied by mount program.

Answer 20

• handles mounting and pivoting over to the final real root filesystem
• if special hardware drivers are needed before the mass storage can be accessed, they must be in the initramfs image
• at the end of boot process, starts a number of text-mode login prompts
• these enable you to type username, followed by password and to eventually get a command shell, not seen when running a system with a graphical login interface

Question 21

How can you access the terminals running command shells?

Answer 21

• ALT+ function key (F1, F2)
• ## with a graphical environment switching to a text console requires pressing CTRL + ALT + F7/F1

Question 22

What does bash stand for?

Answer 22

• GNU Bourne Again Shell