Boot Processes

Question 1

What is the sequence of the Linux boot process?

Answer 1

BIOS/UEFI → MBR/Bootloader → Kernel Initialization → Init System & Services.

Question 2

What is POST in BIOS?

Answer 2

Power-On Self Test; checks hardware integrity before loading the OS.

Question 3

Where is the Master Boot Record located?

Answer 3

In the first 512 bytes of the bootable storage device (e.g., /dev/sda).

Question 4

What does the first 446 bytes of the MBR contain?

Answer 4

Primary bootloader code.

Question 5

What tool is responsible for loading the Linux kernel?

Answer 5

GRUB (Grand Unified Bootloader).

Question 6

What is the purpose of GRUB Stage 2?

Answer 6

It provides the user interface and reads configuration from /boot/grub/grub.cfg.

Question 7

What does the Linux kernel do after decompression?

Answer 7

Detects hardware, sets up memory management, loads drivers, and mounts the root filesystem.

Question 8

What is initramfs used for?

Answer 8

Temporary root filesystem that loads drivers and mounts the real root filesystem.

Question 9

What replaced SysV init in modern Linux systems?

Answer 9

systemd, using targets instead of runlevels.

Question 10

What command shows the current runlevel?

Answer 10

who -r

Question 11

What does /etc/fstab define?

Answer 11

Filesystem mount points and options.

Question 12

How can you mount all filesystems listed in /etc/fstab?

Answer 12

mount -a

Question 13

What is single-user mode used for?

Answer 13

System recovery and maintenance tasks.

Question 14

What is rescue.target in systemd?

Answer 14

Single-user mode for maintenance with minimal services.

Question 15

What are common causes of a kernel panic during boot?

Answer 15

Missing initrd, incorrect root device, hardware failure, or corrupted kernel image.

Question 16

How can you rebuild initramfs?

Answer 16

update-initramfs -u

Question 17

How can you rebuild the GRUB configuration?

Answer 17

update-grub

Question 18

What command visualizes boot performance?

Answer 18

systemd-analyze plot > boot.svg

Question 19

How do you check the total boot time?

Answer 19

systemd-analyze

Question 20

What command lists slowest boot services?

Answer 20

systemd-analyze blame

Question 21

What is the difference between initrd and initramfs?

Answer 21

initrd uses a block device filesystem; initramfs uses a cpio archive in RAM.

Question 22

What mode does the CPU operate in during BIOS execution?

Answer 22

Real mode (16-bit).

Question 23

How does the system switch from real mode to protected mode?

Answer 23

Loads the Global Descriptor Table (GDT) and sets a bit in CR0 register.

Question 24

How can you enter single-user mode from GRUB?

Answer 24

Append ‘single’ or ‘systemd.unit=rescue.target’ to kernel parameters.

Question 25

What is emergency.target used for?

Answer 25

Minimal recovery shell when the system cannot boot normally.

Question 26

How do you load a linux kernel?

Answer 26

Bootloader reads compressed kernel image and initramfs into memory and jumps to kernel entrypoint

Question 27

How do you load a module into the linux kernel?

Answer 27

Kernel modules are loaded at runtime with a tool like modprobe lsmod, modinfo for module info rmmod for removing