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Linux Master 2· AssociateWeek 2 · Day 5~17 min read

Day 5 - Week 2 Review: From Installation to Boot in One Line

📌 Key Takeaways

The flow is disk → partition → file system → mount → boot. This order is this week's backbone.
Memorize the pairs — BIOS·MBR / UEFI·GPT·ESP. A good share of questions ask about these pairings.
Memorize the numbers — MBR 2TB · 4 primary partitions, FAT32 4GB per file, runlevels 0 shutdown · 6 reboot.
Journaling starts with ext3, and the inode has no file name — these two are facts that make good standalone questions.
Distinguish the stage of each command: fdisk (divide) → mkfs (lay over) → mount (attach) → fstab (make permanent).

Flow Diagram

  Physical disk  /dev/sda
       │
       │  ① Divide      fdisk · gdisk · parted
       ▼
  Partitions    /dev/sda1  /dev/sda2  swap
       │
       │  ② Lay over    mkfs.ext4 · mkfs.xfs
       ▼
  File systems  ext4 · XFS · FAT32
       │
       │  ③ Attach      mount → temporary
       ▼                /etc/fstab → permanent
  Directory tree  /  /home  /var
       │
       │  ④ Boot        BIOS/UEFI → GRUB2 → kernel → initramfs → systemd
       ▼
  Login screen

What to Memorize as Pairs

Left	Right	Note
BIOS	MBR	The bootloader sits in the disk's first sector
UEFI	GPT + ESP	Supports Secure Boot
ext3	Journaling introduced	ext2 doesn't have it
XFS	Default from RHEL 7+	Strong with large capacity
Btrfs	SUSE default	Snapshots and compression
LILO	Reinstall needed after configuring	The old bootloader
GRUB2	Edit `/etc/default/grub`	`grub.cfg` is auto-generated
Runlevel 3	`multi-user.target`	Text
Runlevel 5	`graphical.target`	GUI

Numbers Summary

Number	What
2TB	The maximum disk size MBR can handle
4	The maximum number of primary partitions in MBR
1	The number of extended partitions per disk
5	The number where logical partition numbering starts
4GB	FAT32's single-file size limit
1 to 2 times	The classic swap size rule (relative to memory)
0 / 6	Runlevel shutdown / reboot
1	The PID of init (systemd)

The 2TB and 4 come from MBR being a single 512-byte sector — bootloader 446 + partition table 64 (16 bytes × 4 slots) + signature 2. With four slots, that's 4 primary partitions, and with positions written in 32 bits, that's 2TB.

Configuration Files and Paths Summary

"Which file do you write it in" is the part most often mixed up this week. It sorts out if you split by when it is read.

File	Contents	Who reads it and when
`/etc/fstab`	The list to mount automatically (6 fields)	At boot, and at `mount -a`
`/etc/mtab` · `/proc/mounts`	The list mounted right now	The system records it. Not a file for people to edit
`/etc/default/grub`	GRUB2 default settings	`grub2-mkconfig` reads it and creates `grub.cfg`
`grub.cfg`	The final configuration GRUB2 actually reads	GRUB2 at boot. Don't edit directly
`/boot/grub/grub.conf`	Old GRUB configuration	Old GRUB at boot. Edit directly
`/etc/lilo.conf`	LILO configuration	Takes effect only after re-running the `lilo` command
`/etc/inittab`	Default runlevel (`id:3:initdefault:`)	init-style boot
`/boot/vmlinuz-version`	The kernel itself	The bootloader loads it into memory
`/boot/initramfs-version.img`	The temporary root file system	Loaded together with the kernel

Memorize the six fields of one /etc/fstab line in order.

/dev/sdb1    /data        ext4    defaults   0      2
① device   ② mount point  ③ type  ④ options  ⑤ dump  ⑥ fsck order

Command Sets Used at Each Stage

Stage	Regular partition	swap
Divide	`fdisk /dev/sdb` → `n` → `w`	Same. Set the type to 82 with `t`
Initialize	`mkfs.ext4 /dev/sdb1`	`mkswap /dev/sdb2`
Start using	`mount /dev/sdb1 /data`	`swapon /dev/sdb2`
Stop using	`umount /data`	`swapoff /dev/sdb2`
Check	`df -h`, `lsblk`	`free -h`, `swapon -s`

fdisk internal commands: p view · n new · d delete · t type · w save and exit · q exit without saving.
If Disklabel type in fdisk -l is dos, it's MBR; if gpt, it's GPT. Id is 83 Linux, 82 swap, 5 extended.
A hard link is ln, a symbolic link is ln -s. The one with the same inode is the hard link.

Now only	Also on the next boot
`mount`	`/etc/fstab`
`swapon`	The swap line in `/etc/fstab`
`systemctl isolate …target`	`systemctl set-default …target`
`init 3`	`/etc/inittab`
Editing with `e` in the GRUB menu	`/etc/default/grub` + `grub2-mkconfig`

Finding the Cause from Symptoms

In real work and in exam passages alike, concepts show up in the form of symptoms.

Symptom	Cause	Check / fix
A 5GB file won't copy to the USB drive	FAT32's 4GB single-file limit	Recreate it as exFAT, etc.
A 3TB disk is recognized only up to 2TB	It was partitioned with MBR	Partition it with GPT (`gdisk`, `parted`)
Space remains but files can't be created, with a "no space" error	The inodes ran out	`df -i`
You mounted a new disk, but after reboot it's empty	It wasn't written in `/etc/fstab`	Add one line and test with `mount -a`
`umount` refuses with `target is busy`	A process is using that directory	`cd` out of it
You edited `/etc/default/grub` but nothing changed	`grub.cfg` wasn't regenerated	`grub2-mkconfig -o …`
A server boots to a graphical screen and eats resources	The default target is `graphical.target`	`systemctl set-default multi-user.target`
After adding a disk, the mount attaches in the wrong place	The `sdb` and `sdc` order shifted	Use a UUID (`blkid`) in `fstab` instead of the device name

Contrasting Confusing Pairs

Category	A	B	Distinguishing criterion
Primary vs extended partition	Holds data	A shell, holds logical ones	Can it store directly?
`/dev/hda` vs `/dev/sda`	Old IDE	SATA, SCSI, USB	Interface type
ext2 vs ext3	No journaling	Has journaling	Failure recovery speed
FAT32 vs exFAT	4GB limit	No limit	Single file size
`mount` vs `/etc/fstab`	Now only	Even after reboot	Permanence
`mkfs` vs `fsck`	Creates anew	Checks and repairs	Creating or fixing
BIOS vs UEFI	MBR · 2TB	GPT · Secure Boot	Firmware generation
init vs systemd	Runlevel numbers	Target names	Boot management approach
Superblock vs inode	Information about the whole file system	Information about one file	Scope of information
Hard link vs symbolic link	Same inode	Separate inode	Does it survive deleting the original?
`mkfs` vs `mkswap`	Creates a file system	Creates a swap area	Does it hold files?
`fstab` vs `mtab`	What to do at boot	The current state	Does a person write it?
`isolate` vs `set-default`	Immediately	From the next boot	Permanence
DVD image vs network install image	Contains the packages	Downloads during install	Is the internet needed?
Live image vs minimal install	Runs without installing	Installs only what's needed	Does it write to disk?

Commonly Mistaken Points

"You store files in an extended partition" → No. It's only a shell, and the actual storage is done by logical partitions.
"Logical partitions start from 3" → They start from 5. It doesn't matter how many primary partitions there are.
"The inode has the file name" → It doesn't. The directory manages the name.
"ext2 also supports journaling" → No. It starts from ext3.
"You edit grub.cfg directly" → It's an auto-generated file, so it gets overwritten. Edit /etc/default/grub.
"Runlevel 0 is reboot" → 0 is shutdown, and 6 is reboot.
"Just mount and it stays forever" → It disappears on reboot. You must write it in /etc/fstab.

Command Summary

Command	What it does
`fdisk -l`	List of disks and partitions
`lsblk`	Disk structure as a tree
`mkfs.ext4 /dev/sdb1`	Create a file system
`mount /dev/sdb1 /data`	Mount
`umount /data`	Unmount
`df -h` / `df -i`	Capacity / inode usage
`fsck /dev/sdb1`	Check a file system
`systemctl get-default`	The current default target
`grub2-mkconfig -o …`	Regenerate the GRUB configuration

Next week we finally type commands ourselves — from the first steps in the shell through file, directory, and account commands.

📖 Glossary

Partition table : A table recording how the disk is divided. There are two schemes, MBR and GPT.
ESP : The EFI System Partition. The area that holds the bootloader in UEFI boot.
initramfs : A temporary file system loaded first in order to mount the root file system.
Journaling : A technique that records changes in advance to speed up failure recovery.
Hard link : Several names pointing to the same inode.
target : The unit of system state that systemd uses in place of runlevels.

📝 Practice Questions

Click a choice to reveal the answer and explanation.

Question 1

Which of the following is the correct order up to the point of using a new disk in Linux?

Question 2

Which of the following is the number at which device numbers given to logical partitions start?

Question 3

Which of the following is the command that checks and repairs file system errors?

Question 4

Which of the following correctly pairs BIOS/UEFI with a partition scheme?

Question 5

Which of the following is the task you must perform after changing settings in GRUB2?

Question 6

Which of the following is the systemd target that specifies booting the system into a text-mode multi-user environment?

Official references

Linux Master 2 official exam syllabus(opens in a new tab)