Day 1 - Primary Subject 1 Mock Exam: Weak Points in Understanding Practical Linux

📌 Key Points

• Week 14 is the final review, mock exam, and strategy week right before the test. Today we sweep through all of Primary Subject 1, "Understanding Practical Linux."
• This subject leans heavily on memorization, and mistakes happen on confusing pairs — GPL/LGPL, runlevels/systemd targets, /bin vs /sbin, absolute/relative paths.
• Linux = Linus's kernel + GNU's tools. What Torvalds made was not the whole OS but the kernel.
• Licenses are ranked by copyleft strength — GPL (strong) > LGPL (weak) > BSD/Apache/MIT (none).
• The boot flow is BIOS/UEFI → GRUB → kernel → initramfs → systemd (PID 1) → target. Runlevel 3 = multi-user, 5 = graphical.
• The "usr" in /usr is not "user" but Unix System Resources. User home directories live in /home.

Weak Point 1: History and Philosophy — Who Made What

• The lineage of Linux is asked as a "name, year, and role" triple.
• You must pair people with their creations accurately.

• GNU had no kernel, and Linux had only a kernel.
• The key to the correct answer is the flow in which the two combined to complete GNU/Linux.

One-line summary: Linux = Linus's kernel + GNU's tools. Neither side alone is a complete OS.

Trap: "Linux is an operating system Torvalds created alone" is wrong. What Torvalds made was the kernel, not the entire OS.

Weak Point 2: Licenses — Subtle Differences Within the GPL Family

• Open-source licenses are distinguished by copyleft strength.
• This comparison is within the scope of the exam.

⚠️ The decisive difference: GPL says "If you use my code, you must disclose yours too," while LGPL says "Using it as a library is fine." Even if commercial software links an LGPL library, it can keep its own source private.

Weak Point 3: Installation — Partitions and Filesystems

• The key to the installation stage is partition design.
• Memorize the role of each mount point.

• The journaling lineage of filesystems is also asked — ext2 (no journaling) → ext3 (journaling added) → ext4 (large capacity, extents).
• Others include XFS (large capacity, default on RHEL 7+) and Btrfs (snapshots, CoW).

Swap rule of thumb: Traditionally, if RAM is 2GB or less, 2x RAM; above that, equal to RAM or only a portion of it. On the exam, "1-2x RAM" is the safe correct answer.

Weak Point 4: Boot — Runlevels and systemd Targets

• The boot sequence and the SysV runlevel ↔ systemd target mapping are within the scope of the exam.

• Boot flow: BIOS/UEFI → bootloader (GRUB) → kernel load → initramfs → init/systemd (PID 1) → target reached.

GRUB key point: The GRUB2 configuration is /boot/grub2/grub.cfg, but do not edit it directly — edit /etc/default/grub and then generate it with grub2-mkconfig.

Command summary: Check the default target with systemctl get-default, change it with systemctl set-default multi-user.target. Check the runlevel with runlevel/who -r.

Weak Point 5: FHS — What Each Directory Means

• The FHS (Filesystem Hierarchy Standard) asks about the purpose of each directory.
• Focus on the confusing pairs.

⚠️ Trap: The "usr" in /usr is not "user" but Unix System Resources. User home directories live in /home.

Weak Point 6: Basic File Commands and Paths

• The distinction between absolute paths (starting with /) and relative paths (./..) is asked.
• The meaning of wildcards (*, ?, []) is asked as well.

Path in one line: An absolute path always points to the same place regardless of location, while a relative path points relative to the current location. In scripts, absolute paths are safer.

Weak Point 7: Distributions and the Kernel Versioning Scheme

• A distribution is a finished product bundling the kernel + GNU tools + a package manager.
• Questions on telling the families apart are common.

• The kernel version notation is also asked.
• In the past, as with 2.6.x, there was a rule that even minor number = stable / odd = development.
• From 3.x onward, this rule was abolished and releases became time-based. Check the current version with uname -r.

uname options: uname -r (kernel release), uname -a (all information), uname -m (machine architecture). On the exam, the answer for "command to check the kernel version" is uname -r.

Distributions in one line: CentOS/Rocky are free RHEL-compatible distributions, and Ubuntu is a popular Debian-based desktop and server distribution. If you know the family, you can infer the package tool.

Weak Point 8: Shell Startup Flow and the Login Procedure

• The procedure from the user logging in after boot to the shell being launched is also within the scope of Primary Subject 1.

• Switching between virtual consoles (Ctrl+Alt+F1~F6) and the GUI (F1 or F7) may also be asked at a general-knowledge level.

Login shell vs non-login shell: A login shell reads ~/.bash_profile, while a non-login shell (a new terminal window) reads ~/.bashrc. Usually .bash_profile sources .bashrc to unify them.

Weak Point 9: The man Pages and Help System

• Linux's built-in documentation system is also asked in Subject 1.
• man pages are distinguished by section number.

• When the same name exists in multiple sections, you distinguish them by number, as in man 5 passwd (file format) and man 1 passwd (command).

Search in one line: When you don't know what command to use, find related commands with apropos keyword, and once you know it, see the details with man command. whatis gives just a quick one-line definition.

Weak Point 10: Prompts and Virtualization Basics

• Finally, we collect the general-knowledge items.
• The prompt's trailing symbol tells you the privilege level — $ for a regular user, # for root. This single character tells you your current privilege at once.
• Virtualization and container basics also come up lightly at the Level 1 stage.

VM vs container: A VM boots an entire guest OS, so it is heavy but has strong isolation, while a container shares the host kernel, so it is light but has relatively weaker isolation. This contrast is the exam focus.

Boot basics wrap-up: Reviewing the prompt symbols # (root), $ (regular user), and % (csh family), together with the shutdown commands shutdown -h now (shut down immediately), shutdown -r now (reboot), init 0 (shut down), and init 6 (reboot), is enough to wrap up Subject 1.

Use the mock exam below to check your weak points in practice.

📖 Glossary

• GNU/Linux : The operating system completed by combining Linus's kernel and GNU's tools. Neither side alone makes an OS.
• Copyleft : The license principle that "works made with my code must be released under the same terms." The GPL is the representative example.
• LGPL : A relaxed GPL under which you do not have to disclose your own source when you use the code by linking it as a library.
• Journaling : A feature that records filesystem changes in advance so the system can recover quickly even after a sudden shutdown. Introduced with ext3.
• swap : An area that uses disk like memory when memory runs short. Typically sized at 1-2x RAM.
• initramfs : A temporary in-memory filesystem used before the kernel mounts the real root filesystem.
• GRUB2 : The standard Linux bootloader. You don't edit grub.cfg directly; you edit /etc/default/grub and then generate it.
• systemd target : A system-state unit that replaces the old runlevels. 3 = multi-user and 5 = graphical correspond to it.
• FHS : The standard layout convention for Linux directories. It defines what goes into which directory.
• /usr : Not "user" but Unix System Resources. Applications and shared resources go here.
• Absolute path / relative path : A path that starts from / and points to the same place regardless of location / a path based on the current location.
• man section : The classification number of the manual. 1 = commands, 5 = file formats, 8 = administration commands.
• apropos / whatis : A keyword search for related commands / a summary showing only a command's one-line definition.
• Hypervisor / container : Heavy virtualization that boots an entire guest OS / lightweight isolation that shares the host kernel.

📝 Practice Questions

Click a choice to reveal the answer and explanation.

Question 1

Which option correctly pairs the person who first developed the Linux kernel with the person who started the GNU Project?

• ALinus Torvalds - Richard Stallman
• BRichard Stallman - Linus Torvalds
• CKen Thompson - Dennis Ritchie
• DAndrew Tanenbaum - Linus Torvalds

Question 2

Which license lets commercial closed-source software link a library and use it without having to disclose its own source?

• AGPL
• BLGPL
• CAGPL
• DAll copyleft licenses force disclosure

Question 3

In systemd, which target corresponds to GUI multi-user mode, and what is the equivalent SysV runlevel?

• Amulti-user.target - runlevel 3
• Brescue.target - runlevel 1
• Cgraphical.target - runlevel 5
• Dpoweroff.target - runlevel 0

Question 4

In the FHS, which statement about the meaning and purpose of the /usr directory is correct?

• AIt is where user home directories are gathered
• BIt stands for Unix System Resources, and static shareable data and applications are located there
• CIt is where logs, which are variable data, are stored
• DIt is a temporary file store that is deleted on reboot

Question 5

Which is the correct order of the Linux boot process?

• AKernel → BIOS/UEFI → bootloader → init/systemd
• BBIOS/UEFI → bootloader (GRUB) → kernel → init/systemd
• CBootloader → BIOS/UEFI → kernel → init/systemd
• DBIOS/UEFI → kernel → bootloader → init/systemd

Question 6

In a GRUB2 environment, what is the correct way to change the boot configuration?

• AEdit /boot/grub2/grub.cfg directly
• BModify /etc/default/grub and then generate the configuration with grub2-mkconfig
• CModify /etc/fstab
• DChange the runlevel in /etc/inittab

Question 7

Which of the following filesystems has no journaling feature?

• Aext3
• Bext4
• Cext2
• DXFS

Question 8

Which standard directory holds system administration commands (mainly root-only)?

• A/bin
• B/sbin
• C/etc
• D/opt

Question 9

Which command changes the system's default boot target to text multi-user mode?

• Asystemctl get-default multi-user.target
• Bsystemctl set-default multi-user.target
• Crunlevel 3
• Dinit multi-user.target

Question 10

Which statement about the wildcard ? is correct?

• AAny string of zero or more characters
• BAny single character
• COne character from within the brackets
• DThe home directory