System Administration and Maintenance (Linux) Reviewer

Comprehensive review flashcards covering Lessons 1 to 8 of System Administration and Maintenance (Linux), including Operating Systems, Kernels, Shells, File Systems, Linux Distributions, Desktop Environments, Package Management, Basic and Administrative Commands, Server Hardening, Ethical Hacking, and Penetration Testing.

How is an operating system (OS) defined?

An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.

What are the core technical characteristics of the Linux kernel?

It is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel.

When and for what hardware architecture was the Linux kernel originally created by Linus Torvalds?

It was conceived and created in $1991$ by Linus Torvalds for his i386-based PC.

For which operating system project was the Linux kernel adopted as a free replacement for UNIX?

The GNU operating system.

What is the defining component of any Linux distribution?

The Linux kernel.

On what exact date was the Linux kernel first released by Linus Torvalds?

September $17$, $1991$.

Why does the Free Software Foundation use the name 'GNU/Linux'?

To emphasize that most Linux distributions are not just the Linux kernel, but share numerous utilities and libraries from the GNU project.

When and where was Linus Benedict Torvalds born?

December $28$, $1969$, in Helsinki, Finland.

Which revision control system was created by Linus Torvalds?

Git.

What award was given to Linus Torvalds in $2014$?

$2014$ IEEE Computer Society Computer Pioneer Award.

What was the original name Linus Torvalds intended for Linux, and what was its derivation?

Freax, derived from 'FREE' and the 'X' needed for Unix.

How is open-source software defined?

Software in which the copyright holder provides the rights to study, change, and distribute the software to anyone and for any purpose, often developed in a public, collaborative manner.

In the GNU/Linux system metaphor, what are the 'bones' and what is the 'meat' of the system?

The Linux kernel represents the bones, while the utilities and development tools from the GNU project represent the meat.

What windowing systems are typically included in desktop Linux distributions?

X11 or Wayland.

Which two commercial Linux distributions are specifically mentioned in the lecture?

Red Hat Enterprise Linux and SUSE Linux Enterprise Server.

What percentage of world cloud infrastructure is powered by Linux?

$90\%$ of all cloud infrastructure.

What percentage of smartphones worldwide are Linux-based?

$74\%$ of smartphones.

Which smart TV operating systems mentioned in the lecture are Linux-based?

Tizen (Samsung) and WebOS (LG).

Which space vehicle avionics systems run a customized version of Linux?

The Falcon $9$'s and the Dragon $2$'s avionics.

What form of license is the GNU General Public License (GPL)?

It is a form of copyleft.

What core requirement does the GNU GPL impose on anyone distributing software based on its source code?

They must make the originating source code (and any modifications) available to the recipient under the same terms.

According to the OS comparison, what are the pros of Windows?

Support for all hardware, ease of use, software support, plug and play feature, and desktop and touchscreen.

According to the OS comparison, what are the cons of Windows?

Virus attacks, paid software, high computer resources, and technical support.

According to the OS comparison, what are the pros of Mac OS?

Fewer virus attacks, good customer support, similar GUI for all products, performance and long life, and default apps.

According to the OS comparison, what are the cons of Mac OS?

Expensive, fewer games and software, and no hardware customization.

According to the OS comparison, what are the pros of Linux?

Open-source, no need for anti-virus, powerful CLI, low system specifications, good at multitasking, and less disk space needed.

According to the OS comparison, what are the cons of Linux?

Hardware drivers, learning curve, software alternative, and games.

Why is anti-virus software characterized as problematic for Windows in the lecture?

Windows users pay for anti-virus that is only about $20\%$ effective, and it severely limits system performance.

How does software installation differ fundamentally between Linux and Windows?

Linux uses a centralized software approach and installs software in predetermined directories, whereas Windows does not.

How do system updates and computer restarts differ between Linux and Windows?

Linux updates everything at once, alerts users, and never restarts without permission; Windows only updates Windows and select MS software, and restarts without user consent.

How are storage drives identified in Linux versus Windows?

Linux uses /dev for drives; Windows uses alphabet letters.

What are the five common mistakes made by new Linux users?

$1$. Choose wrong hardware; $2$. Choose wrong Linux distributions; $3$. Expect Linux to be Windows; $4$. Use Google to find software; $5$. Do not take time to learn Linux.

Who developed Unix at AT&T Bell Laboratories, and in what year?

Ken Thompson and Dennis Ritchie in $1969$.

What language was Unix initially written in, and what happened in $1973$?

It was initially written in assembly language in $1971$, and rewritten in the C programming language by Dennis Ritchie in $1973$.

What happened when UC Berkeley released the Berkeley Software Distribution (BSD) in $1977$?

BSD contained Unix code, causing AT&T to sue.

Who started the GNU project in $1983$, and what was its kernel called?

Richard Stallman started the GNU project; its kernel was Hurd.

Who released MINIX in $1987$, and what were its licensing limitations?

Andrew S. Tanenbaum released MINIX for academic use; its source code was available, but modification and redistribution were restricted.

What was IRIX, and what major file system and graphics API originated in it?

IRIX was a UNIX System V-based OS by Silicon Graphics (SGI) for MIPS systems; it originated the XFS file system and OpenGL graphics API.

What were the defining features of Linux Kernel Version V0.01 released in September $1991$?

A Minix-like kernel for i386(+) AT-machines, using system calls rather than message passing, a fully multi-threaded FS, minimal task switching, and visible interrupts.

What major capabilities were introduced in Linux Kernel V1.0 in March $1994$?

Multi-programming (multiple programs run at the same time) and virtual memory management.

What features were added in Linux Kernel V2.0 in June $1996$?

Restructured memory management, improved task scheduling, improved SCSI support, and network file system support for NCP (Novell) and SMB.

Why was Linux Kernel V3.0 released in July $2011$?

To mark the $20\text{th}$ anniversary of Linux, bringing better virtualization handling, Btrfs data scrubbing, and auto-defragmentation.

What reason did some people advocate for adopting the $4.0$ kernel version number?

To eventually see $4.1.15$, which was the version of Linux SkyNet used for the T-800 Terminator.

What were key features of Linux Kernel V5.9 released in October $2020$?

New slab memory controller, ZSTD-compressed kernel/ramdisk/initramfs support, USB $4$ specification support, and initial IBM POWER10 processor support.

What is the purpose of the 'memfd_secret' system call added to Linux $5.14$?

It creates memory areas visible only in the context of the owning process, unmapped by other processes or kernel page tables.

What are the five main objectives of the operating system kernel?

$1$. Establish communication between user applications and hardware; $2$. Decide the state of incoming processes; $3$. Control disk management; $4$. Control memory management; $5$. Control task management.

How does the kernel handle application requests for hardware access?

Applications make system calls or software interrupts, switching execution from user mode to privileged kernel mode.

What mechanism does the kernel scheduler use to enable multitasking?

Context switching.

What is the kernel used by Microsoft Windows called?

NT Kernel.

Approximately how many lines of code are in the Linux kernel codebase?

$15\text{M}$ (and up to $30\text{M}$ in v6.4 in $2023$).

What kernel is used by Apple OS X and iOS?

Darwin Kernel.

What kernel does Android use?

Linux kernel.

What are the five primary architectural types of operating system kernels?

Monolithic Kernel, Microkernel, Hybrid Kernel, Exo Kernel, and Nano Kernel.

What characterizes a monolithic kernel architecture?

The entire kernel operates in a single address space where all basic services (process, memory, device drivers, file systems) run in kernel space.

What is the main operational advantage and disadvantage of a monolithic kernel?

Advantage: Faster execution due to less context switching; Disadvantage: A single bug can crash the entire system.

What characterizes a microkernel architecture?

A minimalist approach that keeps virtual memory and thread scheduling in kernel space while putting most services in user space.

What are examples of microkernels listed in the lecture?

Mach, L4, AmigaOS, Minix, and K42.

What defines a hybrid kernel architecture?

It combines the speed and design of a monolithic kernel with the modularity and stability of a microkernel (e.g., Windows NT, Netware, BeOS).

What is an exo kernel?

A kernel following the end-to-end principle that provides the fewest hardware abstractions possible and allocates physical resources directly (e.g., Nemesis, ExOS).

What is a nano kernel?

A kernel that offers hardware abstraction without providing system services (e.g., EROS).

What is the primary role of a shell in Linux?

It acts as a command interpreter and interface between the user and the kernel to execute programs and utilities.

Who developed the Bourne Shell (sh), and where was it created?

Steve Bourne at AT&T Bell Labs.

What are the major limitations of the original Bourne Shell (sh)?

It lacks in-built logical/arithmetic functionality, cannot recall previously used commands, and lacks comprehensive interactive features.

What is the complete path-name and default prompts for the GNU Bourne-Again shell (bash)?

Path: /bin/bash; Root prompt: bash-VersionNumber#; Non-root prompt: bash-VersionNumber$.

Who created the C Shell (csh), and what was its distinctive syntax based on?

Bill Joy at the University of California; its syntax was based on the C programming language.

What are the default prompts for the C Shell (csh)?

Root user: hostname#; Non-root user: hostname%.

Who developed the Korn Shell (ksh), and what was its design purpose?

David Korn at AT&T Bell Labs; designed as an enhanced superset of the Bourne shell with C shell-like interactive features.

What does the shell abbreviation 'fish' or 'fsh' stand for?

Friendly Interactive Shell.

What are the default root and non-root prompts for the Z Shell (zsh)?

Root: #; Non-root: %.

What was Linux's first file system, and what were its size and filename limits?

The MINIX file system; maximum volume size of $64\,\text{MB}$ and maximum filename length of $14$ characters.

Who developed the Extended (ext) and Second Extended (ext2) file systems?

Rémy Card.

Why is ext2 still used for flash storage media like SD cards and USB drives?

Its lack of journaling increases performance and minimizes writes, preserving flash memory write cycles.

What are the maximum file and volume sizes for ext2?

Maximum file size: $2\,\text{TB}$; Maximum volume size: $4\,\text{TB}$.

When was ext3 released, and what is its maximum volume size?

November $2001$; maximum volume size of $32\,\text{TB}$.

What are the storage limits of the ext4 file system?

Maximum file size: $16\,\text{TB}$; Maximum volume size: $1\,\text{Exabyte}$; Maximum number of files: $4\,\text{Billion}$.

What underlying design principle powers the Btrfs file system?

The Copy-on-Write (COW) principle with an integrated logical volume manager.

What are the maximum file size, volume size, and file count for Btrfs?

Maximum file size: $16\,\text{EB}$; Maximum volume size: $16\,\text{Exabyte}$; Maximum number of files: $2^{64}$.

Who led the development of ReiserFS, and what was its maximum volume size?

Hans Reiser at Namesys; maximum volume size of $16\,\text{TB}$.

When did Silicon Graphics begin development of XFS, and when was it released under GPL?

Development began in $1993$; released under GPL in May $1999$.

Who originally developed ZFS, and for what operating system?

Sun Microsystems for Solaris.

What are three common use cases for ZFS?

Enterprise Storage Solutions, Backup and Disaster Recovery, and File Server / NAS.

What are the two operational components of NFS (Network File System)?

NFS Server (hosts shared directories) and NFS Client (mounts and accesses shared directories).

Which file systems are utilized by Microsoft Windows?

FAT, NTFS, exFAT, Live File System, and ReFS (Resilient File System).

What restriction applies to the Resilient File System (ReFS) in Windows?

Windows cannot boot from it.

In the Linux filesystem hierarchy, what is the role of the /bin directory?

Contains essential executable program binaries needed for minimal functionality, booting, and single-user recovery (e.g., cat, ls, cp).

In the Linux filesystem hierarchy, what is stored in /boot?

Boot loader files, including kernels and initrd.

In the Linux filesystem hierarchy, what is stored in /dev?

Device files representing hardware or virtual devices (e.g., /dev/null, /dev/sda1, /dev/tty, /dev/random).

In the Linux filesystem hierarchy, what is the purpose of /etc?

Host-specific system-wide configuration files.

In the Linux filesystem hierarchy, what is the purpose of /lib and /lib64?

Libraries essential for the binaries located in /bin and /sbin.

In the Linux filesystem hierarchy, what is the purpose of /mnt?

Mount point for temporarily mounted filesystems.

In the Linux filesystem hierarchy, what is stored in /opt?

Add-on application software packages.

In the Linux filesystem hierarchy, what is /proc?

A virtual filesystem providing process and kernel information.

In the Linux filesystem hierarchy, what is stored in /run?

Run-time variable data since the last boot, such as currently logged-in users and running daemons.

In the Linux filesystem hierarchy, what distinguishes /sbin from /bin?

/sbin contains essential system administrative binaries intended primarily for the root user (e.g., fsck, init, route).

In the Linux filesystem hierarchy, what is stored in /srv?

Site-specific data served by the system, such as web server data, FTP files, or version control repositories.

In the Linux filesystem hierarchy, what is /sys?

Contains information about devices, drivers, and kernel features.

In the Linux filesystem hierarchy, what is /var?

Stores variable data files such as system logs, mail spools, and transient databases.

Who developed Slackware in July $1993$, and what is its design focus?

Patrick Volkerding; focused on simplicity, software purity, and providing no graphical installation.

Who founded Debian in September $1993$, and how often does it release?

Ian Murdock and the Debian Project; releases approximately every two years.

What does the German acronym SUSE stand for, and what configuration tool does it feature?

'Software und System-Entwicklung' (Software and systems development); features the YaST (Yet another Setup Tool) utility.