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Sichere Betriebssysteme > Linux > Flashcards

Linux Flashcards

1
Q

What is Linux?

A

Linux is used to describe an operating system, but was originally the
name of the system kernel only.

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2
Q

Who started to develop Linux?

A

Linus Torvalds
is the developer of Linux. (started in 1991) He made his
system compatible to UNIX.

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3
Q

When was UNIX first released?

A

In 1971

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4
Q

How is the LINUX OS basically built? How does it work?

A

The OS consists of a system kernel that interfaces/connects with the hardware and provides application interfaces to programs.

The kernel is also responsible for managing the available memory, cpu time and devices

Users input commands through the shell, and the kernel receives the tasks from the shell and performs them.

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5
Q

What is the GNU project?

A

The GNU project is a mass collaboration for the development of free software.

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6
Q

In which way are GNU and LINUX connected?

A

The GNU project is a set of Unix applications and programs, that lack an operating system kernel. LINUX provides this kernel.

Therefore the OS known as Linux is based on the Linux kernel but all other components are GNU. Which means the OS should rather be known as GNU/Linux.

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7
Q

What does GNU stand for?

A

GNU is short for “GNU’s Not Unix”, a recursive acronym. (= acronym where the first letter is the acronym itself)

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8
Q

What is meant when you hear GNU/LINUX is “free software”?

A

“[…] free as in free speech, not as in free beer.”

They are free not only in terms of being at no cost, but also free in terms of freedom. This does not mean that there is no copyright, but anybody is free to use and modify the code within the terms of the license.

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9
Q

Name some CPU architectures Linux was ported to?

A

initially: i386 CPUs

later on: x86, ARM, MIPS, PowerPC and SPARC

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10
Q

Who develops Linux nowadays?

A

In the beginning, the only developer was Linus Torvalds.
Very early many other people started contributing to the Linux kernel, fixing bugs or adding features.

Currently, it is estimated that 5000 to 6000 people work on the kernel. It is only an estimation, because teams of developers usually send their changes as a complete team. Still, Linus Torvalds is the one in charge of releasing new versions of the kernel.

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11
Q

How is Linux licensed?

A

At the beginning Linux was restricted to commercial usage. In 1992 the license was change to GNU GPL (general public license), and is stilled used today.

This license is a copyleft license, which means that anybody is free to use, distribute and modify the code as long as the modifications are made available under the same license. This implies that commercial implementations need to be made publicly available, too.

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12
Q

Why are there Linux branches called “-stable” or “-longterm”?

A

Sometimes, not well tested code ends up in the official kernel source, while certain bugs are fixed in the same release. For people who want long-lasting, stable releases without new features, there are these special branches.

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13
Q

Who owns Windows?

A

Microsoft

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14
Q

Who owns Linux?

A

There is no company, no single developer who “owns” the product. Instead, many different people, who have contributed small and big changes to the kernel, “own” the copyright of their work.
The GNU General Public License (GPL) protects the code.

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15
Q

Who distributes Linux?

A

As there is no company behind the Linux kernel or the GNU software suite, no one is responsible for distributing the system. Therefore, several people and firms have taken the opportunity to create systems for installing the operating system and for managing software installations.

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16
Q

What are different Linux “flavors”?

A

Different Linux distributions which take all the code from the open-source projects and compile it for you and combine it into a single operating system you can boot up and install.

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17
Q

What different goals have the Linux distributions “Ubuntu”, “Arch Linux” and “Debian”?

A

Ubuntu for instance tries to be as easy and “human” as possible, while Arch Linux wants to be as customisable and generic as possible. Debian’s goal, on the other hand, is stability and long-term maintenance.

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18
Q

What are the two most common Linux package managers?

A

RPM (Red Hat Package Manager) and DEB (Debian Package Manager)

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19
Q

What are the responsibilities

of package managers?

A

Their responsibility is installation, removal and house-keeping of individual software packages.

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20
Q

Name some examples where Linux runs

A
  • Smartphones/Tablets (Android is based on a Linux kernel)
  • Servers / Super Computers
  • Desktop Computers
  • WiFi SD Cards
  • Routers, NAS boxes, Printers, … * Surveilance Cameras
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21
Q

What are advantages of Linux?

A
  • Wide spread OS on servers
  • You probably already have one or more devices running
  • Linux Open Source Software
  • Free Software
  • Provides a good alternative on the Desktop
  • Fun & Curiosity
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22
Q

Name some major Linux distributions

A

Linux Mint, Ubuntu, Fedora, Debian, openSUSE, Arch Linux, PCLinuxOS, CentOS, Mageia, Slackware Linux, FreeBSD, …

23
Q

Which distribution is the right one?

A

It depends what you are going to do with your operating system and what personal goals you have. Beginners often choose distributions like Ubuntu or Linux Mint, that are easy to install and resemble already well-known user interfaces like Microsoft Windows.

24
Q

What do you know about the Linux distro Ubuntu?

A
  • For Linux newbies
  • For Desktops and Servers
  • Recently, also for Smartphones (Ubuntu Touch)
  • Easy
  • Based on Debian
25
Q

What do you know about the Linux distro Debian GNU/Linux?

A
  • Started in 1993
  • Stable and mature
  • For Desktops and Servers
  • Own package management system (dpkg / apt)
  • Quite easy
  • On the Desktop, sometimes a bit outdated
26
Q

What do you know about the Linux distro openSUSE?

A
  • Started in 1994
  • One of the oldest commercial distributions
  • Stable and mature
  • For Servers and Desktops
  • Enterprise Edition available
  • Own configuration tool (YaST)
  • Red Hat package manager (rpm)
27
Q

What do you know about the Linux distro Arch Linux?

A
  • Started in 2002
  • Minimalistic and Simplistic
  • Rolling-Release Distribution
  • Sometimes a bit unstable
  • For advanced users
  • Own package management system (pacman)
28
Q

What do you know about the Linux distro SoL?

A
  • Austrian Distribution
  • Started in 2001
  • Optimised for Servers
  • No package management (source based)
  • Discontinued
29
Q

What do you know about the Linux distro grml?

A
  • Austrian Distribution
  • Live CD
  • Based on Debian
  • For Administrators and system rescue
30
Q

What are some fundamental differences between Windows and Linux?

A

Windows vs. Linux

File System:
Drives and Folders | only Folders

Case Sensitivity:
not | all files/folders

User Concept:
single user | multi user

Permissions:
no permissions | for each file/folder

Source Availability:
no source code | full source code

Hardware Support:
full support | quite good

Outdated Hardware:
no support | often, still full support

Software Installation:
decentralized (own installers) | central installer

Price:
several hundred € | free

Support:
paid support | no/community support

31
Q

What does GUI stand for? What’s the opposite of it?

A

graphical user interface (GUI)

Opposite: command line interface (CLI)

32
Q

CLI vs. GUI: What’s better?

A

Depends on the use case:

Pro CLI:

  • CLI is often faster
  • some servers don’t need a GUI
  • GUI needs extra system resources and may lead to instabilities (if GUI crashes)
  • not all systems support mode user interfaces
  • everything that can be done in GUI can also be done in CLI

Pro GUI:

  • easier for beginners
  • customizable appearance
33
Q

What do you need if you want to set up a Linux OS?

A
  • A computer
  • Enough disk space
  • Enough performance
  • Basic understanding of devices, partitions and filesystems
  • A bit of time (and sometimes patience)
34
Q

How much disk space is enough for Linux?

A

“Enough” depends very much on the application. A basic Linux installation can be “squeezed” into as little as 4 MB. Apart from the basic system, services like web servers or database servers require additional performance, disk space and RAM as well as disk storage for their data files.

35
Q

How much performance is needed for Linux?

A

The performance requirements vary depending on the application. Simple router platforms don’t need much but database servers need as much CPUs and RAM as possible. Available RAM is often more important than plain CPU performance -> (add a SSD if needed).

36
Q

What’s a Harddisk?

A

The term “harddisk” describes the physical drive installed in a computer where all files and folders are stored permanently. Harddisks, or fixed disks, consist of rotating, magnetic disks that store data on its surface. Nowadays, Solid State Drives (SSDs) often replace harddisks due to their higher performance and lower power consumption. They do not contain rotating parts, but store their data on flash chips.

37
Q

What’s a main difference between a harddisk and a RAM?

A

In contrast to the temporary RAM storage, files on a harddisk are not lost if no power is applied.

38
Q

How can you access the hard disk on Linux?

A

On Linux, the harddisk can be accessed as a file on the dev filesystem. The first harddisk is “/dev/sda”, the second one “/dev/sdb” and so on.

39
Q

What is a Partition?

A

For practical reasons (separation), former size restrictions, one physical harddisk can be divided into several logical parts called partitions. One physical harddisk can have one or several partitions, depending on the partition schemes and the desired effect.

Each partition can hold a filesystem for storing data and is represented as one drive within Windows (“C:”, “D:”, …), but as regular files in the dev filesystem on Linux

40
Q

What does MBR stand for?

A

Master Boot Record = partition scheme

41
Q

What is a filesystem?

A

A filesystems controls how files are stored on a device.

42
Q

What is a Linux distribution?

A

A collection of Linux Kernel and free programs

43
Q

Explain the relationship between harddisk, partition and filesystem.

A

In order to install an operating system on an empty computer, you need a storage medium - the so-called hard disk. It is then divided into several partitions in order to install different system or to separate data and operating system. During operating system installation, a file system has to be created so that files and folders can be saved.

44
Q

Why would you NOT install a graphical user interface on a Server?

A
  • my server should use the fewest resources so it can have them available for what it does best (= best use of resources)
  • few services increase security by minimizing the attack surface
  • if the need for a graphical interface arises, there are web based solutions
  • Graphical interfaces introduce additional (most of the time not needed) complexity
  • more packages that need updating -> more server downtime
  • The GUI may include other network services that are inappropriate for a server.
45
Q

Name some native LINUX filesystems

A

ext4, btrfs, zfs, jfs

46
Q

Which filesystem does Windows use?

A

Early versions of Windows used FAT filesystems, while later versions require more modern systems like NTFS or exFAT.

47
Q

What does RAID stand for?

A

Redundant Array of Inexpensive Disks

48
Q

What does RAID describe?

A

The possibility to use and combination of cheap harddisks for increased data security.

49
Q

How does RAID work? What’s the difference between hardware and software based RAID?

A

Hardware based RAID solutions simulate one physical harddisk for every array, while the operating system is not necessarily aware of the existence of the RAID system. In contrast to hardware solutions, software RAID is cheaper to implement and on Linux nearly as secure as hardware RAID. However, as the OS has to do the RAID handling work, this implementation is usually slower.

50
Q

Which RAID levels are there? Which are most common?

A

There are several RAID levels defined, which describe the principle of operation. The most common ones are levels 0, 1 and 5 for small systems, while RAID levels 4 and 6 can have advantages with more disks.

51
Q

Explain RAID 0

A

Stripe. Multiple disks are used for increased storage capacity

52
Q

Explain RAID 1

A

Mirroring. All disks store the same data for increased data security

53
Q

Explain RAID 5

A

Stripe Parity. Multiple disks are used for increased storage capacity and data security

Sichere Betriebssysteme (6 decks)

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