starts a doc split and adds some exercises
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waldek
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# Users
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## Adding and removing users
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## Switching user
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# Permissions
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## Octal number system
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## Changing permissions
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## Changing ownership
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# Remote control of a server
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## History
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## SSH and SFTP
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# Bandit
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# Introduction to Linux
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## Where does Linux originate from?
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* The spiritual mother of Linux is [Unix](https://en.wikipedia.org/wiki/Unix).
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* [POSIX](https://en.wikipedia.org/wiki/POSIX) is not an OS in itself but a **standard**.
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* Which OS's are [POSIX compliant](https://en.wikipedia.org/wiki/POSIX#POSIX-oriented_operating_systems)
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## Who is behind this project?
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* Who is [Richard Stallmann](https://en.wikipedia.org/wiki/Richard_Stallman)?
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* Who is [Linus Torvalds](https://en.wikipedia.org/wiki/Linus_Torvalds)?
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## What is the deal with 'GNU-slash-Linux'?
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* [GNU/Linux](https://en.wikipedia.org/wiki/GNU/Linux_naming_controversy) controversy
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* What is a [kernel](https://en.wikipedia.org/wiki/Kernel_(operating_system))
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* What does [GNU](https://www.gnu.org/software/) bring to the table?
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* What's the deal with [userspace and kernelspace](https://unix.stackexchange.com/questions/137820/whats-the-difference-of-the-userland-vs-the-kernel)?
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* [userspace](http://www.linfo.org/user_space.html)
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* [kernelspace](http://www.linfo.org/kernel_space.html)
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## Where can you *get* some Linux?
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* You probably already have a Linux computer running at [home](https://opensource.com/article/19/8/everyday-tech-runs-linux)!
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## Debian
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* [Reasons](https://www.debian.org/intro/why_debian) to choose Debian.
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* Why is Debian called [the universal operating system](https://www.reddit.com/r/debian/comments/22j0wf/so_why_debian_is_called_the_universal_operating/)?
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* [comparison](https://en.wikipedia.org/wiki/Comparison_of_instruction_set_architectures) of CPU architectures
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* [download](https://www.debian.org/distrib/netinst) Debian
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# How to create a virtual machine
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In order to run virtual machines, or VM's, we need a **host** program.
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One of the most popular ones out there is called `virtualbox`.
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It should be installed on your machine but in case it's not you can download it [here](https://www.virtualbox.org/wiki/Downloads).
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If you **expand** the section below you'll see a step by step walk-through of a VM creation in virtualbox with some notes on each step with best practice pointers.
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<details>
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<summary>Expand me...</summary>
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**Nice!**
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1. Name your machine and select *linux* if it's not chosen automatically.
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1. Set the amount of RAM for your machine.
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This can be anything between an absolute minimum and your physical machine's limit.
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You can't *magically* use more RAM than physically available!
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1. You need a virtual hard drive to store the OS and all your data to.
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1. The format doesn't matter that much.
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I always go for the default one.
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1. Most of the time you'll want dynamic size meaning the disk **file** will only take up as much **space** as it needs.
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For example, if you set a size of 50GB for your disk and your OS plus personal files take up 12GB, the actual space this image takes op on the physical disk of your **host** will be about 12GB.
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1. We'll soon discover **how much space** a basic Linux installation takes up but for now I would recommend the following.
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* **with** a graphical environment: 20GB
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* **without** a graphical environment: 10GB (minimal/server/headless install)
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1. By default your machine will have only **one** CPU core but you can add more via the settings.
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This is something you can change whenever you need more processing power but the same rule as with the RAM applies, it's not a magical way to add resources to your machine.
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1. Last but not least we need to insert the installation disk into the virtual machine and boot it up!
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</details>
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# Breakdown of the Debian installation
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All right, enough talking, let's get started!
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I'll install a full blown and modern graphical Debian machine and I would like you to **not** do it yourself but take **notes** on each step so you'll be able to reference your notes later **when** I ask you to install a machine yourself.
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Below is a gain a step by step walk through with some of my tips but a more details guide can be found in the [Debian Administrator Handbook](https://debian-handbook.info/browse/stable/sect.installation-steps.html).
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This book is a real *bible* of information and I highly advise you to read through it.
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My most important notes would be the following.
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* **Read** each section carefully and you'll know what to do.
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* Don't set a root password but use `sudo` instead.
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* Don't install a graphical environment if you don't need one.
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It's a lot easier to add one later than to remove it.
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* Don't forget to install `grub` at the end otherwise your installation will not be able to boot.
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You *can* recover from this mistake with [supergrub2](https://www.supergrubdisk.org/super-grub2-disk/) but that's for an other day.
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<details>
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<summary>Expand me...</summary>
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</details>
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# Exercise
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OK, now it's up to you!
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Please install a Debian machine with the default graphical environment.
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Once installed, take some time out to explore the system.
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Which software is installed by default?
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How can you tweak the system settings such as language, keyboard, networking?
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Can you install extra software?
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# Quick look at an idle system
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You can inspect the system by running the *gnome task manager*.
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It lists all your running processes, sorted by CPU percentage, in the first tab which can give you a good idea of what's happening on your system.
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Note that an idle system uses almost **no resources**!
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Plus, a fresh install, with quite a few essential programs such as a browser, music player, text editor, etc only takes up about 5GB of disk space!
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This is mind blowing compared to a windows installation.
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How is this possible?
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That's the magic of a good package manager!
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<details>
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<summary>Expand me...</summary>
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</details>
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# Package managers
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What is a [package manager](https://en.wikipedia.org/wiki/Package_manager)
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## Graphical installation
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Modern Linux has come a long way and it's now quite usable without any command line knowledge.
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We can install extra software from the graphical environment if we want.
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Let's look for `vlc`, a popular open source video player.
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When we look for it from `activities` we *see* a reference to it via the `software` program.
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If we click on it we'll be take to a sort of *app or play store* where we can choose to install or uninstall programs.
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Because adding and removing software from our machine is quite *invasive*, we need to **prove** we have the right to do so.
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A prompt will pop up where you'll need to input **your** password.
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If your password does not work, you probably set a `root` password and you should use that one instead.
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<details>
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<summary>Expand me...</summary>
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</details>
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## Command line installation
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```bash
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waldek@hellodebian:~$ htop
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-bash: htop: command not found
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waldek@hellodebian:~$ apt install htop
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E: Could not open lock file /var/lib/dpkg/lock-frontend - open (13: Permission denied)
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E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), are you root?
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waldek@hellodebian:~$ sudo apt install htop
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[sudo] password for waldek:
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Reading package lists... Done
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Building dependency tree... Done
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Reading state information... Done
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Suggested packages:
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lm-sensors strace
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The following NEW packages will be installed:
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htop
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0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
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Need to get 127 kB of archives.
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After this operation, 328 kB of additional disk space will be used.
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Get:1 http://deb.debian.org/debian bullseye/main amd64 htop amd64 3.0.5-7 [127 kB]
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Fetched 127 kB in 0s (2,030 kB/s)
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Selecting previously unselected package htop.
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(Reading database ... 141359 files and directories currently installed.)
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Preparing to unpack .../htop_3.0.5-7_amd64.deb ...
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Unpacking htop (3.0.5-7) ...
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Setting up htop (3.0.5-7) ...
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Processing triggers for mailcap (3.69) ...
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Processing triggers for desktop-file-utils (0.26-1) ...
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Processing triggers for hicolor-icon-theme (0.17-2) ...
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Processing triggers for gnome-menus (3.36.0-1) ...
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Processing triggers for man-db (2.9.4-2) ...
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waldek@hellodebian:~$
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```
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The *menu bar* at the bottom shows you can press **F10** to quit.
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This does not work because of a shortcut of gnome-terminal!
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You can deactivate this shortcut in the preferences though.
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But pressing **q** also exits the program.
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## Adding a secondary desktop environment
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During the initial installation we where offered a choice of desktop environments to install.
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This menu was an actual program called `tasksel` we can run again to add different ones!
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As it's a program that can heavily modify the system, we need administrator privileges.
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```bash
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waldek@hellodebian:~$ sudo tasksel
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[sudo] password for waldek:
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```
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# Changing the runlevel
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The **first** process started by the kernel can be discover by `htop` and is `/usr/sbin/init`.
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This is rather vague but we can find out a *bit* more about this program via `ls` which we'll get into more detail later.
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For now just have a look at the output of the following commmand.
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```bash
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waldek@hellodebian:~$ ls -l /usr/sbin/init
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lrwxrwxrwx 1 root root 20 Jul 13 2021 /usr/sbin/init -> /lib/systemd/systemd
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waldek@hellodebian:~$
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```
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Now, what *is* this [systemd](https://en.wikipedia.org/wiki/Systemd)?
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And more importantly, *how* do we interact with it?
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For now just accept that the main program to communicate with `systemd` is `systemctl`.
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A quick look at the `man` pages gives us the following.
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```bash
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SYSTEMCTL(1) systemctl SYSTEMCTL(1)
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NAME
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systemctl - Control the systemd system and service manager
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SYNOPSIS
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systemctl [OPTIONS...] COMMAND [UNIT...]
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DESCRIPTION
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systemctl may be used to introspect and control the state of the "systemd" system and service manager. Please refer to systemd(1) for an
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introduction into the basic concepts and functionality this tool manages.
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```
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```bash
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waldek@hellodebian:~$ sudo systemctl set-default multi-user.target
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[sudo] password for waldek:
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Removed /etc/systemd/system/default.target.
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Created symlink /etc/systemd/system/default.target → /lib/systemd/system/multi-user.target.
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waldek@hellodebian:~$ sudo reboot now
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```
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After the reboot you'll be confronted with the following screen.
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Don't stress, your machine is not broken!
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It's just running in a more *minimal* mode.
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You can log in just as with the graphical login window but you'll only have a command line to interact with the machine.
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A quick look at `htop` tells us not a lot of stuff is running, just the bare minimum.
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To *undo* this change and regain the graphical interface again you can run the following commands.
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```bash
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waldek@hellodebian:~$ sudo systemctl set-default graphical.target
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[sudo] password for waldek:
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Removed /etc/systemd/system/default.target.
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Created symlink /etc/systemd/system/default.target → /lib/systemd/system/graphical.target.
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waldek@hellodebian:~$ sudo reboot now
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```
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# Exercise
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Please create a second virtual machine and install a **minimal** Debian.
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Minimal means **no graphical environment**.
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I advise you to **not** set a root password.
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Once this machine is up and running, install a few programs.
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The only one we saw up until now is `htop` but maybe try out `bmon`, `elinks` and/or `ranger`.
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Once these are installed have a look at the running services and programs via `htop` and compare it to both your graphical installation **and** your graphical install but running in `multi-user.target`.
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# Guest additions
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Let's make our user experience a bit nicer.
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Virtual machines can *integrate* with the host machine more fluently when you install the guest additions in the VM.
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It's a three step process.
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1. install the required packages to build the guest additions in you VM
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1. insert the guest additions CD into your VM
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1. run the correct script from the CD
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The dependencies can be installed as follows.
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First you `update` your package list, next you install three packages.
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* `build-essential`
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* `dkms`
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* `linux-headers-$(uname -r)`
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The *third* package name is a bit weird looking no?
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This is a bit of command line kung fu.
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The actual *name* of the package is as follows.
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```
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waldek@hellodebian:~$ echo linux-headers-$(uname -r)
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linux-headers-5.10.0-11-amd64
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waldek@hellodebian:~$
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```
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The `$(uname -r)` is a call to a program called `uname` with the option `-r`.
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We'll go more into detail on this later.
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```
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waldek@hellodebian:~$ sudo apt update
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Hit:1 http://deb.debian.org/debian bullseye InRelease
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Hit:2 http://deb.debian.org/debian bullseye-updates InRelease
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Hit:3 http://security.debian.org/debian-security bullseye-security InRelease
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Reading package lists... Done
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Building dependency tree... Done
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Reading state information... Done
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All packages are up to date.
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waldek@hellodebian:~$ sudo apt install build-essential dkms linux-headers-$(uname -r)
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Reading package lists... Done
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Building dependency tree... Done
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Reading state information... Done
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The following additional packages will be installed:
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binutils binutils-common binutils-x86-64-linux-gnu dctrl-tools dpkg-dev fakeroot g++ g++-10 gcc gcc-10 libalgorithm-diff-perl
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libalgorithm-diff-xs-perl libalgorithm-merge-perl libasan6 libatomic1 libbinutils libc-dev-bin libc-devtools libc6-dev libcc1-0 libcrypt-dev
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libctf-nobfd0 libctf0 libfakeroot libgcc-10-dev libitm1 liblsan0 libnsl-dev libstdc++-10-dev libtirpc-dev libtsan0 libubsan1
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linux-compiler-gcc-10-x86 linux-headers-5.10.0-11-common linux-headers-amd64 linux-kbuild-5.10 linux-libc-dev make manpages-dev patch
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Suggested packages:
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binutils-doc debtags debian-keyring g++-multilib g++-10-multilib gcc-10-doc gcc-multilib autoconf automake libtool flex bison gdb gcc-doc
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gcc-10-multilib gcc-10-locales glibc-doc libstdc++-10-doc make-doc ed diffutils-doc
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The following NEW packages will be installed:
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binutils binutils-common binutils-x86-64-linux-gnu build-essential dctrl-tools dkms dpkg-dev fakeroot g++ g++-10 gcc gcc-10 libalgorithm-diff-perl
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libalgorithm-diff-xs-perl libalgorithm-merge-perl libasan6 libatomic1 libbinutils libc-dev-bin libc-devtools libc6-dev libcc1-0 libcrypt-dev
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libctf-nobfd0 libctf0 libfakeroot libgcc-10-dev libitm1 liblsan0 libnsl-dev libstdc++-10-dev libtirpc-dev libtsan0 libubsan1
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linux-compiler-gcc-10-x86 linux-headers-5.10.0-11-amd64 linux-headers-5.10.0-11-common linux-headers-amd64 linux-kbuild-5.10 linux-libc-dev make
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manpages-dev patch
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0 upgraded, 43 newly installed, 0 to remove and 0 not upgraded.
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Need to get 62.0 MB of archives.
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After this operation, 258 MB of additional disk space will be used.
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Do you want to continue? [Y/n] y
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```
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Once this is done we can **insert** the CD.
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You can verify the disk's content via the files explorer in gnome.
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Now, open a terminal and run the following.
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```
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waldek@hellodebian:~$ cd /media/cdrom0/
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waldek@hellodebian:/media/cdrom0$ ls
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AUTORUN.INF NT3x TRANS.TBL VBoxLinuxAdditions.run VBoxWindowsAdditions.exe
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autorun.sh OS2 VBoxDarwinAdditions.pkg VBoxSolarisAdditions.pkg VBoxWindowsAdditions-x86.exe
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cert runasroot.sh VBoxDarwinAdditionsUninstall.tool VBoxWindowsAdditions-amd64.exe
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waldek@hellodebian:/media/cdrom0$ sudo bash VBoxLinuxAdditions.run
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Verifying archive integrity... All good.
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Uncompressing VirtualBox 6.1.28 Guest Additions for Linux........
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VirtualBox Guest Additions installer
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Copying additional installer modules ...
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Installing additional modules ...
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VirtualBox Guest Additions: Starting.
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VirtualBox Guest Additions: Building the VirtualBox Guest Additions kernel
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modules. This may take a while.
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VirtualBox Guest Additions: To build modules for other installed kernels, run
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VirtualBox Guest Additions: /sbin/rcvboxadd quicksetup <version>
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VirtualBox Guest Additions: or
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VirtualBox Guest Additions: /sbin/rcvboxadd quicksetup all
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VirtualBox Guest Additions: Building the modules for kernel 5.10.0-11-amd64.
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update-initramfs: Generating /boot/initrd.img-5.10.0-11-amd64
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VirtualBox Guest Additions: Running kernel modules will not be replaced until
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the system is restarted
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waldek@hellodebian:/media/cdrom0$ sudo reboot now
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```
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Once the machine is rebooted you'll can resize the window and the screen resolution will adapt automatically!
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You can also enable copy/paste and drag and drop between your host and VM now.
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