1208 lines
64 KiB
Markdown
1208 lines
64 KiB
Markdown
# 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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# Introduction to the command line
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We'll be using a few new *words* to reference the command line such as *shell*, *bash* and *terminal* through out the course.
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They all pretty much mean the same thing but with some small, and not so important, differences between them.
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Essentially a command line is a **textual interface** for humans to operate a computer.
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What is very important to understand is that textual commands and graphical actions operate on the **same** computer.
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For example, if you create a file via the command line, it will show up in you file explorer and vice versa.
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The graphical and textual interfaces are just different *representations* of the same machine.
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Now open up a terminal and you'll see the following.
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```
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waldek@hellodebian:~$
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```
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This is what we call a [prompt](https://en.wikipedia.org/wiki/Command-line_interface#Command_prompt).
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It's not much but it's our *window* into the computer.
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As with most things in life you can question it's *who, where, what and when*.
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This information is actually **embedded** in the prompt.
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Let's break it down.
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* `waldek` is **who** I am on this computer
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* `hellodebian` is the **what**, as in what computer I'm operating on
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* `~` is **where** I am located on this computer
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What about the *when* then?
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Let's type in `date` and see what happens.
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```
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waldek@hellodebian:~$ date
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Fri 18 Feb 2022 03:46:59 PM CET
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waldek@hellodebian:~$
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```
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There we see our **when**!
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But this miniscule operation illustrates us the **fundamental** operation of a command line!
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1. we have a prompt where we can run a program
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2. the program runs and outputs it's information on the terminal
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3. once the program **finishes** we can run an other program
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I'm deliberately saying program here but is `date` *really* a program?
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It's a bit basic no?
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Well, it is a program and most *commands* you'll type into your terminal are actually programs.
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We can illustrate this as follows.
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```
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waldek@hellodebian:~$ vlc
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VLC media player 3.0.16 Vetinari (revision 3.0.13-8-g41878ff4f2)
|
||
[0000559c46ee95b0] main libvlc: Running vlc with the default interface. Use 'cvlc' to use vlc without interface.
|
||
[0000559c46f89790] main playlist: playlist is empty
|
||
|
||
```
|
||
|
||
Vlc is now running and the terminal is *blocked* meaning we can't run other programs or commands in it.
|
||
If you try to run the `date` command again, or `ls` or `htop`, it won't work!
|
||
Try it out if you don't believe me.
|
||
But what happens if you **close** vlc?
|
||
The commands you typed get executed!
|
||
This is an illustration of the **sequential** nature of a command line.
|
||
|
||
Now, I don't think we have sufficiently *proven* that `date` is a full blown program so let's dig a bit deeper.
|
||
|
||
```
|
||
waldek@hellodebian:~$ which vlc
|
||
/usr/bin/vlc
|
||
waldek@hellodebian:~$ which date
|
||
/usr/bin/date
|
||
waldek@hellodebian:~$ which which
|
||
/usr/bin/which
|
||
```
|
||
|
||
There is quite bit to *unpack* in the example above.
|
||
First, what on earth is `which`?
|
||
Well, it's *also* a program and it's sole purpose in life is to tell you **where** a program is located on your system.
|
||
Because `which` by itself does not make a lot of sense it needs what we call an **argument**.
|
||
Here the argument is the name of the program we want to know it's location of.
|
||
The existence of arguments is the second big thing we discovered here.
|
||
The third new thing we can observe here is what we call **paths**, meaning locations on the system.
|
||
For example, `vlc` is a *binary* program located in a **folder** called `bin` which is located in a folder called `usr` which is at the *root* of your system.
|
||
If this sounds complicated, don't worry, we'll go into detail a bit later.
|
||
|
||
Now that we know **where** some of our programs are located, let's find out **what** they are.
|
||
The methodology is the same as with `which` but we'll use an other program called `file` who's purpose in life is to tell more about the **content** of a certain file.
|
||
Logically, `file` needs an argument and this argument is the **path** to the file you want to inspect.
|
||
|
||
```
|
||
waldek@hellodebian:~$ file /usr/bin/vlc
|
||
/usr/bin/vlc: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=51c40f8234213415771b3a344cab25a140543f8a, for GNU/Linux 3.2.0, stripped
|
||
waldek@hellodebian:~$ file /usr/bin/date
|
||
/usr/bin/date: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=b740f054aaef6a85aff024858c914c7eae70a6a5, for GNU/Linux 3.2.0, stripped
|
||
waldek@hellodebian:~$ file /usr/bin/which
|
||
/usr/bin/which: POSIX shell script, ASCII text executable
|
||
waldek@hellodebian:~$ file $(which which) # this is some command line kung fu...
|
||
/usr/bin/which: POSIX shell script, ASCII text executable
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
Here we learn that both `vlc` and `date` are **executables**, compiled for an x86-64 system.
|
||
I would say they are both created *equally* no?
|
||
Both are actual programs.
|
||
But what about `which`?
|
||
It's also an executable but not compiled, it's a *POSIX shell script*.
|
||
So not all programs *are* created equally?
|
||
|
||
## Compiled vs interpreted
|
||
|
||
Executing a file, or program, means you take this file and tell the computer it needs to execute the actions that are stored in the file.
|
||
Compiled programs contain actual [instructions](https://en.wikipedia.org/wiki/Instruction_set_architecture#Instructions) the computer understands out of the box.
|
||
This means that programs that are compiled are always compiled for a specify architecture which in our case is x86-64.
|
||
On a Raspberry Pi this would be armhf or arm64.
|
||
|
||
Interpreted programs are not compiled to machine code but when we run them each line is passed to an appropriate **interpreter** and executed **line by line**.
|
||
The first line of a script is often the path to the interpreter that *understands* the code that will follow.
|
||
Popular interpreted languages are `bash`, `sh`, `python`, `php`, ...
|
||
|
||
We can take it *one* more step forward and peak into the *content* of the files.
|
||
A nice little program to do this is called `head` who's purpose in life is to show the first few lines of a file.
|
||
First for `vlc`.
|
||
|
||
```
|
||
waldek@hellodebian:~$ head /usr/bin/vlc
|
||
ELF>@<40>1@8
|
||
HHh,h<h<<3C><><EFBFBD>,<2C><<3C>< <20><><EFBFBD>DDP<44>td###<23><>Q<EFBFBD>tdR<64>tdh,h<h<<3C><>/lib64/ld-linux-x86-64.so.2GNUQ<EFBFBD><EFBFBD>4!4w4L<34>%<25>@T?<3F>GNU)<29>)*<2A>e<EFBFBD>m9<6D>y<EFBFBD><79><EFBFBD><EFBFBD> <20><>)F <20>, X<>`
|
||
Pco<EFBFBD><EFBFBD><EFBFBD><EFBFBD>v<EFBFBD><EFBFBD>ZD<EFBFBD>
|
||
<20><>/<2F><><EFBFBD>h<EFBFBD>"<22> _ITM_deregisterTMCloneTable__gmon_start___ITM_registerTMCloneTablelibvlc_set_app_idlibvlc_newlibvlc_set_user_agentlibvlc_get_changesetlibvlc_get_versionlibvlc_set_exit_handlerlibvlc_add_intflibvlc_playlist_playlibvlc_releasesigwaitflockfilepthread_killpthread_sigmaskpthread_mutex_lockpthread_mutex_unlockfunlockfilesigactiondlsymdlerrorfflushsignal__stack_chk_failabortisattysigemptysetrand_r__fprintf_chksigaddsetmemcpystderrsigdelsetalarmfwritegeteuid__vfprintf_chk__cxa_finalizepthread_self__libc_start_main__register_atforklibvlc.so.5libpthread.so.0libdl.so.2libc.so.6GLIBC_2<EFBFBD>ri5GLIB<EFBFBD>ti.14GL<EFBFBD>u<EFBFBD>i2.4Glh<EFBFBD>p<EFBFBD>@<40>?<3F>?GLIBC_2.3.G u<>i lW u<>i lb<6C><62>xii
|
||
<EFBFBD>?
|
||
<20>?<3F>?) @*<2A>><3E>><3E>><3E>><3E>><3E>><3E><>> <09>>
|
||
??? ?(?0?8?@?H?P?X?`?<3F>h??x?<3F>?<3F>?<3F>? <20>?!<21>?"<22>?#<23>?$<24>?%<25>?&<26>?'<27>?(H<>H<EFBFBD><48>/H<><48>t<EFBFBD><74>H<EFBFBD><48><EFBFBD>5<EFBFBD>.<2E>%<25>.@<40>%<25>.h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%z.h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%r.h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%j.h<><68><EFBFBD><EFBFBD><EFBFBD>%b.h<><68><EFBFBD><EFBFBD><EFBFBD>%Z.h<><68><EFBFBD><EFBFBD><EFBFBD>%R.h<><68><EFBFBD><EFBFBD><EFBFBD>%J.h<>p<EFBFBD><70><EFBFBD><EFBFBD>%B.<2E>`<60><><EFBFBD><EFBFBD>%:.h <09>P<EFBFBD><50><EFBFBD><EFBFBD>%2.h
|
||
<EFBFBD>@<40><><EFBFBD><EFBFBD>%*.h
|
||
<20>0<EFBFBD><30><EFBFBD><EFBFBD>%".h
|
||
<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%.h<><68><EFBFBD><EFBFBD><EFBFBD>% <20> <20><><EFBFBD><EFBFBD>%<25>.h
|
||
.h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%.h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD>%<25>-h<>p<EFBFBD><70><EFBFBD><EFBFBD>%<25>-h<>`<60><><EFBFBD><EFBFBD>%<25>-h<>P<EFBFBD><50><EFBFBD><EFBFBD>%<25>-h<><68>@<40><><EFBFBD><EFBFBD>%<25>-h0<68><30><EFBFBD><EFBFBD>%<25>-h<> <20><><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD>%<25>-h<><68><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>1<EFBFBD>L<EFBFBD><4C>H<EFBFBD><48><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>k<EFBFBD><6B><EFBFBD><EFBFBD>S<EFBFBD>[Hc<48>H<EFBFBD>G<EFBFBD><47><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD>:<3A><><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD>-<2D><><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD> <20><><EFBFBD><EFBFBD>
|
||
L<><4C>
|
||
H<><48>H<EFBFBD>5<EFBFBD>
|
||
fHn<48>H<EFBFBD>BfHn<48>H<EFBFBD><48> H<><48><EFBFBD>fl<66>I<EFBFBD>H)<29>L<EFBFBD>t$L<><4C>I<EFBFBD><49><EFBFBD>H<EFBFBD><48>L<EFBFBD><4C><EFBFBD>I<EFBFBD>~<7E>o<EFBFBD><6F><EFBFBD>Lc<4C>K<EFBFBD><4B><EFBFBD>L<EFBFBD><4C><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>I<EFBFBD><49>H<EFBFBD><48><EFBFBD><EFBFBD>H<EFBFBD><48>H<EFBFBD><48><EFBFBD><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD>5<EFBFBD><35>S<EFBFBD><53><EFBFBD>H<EFBFBD>
|
||
H<EFBFBD>/
|
||
L<><4C>H<EFBFBD>5
|
||
<20>v<EFBFBD><76><EFBFBD>H<EFBFBD>
|
||
H<>5
|
||
L<><4C><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD>5!
|
||
L<><4C><EFBFBD>!<21><><EFBFBD>H<EFBFBD>5
|
||
|
||
L<EFBFBD><EFBFBD><EFBFBD>'<27><><EFBFBD>H<EFBFBD><48><EFBFBD><EFBFBD><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD>H<EFBFBD><48><EFBFBD>L<EFBFBD><4C><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD>S<EFBFBD><53><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD>F<EFBFBD><46><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD>5<EFBFBD><35><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>1<EFBFBD>L<EFBFBD><4C><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>L<EFBFBD><4C><EFBFBD>5<EFBFBD><35><EFBFBD><EFBFBD>8<EFBFBD><38><EFBFBD><EFBFBD><EFBFBD>I<EFBFBD><49><EFBFBD>&<26><><EFBFBD>H<EFBFBD>=<3D>*M<><4D>H<EFBFBD><48><EFBFBD>@<40><><EFBFBD>u
|
||
H<><48><EFBFBD>1<EFBFBD><31><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>n<EFBFBD><6E><EFBFBD>A<EFBFBD>H<EFBFBD>E<EFBFBD>dH+%(u?H<>e<EFBFBD>D<EFBFBD><44>[A\A]A^]<5D>I<EFBFBD>M<EFBFBD>H<EFBFBD>=\*H<><48>
|
||
CH<EFBFBD>=L<><4C><EFBFBD><EFBFBD><EFBFBD>)<29>DH<44>=<3D>)H<><48>)H9<48>tH<74><48>)H<><48>t<EFBFBD>f.<2E>1<EFBFBD><31><EFBFBD><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD>=<3D>)H<>5<EFBFBD>)H)<29>H<EFBFBD><48>H<EFBFBD><48>?H<><48>H<EFBFBD>H<EFBFBD><48>tH<74>U)H<><48><EFBFBD><EFBFBD>fD<66><44><EFBFBD>=q)u/UH<55>=6)H<><48>t
|
||
H<>=:)<29><><EFBFBD><EFBFBD><EFBFBD>h<EFBFBD><68><EFBFBD><EFBFBD>I)]<5D><><EFBFBD><EFBFBD><EFBFBD>{<7B><><EFBFBD>f.<2E><>1<EFBFBD><31><EFBFBD>$<24><><EFBFBD>@H<>?<3F><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>)<29><>AUI<55><49>ATI<54><49>UH<55><48>SH<53><48>H<EFBFBD><48><EFBFBD>L<EFBFBD>D$@L<>L$H<><48>t7)D$P)L$`)T$p)<29>$<24>)<29>$<24>)<29>$<24>)<29>$<24>)<29>$<24>dH<64>%(H<>D$1<>H<EFBFBD>={(H<>T$ H<><48>$<24>$ <20>D$0H<30>DH<44>T$<24><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>
|
||
<20><>v1H<31>=B(<28><><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD>D$dH+%(uH<75><48><EFBFBD>[]A\A]<5D><><EFBFBD><EFBFBD>H<EFBFBD>=(I<><49>1<EFBFBD><31>
|
||
H<EFBFBD><EFBFBD>H<EFBFBD>=7 H<>5H<35>=?'<27><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>e<EFBFBD><65><EFBFBD><EFBFBD>#<23><><EFBFBD><EFBFBD><EFBFBD><EFBFBD>f<EFBFBD>ATI<54><49><EFBFBD>f<EFBFBD><66><EFBFBD>H<EFBFBD>=<3D>'L<><4C>H<EFBFBD>I<EFBFBD><49><EFBFBD>1<EFBFBD><31><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD>i<EFBFBD><69><EFBFBD>1<EFBFBD>1<EFBFBD><31>.(<28>f<EFBFBD><66>=(UH<55><48>u#H<>5H<35><48><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD><48>t5H<35><48>]<5D><>DI<44><49>1<EFBFBD>H<EFBFBD>
|
||
<EFBFBD>H<EFBFBD>H<EFBFBD>5<EFBFBD>H<EFBFBD>=7&<26><>&<26><><EFBFBD><EFBFBD>X1<58>Z]A\A]<5D>H<EFBFBD><48><EFBFBD><EFBFBD><EFBFBD>ff.<2E><><EFBFBD>='UH<55><48>u#H<>5<EFBFBD>H<EFBFBD><48><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>H<EFBFBD><48>t5H<35><48>]<5D><>DI<44><49>1<EFBFBD>H<EFBFBD><48>RH<52>
|
||
!"<22><><EFBFBD><EFBFBD>H<EFBFBD>H<EFBFBD><48>DESKTOP_STARTUP_ID--no-ignore-config--media-library--dbusvlcorg.VideoLAN.VLCVLC/3.0.16VLC media playerglobalhotkeys,noneVLC is not supposed to be run as root. Sorry.
|
||
If you need to use real-time priorities and/or privileged TCP ports
|
||
you can use %s-wrapper (make sure it is Set-UID root and
|
||
```
|
||
|
||
And now of `which`.
|
||
|
||
```
|
||
waldek@hellodebian:~$ head /usr/bin/which
|
||
#! /bin/sh
|
||
set -ef
|
||
|
||
if test -n "$KSH_VERSION"; then
|
||
puts() {
|
||
print -r -- "$*"
|
||
}
|
||
else
|
||
puts() {
|
||
printf '%s\n' "$*"
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
Notice how the `vlc` file is mostly **not human readable** but we can still make out some keywords?
|
||
The `which` file however is perfectly readable!
|
||
The first line of the `which` file is `#! /bin/sh` which is the path to the interpreter.
|
||
The `#!` is called a [shebang](https://en.wikipedia.org/wiki/Shebang_(Unix)).
|
||
We can dig into this to learn more about this mysterious `sh`.
|
||
|
||
```
|
||
waldek@hellodebian:~$ file /bin/sh
|
||
/bin/sh: symbolic link to dash
|
||
waldek@hellodebian:~$ which dash
|
||
/usr/bin/dash
|
||
waldek@hellodebian:~$ file /usr/bin/dash
|
||
/usr/bin/dash: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=cb6911fd56559717336c938bef1ce479b0a85b35, for GNU/Linux 3.2.0, stripped
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
Surprise surprise!
|
||
The *interpreter* is a compiled program!
|
||
When you think about it it does make sense because at the end of the day the computer *only* understands machine instructions.
|
||
So when you execute a script each line of code is converted to machine instructions on the spot.
|
||
This makes scripts easier to write but slower at execution.
|
||
|
||
# More about paths
|
||
|
||
The prompt in our terminal tells us who we are, on which machine, and **where** we are located.
|
||
This where is symbolized with the `~` character.
|
||
But where is this where?
|
||
|
||
```
|
||
waldek@hellodebian:~$ pwd
|
||
/home/waldek
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
The `pwd` program **p**rints our **w**orking **d**irectory, meaning where we are located on our system.
|
||
A user's home directory is symbolized with this tilde character.
|
||
We can move around our system with the `cd` command which is an abbreviation of **c**hange **d**irectory.
|
||
`cd` by itself seems to to *nothing* but this is not the case.
|
||
It's a *shortcut* to go to your user's home directory.
|
||
Let's try this out.
|
||
|
||
```
|
||
waldek@hellodebian:~$ cd
|
||
waldek@hellodebian:~$ cd /usr/bin
|
||
waldek@hellodebian:/usr/bin$ cd
|
||
waldek@hellodebian:~$ cd -
|
||
/usr/bin
|
||
waldek@hellodebian:/usr/bin$ cd
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
The first line appears to do nothing because we are already in our home directory.
|
||
Next we move to the directory which contains the programs we discovered before and we see our prompt change.
|
||
It now shows *where* we are located!
|
||
The next line takes us back to our home and from there we can move *back to where we were before* with the `cd -` command.
|
||
This last command is also a handy *shortcut*!
|
||
|
||
Moving around is nice but once we arrive at our destination it would be practical to be able to list the files in that directory no?
|
||
This can be done with the `ls` program.
|
||
For example.
|
||
|
||
```
|
||
waldek@hellodebian:~$ cd /usr/bin/
|
||
waldek@hellodebian:/usr/bin$ ls
|
||
'[' getconf nmtui-hostname systemd-escape
|
||
7z getent nohup systemd-hwdb
|
||
7za getfacl notify-send systemd-id128
|
||
7zr getkeycodes nproc systemd-inhibit
|
||
aa-enabled getopt nroff systemd-machine-id-setup
|
||
aa-exec gettext nsenter systemd-mount
|
||
aconnect gettext.sh nslookup systemd-notify
|
||
add-apt-repository gio nstat systemd-path
|
||
addpart gio-querymodules nsupdate systemd-resolve
|
||
addr2line gjs ntfs-3g systemd-run
|
||
alsabat gjs-console ntfs-3g.probe systemd-socket-activate
|
||
alsaloop gkbd-keyboard-display ntfscat systemd-stdio-bridge
|
||
alsamixer glib-compile-schemas ntfscluster systemd-sysusers
|
||
alsatplg gmake ntfscmp systemd-tmpfiles
|
||
alsaucm gnome-calculator ntfsdecrypt systemd-tty-ask-password-agent
|
||
|
||
# ------------------------------------
|
||
# --- cropped the list for clarity ---
|
||
# ------------------------------------
|
||
|
||
gdk-pixbuf-csource nisdomainname system-config-printer-applet zforce
|
||
gdk-pixbuf-pixdata nl systemctl zgrep
|
||
gdk-pixbuf-thumbnailer nm systemd zipdetails
|
||
gdm-control nm-applet systemd-analyze zipgrep
|
||
gdmflexiserver nmcli systemd-ask-password zipinfo
|
||
gdm-screenshot nm-connection-editor systemd-cat zless
|
||
gedit nm-online systemd-cgls zmore
|
||
gencat nmtui systemd-cgtop znew
|
||
geqn nmtui-connect systemd-delta
|
||
GET nmtui-edit systemd-detect-virt
|
||
waldek@hellodebian:/usr/bin$
|
||
```
|
||
|
||
That's a **lot** of programs!
|
||
Can you find `cd` in there?
|
||
Spoiler alert, you wont...
|
||
Maybe it's located somewhere else?
|
||
Let's have a look.
|
||
|
||
```
|
||
waldek@hellodebian:/usr/bin$ which cd
|
||
waldek@hellodebian:/usr/bin$
|
||
```
|
||
|
||
`cd` is not a program but a builtin command.
|
||
From a practical point of view there is no difference but I do like to mention it for completeness.
|
||
Later down the line it will help you to contextualize the differences between shells a bit better.
|
||
But built into *what*?
|
||
Below you can see a snippet of a part of the `bash-builtin` manual.
|
||
For now just accept the specific shell we're using is called `bash`.
|
||
|
||
```
|
||
BASH-BUILTINS(7) Miscellaneous Information Manual BASH-BUILTINS(7)
|
||
|
||
NAME
|
||
bash-builtins - bash built-in commands, see bash(1)
|
||
|
||
SYNOPSIS
|
||
bash defines the following built-in commands: :, ., [, alias, bg, bind, break, builtin, case, cd, command, compgen, complete, continue, de‐
|
||
clare, dirs, disown, echo, enable, eval, exec, exit, export, fc, fg, getopts, hash, help, history, if, jobs, kill, let, local, logout, popd,
|
||
printf, pushd, pwd, read, readonly, return, set, shift, shopt, source, suspend, test, times, trap, type, typeset, ulimit, umask, unalias,
|
||
unset, until, wait, while.
|
||
```
|
||
|
||
## Absolute and relative paths
|
||
|
||
> All roads lead to Rome.
|
||
|
||
There are multiple ways to go to the same location on your system.
|
||
You can always go either in an **absolute** way, or in *multiple* **relative** ways.
|
||
The root of your system is `/` and to list what we can find there we can use `ls`.
|
||
|
||
```
|
||
waldek@hellodebian:~$ cd /
|
||
waldek@hellodebian:/$ ls
|
||
bin dev home initrd.img.old lib32 libx32 media opt root sbin sys usr vmlinuz
|
||
boot etc initrd.img lib lib64 lost+found mnt proc run srv tmp var vmlinuz.old
|
||
waldek@hellodebian:/$
|
||
```
|
||
|
||
From here we can go back home in multiple ways.
|
||
|
||
```
|
||
waldek@hellodebian:/$ cd
|
||
waldek@hellodebian:~$ cd -
|
||
/
|
||
waldek@hellodebian:/$ cd home/waldek/
|
||
waldek@hellodebian:~$ cd -
|
||
/
|
||
waldek@hellodebian:/$ cd /home/waldek/
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
The first one is the handy shortcut we learned, and we go back to the root of our system with the `cd -` shortcut.
|
||
The following two manipulations look very similar but there is a subtle difference.
|
||
The first one `home/waldek` is a **relative** path, and the second one `/home/waldek` is an **absolute** one.
|
||
Relative paths depend on where you are located, absolute ones always point to the same location.
|
||
An example.
|
||
|
||
```
|
||
waldek@hellodebian:~$ cd /usr/bin/
|
||
waldek@hellodebian:/usr/bin$ cd /home/waldek/
|
||
waldek@hellodebian:~$ cd -
|
||
/usr/bin
|
||
waldek@hellodebian:/usr/bin$ cd home/waldek
|
||
-bash: cd: home/waldek: No such file or directory
|
||
waldek@hellodebian:/usr/bin$
|
||
```
|
||
|
||
The second command fails because from where I'm standing, there is no folder called `home/waldek`!
|
||
I can however still go to my home in a relative way but I need to *go back* a few directories first.
|
||
|
||
```
|
||
waldek@hellodebian:/usr/bin$ cd ../../home/waldek/
|
||
waldek@hellodebian:~$ pwd
|
||
/home/waldek
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
The `..` means go **back** one directory so in our example we go back **two** directories, which brings us to the `/` of our system and from there we go **up** to `home` and then `waldek`.
|
||
|
||
## `root` and `/` and `/root` are not the same thing
|
||
|
||
The word *root* has multiple meanings and can be a bit confusing at the start.
|
||
Every Linux machine will have a `root` user **and** a `/` of the system.
|
||
The `root` user is an account essential to the proper working of a Linux system, whereas `/` is a location, the *root* of the filesystem.
|
||
The `/root` is also a location but is the **home** of the user `root`, located at the `/` of the filesystem.
|
||
If this sounds confusing read the above paragraph slowly until you see the differences.
|
||
I do want to note that the name of the user `root` *can* change but it's ID will always be `0`.
|
||
We'll go into detail about users and ID's later down the line.
|
||
|
||
# Exercise
|
||
|
||
Explore your system a bit using `cd` and `ls`.
|
||
You'll probably encounter some weird messages along the way.
|
||
Keep note of them so we can discuss it together.
|
||
|
||
# A pit stop to review what we've learned so far
|
||
|
||
Below is a list of programs and command we've seen so far.
|
||
We've seen that some take arguments, some don't.
|
||
This list will grow as we go so I advise you to take some notes of your own.
|
||
|
||
|command|description|
|
||
|---|---|
|
||
|systemctl|manipulate running services|
|
||
|apt|the Debian package manager|
|
||
|htop|a command line task manager we installed|
|
||
|vlc|a video player we installed|
|
||
|date|display the time of day|
|
||
|which|show the path to an executable|
|
||
|file|print more information about a file's content|
|
||
|head|show the first lines of a file|
|
||
|pwd|print working directory|
|
||
|cd|change directory|
|
||
|ls|list content of a directory|
|
||
|
||
# Arguments and flags
|
||
|
||
The `ls` program is one of the most used commands.
|
||
It's like a very basic *file explorer* in a graphical environment and just like it's graphical counter part you can use it to display it's data in different ways.
|
||
Think of the *details* versus *thumbnail* views in your favorite explorer.
|
||
But how do you do this?
|
||
We can **add flags or options** to the program to modify it's behavior.
|
||
Have a look at the output below.
|
||
|
||
```
|
||
waldek@hellodebian:~$ ls
|
||
Desktop Documents Downloads Music Pictures Public Templates Videos
|
||
waldek@hellodebian:~$ ls -l
|
||
total 32
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Desktop
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Documents
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Downloads
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Music
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Pictures
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Public
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Templates
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Videos
|
||
waldek@hellodebian:~$ ls -a
|
||
. .bashrc Desktop .gnupg .profile Templates .vboxclient-seamless.pid
|
||
.. .cache .dmrc .local Public .vboxclient-clipboard.pid Videos
|
||
.bash_history .config Documents Music .python_history .vboxclient-display-svga-x11.pid .Xauthority
|
||
.bash_logout .dbus Downloads Pictures .ssh .vboxclient-draganddrop.pid .xsession-errors
|
||
```
|
||
|
||
The `-l` and `-a` additions are what we call *flags* or *options*.
|
||
Aren't they just extra *arguments*?
|
||
There is no real rule to the naming of this concept but [this](https://unix.stackexchange.com/questions/285575/whats-the-difference-between-a-flag-an-option-and-an-argument) is a rather interesting take.
|
||
|
||
We can combine arguments if we want, and some programs even allow *concatenation* of arguments.
|
||
Have a look below to understand what I mean by that.
|
||
|
||
```
|
||
waldek@hellodebian:~$ ls -a -l
|
||
total 112
|
||
drwxr-xr-x 16 waldek waldek 4096 Feb 21 18:12 .
|
||
drwxr-xr-x 3 root root 4096 Feb 18 12:49 ..
|
||
-rw------- 1 waldek waldek 2772 Feb 22 10:45 .bash_history
|
||
-rw-r--r-- 1 waldek waldek 220 Feb 18 12:49 .bash_logout
|
||
-rw-r--r-- 1 waldek waldek 3526 Feb 18 12:49 .bashrc
|
||
drwx------ 16 waldek waldek 4096 Feb 18 14:24 .cache
|
||
drwx------ 20 waldek waldek 4096 Feb 18 14:23 .config
|
||
drwx------ 3 waldek waldek 4096 Feb 18 12:52 .dbus
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Desktop
|
||
-rw-r--r-- 1 waldek waldek 35 Feb 18 13:33 .dmrc
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Documents
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Downloads
|
||
drwx------ 2 waldek waldek 4096 Feb 18 15:07 .gnupg
|
||
drwxr-xr-x 3 waldek waldek 4096 Feb 18 12:50 .local
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Music
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Pictures
|
||
-rw-r--r-- 1 waldek waldek 807 Feb 18 12:49 .profile
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Public
|
||
-rw------- 1 waldek waldek 11 Feb 21 18:12 .python_history
|
||
drwx------ 2 waldek waldek 4096 Feb 21 12:45 .ssh
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Templates
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-clipboard.pid
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-display-svga-x11.pid
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-draganddrop.pid
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-seamless.pid
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Videos
|
||
-rw------- 1 waldek waldek 56 Feb 18 13:33 .Xauthority
|
||
-rw------- 1 waldek waldek 2701 Feb 18 13:33 .xsession-errors
|
||
waldek@hellodebian:~$ ls -la
|
||
total 112
|
||
drwxr-xr-x 16 waldek waldek 4096 Feb 21 18:12 .
|
||
drwxr-xr-x 3 root root 4096 Feb 18 12:49 ..
|
||
-rw------- 1 waldek waldek 2772 Feb 22 10:45 .bash_history
|
||
-rw-r--r-- 1 waldek waldek 220 Feb 18 12:49 .bash_logout
|
||
-rw-r--r-- 1 waldek waldek 3526 Feb 18 12:49 .bashrc
|
||
drwx------ 16 waldek waldek 4096 Feb 18 14:24 .cache
|
||
drwx------ 20 waldek waldek 4096 Feb 18 14:23 .config
|
||
drwx------ 3 waldek waldek 4096 Feb 18 12:52 .dbus
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Desktop
|
||
-rw-r--r-- 1 waldek waldek 35 Feb 18 13:33 .dmrc
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Documents
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Downloads
|
||
drwx------ 2 waldek waldek 4096 Feb 18 15:07 .gnupg
|
||
drwxr-xr-x 3 waldek waldek 4096 Feb 18 12:50 .local
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Music
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Pictures
|
||
-rw-r--r-- 1 waldek waldek 807 Feb 18 12:49 .profile
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Public
|
||
-rw------- 1 waldek waldek 11 Feb 21 18:12 .python_history
|
||
drwx------ 2 waldek waldek 4096 Feb 21 12:45 .ssh
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Templates
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-clipboard.pid
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-display-svga-x11.pid
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-draganddrop.pid
|
||
-rw-r----- 1 waldek waldek 5 Feb 18 15:06 .vboxclient-seamless.pid
|
||
drwxr-xr-x 2 waldek waldek 4096 Feb 18 12:50 Videos
|
||
-rw------- 1 waldek waldek 56 Feb 18 13:33 .Xauthority
|
||
-rw------- 1 waldek waldek 2701 Feb 18 13:33 .xsession-errors
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
# Getting help
|
||
|
||
## Options
|
||
|
||
OK, so we have *a lot* of programs we can use on the command line, plus we can change how they work by adding obscure characters.
|
||
How on earth can we *discover* what a program can and can't do?
|
||
Introducing the **most important flag**: `--help`.
|
||
|
||
Most programs come with builtin help to explain you how to use the program.
|
||
Often, but not always, this help can be displayed on the terminal by adding the `--help` flag.
|
||
Let's investigate this.
|
||
|
||
```
|
||
waldek@hellodebian:~$ ls --help
|
||
Usage: ls [OPTION]... [FILE]...
|
||
List information about the FILEs (the current directory by default).
|
||
Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.
|
||
|
||
Mandatory arguments to long options are mandatory for short options too.
|
||
-a, --all do not ignore entries starting with .
|
||
-A, --almost-all do not list implied . and ..
|
||
--author with -l, print the author of each file
|
||
-b, --escape print C-style escapes for nongraphic characters
|
||
--block-size=SIZE with -l, scale sizes by SIZE when printing them;
|
||
e.g., '--block-size=M'; see SIZE format below
|
||
-B, --ignore-backups do not list implied entries ending with ~
|
||
-c with -lt: sort by, and show, ctime (time of last
|
||
modification of file status information);
|
||
with -l: show ctime and sort by name;
|
||
otherwise: sort by ctime, newest first
|
||
-C list entries by columns
|
||
--color[=WHEN] colorize the output; WHEN can be 'always' (default
|
||
if omitted), 'auto', or 'never'; more info below
|
||
-d, --directory list directories themselves, not their contents
|
||
-D, --dired generate output designed for Emacs' dired mode
|
||
-f do not sort, enable -aU, disable -ls --color
|
||
-F, --classify append indicator (one of */=>@|) to entries
|
||
--file-type likewise, except do not append '*'
|
||
--format=WORD across -x, commas -m, horizontal -x, long -l,
|
||
single-column -1, verbose -l, vertical -C
|
||
--full-time like -l --time-style=full-iso
|
||
-g like -l, but do not list owner
|
||
--group-directories-first
|
||
group directories before files;
|
||
can be augmented with a --sort option, but any
|
||
use of --sort=none (-U) disables grouping
|
||
-G, --no-group in a long listing, don't print group names
|
||
-h, --human-readable with -l and -s, print sizes like 1K 234M 2G etc.
|
||
--si likewise, but use powers of 1000 not 1024
|
||
-H, --dereference-command-line
|
||
follow symbolic links listed on the command line
|
||
--dereference-command-line-symlink-to-dir
|
||
follow each command line symbolic link
|
||
that points to a directory
|
||
--hide=PATTERN do not list implied entries matching shell PATTERN
|
||
(overridden by -a or -A)
|
||
--hyperlink[=WHEN] hyperlink file names; WHEN can be 'always'
|
||
(default if omitted), 'auto', or 'never'
|
||
--indicator-style=WORD append indicator with style WORD to entry names:
|
||
none (default), slash (-p),
|
||
file-type (--file-type), classify (-F)
|
||
-i, --inode print the index number of each file
|
||
-I, --ignore=PATTERN do not list implied entries matching shell PATTERN
|
||
-k, --kibibytes default to 1024-byte blocks for disk usage;
|
||
used only with -s and per directory totals
|
||
-l use a long listing format
|
||
-L, --dereference when showing file information for a symbolic
|
||
link, show information for the file the link
|
||
references rather than for the link itself
|
||
-m fill width with a comma separated list of entries
|
||
-n, --numeric-uid-gid like -l, but list numeric user and group IDs
|
||
-N, --literal print entry names without quoting
|
||
-o like -l, but do not list group information
|
||
-p, --indicator-style=slash
|
||
append / indicator to directories
|
||
-q, --hide-control-chars print ? instead of nongraphic characters
|
||
--show-control-chars show nongraphic characters as-is (the default,
|
||
unless program is 'ls' and output is a terminal)
|
||
-Q, --quote-name enclose entry names in double quotes
|
||
--quoting-style=WORD use quoting style WORD for entry names:
|
||
literal, locale, shell, shell-always,
|
||
shell-escape, shell-escape-always, c, escape
|
||
(overrides QUOTING_STYLE environment variable)
|
||
-r, --reverse reverse order while sorting
|
||
-R, --recursive list subdirectories recursively
|
||
-s, --size print the allocated size of each file, in blocks
|
||
-S sort by file size, largest first
|
||
--sort=WORD sort by WORD instead of name: none (-U), size (-S),
|
||
time (-t), version (-v), extension (-X)
|
||
--time=WORD change the default of using modification times;
|
||
access time (-u): atime, access, use;
|
||
change time (-c): ctime, status;
|
||
birth time: birth, creation;
|
||
with -l, WORD determines which time to show;
|
||
with --sort=time, sort by WORD (newest first)
|
||
--time-style=TIME_STYLE time/date format with -l; see TIME_STYLE below
|
||
-t sort by time, newest first; see --time
|
||
-T, --tabsize=COLS assume tab stops at each COLS instead of 8
|
||
-u with -lt: sort by, and show, access time;
|
||
with -l: show access time and sort by name;
|
||
otherwise: sort by access time, newest first
|
||
-U do not sort; list entries in directory order
|
||
-v natural sort of (version) numbers within text
|
||
-w, --width=COLS set output width to COLS. 0 means no limit
|
||
-x list entries by lines instead of by columns
|
||
-X sort alphabetically by entry extension
|
||
-Z, --context print any security context of each file
|
||
-1 list one file per line. Avoid '\n' with -q or -b
|
||
--help display this help and exit
|
||
--version output version information and exit
|
||
|
||
The SIZE argument is an integer and optional unit (example: 10K is 10*1024).
|
||
Units are K,M,G,T,P,E,Z,Y (powers of 1024) or KB,MB,... (powers of 1000).
|
||
Binary prefixes can be used, too: KiB=K, MiB=M, and so on.
|
||
|
||
The TIME_STYLE argument can be full-iso, long-iso, iso, locale, or +FORMAT.
|
||
FORMAT is interpreted like in date(1). If FORMAT is FORMAT1<newline>FORMAT2,
|
||
then FORMAT1 applies to non-recent files and FORMAT2 to recent files.
|
||
TIME_STYLE prefixed with 'posix-' takes effect only outside the POSIX locale.
|
||
Also the TIME_STYLE environment variable sets the default style to use.
|
||
|
||
Using color to distinguish file types is disabled both by default and
|
||
with --color=never. With --color=auto, ls emits color codes only when
|
||
standard output is connected to a terminal. The LS_COLORS environment
|
||
variable can change the settings. Use the dircolors command to set it.
|
||
|
||
Exit status:
|
||
0 if OK,
|
||
1 if minor problems (e.g., cannot access subdirectory),
|
||
2 if serious trouble (e.g., cannot access command-line argument).
|
||
|
||
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
|
||
Full documentation <https://www.gnu.org/software/coreutils/ls>
|
||
or available locally via: info '(coreutils) ls invocation'
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
The output above teaches us that the options `-la` change the output so it becomes:
|
||
|
||
* `-a, --all do not ignore entries starting with .`
|
||
* `-l use a long listing format`
|
||
|
||
To *not ignore entries starting with .* we can use two different flags, `-a` or `--all`.
|
||
The former is called short arguments and the latter long ones.
|
||
The long ones are more *verbose* so it's often easier to understand what a line *does* just by reading it.
|
||
Note that `ls` only has one way of showing the help by adding `--help` whereas the help for `htop` can be shown with both `-h` or `--help`.
|
||
This inconsistency is sadly a byproduct of the decentralized nature of Linux.
|
||
To add to this mess some programs use *single dash long form* (`-help`) but those programs are rather rare.
|
||
|
||
## Manuals
|
||
|
||
The `--help` flag is tremendously useful as it gives you an overview of how you can modify a programs behaviour, kind of like settings, but it doesn't always explain you what a program is *for*.
|
||
The is where the manuals come into play.
|
||
I see the `--help` flag as a *cheat sheet* to quickly discover options and the man pages as a reference.
|
||
We can read the manual by calling the `man` program with an argument.
|
||
This argument is the *name* of the program you want to read the manual for.
|
||
Same idea as with `which`.
|
||
|
||
```
|
||
waldek@hellodebian:~$ man ls
|
||
```
|
||
|
||
You're now in a program called `less`, which is a [pager](https://en.wikipedia.org/wiki/Terminal_pager).
|
||
You can scroll the manual with the arrows of `vi` based navigation (which we'll get into later).
|
||
If you hit `h` you'll see the builtin documentation of `less` and press `q` to quit (twice if you're in the help section).
|
||
This brings you back to your prompt.
|
||
It's worth reading the [wikipedia entry](https://en.wikipedia.org/wiki/Man_page) of the `man` command to understand it's history and operation.
|
||
|
||
The output below illustrates the *tree* of a terminal that's reading a manual.
|
||
In a `bash` shell you invoke `man ls` which in turn runs the `pager` program to display the content.
|
||
If you're intrigued by this `pstree` program go and read the manual!
|
||
|
||
```
|
||
waldek@hellodebian:~$ pstree 10845 -a
|
||
bash
|
||
└─man ls
|
||
└─pager
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
Not every command has a manual.
|
||
For example, `cd` does not have one.
|
||
This is kind of logical because `cd` is a builtin.
|
||
To learn more about builtin commands you can use the `help` program.
|
||
On it's own it gives you all the builtin command you can invoke and with an argument it outputs the help about that specific command.
|
||
|
||
```
|
||
waldek@hellodebian:~$ help
|
||
GNU bash, version 5.1.4(1)-release (x86_64-pc-linux-gnu)
|
||
These shell commands are defined internally. Type `help' to see this list.
|
||
Type `help name' to find out more about the function `name'.
|
||
Use `info bash' to find out more about the shell in general.
|
||
Use `man -k' or `info' to find out more about commands not in this list.
|
||
|
||
A star (*) next to a name means that the command is disabled.
|
||
|
||
job_spec [&] history [-c] [-d offset] [n] or history -anrw [filename] or history -ps>
|
||
(( expression )) if COMMANDS; then COMMANDS; [ elif COMMANDS; then COMMANDS; ]... [ else>
|
||
. filename [arguments] jobs [-lnprs] [jobspec ...] or jobs -x command [args]
|
||
: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [>
|
||
[ arg... ] let arg [arg ...]
|
||
[[ expression ]] local [option] name[=value] ...
|
||
alias [-p] [name[=value] ... ] logout [n]
|
||
bg [job_spec ...] mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C c>
|
||
bind [-lpsvPSVX] [-m keymap] [-f filename] [-q name] [-u name] [-r keyse> popd [-n] [+N | -N]
|
||
break [n] printf [-v var] format [arguments]
|
||
builtin [shell-builtin [arg ...]] pushd [-n] [+N | -N | dir]
|
||
caller [expr] pwd [-LP]
|
||
case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac read [-ers] [-a array] [-d delim] [-i text] [-n nchars] [-N nchars] [-p>
|
||
cd [-L|[-P [-e]] [-@]] [dir] readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C>
|
||
command [-pVv] command [arg ...] readonly [-aAf] [name[=value] ...] or readonly -p
|
||
compgen [-abcdefgjksuv] [-o option] [-A action] [-G globpat] [-W wordlis> return [n]
|
||
complete [-abcdefgjksuv] [-pr] [-DEI] [-o option] [-A action] [-G globpa> select NAME [in WORDS ... ;] do COMMANDS; done
|
||
compopt [-o|+o option] [-DEI] [name ...] set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
|
||
continue [n] shift [n]
|
||
coproc [NAME] command [redirections] shopt [-pqsu] [-o] [optname ...]
|
||
declare [-aAfFgiIlnrtux] [-p] [name[=value] ...] source filename [arguments]
|
||
dirs [-clpv] [+N] [-N] suspend [-f]
|
||
disown [-h] [-ar] [jobspec ... | pid ...] test [expr]
|
||
echo [-neE] [arg ...] time [-p] pipeline
|
||
enable [-a] [-dnps] [-f filename] [name ...] times
|
||
eval [arg ...] trap [-lp] [[arg] signal_spec ...]
|
||
exec [-cl] [-a name] [command [argument ...]] [redirection ...] true
|
||
exit [n] type [-afptP] name [name ...]
|
||
export [-fn] [name[=value] ...] or export -p typeset [-aAfFgiIlnrtux] [-p] name[=value] ...
|
||
false ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
|
||
fc [-e ename] [-lnr] [first] [last] or fc -s [pat=rep] [command] umask [-p] [-S] [mode]
|
||
fg [job_spec] unalias [-a] name [name ...]
|
||
for NAME [in WORDS ... ] ; do COMMANDS; done unset [-f] [-v] [-n] [name ...]
|
||
for (( exp1; exp2; exp3 )); do COMMANDS; done until COMMANDS; do COMMANDS; done
|
||
function name { COMMANDS ; } or name () { COMMANDS ; } variables - Names and meanings of some shell variables
|
||
getopts optstring name [arg ...] wait [-fn] [-p var] [id ...]
|
||
hash [-lr] [-p pathname] [-dt] [name ...] while COMMANDS; do COMMANDS; done
|
||
help [-dms] [pattern ...] { COMMANDS ; }
|
||
waldek@hellodebian:~$ help cd
|
||
cd: cd [-L|[-P [-e]] [-@]] [dir]
|
||
Change the shell working directory.
|
||
|
||
Change the current directory to DIR. The default DIR is the value of the
|
||
HOME shell variable.
|
||
|
||
The variable CDPATH defines the search path for the directory containing
|
||
DIR. Alternative directory names in CDPATH are separated by a colon (:).
|
||
A null directory name is the same as the current directory. If DIR begins
|
||
with a slash (/), then CDPATH is not used.
|
||
|
||
If the directory is not found, and the shell option `cdable_vars' is set,
|
||
the word is assumed to be a variable name. If that variable has a value,
|
||
its value is used for DIR.
|
||
|
||
Options:
|
||
-L force symbolic links to be followed: resolve symbolic
|
||
links in DIR after processing instances of `..'
|
||
-P use the physical directory structure without following
|
||
symbolic links: resolve symbolic links in DIR before
|
||
processing instances of `..'
|
||
-e if the -P option is supplied, and the current working
|
||
directory cannot be determined successfully, exit with
|
||
a non-zero status
|
||
-@ on systems that support it, present a file with extended
|
||
attributes as a directory containing the file attributes
|
||
|
||
The default is to follow symbolic links, as if `-L' were specified.
|
||
`..' is processed by removing the immediately previous pathname component
|
||
back to a slash or the beginning of DIR.
|
||
|
||
Exit Status:
|
||
Returns 0 if the directory is changed, and if $PWD is set successfully when
|
||
-P is used; non-zero otherwise.
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
Last but not least there are a few extra programs to give you quick and condensed information about a program, `whatis` and `apropos`.
|
||
|
||
```
|
||
waldek@hellodebian:~$ whatis bash
|
||
bash (1) - GNU Bourne-Again SHell
|
||
waldek@hellodebian:~$ apropos bash
|
||
bash (1) - GNU Bourne-Again SHell
|
||
bash-builtins (7) - bash built-in commands, see bash(1)
|
||
bashbug (1) - report a bug in bash
|
||
builtins (7) - bash built-in commands, see bash(1)
|
||
dh_bash-completion (1) - install bash completions for package
|
||
rbash (1) - restricted bash, see bash(1)
|
||
waldek@hellodebian:~$
|
||
```
|
||
|
||
# Exercise
|
||
|
||
**Read** some manual pages on the commands we've seen until now.
|
||
**Apply** some options you read about in the manual to experiment with said programs.
|
||
|
||
# Creating and modifying
|
||
|
||
## Directories
|
||
|
||
## Files
|
||
|
||
### `nano`
|
||
|
||
### `vi` and `vim`
|