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--- pandoc:linux-wochen-wien:linux-101:linux-101 [2018/01/31 11:11] – Pandoc Auto-commit pandoc
+++ pandoc:linux-wochen-wien:linux-101:linux-101 [2020/10/20 08:09] – Pandoc Auto-commit pandoc
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+====== History ======
+==== Unix — Linux’ predecessor ====
+> Unix is from the ’70s:
+  * terminals are monochrome
+  * computers are big and expensive
+  * many people use the same computer
+  * networking becomes important
+> Unix is free to modify:
+  * universities and companies have modified unix
+  * released as BSD/Solaris/HP-UX/IRIX
+  * fertile environment
+  * rise of similar, non-collaborating features
+> Unix becomes the GCD of computing.
+==== Hacker culture ====
+> Freedom at stake:
+  * the way of sharing programs is changing
+  * best case: bsd-style license
+  * usually: corporate licenses
+    * exclude freedom of sharing code with anyone
+> Sharing is caring:
+  * write code
+  * give away/sell product
+    * include **sourcecode**
+    * include the freedom/restriction to do share code under the same license
+> People want to save their idea of moral responsibility by formalising it as a licenses
+==== GNU ====
+{{..:gnu.svg?0x200}}
+> In 1984 RMS starts the **GNU** project, with the goal to provide a **free Unix**-compatible OS
+> Steps to success:
+  * Write a license (GPL)
+    * respect the freedom of the users
+    * endorse ‘sharing is caring’
+    * make the license transitive
+  * Write an Editor (emacs)
+  * Write a Compiler (gcc)
+  * Write common utilities (coreutils)
+  * Write everything else
+  * Write a kernel (hurd)
+  * Rewrite the kernel (hurd)
+  * One more time (hurd)
+> Even though this project gets mocked for hurd, it is essential for Linux’ success!
+==== Linux ====
+{{..:gnu_tux.svg?0x220}}
+> In 1992 Linus Torvalds writes his own little **terminal emulator**, to be able to remotely access his university account.
+> Later this code evolves into the **Linux kernel**, that together with many **GNU utilities** becomes **GNU/Linux** — a.k.a Linux
+^Segment            ^             Linux variant             ^  Market share ([[https://en.wikipedia.org/wiki/Usage_share_of_operating_systems#Market_share_by_category|Source]])^
+|Desktop            |      Debian / Fedora / Arch / …       |                                                                                                                ~2%|
+|Smartphone / Tablet|                Android                |                                                                                                               ~70%|
+|Server             |  Debian / RHEL / Gentoo / … / CUSTOM  |                                                                                                               ~65%|
+|**Supercomputer**  |          **CentOS** / CUSTOM          |                                                                                                               ~99%|
+|Mainframe          |              RHEL / SLES              |                                                                                                               ~30%|
+|Embedded           |              Android / …              |                                                                                                               ~30%|
+==== Linux on Supercomputers ====
+{{..:os_supercomputers.svg}}
+====== Prerequisites ======
+==== Assumptions ====
+> You are familiar with either:
+  * **computers** in general
+  * **Windows**
+  * **macOS**
+> When something breaks, you:
+  * ask for **assistance** //or//
+  * **read** up on the subject and **fix it** //and//
+  * **don’t** go on **using** it until it’s completly **dead**
+==== What do you know about Linux? ====
+> by a show of hands:
+{{..:tux.svg?0x500}}
+  * Nothing
+  * I know my way around when it comes to:
+    * files and directories
+    * the shell basics
+    * most core utilities
+    * variables
+    * scripts
+    * streams
+  * All of the above and I want to take over
+====== Filesystems ======
+==== Filesystem 101 ====
+  - Everything starts at the root
+    * the root is a directory
+    * ''%%/%%'' denotes the root directory
+  - the filesystem has different kinds of objects
+    - files
+    - directories
+      * containers for multiple objects
+    - links to objects, which either
+      * add a second name for the same object
+      * point to a position in the filesystem
+  - objects can be referenced by their path
+    * absolute: ''%%/dir1/dir2/object%%''
+    * relative: ''%%dir2/object%%''
+  - special objects in directories:
+    * ''%%.%%'' — is a reference to the directory itself
+    * ''%%..%%'' — is a reference to the parent directory
+  - the system may consist of multiple filesystems
+    * filesystems may be mounted at any (empty) directory
+==== The Filesystem represented as an ADT ====
+> These are the helper types:
+<code>
+type Name     = String
+type Children = [FSObject]
+type Path     = [FSObject]
+data LinkType = Soft | Hard
+</code>
+> This is the code describing a trivial Linux-ish filesystem in a mathematical notation:
+<code>
+data FSObject = File Name
+              | Dir  Name Children
+              | Link Name Path LinkType
+</code>
+> Missing:
+  * Special files
+    * device
+    * fifo pipe
+    * socket
+  * Attributes
+  * Advanced FS features
+    * data integrity
+    * device managment
+    * subvolume support
+==== FHS intro ====
+{{..:linux_directories.jpg}}
+==== FHS ====
+> The **Filesystem Hierarchy Standard** is a guideline for the structuring of local filesystems.
+It aims for better **interoperability** between different Systems, by making it easy to figure out the **location** of any **kind of file**.
+^Directory  ^Purpose                                                              ^
+|**/**      |root of the hierarchy                                                |
+|**/bin/**  |basic binary files                                                   |
+|**/boot/** |files for boot support                                               |
+|**/dev/**  |virtual files, for direct access to devices                          |
+|**/etc/**  |system-wide confidurations - historical, misleading name             |
+|**/home/** |users’ home direcories are located here                              |
+|**/lib/**  |library files for ''%%/bin/%%'' ''%%/sbin%%''                        |
+|**/media/**|removable media mounts                                               |
+|**/mnt/**  |temporary mounts                                                     |
+|**/opt/**  |optional applications                                                |
+|**/proc/** |system-internals accessable as files                                 |
+|**/root/** |home directory of root                                               |
+|**/run/**  |variable data should be removed while booting                        |
+|**/sbin/** |like ''%%/bin/%%'', but require special permissions                  |
+|**/srv/**  |data served to other systems                                         |
+|**/sys/**  |statistics about devices                                             |
+|**/tmp/**  |temporary files, can be removed while booting                        |
+|**/usr/**  |most higher level applications are inside, looks a lot like ''%%/%%''|
+|**/var/**  |files that change often (cache/db/log/mail/…)                        |
+==== Corner cases of FHS ====
+> Some systems don’t comply with the FHS, for various reasons.
+=== VSC3 ===
+  * As the OS is basically a CentOS, the ''%%/lib/%%'' and ''%%/lib64/%%'' are just symlinks
+=== Distributions bringing new ideas to the table ===
+> [[http://gobolinux.org/|GoboLinux]]:
+  * installed software packages get their own directory
+  * filesystem itself is a package store
+> [[http://nixos.org/|NixOS]]:
+  * solves the problem of user installable packages
+  * dependency management extended in a way, that aims to make trust a non-issue
+====== Shell ======
+==== Login ====
+> The default login screen on most distributions looks something like this:
+<code>
+<<< Welcome to ${DISTRO} - tty{1..6} >>>
+${MACHINE_NAME} login:
+password:
+</code>
+<code>
+username
+<blank while typing>
+</code>
+<HTML>
+<div class="incremental">
+<div>
+<hr style="clear: both;">
+</HTML>
+> remote login looks similar:
+<code bash>
+$ ssh username@remote
+password:
+</code>
+<HTML>
+</div>
+<div>
+<hr style="clear: both;">
+</HTML>
+{{..:tango_locked.svg?0x100}} {{..:tango_unlocked.svg?0x100}}
+<HTML>
+</div>
+</HTML>
+> If the login was not successful, just try again.
+> Beware, that systems may be configured to lock your account if too many attempts were made.
+<HTML>
+</div>
+</HTML>
+==== Prompt ====
+> This is how the prompt looks by default:
+{{..:tango_terminal.svg?0x100}}
+<code bash>
+[myname@l3_ ~]$
+</code>
+  * tells you:
+    * who you are
+    * which computer you’re on
+    * which directory you’re in
+  * can be configured
+    * variable ''%%$PS1%%''
+    * default: ''%%echo $PS1%%''
+> Ways to get help when you’re stuck:
+  * ''%%man%%''
+    * manual for specified topic
+    * find man-pages: ''%%apropos%%''
+  * ''%%whatis%%''
+  * ''%%info%%''
+  * most commands support a ''%%-h%%''/''%%--help%%'' flag
+  * colleagues are often helpful
+  * the internet is often helpful
+==== Execution ====
+To execute a program, we call it:
+<code python>
+nano file.txt
+./a.out -flag=value
+gcc -I/home/lv12345/myuser/include
+module load non-existent-module
+</code>
+  * Every command that is executed will provide a return-value on exit.
+    * {{..:tango_ok.png?0x30}} A value of ''%%0%%'' means success
+    * {{..:tango_cancel.png?0x30}} any other value means failure
+=== Program Arguments ===
+> The default way to apply arguments to a program is to write a space separated list of arguments after the program when calling it.
+> Patterns and expansions are defining multiple arguments with little overhead:
+  * the most important patterns are:
+    * **?** — matches one character
+    * ***** — matches any character sequence
+  * the most important expansions are:
+    * **A{1,9}Z** — expands to A1Z A9Z
+    * **A{1..9}Z** — expands to A1Z A2Z … A9Z
+==== Control Flow ====
+=== Chaining Commands ===
+<code bash>
+false ;  echo "Should I be Printed?"
+false && echo "Should I be Printed?"
+false || echo "Should I be Printed?"
+</code>
+<code bash>
+Should I be Printed?
+Should I be Printed?
+</code>
+=== Loops ===
+<code bash>
+for i in *
+do
+  mv $i{,.bak}
+done
+</code>
+<code bash>
+while true
+do
+  echo "Annoying Hello World"
+  sleep 3
+done
+</code>
+> Or as one-liners:
+<code bash>
+for i in *; do mv $i{,.bak}; done
+while true; do echo "Annoying Hello World"; sleep 3; done
+</code>
+==== Aliases ====
+Whenever you have a command, which you:
+  - run often and it
+    * has a long list of parameters you always use
+    * is dangerous
+  - which is an aggregate of many other commands
+    * but you don’t want to write a script
+you can define an alias for it:
+<code bash>
+alias ll='ls -alh'
+alias myProject='cd $ProjectDir; testSuite; compile && testSuite; cd -'
+</code>
+==== History ====
+{{..:tango_search.svg?0x100}}
+> Your shell keeps a log of all the commands you executed.
+  * the ''%%history%%'' command is used to access this history
+  * for fast reuse of commands try the ''%%<CTRL>-R%%'' keys
+==== Streams ====
+=== Redirects ===
+> Write **output** to a **file** or **file-descriptor**
+^Command^Redirect          ^Append             ^Description                              ^
+|program|''%%>  std.log%%''|''%%>>  std.log%%''|redirect ''%%stdout%%'' to a file        |
+|program|''%%2> err.log%%''|''%%2>> err.log%%''|redirect ''%%stderr%%'' to a file        |
+|program|''%%2>&1%%''      |                   |redirect ''%%stderr%%'' to ''%%stdout%%''|
+=== Pipes ===
+> Write **output** into the **input**-stream of another process
+^Command^Pipe                     ^Description                          ^
+|program|''%%| grep -i foo%%''    |pipe ''%%stdout%%'' into ''%%grep%%''|
+|program|''%%| tee file1 file2%%''|overwrite files and ''%%stdout%%''   |
+|program|''%%| tee -a file%%''    |append to files and ''%%stdout%%''   |
+====== Environment Variables ======
+==== Setting, getting and unsetting ====
+=== Set ===
+<code python>
+LANG=de_AT.UTF-8 firefox
+env LANG=de_AT.UTF-8 firefox
+</code>
+<code python>
+export LANG=de_AT.UTF-8
+</code>
+=== Get ===
+<code python>
+env
+echo ${LANG}
+</code>
+=== Unset ===
+<code python>
+unset LANG
+env -u LANG
+</code>
+==== Use cases ====
+> Some variables that could affect you are:
+<code python>
+$EDITOR            # the default editor for the CLI
+$PAGER             # utility to read long streams
+$PATH              # program paths, in priority order
+</code>
+> if you’re aiming for programming, these could be more interresting:
+<code python>
+$LIBRARY_PATH      # libraries to link by the compiler
+$LD_LIBRARY_PATH   # libraries to link at runtime
+$CC                # sometimes used to set default C compiler
+$CFLAGS            # default flags for compiling C
+</code>
+====== Core Utilities ======
+==== Looking around ====
+> **looking around** is done by the **''%%ls%%''** (list) command
+<code>
+$ ls      # shows files and directories
+$ ls -a   # includes hidden ones
+$ ls -l   # detailed view
+</code>
+<code>
+testdir  test
+.  ..  testdir  test
+drwxr-xr-x 1 myuser p12345 0 Apr 13 11:55 testdir
+-rw-r--r-- 1 myuser p12345 4 Apr 13 11:55 test
+</code>
+{{..:linux_directories.jpg?0x400}}
+^command               ^                                  result^
+|**''%%ls /%%''**      |  ''%%bin  dev  etc  home  sbin  usr%%''|
+|**''%%ls /home%%''**  |                    ''%%user1  user2%%''|
+==== Moving around ====
+> **moving around** is done by the **''%%cd%%''** (change directory) command
+> **finding** the current **position** in the filesystem is done by the **''%%pwd%%''** (print working directory) command
+<code>
+$ cd /bin   # go to an absolute directory
+$ cd [~]    # go home
+$ cd -      # go to previous directory
+</code>
+<code>
+$ pwd   # /bin
+$ pwd   # /home/user1
+$ pwd   # /bin
+</code>
+{{..:linux_directories.jpg?0x400}}
+==== Copying & moving files around ====
+> **moving files around** is done by the **''%%mv%%''** (move) command
+> **copying** is done by the **''%%cp%%''** (copy) command
+<code>
+$ mv old   new     # rename old to new
+$ mv old   dir/    # move old into dir
+$ mv file1 file2   # overwrite file2 with file1
+                   # (BEWARE)
+</code>
+<code>
+$ cp -i input input.bak   # input to input.bak
+$ cp -i input backup/     # input into backup
+$ cp -a dir1/ dir2        # exact copy of dir1
+</code>
+{{..:screenshot_mv.png?0x350}} {{..:screenshot_cp.png?0x350}}
+==== Finding stuff ====
+> To look at everything
+  - in your home directory
+  - and nested up to three levels deep inside it
+  - that ends in ''%%.txt%%''
+  - or starts with ''%%log_%%''
+  - and is an ordinary file
+  - concatenated as one stream:
+<code bash>
+find \
+  ~ \
+  -maxdepth 3 \
+  -iname "*.txt" \
+  -or -iname "log_*" \
+  -type f \
+  -exec cat '{}' \; | less
+</code>
+<code bash>
+find \
+  ~ \
+  -maxdepth 3 \
+  -iname "*.txt" \
+  -or -iname "log_*" \
+  -type f \
+  -exec cat '{}' +  | less
+</code>
+==== Creating and deleting ====
+=== directories ===
+> **creating directories** is done by the **''%%mkdir%%''** (make directory) command:
+> **deleting directories** is done by the **''%%rmdir%%''** (remove directory) command:
+<code bash>
+$ mkdir newdir       # create directory newdir
+$ mkdir -p new/dir   # create dir inside of new
+</code>
+<code>
+$ rmdir emptydir      # removes emptydir
+$ rmdir -v emptydir   # removes emptydir (verbose)
+</code>
+=== files ===
+> **creating files** is done by the **''%%touch%%''** or **''%%echo%%''** commands:
+> **deleting files** is done by the **''%%rm%%''** (remove) command:
+<code bash>
+$ touch file          # create empty file
+$ echo "abc" > file   # create/overwrite file
+</code>
+<code>
+$ rm file      # removes file
+$ rm -ri dir   # removes dir recursively
+</code>
+==== Contents of files ====
+> **viewing** is done by the **''%%less%%''** command:
+> **concatenating** is done by the **''%%cat%%''** command:
+<code>
+$ less file.txt      # exit with 'q'
+$ less -R file.txt   # keep colors
+$ cat file1 file2 | less
+</code>
+<code>
+$ cat file
+$ cat -A printable
+$ cat -n numbered
+</code>
+<code>
+$ echo "VSC is great" > file
+$ cat file
+VSC is great
+</code>
+<code>
+$ echo "VSC is awesome" >> file
+$ cat file
+VSC is great
+VSC is awesome
+</code>
+<code>
+$ cat file | grep awesome
+VSC is awesome
+</code>
+<code>
+$ grep awesome file
+VSC is awesome
+</code>
+==== Space accounting ====
+> viewing **used space** is done by the **''%%du%%''** (disk usage) command:
+> viewing **free space** is done by the **''%%df%%''** (disk free) command:
+<code>
+$ du -h file1 file2   # human readable output
+$ du -s dir           # summarize
+</code>
+<code>
+$ df -h       # human readable output
+$ df -t nfs   # only list filesystems of a type
+</code>
+{{..:screenshot_df.png?0x440}}
+==== Recap ====
+<code>
+$ mv space.log space.log.bak
+</code>
+<code>
+$ df -h | grep "lv12345\|lv54321" > space.log
+</code>
+<code>
+$ cat space.log
+</code>
+<code>
+nfs05.ib.cluster:/e/lv12345    200G  185G   16G  93% /home/lv12345
+nfs04.ib.cluster:/e/lv54321   1000G  979G   22G  98% /home/lv54321
+</code>
+> we do this often, let’s wrap it up!
+==== Recap++ ====
+<code>
+$ mv space.log space.log.bak
+</code>
+<code>
+$ df -h | grep "lv12345\|lv54321" > space.log
+</code>
+<code>
+$ cat space.log
+</code>
+<code>
+nfs05.ib.cluster:/e/lv12345    200G  185G   16G  93% /home/lv12345
+nfs04.ib.cluster:/e/lv54321   1000G  979G   22G  98% /home/lv54321
+</code>
+> we do this often, let’s wrap it up!
+<code>
+$ echo '#!/bin/bash' > spacelog.sh
+$ echo 'mv space.log space.log.bak' >> spacelog.sh
+$ echo 'df -h | grep "lv12345\|lv54321" > space.log' >> spacelog.sh
+$ echo 'cat space.log' >> spacelog.sh
+</code>
+<code>
+$ chmod +x spacelog.sh
+</code>
+<code>
+$ ./spacelog.sh
+</code>
+==== Sed and awk ====
+> **sed** (stream editor) and **awk** are powerful tools when working with the command line
+<code>
+$ mycommand | sed "..."
+</code>
+<code>
+$ mycommand | awk '{...}'
+</code>
+> Using sed and awk in action
+^program  ^             command              ^description                                                                ^
+|sed      |        ''%%s/old/new/%%''        |replace ''%%old%%'' with ''%%new%%''                                       |
+|sed      |  ''%%/from/,/to/ s/old/new/%%''  |replace ''%%old%%'' with ''%%new%%'', between ''%%from%%'' and ''%%to%%''  |
+|awk      |      ''%%'print $5, $3'%%''      |print columns 5 and 3 of every line                                        |
+Example script:
+<code bash>
+#!/bin/bash
+mv space.log space.log.bak
+df -h | grep "lv12345\|lv54321" > space.log
+cat space.log
+</code>
+<code bash>
+#!/bin/bash
+mv space.log space.log.bak
+df -h | grep "lv12345\|lv54321" > space.log
+cat space.log | sed "s|/home/lv12345|ProjectA|" \
+              | awk '{print $6, "free:", $4}' \
+              | column -t
+</code>
+====== Scripting ======
+==== Ownership and Permissions ====
+> Just to ensure, that you are able to run your scripts
+=== chown ===
+> Change the owner of files and directories by:
+<code bash>
+chown -R user:group dirs files
+</code>
+=== chmod ===
+> Change the mode of files and directories by:
+<code bash>
+chmod -R u=rw,g+w,o-rwx dirs files
+chmod -R 644            dirs files
+</code>
+==== Shebang ====
+A little test program, which we mark as executable and hand it over to the corresponding interpreter:
+<code bash>
+cat << EOF > test.sh
+echo "${LANG}"
+echo "${PATH}"
+EOF
+</code>
+<code bash>
+chmod +x test.sh
+</code>
+<code bash>
+bash test.sh
+</code>
+> Don’t we have an OS, capable of executing everything it recognises as a executable?
+> Yes, we do!
+<code bash>
+cat << EOF > test.sh
+#!/bin/bash
+echo "${LANG}"
+echo "${PATH}"
+EOF
+</code>
+<code bash>
+chmod +x test.sh
+</code>
+<code bash>
+./test.sh
+</code>
+==== Functions (more like Procedures) ====
+Programming in bash would be cumbersome without functions, so here we go:
+<code bash>
+printAllNumbers () {
+echo "1 2 3"
+echo "done"
+}
+</code>
+=== Arguments ===
+> This isn’t good, as were only getting a fixed amount of numbers. let’s try a recursive approach
+<code bash>
+#!/bin/bash
+printAllNumbersFrom () {
+num=$1
+echo "${num}"
+printAllNumbersFrom "$(($num + 1))"
+}
+printAllNumbersFrom $2
+</code>
+====== Editors ======
+==== General ====
+  * Many different editors
+    * Unique (dis-)advantages
+    * Different look and feel
+  * Editors should provide us with
+    - Simple text editing
+    - Copy and paste
+    - Search and replace
+    - Saving changes
+    - Wide availability
+=== Two editors that satisfy our needs: ===
+  * nano
+  * vim
+=== Common starting point ===
+<code bash>
+nano filename
+</code>
+<code bash>
+vim filename
+</code>
+==== Nano ====
+{{..:screenshot_nano.png}}
+==== Nano explained ====
+> This editor is focused on being easy to use, but still providing every feature a user might need.
+=== Interface ===
+> The interface consists of four parts, namely from top to bottom:
+  * Title bar
+  * Text area
+  * Command line
+  * Key bindings
+=== Usage ===
+> Nothing special, key-bindings visible while editing
+^Feature       ^                 Usage                 ^
+|Navigation    |              Arrow keys               |
+|Actual editing|         Typing text, as usual         |
+|Cut/Paste line|  ''%%<CTRL>%%''+k / ''%%<CTRL>%%''+u  |
+|…             |    explained in key bindings field    |
+=== Short ===
+> Use this editor if you are new to the command line.\\
+> It is straight forward, but can be extended on the way.
+  * Auto-indentation
+  * Syntax highlighting
+  * Multi-buffer
+{{..:screenshot_nano.png?0x300}}
+==== Vi(m) ====
+{{..:screenshot_vim.png}}
+==== Vi(m) explained ====
+> This editor is focused on productivity and efficiency, providing everything a user might need.
+=== Interface ===
+> The simple interface consists of two parts:
+  * Text area
+  * Command line
+> Since this editor is very easy to extend, after setting up a few plugins, it will probably look quite different!
+=== Usage ===
+> This is a multimode editor, you’ll have to switch modes whenever you change what you want to do.
+^Feature   ^                    Usage                    ^
+|Navigation|              hjkl / Arrow keys              |
+|Writing   |  change to input mode, then write as usual  |
+|Commands  |     exit current mode, press ''%%:%%''      |
+|…         |           explained on next slide           |
+=== Short ===
+> Use this editor if you like a challenge.\\
+> It is fast and very nice — but you’ll sometimes get hurt on the way.
+  * Auto-indentation, Syntax highlighting, Multi-buffer – just like nano
+  * File/Project Management
+  * Use a plugin manager
+{{..:screenshot_vim.png?0x300}}
+==== Vi(m) modes and keys ====
+  * any mode:
+    * back to the **default mode**: **''%%<ESC>%%''**
+  * command mode (followed by ''%%<RETURN>%%''):
+    * **save** current file: **''%%w [filename]%%''**
+    * **quit** the editor
+      * after saving: **''%%q%%''**
+      * without confirmation: **''%%q!%%''**
+    * **help**: **''%%h [topic]%%''**, e.g. **''%%h tutorial%%''**
+    * **search and replace**: **''%%%s/old/new/gc%%''**
+  * //default mode//:
+    * enter **input mode**: **''%%i%%''**
+    * enter **command mode**: **''%%:%%''** //(colon)//
+    * **mark**
+      * **character**-wise: **''%%v%%''**
+      * **line**-wise: **''%%<SHIFT>-v%%''**
+    * **delete**
+      * **character**-wise: **''%%x%%''**
+      * **line**-wise: **''%%dd%%''**
+      * **marked content**: **''%%d%%''**
+    * **search**: **''%%/abc%%''**
+====== QED ======
+==== Fin ====
+{{..:tux_banner.png?0x600}}
+  * Questions?
+  * Need help installing Linux?
+  * Contact: <Email>
+<HTML>
+<!--
+> Public domain:
+- [Ubuntu Tango Icons](https://wiki.ubuntuusers.de/Wiki/Icons/Tango/)
+> Mixed (CC, public domain, ...)
+- [Wikipedia Tango Icons](https://commons.wikimedia.org/wiki/Tango_icons)
+# Timers
+## Systemd Units
+## Systemd Timers
+## Putting it together
+## Background
+### What is GNU/Linux {.incremental}
+![](pictures/gnu.svg){height=200px style="float: left;" .incremental}
+<div class="columns">
+> - It's a collection of Software, including:
+>     - **Linux** itself, as the `kernel`
+>     - basic tools, mostly from the **GNU** project
+>     - additional, specialised software for most tasks
+> - the **OS** that powers the internet, the mobile world and more
+> - **opensource** and **free software** effort to retain essential freedoms of the user
+</div>
+### Reasons for Linux {.incremental}
+![](pictures/tux.svg){height=200px style="float: right;".incremental}
+<div class="columns">
+> - Wide Adoption
+> - Stable platform
+> - Anyone can try and use Linux
+> - Easy adaption to custom environments
+</div>
+### Basic Usage {.incremental}
+![](https://upload.wikimedia.org/wikipedia/commons/6/66/Utilities-terminal.svg){height=200px style="float: left;" .incremental}
+<div class="columns">
+> - using and understanding the shell
+> - moving through the directory structure
+> - moving files and directories
+> - editing files
+> - writing and executing scripts
+> - environment and variables
+</div>
+## CLI Basics
+<div class="columns">
+### Shell
+> The shell used on the VSC is called **bash**. It's the most common shell today, preinstalled by most Linux and macOS versions.
+> - It's behaviour is controlled by the file **.bashrc**
+>     - loaded at login
+>     - can be customized
+>     - is a shell script
+> - Has some usability features
+>     - most of the time commands can be auto-completed by pressing `TAB`
+>     - can recall history with `CTRL-R` or `history`
+> - Provides a full programming language/environment
+>     - can do native processing of Strings, Integers and Arrays
+>     - can execute any program
+>     - is turing-complete, but not considered a general-purpose language
+### Environment
+> The shell and some default tools are configured through **variables**.
+> - list variables with `env`
+> - modify them with `export X=Y`
+> - get the content by prepending it with a dollar sign `$A`
+> - useful in scripts
+<div class="incremental">
+Some variables that could affect you are:
+```
+$EDITOR # the default editor for the CLI
+$PAGER  # utility to read long streams
+$PATH   # program paths, in priority order
+```
+</div>
+</div>
+## Executing Commands
+<div class="columns">
+<div class="incremental">
+To execute a program, we call it:
+```{.bash}
+nano file.txt
+./a.out -flag=value
+gcc -I/home/lv12345/myuser/include
+module load non-existent-module
+```
+</div>
+> - Every command that is executed will provide a return-value on exit.
+>     - ![](https://media-cdn.ubuntu-de.org/wiki/attachments/21/07/dialog-ok.png){height=30px} A value of `0` means success
+>     - ![](https://media-cdn.ubuntu-de.org/wiki/attachments/39/07/dialog-cancel.png){height=30px} any other value means failure
+</div>
+### Program Arguments {.incremental}
+<div class="incremental">
+> The default way to apply arguments to a program is to write a space separated list of arguments after the program when calling it.
+> Patterns and expansions are defining multiple arguments with little overhead:
+</div>
+<div class="columns">
+> - the most important patterns are:
+>     - **?** --- matches one character
+>     - **\*** --- matches any character sequence
+> - the most important expansions are:
+>     - **A{1,2}Z**  --- expands to A1Z A2Z
+>     - **1{a..z}A**     --- expands to 1aA 1bA ... 1zA
+</div>
+### Chaining Commands {.incremental}
+<div class="columns incremental">
+``` {.bash .numberLines}
+false ;  echo "Should I be Printed?"
+false && echo "Should I be Printed?"
+false || echo "Should I be Printed?"
+```
+``` {.bash .numberLines}
+Should I be Printed?
+Should I be Printed?
+```
+</div>
+<!--
+- - -
+### Using Patterns and Expansions {.incremental}
+<div class="columns">
+> - the most important patterns are:
+>     - **?** --- matches one character
+>     - **\*** --- matches any character sequence
+> - the most important expansions are:
+>     - **A{1,2}Z**  --- expands to A1Z A2Z
+>     - **1{a..z}A**     --- expands to 1aA 1bA ... 1zA
+</div>
+-->
+<!--
+## Loops
+> look like this in a shell:
+<div class="columns incremental">
+```{.bash}
+for i in *
+do
+  mv $i{,.bak}
+done
+```
+```{.bash}
+while true
+do
+  echo "Annoying Hello World"
+  sleep 3
+done
+```
+</div>
+#### Generating parameters in bash {.incremental}
+<div class="columns incremental">
+```{.bash}
+i=1
+while [ $i -lt 10 ]
+do
+  j=1
+  while [ $j -le $i ]
+  do
+    echo "$i $j" # Your command comes here
+    let j+=1
+  done
+  let i+=1
+done
+unset i j
+```
+```{.bash}
+1
+1
+2
+1
+2
+3
+...
+6
+7
+8
+9
+```
+</div>
+## Getting familiar with the CLI
+<div class="columns">
+> This is how the prompt looks by default:
+``` {.bash}
+[myname@l3_ ~]$
+```
+![](src/Screenshot_vsc3_login.png){height=190px .incremental}
+![](src/Screenshot_vsc3_login_prompt.png){height=190px .incremental}
+![](src/Screenshot_vsc3_login_prompt2.png){height=190px .incremental}
+</div>
+<div style="float: left">
+#### Prompt {.incremental}
+> - it's "promting" you to enter a command
+> - tells you:
+>     - who you are
+>     - which computer you're on
+>     - which directory you're in
+> - can be configured to show more information
+>     - setting is in a variable called `PS1`
+>     - default value of `$PS1`: `[\u@\h \w]\$`
+>     - can add date, time and the output of custom commands
+> - see `man bash` for details about your shell
+</div>
+<div style="float: right" class="incremental">
+#### In case of confusion
+> there are many ways of getting further:
+> - the `man` command
+>     - opens the manual for a specified topic
+>     - especially nice to find man-pages: `apropos`
+> - the `whatis` command
+> - the `info` command
+>     - is more complex and more like a browser
+> - most commands support a `-h`/`--help` flag
+> - colleagues are often helpful
+> - the internet is often helpful
+</div>
+<div style="float: left" class="incremental">
+![`apropos help`](src/Screenshot_vsc3_apropos.png){width=270px .incremental}
+</div>
+## Shell - More than a prompt
+### Simple Input/Output
+<div class="columns incremental">
+Any program running in the shell can by default read from the keyboard and write to the screen.
+We try this with the `cat` command, which is short for concatenate.
+```{.bash}
+cat
+some text   # Input
+some text   # Output
+<CTRL>-d
+```
+</div>
+### Piping Input/Output
+<div class="columns incremental">
+Since echoing input back to the user isn't particularly useful, we'll be echoing back filtered output.
+We add a pipe, which redirects the output of the command before it to the command following it, and filter for any line containing `VSC`.
+```{.bash}
+cat | grep VSC
+  2  3   # Input, no Output
+VSC 3   # Input
+VSC 3   # Output
+<CTRL>-d
+```
+</div>
+### Redirecting Input/Output
+<div class="columns incremental">
+Now we can write the resulting stream into a file called VSC.txt.
+This is done by adding a greater-sign between the end of the command and the filename of the resulting document.
+```{.bash}
+cat | grep VSC > VSC.txt
+  2  3   # Will not be in VSC.txt
+VSC 3   # Will be in VSC.txt
+<CTRL>-d
+```
+<!--
+```{.bash}
+cat VSC.txt
+VSC 3
+```
+-->
+<!--
+</div>
+## Cool Tools
+### Less is More
+<div class="columns">
+Since piping output is awesome we want to have a program, that can handle all the output of the other programs and present it in screen-sized parts.
+Hence the program `less`, which is just `more`.
+```{.bash}
+find ~ -iname "*.txt" -type f -exec cat '{}' \; | less
+```
+</div>
+### Permissions
+<div class="columns">
+If some file can't be accessed/modified, there is a chance that you haven't got the rights to do so.
+For these cases there is the tool `chmod`, which changes the mode of a file.
+```{.bash}
+chmod a=w file
+chmod u+x file
+chmod g-w file
+chmod o=r file
+```
+</div>
+### Aliasing commands
+<div class="columns">
+you should define an `alias`, whenever there is a command which:
+- is run with parameters which don't change between runs
+- has some hard to remember name
+- needs a non-default safeguard
+```{.bash}
+alias f='find ~ -type f -iname'
+alias rm='rm -i'
+alias def-env='cd ~/projectA && \
+               module purge && \
+               module load x/1 y/2 z/3'
+```
+</div>
+## Filesystem 101
+<div class="columns">
+> 1. Everything starts at the root
+>     - the root is a directory
+>     - `/` denotes the root directory
+> 2. the filesystem has different kinds of objects
+>     1. files
+>     2. directories
+>         - containers for multiple objects
+>     3. links to objects, which either
+>         - add a second name for the same object
+>         - point to a position in the filesystem
+> 3. objects can be referenced by their path
+>     - absolute: `/dir1/dir2/object`
+>     - relative: `dir2/object`
+> 4. special objects in directories:
+>     - `.` --- is a reference to the directory itself
+>     - `..` --- is a reference to the parent directory
+</div>
+##### The Filesystem represented as an ADT {.incremental}
+<div class="incremental columns">
+> These are the helper types:
+```{.haskell}
+type Name     = String
+type Children = [FSObject]
+type Path     = [FSObject]
+data LinkType = Soft | Hard
+```
+> This is the code describing the trivial Linux-ish filesystem in a mathematical notation:
+```{.haskell}
+data FSObject = File Name
+              | Dir  Name Children
+              | Link Name Path LinkType
+```
+</div>
+- - -
+### Getting and Manipulating our position in the FS
+<div class="columns">
+> - `'ls'`: short for `'list'`
+> - `'tree'`: tree view of files and directories
+> - `'pwd'`: short for `'print work directory'`
+> - `'cd'`: short for `'change directory'`
+</div>
+<div class="incremental">
+> Example for **looking around**:
+<div class="columns incremental">
+```
+$ ls          # shows files and directories
+$ ls -a       # includes hidden ones
+$ ls -l       # detailed view
+```
+```
+testdir  testfile
+.  ..  testdir  testfile
+drwxr-xr-x 1 myuser p12345 0 Apr 13 11:55 testdir
+-rw-r--r-- 1 myuser p12345 4 Apr 13 11:55 testfile
+```
+</div>
+</div>
+<div class="incremental">
+> Example for **moving around**, starting at the home directory:
+</div>
+<div class="columns incremental">
+```
+$ pwd
+$ cd ..; pwd
+$ cd /global; pwd
+$ cd; pwd
+$ cd -; pwd
+```
+```
+/home/lv12345/myname
+/home/lv12345
+/global
+/home/lv12345/myname
+/global
+```
+</div>
+- - -
+### Moving files and directories
+<div class="columns">
+> - `'mv'`: short for `'move'`
+> - `'cp'`: short for `'copy'`
+</div>
+<div class="incremental">
+> Example:
+<div class="columns">
+```
+$ cp file.orig file.copy
+$ mv file.orig file.copy
+$ cp file.orig dir
+$ mv file.orig dir
+$ cp dir1 dir2    # ERROR
+$ cp -r dir1 dir2 # WORKS
+$ mv dir1 dir2    # WORKS
+```
+> - copying or moving directories can result in unexpected behaviour:
+>     - if dir2 is an existing directory, dir1 will become a subdirectory of dir2
+>     - if dir2 is non-existent, dir1 will become dir2
+</div>
+<div class="columns">
+##### Transfer to/from Cluster
+> - `'scp'`: short for `'secure copy'`
+>     - arguments can be either local or remote files and direcotries
+> - `'rsync'`: short for `'remote syncronization'`
+>     - similar to regular `mv`/`cp`/`scp`, except:
+>         - pedantic about trailing slashes
+>         - can merge directories
+>         - can delete/overwrite changed files
+</div>
+`rsync` seems easy to use, but the advanced options could remove data from both sides of your transfer! It's a **syncronazation** utility, no simple move/copy tool
+</div>
+<!--
+- - -
+##### SCP
+```
+$ cp file.orig file.new
+$ scp user@host:dir/file.orig file.new
+$ scp file.orig user@host:dir/file.new
+```
+- this is easy to use and preferable for little, one time transfers
+[ID1]: src/tux.svg "Hover Text 1" {height=150px style="margin: 10px;"}
+[ID2]: src/tux.svg "Hover Text 2"
+- ![Test][ID1]
+- ![Test](src/tux.svg "Hover Text 1"){height=150px style="margin: 10px;"}
+- [<font color=#cc3300>&#x27A0;</font>][ID2]
+- - -
+##### RSYNC
+```
+$ rsync dir1 dir2        # Local copy
+$ rsync -e ssh dir1 dir2 # Remote copy
+# These two have the same result:
+$ rsync dir1  dir2
+$ rsync dir1/ dir2/dir1
+# This doesn't:
+$ rsync dir1/ dir2
+```
+- there are many useful options, like:
+    - `-a` $\rightarrow$ Archive mode, usually you want this
+    - `-v` $\rightarrow$ Verbose mode
+    - `-p` $\rightarrow$ Preserve permissions
+    - `...` $\rightarrow$ RTFM or don't use those options
+- the `-e ssh` option tells rsync to connect via ssh to the remote machine
+    - in this case the remote location is written like this:
+         - user@host:remoteDir
+- trailing slashes have an effect on where your files will go
+-->
+<!--
+## Copyleft
+Third party content and its licensing information can be found at:
+- [Levitating Gnu](https://www.gnu.org/graphics/meditate.html):
+    - María del Pilar Saenz: [GFDL](https://www.gnu.org/copyleft/fdl.html)
+- [Tux](https://pixabay.com/en/tux-penguin-animal-cute-linux-158547/):
+    - [CC0 Public Domain](https://creativecommons.org/publicdomain/zero/1.0/deed.en)
+- [Tux and Gnu](https://commons.wikimedia.org/wiki/File:GNU_and_Tux.svg):
+    - Aurelio A. Heckert: [Free Art License](http://artlibre.org/licence/lal/en/)
+    - Larry Ewing, Simon Budig and Anja Gerwinski: probably [CC-BY](https://creativecommons.org/licenses/by/4.0/)
+- [Tango Icons](https://commons.wikimedia.org/wiki/Tango_icons ):
+    - Public Domain
+## Copyright
+The not explicitly licensed or non freely-redistributable licensed stuff:
+- [the Good, the Bad & the Ugly](http://cinetropolis.net/wp-content/uploads/2013/10/the-good-the-bad-and-the-ugly-t-anderson-banner.jpg):
+    - [Dunno]()
+## TestStuff
+😁 $\rightarrow$ 😄
+😁 $\Rightarrow$ 😄
+😁 $\longrightarrow$ 😄
+😁 $\Longrightarrow$ 😄
+https://apps.timwhitlock.info/emoji/tables/unicode#emoji-modal
+[//]:#(Das ist ein Kommentar, dass nirgends aufscheint)
+[TuxAndGnu]: https://upload.wikimedia.org/wikipedia/commons/5/53/GNU_and_Tux.svg "Tux and Gnu"
+[VSC]: https://vsc.ac.at "Vienna Scientific Cluster"
+## ToDo
+- nano/vi
+- df -h .
+- du -sh ./*
+- cat | sort | uniq | tr | awk | sed
+- example
+## table
+head1 | head2 | head3
+:-----|:-----:|-----:
+p1 | e11 | e12
+p1 | e11 | e12e12
+p1 | e12e12e12e12e12 | e12
+head1 | head2 | head3
+:-----|:-----:|-----:
+p1 | e11 | e12
+p1 | e11 | e12e12
+p1 | e12e12e12e12e12 | e12
+-->
+</HTML>