From be1b7c1d54d45de64130a0db5f719bde5ea3b869 Mon Sep 17 00:00:00 2001
From: arian <arian@arian.li>
Date: Fri, 9 Feb 2024 17:53:52 +0100
Subject: [PATCH] added M305

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+title = 'Linux'
+date = 2024-02-08T21:38:20+01:00
+draft = true
++++
+
+{{< toc >}}
+
+# Notes and source
+Notes based on: <https://geek-university.com/course/free-linux-course/> (as of 2020)
+
+**This page is the only English one, as it's the only learning resource we used that is not in German!**
+
+# Important directories
+- `/boot`   -> boot files
+- `/bin`    -> pre-installed executables
+- `/dev`    -> devices (i.e. hard drive, etc.)
+- `/sbin`   -> pre-installed executables that require root
+- `/etc`    -> configuration
+- `/home`   -> user data
+- `/lib`    -> shared libraries
+- `/media`  -> removable media
+- `/usr`    -> shared data (i.e. wallpapers, fonts, applications, etc.)
+- `/var`    -> variable data (i.e. logs, etc.)
+- `/tmp`    -> temporary data (gets wiped at boot)
+
+# How to install Linux
+- Go to official website
+- Download ISO
+- Flash USB-Drive
+- Boot into ISO (boot order or one-time boot menu)
+- Install
+
+# Shell
+- Interprets commands
+- Run via terminal emulator
+- Examples:
+  - bash
+  - zsh
+  - korn shell (ksh)
+
+# Bash
+- Standard shell on most systems
+- "Bourne Again SHell"
+
+# Links
+- Soft / hard links
+- Soft link = symlink
+- Symlink = points to file or directory
+- Hard link = points to inode (place on hd/ssd)
+- `ln`
+
+
+# Wildcards
+- `?`     -> any single character
+- `*`     -> any string of any length
+- `[ ]`   -> any single character mentioned in the brackets
+
+# Streams
+- 3 streams
+- Standard input (STDIN)
+- Standard output (STDOUT)
+- Standard error (STDERR)
+
+# Redirection
+| Symbol | Redirects to / from                                   |
+|--------|-------------------------------------------------------|
+| >      | redirect stdout to file (create/overwrite)            |
+| >>     | redirect stdout to file (create/append)               |
+| 2>     | redirect stderr to file (create/overwrite)            |
+| &>     | redirect stdout and stderr to file (create/overwrite) |
+| <      | redirect file to stdin (create/overwrite)             |
+| <<     | redirect file to stdin (create/append)                |
+
+# Piping
+`command1 | command2`
+
+- output of command1 used as stdin for command2
+
+# Some noteworthy commands
+## Sort
+`sort file.txt`
+
+Sorts files alphabetically. See `man sort` for more info
+
+## Find
+`find [path] [expression]`
+
+Searches directories and sub-directories for files. See `man find` for more info
+
+## Locate
+`locate [pattern]`
+
+Searches for files (less complicated than find). See `man locate` for more info
+ 
+## Word count
+`cat file | wc`
+
+Counts words, lines, etc in files. See `man wc` for more info
+
+## File
+`file file.extension`
+
+Takes an "educated guess", what type of file `file.extension` is
+
+## Head / Tail
+`cat file | head` and `cat file / tail`
+
+Show only a select number of lines, starting at the top (head) or at the bottom (tail)
+
+See `man head` and `man tail` for more info
+
+## Tar
+Is used to compress/extract folders and files. See `man tar` for more info
+
+# Processes
+## Interfacing with processes
+- ps
+- htop
+- kill
+- killall
+
+## Signals
+Signals are sent to processes to "tell" them what to do. Most important signals:
+
+| Signal  | Description                           |
+|---------|---------------------------------------|
+| SIGKILL | forcefully stop process               |
+| SIGTERM | stop process and associated processes |
+| SIGSTOP | pause process                         |
+| SIGCONT | continue process                      |
+
+# Installing applications
+- Depends on distro
+
+| Distro | Package command |
+|--------|-----------------|
+| Debian | apt             |
+| RedHat | yum             |
+| Arch   | pacman          |
+| Gentoo | emerge          |
+
+# User management
+Commands: `usermod`, `groupmod`
+
+## /etc/passwd
+`username:password:UID:GID:comment:homedir:login shell`
+
+# Permissions
+- 3 permissions
+    - `r`   -> read
+    - `w`   -> write
+    - `x`   -> execute
+- 3 classes
+    - Owner
+    - Group
+    - Rest
+
+Arranged like this:
+```
+| owner     | group     | other     |
+| r | w | x | r | w | x | r | w | x |
+```
+
+# File systems
+Handles the way that data is stored. Linux is compatible with a lot of them:
+
+- ext4 (deprecated: ext3 / ext2 / ext)
+- BtrFS
+- ReiserFS
+- XFS
+- ZFS
+- FAT