Linux

Notes and source

Notes based on: https://geek-university.com/linux-online-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

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:

Installing applications

• Depends on distro

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