Skip to content

Latest commit

 

History

History
162 lines (133 loc) · 5.1 KB

2-operating-systems-and-linux-basics.md

File metadata and controls

162 lines (133 loc) · 5.1 KB
Raw

2 - Operating Systems & Linux Basics

Virtualization & Virtual Machines

You need a hypervisor to run multiple virtual machines using a physical Host OS Most popular hypervisor is VirtualBox (Used this in the past but sinds I switched to M1 I needed to use UTM because VirtualBox does not support M1 ) VMs are isolated Type 2 vs Type 1 Hypervisor: Type 1 installed directly on hardware for servers, Type 2 uses host OS on personal computer

  • Benefits Type 2: learn & experiment, don’t endanger main OS, test app on different OS
  • Benefits Type 1: efficient usage of hardware resources, abstraction of OS from hardware via VMI (Virtual Machine Image) with backups/snaphots

Linux File System

Everything in Linux is a file(In MAC / Windows it is not the case) A root user has its own home directory. This directory can be different in different oses (In MAC it is /Users/username)

Linux folder structure

  • /home/{Username} dir of non-root users (If the user is created with a home directory)
  • /bin executables for essential system cmd
  • /sbin system binaries, need super user privileges to execute
  • /lib shared lib that execs from /bin or /sbin use
  • /usr was used for user home dir (histroic reasons due to storage limitations)
  • /usr/local programs that YOU install on computer (3rd party apps) available for all users
  • /opt 3rd party programs you install that DONT split its components
  • /boot files required for booting
  • /etc system config
  • /dev device files (webcam, mouse, keyboard etc)
  • /var stores logs
  • /var/cache
  • /tmp temporary resources required for processes
  • /media removable media
  • /mnt temporary mount points

Hidden files (starts with a dot)

Commands

  • pwd = show current dir
  • ls = list contents
  • cd = change dir (cd / = change to root dir and empty cd is go to home)
  • mkdir = make dir
  • touch = create file
  • rm = delete file
  • rm -r = delete non-empty dir with files in it
  • rmdir = delete empty dir
  • clear = clears terminal
  • mv = rename file to new name
  • cp -r = copy contents folder to new folder
  • ls -R = list all folders and files in each
  • history = lists all recent cmd in terminal
  • ls -a = display hidden files
  • ls -l = print files in long list format (ls -la for listing hidden files)
  • cat = show contents file
  • uname -a = show system & kernel
  • cat /etc/os-release = show release version
  • lscpu = cpu info
  • lsmem = memory info
  • sudo = grants super user privileges for cmd
  • su - = become user
  • | = pipe, passes output of one cmd as input of next cmd
  • | less = displays reader friendly format for info in CLI
  • | grep = filter input based on pattern search

  • = redirect, takes output from previous cmd and sends it to file that you give (overrides contents file)

  • = appends text to end of file

  • Can pass multiple cmd in one line separated by ;

Package manager: APT

Resolves dependencies for installing software Ensure integrity & authenticity of package Downloads, installs or updates existing software from repo Knows where to put all files in system

apt search <package name> apt install <package name> apt remove <package name> apt update apt upgrade apt autoremove apt full-upgrade

VIM text editor

  • :wq = quit and save
  • :q! = quit without saving
  • dd = delete line
  • d10d = delete next 10 lines
  • u = undo
  • A = jump to end of line, switch insert mode
  • $ = jump to end line, without switch insert mode
  • 0 = jump to beginning of line
  • 12G = jump to line 12
  • /pattern = search for pattern
  • n = jump to next match
  • N = jump to previous match
  • :%s/old/new = replace old with new throughout file

Users, Groups & Permissions

3 user categories:

  • Root user
  • Regular user
  • Service user (best practice for security) (no login shell) These users can be used for nexus or docker as an example

Can group users and define group permissions Users can have multiple groups

Commands

  • adduser
  • passwd
  • su -
  • su - switch root user
  • groupadd
  • deluser
  • groupdel >groupname>
  • usermod [OPTIONS]
  • usermod -g
  • usermod -G (overrides secondary groups list)
  • usermod -aG (appends to existing list)
  • gpasswd -d
  • groups (lists users groups)
  • exit (logout user)
  • chown : (change file ownership)
  • chgrp

Permissions

(owner)

  • r = read
  • w = write
  • x = execute
  • -= No permission

(group)

  • r = read
  • w = write
  • x = execute
  • -= No permission

(other)

  • r = read
  • w = write
  • x = execute
  • -= No permission
Chmod
  • chmod -x (remove execute permissions for all owners)
  • chmod g-w (remove write permissions for group)
  • chmod g+x (add execute permissions for group)
  • chmod u+x (add execute permission for user)
  • chmod o+x (add execute permission for others)
  • chmod g=rwx (sets specific block permissions for group)
  • chmod 777 (gives all permission to all owners)