/linux-basics

Linux Basics

Below is a list of topics and skills a person should have to be minimally comfortable working with linux. If you understand all of the topics below, you should be able to login and navigate the system.

Linux distros

- linux is very modular, you can swap out nearly any part of the system with some alternative
- The one component you cant swap is the kernel, all linux distros use the linux kernel
- There are operating systems with different kernels such as Unix, BSD, MacOS and others might use some of the same components as linux, but they arent linux because they dont use the linux kernel.
- there are thousands of linux distros with different combinations of major components.
- some of the major componets and features include:
    - init system (systemd, upstart, sysVinit)
    - window manager (none, Gnome, KDE, XFCE, Cinnamon, Mate, and many more)
    - package manager (yum, apt, dnf, pacman, apk, and more)
    - file system (ext3, ext4, zft, btrfs, and more)
    - release model (fixed or rolling)

see also: https://distrowatch.com

Create a VM for learning

Below are instructions to create a temp linux VM

On Mac

# install homebrew
brew cask install virtualbox
brew cask install vagrant

# create a Vagrant file that defines a centos (systemd, yum) VM
# see also https://app.vagrantup.com/boxes/search
mkdir centos8
cd centos8
vagrant init centos/8

# download a centos image and start it
vagrant up

# ssh into the running VM (type 'exit' to logout)
vagrant ssh

# stop the VM
vagrant halt

On Windows

TODO

Init Systems

init systems are responsible for running all processes
they have PID 0 (process id 0)
they are run by the root user
There are several different init systems, and you should be aware
    of which one your distro is using as it will effect how you admin the box
Systemd is the modern and probably most popular option
    the rest of this doc assumes systemd
see also: https://www.computernetworkingnotes.com/linux-tutorials/differences-between-sysvinit-upstart-and-systemd.html

Package managers

There are many package managers that a distro might use.
The 2 most popluar are RPM/YUM and DEB/APT.
It's important to know which package manager your system uses so you will know how to install
and update software.

Installing software

Using Apt (debian, ubuntu)

sudo apt update
sudo apt upgrade
apt search nginx
sudo apt install nginx
apt list
apt list | grep nginx

Using Yum (red hat, centos)

sudo yum update
sudo yum upgrade
yum search nginx
sudo yum install nginx
yum list
yum list | grep nginx

Shells - Bash and Zsh

https://learnxinyminutes.com/docs/bash/

bash, zsh, macos
chsh
~/.bash_profile, ~/.
$PATH
alias
env
export
unset

List running processes

ps
ps -ef
top
htop

list enabled services

systemctl list-unit-files
systemctl status nginx
systemctl enable

Find files

find
locate
sudo updatedb

Navigate file system

cd
cd ~
pwd
ls -la

cd ..
cd ../../
cd /
pushd
popd

important directories and files

~
.
..
/
/etc
/var
/var/log
/var/log/messages
/opt
/dev
/usr/bin
/usr/local/bin

working with files

ls
cat
grep
cut
awk
vim
https://learnxinyminutes.com/docs/vim/

Block storage / attached disks

lsblk
du
df
mount
/etc/fstab

Networking basics

ifconfig
ip a
systemctl status network

Security

selinux
firewalld
permissions
chmod
chown
whoami
su, sudo