Fundamental Concepts

The Kernel

A special computer program that manages and allocates computer resources (i.e the CPU, RAM and devices)

The Shell

A shell is a special-purpose program designed to read commands typed by a user and execute appropriate programs in response to those commands.

Examples: Bash, Zsh

# Print hello world to the shell
echo 'Hello World'

Users and Groups

Users

Every user of the system has a unique login name (username) and a corresponding numeric user ID. Each user is defined by a line in the system password file /etc/passwd

chu:x:1012:1013:Chu Huynh,,,:/home/chu:/bin/bash

User ID: 1012
Group ID : 1013 - group ID of the first of the groups of which the user is a member
Home directory: /home/chu
Default shell: /bin/bash

Core utils

Shell
head
tail
cat
tee
ps
kill