If you are just getting started in Linux then these commands should be useful.

File System:

ls     : listing

cd     : change directory

cat     : concatenate

pwd     : print working directory

find    : find stuff    https://tryhackme.com/room/thefindcommand

grep    : find a value within a file. i.e. IP address

man      : manual

help    : help. More info than manual

touch  : create file

mkdir  : create directory/folder

cp           : copy (needs destination too)

scp    : secure copy

mv    : move

rm    : remove (need -R to remove directory)

file    : determine the type of file

echo    : output

nano    : text editor

vim    : advanced text editor

wget    : download from internet

strings: look for strings in a file

chmod: change mode/permissions

Operators:

&    : allows you to run commands in the background of your terminal

&&    : allows you to run multiple commands together in one line of your terminal

>    : direct output elsewhere

>>    : as above but appends so no overwriting

Switches

su    : switch user

l    : login

Common Directories

etc     : stores system files for OS

var    : variable data

root     : home directory for ‘root’ user

tmp    : temporary. wiped when session ended.

Processes

ps        : list processes

ps aux        : list all processes

top        : show all processes in live table

kill        : stop process

systemctl    : interact with systemd

ctrl z        : background process

fg        : foreground process

Automation

cron    : process to execute crontabs. Time based. https://crontab-generator.org/