Notes: Linux Fundamentals Part 1 | THM

Linux

- operating system

- based on UNIX

- open-source

- various variants/versions/distributions of Linux (distros)

- lightweight: Ubuntu Server can run on systems with only 512MB or RAM

Linux common uses:

- websites

- car entainment/control panels

- Point of Sale (PoS) systems: checkout tills and registers in shops

- Critical infrastructure: traffic light controllers or industrial sensors

Common distributions of Linux:

- Ubuntu

- Debian

Terminal

- possible to interact with the system without a GUI

- text-based

Commands

echo: output text

whoami: output which user are you currently logged in as

Commands to interact with filesystem

ls - listing

cd - change directory

cat - concatenate

pwd - print working directory

Command searching for files:

find

Search for filename:

find -name passwords.txt

Search for a file without knowing the name:

find -name *.txt

* is a wildcard (https://tldp.org/LDP/GNU-Linux-Tools-Summary/html/x11655.htm)

Search contents of files:

grep

Search for an IP address in an access log file:

grep "81.143.211.90" access.log

Linux Operators

& - run commands in background

&& - combine multiple commands together in one line

> - redirector = take output from command and direct it elsewhere

>> - same as >, but appends output rather than replacing/overwrite

Operator &

- execute commands in background

Operator &&

- run several commands

F.ex: command1 && command2

Command2 will only run if command1 ran

Operator >

- output redirector (overwrites content)

- take output from a command and send it to somewhere else

f.ex:

command: echo hey > welcome

command: cat welcome

output reading the file welcome:

hey

Operator >>

- output redirector (put content at the end)

f.ex:

command: echo hello >> welcome

command: cat welcome

output reading the file welcome:

hey

hello