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Linux Fundamentals

Linux commands

echo
whoami

man ls
ls -h

cd
cat
pwd

touch
mkdir
cp
mv
rm

cp note note2   
mv note note2
  • find -name passwords.txt
  • find -name fileName.py
  • find -name *.txt
  • find -FileName *.txt

wordcount:

  • wc -l <file>

grep (search):

  • grep "THM" <file>

determine the file type: file <fileName>

  • nano myfile inside nano Ctrl == ^

SHELL OPERATORS

  • & allows running commands in background of terminal

  • && combines commands

  • > redirector, output command

  • >> same output command, appending data

  • echo passwords >> password123

  • echo passwords123 >> tryhackme

Linux part 2

secure shell (SSH) connect to a remote linux machine. your linux machine + attackbox

  1. IP address of remote machine
  2. credentials for login

PERMISSIONS

  • ls -lh
  • su user2
  • user2
/etc    stores system files used by linux 
/var    variable data, accessed by services or apps
/root   home for root system user
/tmp    temporary directory, any user can write to this folder

DOWNLOADING FILES

wget:

  • wget https://assets.tryhackme.com/additional/linux-fundamentals/part3/myfile.txt

TRANSFER FILES FROM HOST:

  • secure copy SCP
  • copy files & directories your system to remote system
  • copy files & directories from remote system to your system

IP address

  • remote system

  • name of file on local system (notes1.txt)

  • name for file on remote system (transferred.txt)

  • scp important.txt ubuntu@x.x.x.x.30:/home/ubuntu/transferred.txt

  • scp ubuntu@x.x.x.x.30:/home/ubuntu/documents.txt notes.txt

SERVING FILES FROM HOST:

  • python3 -m http.server
  • wget http://127.0.0.1:8000/file

PROCESSES 101

programs running on the machine managed by the kernel each process has an ID (PID)

  • view processes ps
  • see all processes ps aux
  • process stats top

Managing processes:

  • kill a command kill PID_NUM kill 1332
  • SIGTERM kill process AND cleanup
  • SIGKILL kill process no cleanup
  • SIGSTOP stop/suspend process

PID 0 = system init system boot 👢 systemd then child processes controlled by systemd but diff process

  • web servers, database server or FTP servers start on boot

manually start Apache server then system launch apache2 on boot:

  • systemctl [option] [service]
  • systemctl start apache2
  • systemctl stop apache2
  • systemctl enable apache2
  • systemctl disable apache2

Intro Back/Foregrounding

  • background state process

  • foreground state process echo , echo & => returns PID

  • Ctrl + Z background a process

  • ps aux | less

  • thm{processes}

System Automation

  • cron process
  • crontabs file
MIN   what minute to execute
HOUR  what hour to execute
DOM   day of month 
MON   what month of year
CMD   the command to be executed

backup file every 12 hours:

Package Management

software submissions as 'apt' repository /etc/apt/

  • add-apt-repository

Task: add the text editor Sublime Text to our Ubuntu machine

  • integrity by GPG Gnu Privacy Guard keys for safety of software
  1. Let's download the GPG key and use apt-key to trust it: wget -qO - https://download.sublimetext.com/sublimehq-pub.gpg | sudo apt-key add -
  2. now add Sublime Text 3's repository to our apt sources list.
  3. create a file named sublime-text.list in /etc/apt/sources.list.d and enter the repository information. touch sublime-text.list
  4. /etc/apt/sources.list.d open and paste in deb https://download.sublimetext.com/ apt/stable
  5. apt update
  6. apt install sublime

System Logs

cd /var/logs

rotating process of auto managing logs

  • access log
  • error log