linux.md

Linux security book - https://linux-training.be/linuxsec.pdf

Linux security courses

• https://www.udemy.com/course/linux-security/learn/lecture/4649564
• https://www.udemy.com/course/hackproof-your-server-linux-security/learn/lecture/7318084#overview

Linux security notes

Linux/Bash notes

• Important bash/linux topics shared - https://www.youtube.com/playlist?list=PLShDm2AZYnK1SdG3dufPdCqk08sOahUBP
• Interesting playlist with interesting topics - https://www.youtube.com/playlist?list=PL5--8gKSku174EnRTbP4DzU2W80Q1vqtm
• Centos is open source fork of red hat enterprise linux
• Debug bash scripts - https://linuxhint.com/debug-bash-script/

Exit codes, chaining commands, -e,

• $? saves the exit code of the previous command. 0=success, 1=failed, A non-zero (1-255) exit status indicates failure.
• cat /etc/passwd && cat 123 returns code 1, cat /etc/passwd || cat 123 returns 0.
• If 1st command success, do not run 2nd command cat 123 || touch 123
• If 1st command fail, run 2nd command touch 123 && cat 123
• #!/bin/bash, if we are not sure of bash path use #!/usr/bin/env bash
• Make a file executable chmod +x ./file.sh
• set +e to turn off the "exit on error" , set -e to turn on "exit on error"
• Return values for bash can only be used for exit codes
• $(command) to print output of a command in a string echo "Files are $(ls)"
• rm $(ls) - Delete all the files from a folder using rm command in the current working dir

fd, stdin, stdout, stderr, file descriptors

• STDIN=0, STDOUT=1, STDERR=2

• https://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-3.html

• /dev/null redirect o/p to this if we dont want to see any output

• XARGS

• sed find awk tr