1) Linux is an OS!
root / sudo
If you are reading this you are likely aware that the administrator on Linux/Unix systems is referred to as root. The root account is the account on which all system processes run and should be the only account that can write to the main filesystem.
Because most of us started our computing lives out using Microsoft Windows there has always been a notion that it is better to be the administrator of the system. Unfortunately this is one of the major causes of insecurity in computing and opens up your system to instability. As most Linux users will tell you, only log in as root to perform maintenance on your system and never log in to a graphical or desktop session using root.
grep is a very useful terminal command used to search for text within files, the default is to print all lines that contain the given string.
Examples:
grep word file -> print all the lines of the file containing the word.
cat file1 | grep keyword
Unix command | grep keyword