Some useful commands

ls                       lists the files and directories

ls -a                     lists the hidden files and directories (files can be made hidden by using a . in front of its   name)

netstat -an     lists the open ports

netstat -rn     displays the internal routing table

pwd                current directory location in terminal

last                  displays the last users who logged into the system and the time in which they did so

lsmod              displays the kernel modules loaded

sudo                super user, previlege escalation

apt-get            installation package (eg. apt-get install gedit)

gunzip 'file'    unzipping file    

tar -xvf 'file'   untaring file

man                if you don't know what a program does for eg. nmap, type man nmap, it will give a lot 
                          of info

uname -a       System info 


df -H              Disk usage

vi                   to view a file

nano              easier tool to view a file than vi


cat                 view a file in the current shell itself i.e; without opening another tab


strings           view text data in a dump file (eg. captured by tcpdump with .dmp extension)


lsof                list open files


gedit             probably the most user friendly text editor, install it using apt-get install gedit

chmod          change mode eg. chmod +x filename creates an exe file

grep             search for data inside a file (eg. grep indy filename displays all lines with indy in it)