Many of these commands require root privilege, use sudo and the command name,  and  when asked enter your password.

• basic tcp/ip commands:

  ifconfig, ping, traceroute

• Updating packages in your system :

  apt update (retrieves list), then apt upgrade (actually update packages)

• Installing packages in your system :

  apt install package name, e.g. apt install nmap

• running a program, script not in the path:

  ./programname

• deleting (removing) files:

  rm -i filename

• deleting (removing) empty directories:

  rmdir directoryname

• deleting (removing) directories and files inside the directories:

  rm -r directoryname

• making a file have owner rwx, group and world rx permissions:

  chmod 755 filename

• making a file have owner rw, group and world r permissions:

  chmod 644 filename

• making a shell script executable:

  chmod u+x scriptname

• changing password:

  passwd

• root changing (creating) user password:

  passwd username

• uncompressing gz files:

  gzip -d filename.tar.gz

• uncompressing tar files:

  tar -xvf filename.tar