Linux Command Line Interface, (CLI from now on) could be at first glance discouraging for the average Joe, since nowadays we are only used to Graphic Interfaces. But don’t let you down, using a command line shell could be, not only very useful, but also kind of funny.
This Tutorial will help you move your first steps in the command shell environment.

First, when a Command Line Interface could be useful for you?

• Remote Connection via SSH: SSH remote connection allows to interact with Udoo without physical access to it. SSH is available only with command line interface.
• Using a minimal Linux Distribution without a graphical interface. Some Linux Distribution come without a Graphical User Interface, in order to maximize available resources. Command line interface is your only bet in this scenario
• Some power-users consider CLI the most convenient way to perform code execution and file-system operations. Even if you are not in this category, you may found out that CLI can be very fast when you get used to it.
• Showing up with your mates, the longest your CLI strings, the more rep you’ll get.

So, let’s start this adventure with the very basic Linux commands:

sudo

Your first ally, allows users to run programs with the security privileges of root, or superuser.Its name is a concatenation of “su” (substitute user) and “do”, or take action . So, if you get an error message saying that “only root can do that”, just use the same command with preceeded by sudo.

sudo

In fewer words:

sudo su

This just enables root privileges once for all, without forcing you to type sudo everytime. It works until you close the shell you are working into.

sudo su

touch

create an empty file

touch

nano

open an handy text editor, to save and exit, press “ctrl” and “x”, and tell yes or no by pressing “y” or “n”

nano

cat

cat shows the content of a file, it speeds up file inspection for smaller files.

cat /etc/hostname

ls

Shows you the content of a folder

ls

cd

opens a specific folder

cd /home
cd ubuntu

cd ..

Brings you to a higher folder level

cd /home/ubuntu
cd .. (/home)

cd /

brings you to root (top filesystem level)

cd /

rm

deletes a file

rm myfile.my

rm -rf

deletes a folder

rm -rf /home/ubuntu/myfolder
rm -rf myfolder

mv

moves a file or a folder. Useful for renaming also

mv myfile /myfolder/myfile
mv myfile mysecondfile

cp

copies a file

cp myfile /home/ubuntu/

cp -R

copies a folder

cp -R myfolder /home/ubuntu/myfolder

mkdir

creates a folder

mkdir myfolder

top

Top is a very useful utility, it basically gives you a complete overview of the system’s status. It produces an ordered list of running processes selected by user-specified criteria. Top shows how much processing power and memory are being used, as well as other information about the running processes.

top

df -h

Shows used and available disk space, in megabytes.

df -h

ifconfig -a

Shows networking useful data, like current ip, netmasks and other statistics.

ifconfig -a

chmod

chmod let you set files permissions. This utility is very important for people concerned about security, but it is useful also for coders, since you can set a script as executable with it .
For a more comprehensive guide on how to use chmod see here

dmesg

Shows the messages resulting from the most recent system boot. It is useful for troubleshooting, since you can see which modules are loaded, which binaries are started and so on.

dmesg

sync

Thanks to this command your SD card lifespan will drastically improve, remember to launch it every time you turn Udoo off, or remove the power. Completes all pending input/output operations. It must be launched as root, or with sudo.

sync

reboot

reboots the system

reboot

shutdown

shuts it down

shutdown now