1.3: Pi OS

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Your Raspberry Pi typically uses the Debian Linux operating system and this section will introduce you to some common Linux commands that you will find useful. Linux is an open source operating system that is similar to Unix, but through the GNU project (GNU's Not Unix) has a General Public License (GNU GPL). Yes, GNU is a recursive acronym and stand for "GNU Not Linux". The most recent versions of Debian Linux are Buster (released in July 2019) Bullseye (released in August 2021) and if you installed your operating system after November 21, 2020 using the instructions outlined in section 1.1 you have installed Bullseye.

Linux is the "kernel" of your computer's operating system, and interpreted language that you access through the shell (command prompt) and gives you access to control the hardware on your computer. Figure When a series of Linux commands are bundled into a script it is often called a BASH script, which stands for Borne Again Shell. We will use BASH scripts both within the Raspberry Pi terminal and through system calls from Python.

Figure \(\PageIndex{1}\): Diagram showing computer kernal connecting hardware to application programs, adapted from Wikipedia Kernel article

Linux File System

Linux uses a tree structure for the file system, and the contents are placed in folders, which are also called directories. You can navigate this system with the "File Manager" of the Raspberry Pi Desktop (figure \(\PageIndex{2}\) or through commands like ls (list) and cd (change directory) of a shell terminal (figure \(\PageIndex{3}\)). You can activate the File Manager by clicking on the two folder icon of the keyboard, and here we are showing the contents of user pi (which is highlighted in the tree structure on the left)

Figure \(\PageIndex{2}\): Raspberry Pi desktop File Manager view of the Filesystem Root Directory showing contents of user Pi. Note in this directory there are 10 other directories and two files. (Belford; CC 0.0)

Figure \(\PageIndex{2}\) shows the Linux root file structure and unless you know what you are doing you should only add/alter files in your user directory. Here we are showing the default user directory of pi, and in this directory we have created a program for your python programs. Not in naming files and directories you should have no blank spaces and we used an underscore in the name Python_programs. We also started the name of the directory with a capital letter, which is a personal preference that will be explained later when we get into key-board shortcuts.

Pi Terminal

The terminal icon on the toolbar opens the command shell (figure \(\PageIndex{3}\))

Figure \(\PageIndex{3}\): Two shell terminals open on a Raspberry Pi desktop. (Belford; CC 0.0)

Note you can run more than one terminal shell at a time. The title in the terminal indicates the path.

Keyboard Shortcuts

The following is a list of Keyboard shortcuts you can use in the shell terminal.

<ctrl><alt>t - Opens the shell terminal
<ctrl>c - Kills current running command
<shift><ctrl>C - Copy
<shift><ctrl>V - Paste
<ctrl> u - wipe out from curser to beginning of line
<ctrul> a - jump to front of line
<ctrl> c - jump to end of line
<ctrl> l - clear screen
<shift><ctrl>+ - increase shell terminal size
<shift><ctrl>- - decrease shell terminal size
<tab> -auto complete

Note that <ctrl> c kills a program while <ctrl> C copies highlighted text.

Keyboarding Tips

<tab> - auto complete is very useful as it lets you see what directories and commands are available, while also avoiding the issue of spelling mistakes. In the following example ( top shell of figure \(\PageIndex{4}\)) you are in the pi directory of figure \(\PageIndex{2}\) and hit the following commands.

P <tab> - nothing happens as there is more than one folder that starts with P
<tab> - hitting a second tab prints the the name of the three folders that start with P, and return the P
y <tab> - it now auto completes Python_programs as there is only one item that starts with Py

Figure \(\PageIndex{4}\): Copy and Paste Caption here. (Copyright; author via source)

Note in the bottom shell of figure \(\PageIndex{4}\) a small "p" was typed, followed by two tabs, and resulted in 194 possibilities. This is because most functions start with a lower case letter and is why I am suggesting you start your folders with a capital letter, as you can then quickly navigate to them without having to type as many letters to come up with a unique name for auto complete to work.

Note, if you try <tab> on a file it needs to be executable for auto complete to work, or you need to be in the nano editor.

Up arrow moves to previous command in the past

Down arrow moves to previous command in the future

<History> Gives Indexed list of past commands that were saved if you properly exited.

!<Index Number> brings the command in history to the command prompt

Navigation Commands

cd

-Change Directory

cd .. - back one level

cd ~ - home directory

cd / - root directory

clear

-clear the shell

cp

-copy directory or file (change path)

cp - r /current directory/ /new directory/ -allows you to move subdirectories

cp -r /home/pi/mydocuments/ /home/pi/experiment_folder

ls

- list directory contents

ls *.py - Shows python files

ls ../ -Shows other files of current directory

ls -a Shows hidden files

ls -l -shows permissions

ls -R -Recursively show list

mkdir [name]

-make a directory, where [name] is the name of the directory

pwd

- Print Working Directory (shows where you are)

rmdir [name]

-remove empty directory

rm -rf [name]

-forced and recursive removal of a director [name]

tree

-Provides directory structure

System Management

Pi Configuration Tool

sudo raspi-config opens the keyboard-based navigation tool.

up/down arrow allows navigation across items
right/left arrow allows you to select and finish choices

Operating system

cat /etc/os-release

need to be in root directory
gives info on CPU

cat /proc/version - information on version of Linux

top

line 1: time, how long system has been up, number of users and load average over last minute, 5 minute and 15 minutes.
line 2: number of tasks and their states (running, sleeping, stopped), and the number of zombies*
line 3: CPU info
line 4: info on memory

The remaining table gives process ID for running processes and information about those processes.

*Zombies are like orphaned pieces of old programs that have not been completely removed from memory

Hardware Information

cat /proc/cpuinfo - information on CPU

memory functions

cat /proc/meminfo -information on memory

free -h -available system memory

CPU Tempera

SD card functions

cat /proc/partitions - information of SD card

df -h - free disk space (-h human readable)

vcgencmd get_men arm && vcgenchmd get_mem gpu - SoC memory split between cpu and gpuation of SD card

System on Chip memory split between CPU and GPU

CPU Temperature

vcgencmd measure temp - information of SD card

External Ports

lsusb - devices attached to USB ports

CPU Temperature

shutdown

sudo shutdown -h now -shuts down now (h for halt)

reboot

sudo reboot -restarts pi from command line. You will not need to resubmit password

User Management

User Permissions

there are three types of users (owner, group and other) and three types of permissions (read, write and execute)

Figure \(\PageIndex{1}\): Copy and Paste Caption here. (Copyright; author via source)

chmod

-allows you to assign permissions to a file or directory

In the above image ls -l showed that everyone had write permissions for the file demo.txt. He command chmod a=rw demo.txt gave everone read and write permissions for the demo.txt document. This was then changed with the command chmod u=rwx, g=rw, o=- demo.txt, which gave the user all permissions, the group read and write and others no permissions.