Linux

Family of free and open-source software operating systems built around the Linux kernel (Fedora, Ubuntu, Red Hat etc.)
Best-known and most-used open source operating system kernel
History of Linux
- Created by Linus Torvalds in 1991
- Linux is modelled *after* Unix, it is not derived *from* Unix.
- Unix for mainframes, Linux for PCs.

Who uses it?

The central part of an operating system
manages the operations of the computer and the hardware - most notably memory and CPU time.
thought of as the program which controls all other programs on the computer
There are two types of kernels:
- A microkernel, which only contains basic functionality;
- A monolithic kernel, which contains many device drivers.

The shell accepts human readable commands and translates them into something the kernel can read and process.
bash(Bourne Again shell), ksh, tcsh and zsh
Terminal - program that opens a window and lets you interact with the shell.
Shell Prompt
There are various ways to get shell access:
- Terminal - X Terminal (XTerm), Gnome Terminal (GTerm), or KDE Terminal (KTerm) application.
- Connect via secure shell (SSH)

Linux is a multi-user operating system
User in the system is uniquely identified by a numerical number called the UID
The root is superuser - has all rights to all files, system services, and softwares.
Permissions - needs to protect users from each other
You can create user groups to manage accesses
Permissions: Read - Write - Execute

"Superuser do"
Running commands with root user permissions
sudo allows a permitted user to execute a command as another user, according to specifications in the /etc/sudoers file.
sudo requires that users authenticate themselves with a password
sudo can log both successful and unsuccessful attempts
To edit the sudoers file, use the visudo command.
Once a user has been authenticated, a timestamp is recorded and the user may use sudo without a password for a short period of time
Use: prepend to any command

pwd - To know which directory you are in
Is - to know what files are in the directory you are in. You can see all the hidden files by using the command “ls -a”
cd - Use the "cd" command to go to a directory
mkdir - create a folder or a directory
rm - to delete files and directories. Use “-r” option to delete a directory
touch - used to create a file
cp - copy files. It takes two arguments: The first is the location of the file to be copied, the second is where to copy
mv - Use the mv command to move files through the command line. We can also use the mv command to rename a file.

echo - helps us move some data, usually text into a file
cat - Use the cat command to display the contents of a file. It is usually used to easily view programs.
df - Use the df command to see the available disk space in each of the partitions in your system.
du - Use du to know the disk usage of a file in your system. If you want to know the disk usage for a particular folder or file in Linux
tar - Use tar to work with tarballs (or files compressed in a tarball archive) in the Linux command line.
zip, unzip - Use zip to compress files into a zip archive, and unzip to extract files from a zip archive.
chmod - Use chmod to make a file executable and to change the permissions granted to it in Linux.

Free and open source operating system and Linux distribution based on Debian
Ubuntu is offered in three official editions:
- Ubuntu Desktop: for Personal computers
- Ubuntu Server: for servers and the cloud
- Ubuntu Core: for Internet of things devices.
PPA: A Personal Package Archive (PPA) is a software repository for uploading source packages to be built and published as an Advanced Packaging Tool (APT) repository by Launchpad(web application that allows users to develop and maintain software).
APT - works with core libraries to handle the installation and removal of software on Debian, Ubuntu

apt: Use apt to work with packages in the Linux command line. Use apt-get to install packages.
This requires root privileges, so use the sudo command with it.
To install - sudo apt-get install ...
sudo apt-get update - update your repository each time you try to install a new package.
You can upgrade the system by typing “sudo apt-get upgrade”