Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus TorvaldsLinux is typically packaged in a Linux distribution. The GNU userland is a key part of most systems based on the Linux kernel, with Android being the notable exception. The Project's implementation of the C library functions as a wrapper for the system calls of the Linux kernel necessary to the kernel-userspace interface, the toolchain is a broad collection of programming tools vital to Linux development (including the compilers used to build the Linux kernel itself), and the coreutils implement many basic Unix tools. The project also develops a popular CLI shell.
At first there was unix which was only CLI based which is command line interface based, but with the evolution of computer system and technology linux came into the world of computers which are GUI(Graphical User Interface based). So GUI makes things easy for people, still there are many application linux which are CLI based which means we have to do that application from shell. Shell helps user to interact with software and the application present in the operating system. On desktop systems, the most popular user interfaces are the GUI shells, packaged together with extensive desktop environments, such as KDE Plasma, GNOME, MATE, Cinnamon, Unity, LXDE, Pantheon and Xfce, though a variety of additional user interfaces exist.Linux are distributed in many interfaces, but it depends on the user totally which interface they will choose to use depending on their application and work. The most popular interface is GNOME and X-Window environment.
There are variety of Linux distribution available in the internet and we can download them easily without any cost as they are open source and this is the main advantage of Linux. Some of the popular distribution is RPM and Debian based