Linux

Linux is an open source monolithic unix-like POSIX-compliant kernel created by Linus Torvalds. Unlike some complete operating systems Linux is a base for OS developers to create an OS with software of their own while using a pre made widely-supported kernel.

Distributions
Linux comes in several distributions with their own package managers and other implementations of things. Many linux distributions include the GNU suite of essential software however a notable few (such as Google's Android) omit GNU and instead opt for their own custom suite of software.

Conventions
Linux distributions have many conventions that make Linux more than a kernel. Here are some:

- Linux file systems usually include ones with unix-like permissions, as well as linux file systems not usually using a file allocation table. - Linux installations usually use the UNIX directory structure with there being one "root" folder (represented as a single forward slash) with other folders including devices, apps, and config files like /dev, /bin, and /etc. - Linux applications usually are stored in ELF format. - Linux systems will usually use a descendent of the Bourne shell for a navigation shell. This includes shells like bash and zsh.

Everything is a file
In linux, even things like hardware are represented as files that can be written to. For example, the file for the first hard drive is /dev/sda. This means that if you want to write bytes directly to the drive you can use an app that lays bytes (like dd) to write directly to that file. This can be done by using the app named echo to output something and piping the output to dd which you specify the hard disk's file to. (The exact command is "echo Something | dd of=/dev/sda". This will ruin your drive's boot sector so please do not do this.)

There are also more liberal concepts of devices in /dev. /dev/null, when written to, discards all data sent to it. If you write to /dev/null and then open it it will still be empty.

There is also another directory, called /proc, that manages other devices. The directory /proc/acpi contains all sorts of subtle devices like the power button and battery.

Trivia
- Linus Torvalds originally meant to call Linux "Freax". One of Linus' coworkers didn't like that name and uploaded the software to the FTP server as "Linux". - Linus was bit by a penguin one time, and that is the reason that the logo of Linux is a penguin.