Linux, the Shell and the Filesystem

Linux and the shell

Linux is an open-source operating system that runs most of the world's servers, cloud infrastructure and Android phones. You often work with it through a text interface called the shell; the most common shell is Bash. Typing commands in the shell is faster, scriptable and more precise than clicking – essential for servers, which usually have no graphical desktop.

One filesystem tree

Unlike Windows with its C: and D: drives, Linux has a single tree that starts at the root, written /. Everything – files, folders, even devices – lives somewhere under it.

• /home – users' personal folders (/home/ada).
• /etc – system configuration files.
• /var – variable data such as logs (/var/log).
• /usr – installed programs and libraries.

Absolute and relative paths

An absolute path starts from root (/home/ada/notes.txt). A relative path is from where you currently are. Two shortcuts appear everywhere: . is the current directory and .. is the parent; ~ is your home folder.

Everything is a file

A defining Unix idea: not just documents but devices, and even running processes, are represented as files. This uniformity is why the same small tools work on almost anything.

Key points

• Linux runs most servers; you drive it through a shell, usually Bash.
• The filesystem is one tree rooted at / – no drive letters.
• Paths are absolute (from /) or relative; ., .. and ~ are key shortcuts.
• “Everything is a file” gives Unix its uniform, composable design.