Paths and the Directory Tree

One tree, no drive letters

Windows gives every disk a letter: C:\, D:\. Linux has a single tree. Everything starts at the root directory, written /, and every file on every disk sits somewhere beneath it ^{1 2}. A second disk or a USB stick isn’t a new letter; it’s attached, or mounted, at a folder in the same tree, such as /media/me/USBSTICK ^{1 3}.

Paths are written with forward slashes: /home/me/photos, not \. Under WSL, your Windows C: drive is just one more mounted directory, /mnt/c ⁴.

Where am I, and what’s here?

Three commands do almost all your moving around ^{1 2}:

me@linuxbox:~$ pwd
/home/me
me@linuxbox:~$ ls
Desktop  Documents  Downloads  photos
me@linuxbox:~$ cd photos
me@linuxbox:~/photos$ pwd
/home/me/photos

• pwd, print working directory: where you are.
• ls: what’s here. Give it a path to look elsewhere: ls /etc.
• cd: change directory.

You start each session in your home directory, /home/<you>. It’s the one place an ordinary user can write freely ¹.

Absolute and relative paths

An absolute path starts with / and spells out the route from the root: /home/me/photos. It means the same thing no matter where you are.

A relative path doesn’t start with /; it’s followed from your current directory. From /home/me, the path photos means /home/me/photos ².

Some special names ^{1 2}:

And some cd shortcuts ¹:

me@linuxbox:~/photos$ cd ..        # up one level, to /home/me
me@linuxbox:~$ cd /etc             # anywhere, by absolute path
me@linuxbox:/etc$ cd -             # back to where you just were
/home/me
me@linuxbox:~$ cd                  # no argument: home

Everything after # on a line is a comment: the shell ignores it. You’ll see comments in examples throughout this course.

A tour of the tree

The Filesystem Hierarchy Standard says what goes where, so every distribution looks broadly alike ³. The directories worth knowing now ^{1 3}:

“Everything is a file” is an old Unix idea, and /dev and /proc are where you see it most plainly: a disk, a terminal, and the kernel’s view of your CPU all show up as names in the tree ¹.

File names on Linux

Four rules that trip up people coming from Windows ¹:

1. Names starting with a dot are hidden. ls skips them; ls -a shows them. Your home directory is full of them: .bashrc, .profile, .config/. That’s where programs keep your settings.
2. Names are case-sensitive. File1 and file1 are different files, and CD Documents is “command not found.”
3. Extensions are optional. Linux decides what a file is by its contents, not its name, though many programs still look at the extension. file tells you what something really is (next lesson).
4. Avoid spaces and most punctuation in names you create. Stick to letters, digits, ., -, and _: tax-2026.pdf, garden_notes.txt. Every space is something you’ll have to quote later.

Your turn

So

Linux keeps everything in one tree under /. Absolute paths start at the root; relative paths start where you are, with ., .., and ~ as shortcuts. Settings live in /etc, your files in /home, programs in /usr, changing data in /var, and names are case-sensitive, extension-optional, and best kept free of spaces.